arXiv:1306.3436v1 [hep-ph] 14 Jun 2013
Contents
1. 38 The Generator Services Project http sftweb cern ch generators 28 39 ALICE Collaboration K Aamodt et al Charged particle multiplicity measurement in proton proton collisions at s 7 TeV with ALICE at LHC Eur Phys J C68 2010 345 354 1004 3514 40 ATLAS Collaboration G Aad et al Charged particle multiplicities in pp interactions measured with the ATLAS detector at the LHC New J Phys 13 2011 053033 1012 5104 41 ATLAS Collaboration G Aad et al Measurement of underlying event characteristics using charged particles in pp collisions at v s 900GeV and 7 TeV with the ATLAS detector Phys Rev D83 2011 112001 1012 0791 42 B Cooper J Katzy M Mangano A Messina L Mijovic et al Importance of a consistent choice of alpha s in the matching of AlpGen and Pythia Eur Phys J C72 2012 2078 1109 5295 43 OPAL Collaboration K Ackerstaff et al Measurements of flavor dependent fragmentation functions in ZO to q anti q events Eur Phys J C7 1999 369 381 hep ex 9807004 44 CDF Collaboration D Acosta et al Study of jet shapes in inclusive jet production in pp collisions at s 1 96 TeV Phys Rev D71 2005 112002 hep ex 0505013 45 M L Mangano M Moretti F Piccinini and M Treccani Matching matrix elements and shower evolution for top quark production in hadronic collisions JHEP 0701 2007 013 hep ph 611179 46 AGI2. The merging code is located in SSCRIPTS mcprod merge Once a new source histogram h0 h1 or h2 in figure 11 is obtained it should be merged to a common destination with the prior compatible histograms in the database The run of the merging script S SSCRIPTS mcprod merge merge sh source destination handles the merging of the ASCII histogram inputs as well as the book keeping of the event multi plicities and the sample cross section The merging code runs in two steps as follows e first histograms that populate exactly the same regions of phase space are merged in order to increase the statistical precision of the results This is denoted as step 4 1 in figure 11 e Inthe second pass of the code the use cases where a number of distinct generation runs are best suited to populate the phase space needed for the final histograms are handled This is denoted as step 4 2 in figure 11 This step is omitted in cases where a single generation run populates the whole phase space An example use case that requires only one pass of the merging code is the standard one of combining multiple runs with different random number seeds but otherwise identical settings An example use case of the run that requires the second pass of the merging code is filling of the histograms for the production of W Z bosons in association with jets at the LHC in the context of multi leg matrix element matched samples The physics distributions of interest hav
3. 1 2 extra partons The exclusive match ing criterion must be used for all but the highest multiplicity sub sample which is matched inclusively The merging code contains a procedure to detect and correctly sum such histograms to the final larger statistics physics distributions The correct merging procedure of the histogram data depends on the normalization already as sumed in the RIVET routines In practice all the current use cases could be addressed by adding two merging modes ALPGEN_XSECT and ALPGEN_FIXED to the merging machinery The ALPGEN_XSECT mode is used for histograms from RIVET runs when no normalization is performed by RIVET The ALPGEN FIXED mode is used for histograms that are normalized according to the cross section by RIVET The new histograms from the run with Np partons is merged with the existing histograms for the Np sub sample The weights for merging of all the Np samples needed to form the generator prediction for the observable are than evaluated such that all the Np sub samples are normalized to the same integrated luminosity in ALPGEN_XSECT or with unit weights for ALPGEN_FIXED mode correspondingly The histogram METADATA e g cross section and the number of events described in section 3 1 is consistently updated with the merged values In addition the sub sample specific fields are added in the format samples_X X_h0 X_h1 X_h2 Here X denotes a quantity e g cross section The X_h deno
4. appears before the Total o label because the relevant definitions are in consecutive lines in mcplots conf The labels associated with the jets process encased by red boxes in figure 10 have been generated by including the line jets Jets Jet production The internal name jets is left of the equality sign the HTML name Jets i e the text in solid red boxes is defined in the centre while the plot label Jet production i e the text in dashed red boxes stands to the right MCPLOTS allows for both an HTML name and a plot label so that a the web page is 14 Menu Jets Transverse Minor Front Page Generator Group gt LHC home 2 0 gt Generator Versions Generator Validation Update History pp 7000 GeV Analysis filter ALL ar ALL ee Specific analysis Latest analyses el Alogen Herwig Pythia6 Pythia8 Sherpa Epos Phojet Custom Subgroup Default K MJ LHC Tunes Tevatron Tunes Diffraction CMS 125 lt pT lt 200 Jet production mo mo Centra Transverse Minar 125 lt py lt 200 eo oms o Herwig Harwig Pythia 6 Pythias gt Sherpa Pythia 6 Pythias gt Sherpa 1N dNid In T__ Aivet 5 2 2 200k events 1N dNid In T__ S Di jet mass E Gap fraction vs Ay ee HT E A 5 Jet Fragmentation Differential shape S Es 3 2 ntegral shape Jet multiplicity 15 Ratios of jet multiplicity do jet dpT R32 vs H
5. downloaded in PDF format Data from 41 3 Architecture and Implementation 3 1 Histogram and Data Format On MCPLOTS a common numerical file format is used for both experimental data and MC generator results The format is based on RIVET s flat format for histograms see section 4 1 of the RIVET manual 14 with modifications to store additional information which is necessary for histograms merging The format itself is a plain text ASCH file which has the advantage of being both human and machine readable and writable The file is divided into sections Each section has the following format BEGIN type paraml valuel param2 value2 binl contents bin2 contents END type The following types of sections have been defined e PLOT description of plot parameters for example axis labels or scale type linear logarithmic e HISTOGRAM plot data bin contents used by the plotting tool to produce the plots e HISTOSTATS PROFILESTATS additional histogram or profile statistical data used to merge histograms from different subruns e METADATA description of MC generator parameters for example generator name and ver sion simulated process and cross section etc Section contents can be of two kinds parameter value definitions or bin value definitions Pa rameter value definitions have the same format for all types of sections Bin value definitions contain several values on each line e g describing the b
6. from left to right alphabetically For many observables measurements have been made using a variety of different cuts and triggers These are indicated both above the plots and on the plots themselves so as to minimize the potential for misinterpretation In the example of charged particle multiplicity distributions shown in figure 4 the two first plots that appear are thus ALICE left for their INEL gt 0 cuts 39 and ATLAS right using their Nen gt 1 and pr gt 2 5 GeV cuts 40 We explain how to find the correct references and run cards for each plot and generator below Note that for the Monte Carlo runs the number of events in the smallest sample is shown along the right hand edge of each plot Le if two generators were used and the statistics were N and N events respectively the value printed is min N1 N2 Underneath each plot is shown a ratio pane showing the same results normalized to the data or to the first MC curve if there are no data points on the plot This is illustrated in figure 5 The vertical range of the ratio plot is fixed to 0 5 1 5 thus larger deviations than this will exceed the boundaries of the ratio plot The central shaded yellow band corresponds to the experimental uncertainty at the lo level as reported by RIVET For MC to MC comparisons it represents the statistical uncertainty of the reference MC Immediately below the ratio pane are links to download the plot main plot ratio pane in hi
7. in PYTHIA 8 Say the myTune tune of our example would only differ from default HERWIG by having unit probability for colour reconnections The corresponding HERWIG input setting set Herwig Hadronization ColourReconnector ReconnectionProbability 1 00 should then be stored in a file called herwig myTune tune in the SCARDS directory After following the above steps we have included a new MC generator version and or new tunes into the MCPLOTS event generation machinery See section 4 4 1 for how to include new tunes in new or existing tune groups on the site including how to assign tune specific default marker symbols line styles etc For generator chains like ALPGEN HERWIG changing the file SSCRIPTS mcprod runRivet sh might also be necessary to add accepted chains of versions This will be explained below 18 5 2 Producing MC results Once new processes analyses versions or tunes have been added we need to produce results for these new settings This can be done through volunteer computing or manually We will here since manual small scale production can be very useful for debugging purposes describe how to produce MC results manually The top level script for producing and analysing of MC generator results is SSCRIPTS mcprod runAll sh mode nevt filter queue where the two first arguments are mandatory and the two latter ones are optional with the following meanings mode Parameter governi
8. numbers for all curves appearing on the plot together with the relevant experimental reference When combining an ME generator X with a dif ferent shower generator Y both names and version numbers are shown explicitly This is not only to give proper credit to the authors but since the physics interpretation of the calculation depends on how it was performed Acknowledgements We are indebted to many members of the Monte Carlo community for their feedback and help with validations of the generators and analyses included on MCPLOTS Many short term students visi tors and fellows have contributed with RIVET analyses and other content to the site in particular D Konstantinov the MCPLOTS plotting tool A Pytel server infrastructure and the MC validation view S Sen forward LHC analyses in RIVET and on MCPLOTS and implementation of the EPOS and PHOJET generators and J Winter the tt MC analyses We thank J Katzy for carefully reading this manuscript and giving feedback on the MCPLOTS site M Mangano for his strong support of this project from its inception to completion and for help with the ALPGEN implementation and T Pierog for help with the EPOS implementation We express our profound admiration of the teams responsible for the development of RIVET CERNVM and LHC HOME 2 0 without which the TEST4THEORY project would have been impossi ble Thanks also to the many volunteers who have provided computing resources especially
9. to those who have taken active part in the alpha and beta testing phases of TEST4THEORY We also thank the CERN PH SFT group in particular the Generator Services GENSER team and the CERN IT Division This work was supported in part by the LHC Physics Center at CERN LPCC by the Marie Curie research training network MCnet contract number MRTN CT 2006 035606 and by the National Science Foundation under Grant No NSF PHY11 25915 References 1 MCnet Collaboration A Buckley J Butterworth S Gieseke D Grellscheid S H che et al General purpose event generators for LHC physics Phys Rept 504 2011 145 233 1101 2999 2 P Skands Introduction to QCD 1207 2389 Lectures given at TASI 2012 3 M H Seymour and M Marx Monte Carlo Event Generators 1304 6677 Lectures given at 69th Scottish Universities Summer School in Physics 4 A Buckley H H th H Lacker H Schulz and J E von Seggern Systematic event generator tuning for the LHC Eur Phys J C65 2010 331 357 0907 2973 26 5 P Z Skands Tuning Monte Carlo Generators The Perugia Tunes Phys Rev D82 2010 074018 1005 3457 6 R Corke and T Sj strand Interleaved Parton Showers and Tuning Prospects JHEP 1103 2011 032 1011 1759 7 S Gieseke C A Rohr and A Siodmok Tuning of the multiple parton interaction model in Herwig using early LHC data In proceedings of MPI LHC 2011 DE
10. used for MLM matching see 45 are passed in section addPS O sees In order to keep the parameter cards easy to interpret the format in the params files matches the standard format used by ALPGEN The code responsible for parameter parsing resides in SSCRIPTS mcprod alpgen utils_alp This directory also contains a dictionary of unweighting and MLM matching efficiencies that enables the generation of a number of final ALPGEN PS generator events as specified by the user The driver scripts for weighted and unweighted event generation reside in directory SSCRIPTS mcprod alpgen mcrun_alp This directory also contains generator level event filters used by some of the analyses in order to enable efficient filling of the histograms The parameters specific to ALPGEN can be passed by to the MCPLOTS scripts or from the com mand line as well The tune specific ALPGEN parameters are passed at the time of the tune setup The event generation scripts support the usage of parameters not directly related to the tune The step 2 in figure 11 corresponds to ensuring that the output of the event generation is provided in the standard event record format HEPMC For many of the FORTRAN generators the conver sion to the HEPMC event record as well as utilities for parameter settings and the event generation 22 executable are provided by A Generator Interface Library AGILE 46 The C generators are generally able to handle these tasks direct
11. 29 to pass parton level information back and forth e The LHC HOME 2 0 framework for volunteer cloud computing 30 33 LHC HOME 2 0 in turn relies on the CERNVM computing environment 34 35 a Virtual Machine environment based on Scientific Linux and on the COPILOT job submission system 35 36 The main benefit of using CERNVM is that this has enabled MCPLOTS to draw on significant computing resources made available by volunteers via LHC HOME 2 0 Through the intermediary of IR sensitive observables change value when adding an infinitely soft particle or when splitting an existing particle into two collinear ones Such variables have larger sensitivity to non perturbative physics than IR safe ones see e g 2 11 Note also that we here use the word IR as a catchall for both the soft and collinear limits Note this idea was first raised in the now defunct JETWEB project 12 The CERN Generator Services GENSER project also maintains a set of web pages with basic generator validation plots calculations CERNVM generator authors can concentrate on developing code that is compatible with the Scientific Linux operating system a fairly standard environment in our field This code can then be run on essentially any user platform by encapsulating it within CERNVM The resulting TEST4THEORY project 33 37 was the first application developed for the LHC HOME 2 0 framework see 30 33 and it represents the world s f
12. ARDS SSCRIPTS mcprod configuration where the location of the SCRIPTS directory was defined in section 3 2 For the example of the OPAL analysis we wish to run a standard set of hadronic Z decays and hence we may reuse the existing cards SCARDS herwigt zhad params SCARDS pythia6 zhad params SCARDS pythia8 zhad params SCARDS sherpa zhad params SCARDS vincia zhad params The generator and process names refer to the internal names used for each generator and pro cess on the MCPLOTS site The site is constructed such that any new process names automatically appear on the web menus and each can be given a separate HTML and LaTeX name as described in section 4 4 In this example hadronic Z decays are labelled zhad For processes for which the CARDS directory does not already contain a useful set of card files new ones must be defined by referring to the documentation of examples of each generator code separately This is the only generator dependent part of the MCPLOTS machinery Having decided which cards to use for the hard process es information on which observables are are available in the RIVET analysis corresponding to our OPAL measurement are contained in the file SRIVET share Rivet OPAL_1998 _S3780481 plot Decide which individual distributions of that analysis you want to add to MCPLOTS and what observ ables and cuts they correspond to In our case we shall want to add the distributions d01 x01 y01 and d02 x01 y01 whic
13. CERN PH TH 2013 105 DESY 13 104 LU TP 13 23 1306 3436v1 hep ph 14 Jun 2013 arXiv MCPLOTS a particle physics resource based on volunteer computing A Karneyeu L Mijovic S Prestel P Z Skands Institute for Nuclear Research Moscow Russia Deutsches Elektronen Synchrotron DESY 22603 Hamburg Germany Irfu SPP CEA Saclay bat 141 F 91191 Gif sur Yvette Cedex France Dept of Astronomy and Theoretical Physics Lund University Sweden European Organization for Nuclear Research CERN CH 1211 Geneva 23 Switzerland o FW N Fe Abstract The meplots cern ch web site MCPLOTS provides a simple online repository of plots made with high energy physics event generators comparing them to a wide variety of experimental data The repository is based on the HEPDATA online database of experimental results and on the RIVET Monte Carlo analysis tool The repository is continually updated and relies on computing power donated by volunteers via the LHC HOME 2 0 platform 1 Introduction Computer simulations of high energy interactions are used to provide an explicit theoretical reference for a wide range of particle physics measurements In particular Monte Carlo MC event generators 1 3 enable a comparison between theory and experimental data down to the level of individual particles An exact calculation taking all relevant dynamics into account would require a solution to infinite order perturbation theory couple
14. LOTS and CERNVM development teams The code should then be provided to the GENSER team for inclusion in the standard CERN generator repository The complete procedure is described in more detail in section 6 2 User Guide In this section we describe the graphical interface on the MCPLOTS web site and how to navigate through it Care has been taken to design it so as to make all content accessible through a few clicks in a hopefully intuitive manner 2 1 The Main Menu Menu gt Front Page LHC home 2 0 Generator Versions Generator Validation Update History toh 2 Figure 1 The main MCPLOTS menu The main menu shown in figure 1 is always located at the top left hand corner of the page The Front Page link is just a home button that takes you back to the starting page for MCPLOTS and the LHC home 2 0 one takes you to the external LHC HOME 2 0 web pages where you can connect your computer to the volunteer cloud that generates events for MCPLOTS The Generator Versions link opens a configuration page that allows you to select which generator versions you want to see results for on the site The default is simply to use the most recently imple mented ones but if your analysis for instance uses an older version of a particular generator you can select among any of the previously implemented versions on the site by choosing that specific version on the Generator Versions page All displayed content on the site will thereafter r
15. Le project http agile hepforge org 47 ATLAS Collaboration G Aad et al Measurement of the production cross section for W7 bosons in association with jets in pp collisions at s 7 TeV with the ATLAS detector Phys Lett B698 2011 325 345 1012 5382 48 CMS Collaboration S Chatrchyan et al Study of the dijet mass spectrum in pp W jets events at s 7 TeV Phys Rev Lett 109 2012 251801 1208 3477 49 CMS Collaboration S Chatrchyan et al Event shapes and azimuthal correlations in Z jets events in pp collisions at s 7 TeV Phys Lett B722 2013 238 261 1301 1646 50 ATLAS Collaboration G Aad et al Measurement of kT splitting scales in W7 v events at sqrt s 7 TeV with the ATLAS detector Eur Phys J C73 2013 2432 1302 1415 51 ATLAS Collaboration G Aad et al Measurement of the cross section for W boson production in association with b jets in pp collisions at sqrt s 7 TeV with the ATLAS detector 1302 2929 52 CMS Collaboration S Chatrchyan et al Studies of jet mass in dijet and W Z jet events JHEP 1305 2013 090 1303 4811 53 ATLAS Collaboration G Aad et al Measurement of the production cross section of jets in association with a Z boson in pp collisions at s 7 TeV with the ATLAS detector 1304 7098 29 54 CMS Collaboration S Chatrchyan et al Measurement of the hadronic activity in events with a Z and two j
16. S location accordingly afs cern ch sw lcg external MCGenerators or from the CVMFS replica which is used by CernVM virtual machines running in the BOINC cluster covmfs sft cern ch lcg external MCGenerators nttp svnweb cern ch world wsvn mcplots trunk doc readme txt section on Adding a new generator contact genser dev cern ch for new generator support 20 weight w N h N Zh weight w N h N Zh if 2 sub samples necessary lle ove ile sss use observable specific weight Physical Distributions Figure 11 A schematic representation of the path from the Event Generation to the Physical Dis tributions produced within the MCPLOTS framework The sequential steps are labelled 1 4 Their technical implementation in the MCPLOTS framework is described in section 6 Runs of MCPLOTS scripts with a generator not supported by GENSER is currently not implemented For generator not supported by GENSER user can only run the MCPLOTS scripts by checking them out making private modifications and private generation runs We explain the updates needed for implementation of the new generator supported by GENSER with the help of the figure figure 11 The figure shows the schematic representation of the path from the Event Generation to the Physical Distributions produced within the MCPLOTS framework The sequential steps are labelled 1 4 6 1 Steps 1 3 from the Event Generati
17. S Y PROC 2012 03 8 H Schulz and P Skands Energy Scaling of Minimum Bias Tunes Eur Phys J C71 2011 1644 1103 3649 9 ATLAS Collaboration Summary of ATLAS Pythia 8 tunes ATL PHYS PUB 2012 003 ATL COM PHYS 2012 738 10 J Alcaraz Maestre et al The SM and NLO Multileg and SM MC Working Groups Summary Report 1203 6803 11 G P Salam Elements of QCD for hadron colliders 1011 5131 Lectures given at ESHEP 2009 12 J Butterworth and S Butterworth JetWeb A WWW interface and database for Monte Carlo tuning and validation Comput Phys Commun 153 2003 164 178 hep ph 0210404 13 A Buckley and M Whalley HepData reloaded Reinventing the HEP data archive 1006 0517 http durpdg dur ac uk 14 A Buckley J Butterworth L L nnblad H Hoth J Monk et al Rivet user manual 1003 0694 15 M Dobbs and J B Hansen The HepMC C Monte Carlo event record for High Energy Physics Comput Phys Commun 134 2001 41 46 16 M Cacciari and G P Salam Dispelling the N 2 myth for the ky jet finder Phys Lett B641 2006 57 61 hep ph 0512210 http fastjet fr 17 M Cacciari G P Salam and G Soyez FastJet user manual 1111 6097 18 M Whalley D Bourilkov and R Group The Les Houches accord PDFs LHAPDF and LHAGLUE hep ph 0508110 19 D Bourilkov R C Group and M R Whalley LHAPDF PDF use from
18. T R32 vs pT ap fraction vs Ay FB Gap fraction vs Ay LJ os L f Gap fraction vs pT FB 5 Gap fraction vs pT LJ pdf eps png show details Gap frac vs Veto scale FB Gap frac vs Veto scale LJ Njet vs Ay FB Njet vs Ay LJ Njet vs pT FB Njet vs pT LJ gt Cross sections 1 6 2 SE 2 paf eps png show details eteuuurgaed Figure 10 Snapshot of an MCPLOTS page to serve as an illustration of web page labels Most label items are produced by processing the file SWWW mcplots conf Section 4 4 discusses changes of SWWW mcplots conf using the text encased by coloured boxes as examples adequately labelled and b the information on the plot is sufficient to distinguish it from all other figures of the reproduced article even if the plot is stored separately Since the plotting tool uses LaTeX the plot label should be specified in LaTeX format except that the hash symbol should be used instead of the back slash symbol Note that the exclamation marks are mandatory as they are also used to separate different types of observable names When defining observable names it is possible to group a set of observables into a submenu by specifying an optional submenu name after the equality sign but before the first exclamation mark This means that the translation of internal observable names proceeds by adding lines like observable_name HTML submenu HTML name plot label in LaTeX f
19. avial Magic Michel Greysh 1 91G Buntec 1 806 ancien 1 65G 8 77 Figure 12 TEST4THEORY Leaderboard top contributors in number of events generated as of May 2013 The up to date online version can be consulted at 37 element to the parton shower generator the automatic extraction of the information needed for the consistent merging would fail 7 Conclusions Initial tests of LHC HOME 2 0 with the TEST4THEORY pilot project started in the fall of 2010 The system is now fully operational with several thousand volunteers donating CPU cycles on a daily basis and individual volunteers already having generated billions of events each cf the Test4Theory Leaderboard reproduced in figure 12 These contributions have made a crucial difference in being able to generate the massive amounts of statistics required for the innumerable combinations of generators tunes and experimental analyses provided on MCPLOTS In this paper we have provided an elementary user guide for the site and summarized its technical implementation We intend the site to be broadly useful to the particle physics community as a resource for MC validation and tuning and as an explicit browsable repository of RIVET analyses It also provides a possibility for the public to engage in the scientific process In the near future we plan to extend the site by adding more possibilities for users to create their own plots and control how they look We will als
20. cplots dev according to the suggestions of the development web page update To give some examples the code of the public web page can be updated to revision number 2000 by SSCRIPTS updateServer sh r 2000 Further changing the web page to only show results of the above EPOS runs means running SSCRIPTS updateServer sh r 2000 d SHOME release 2000 epos dat After these steps the official release of meplots cern ch is publicly available Since official releases are usually scheduled on a monthly or longer time scale we advocate caution when running the update script Always thoroughly check the site and functionality after performing an update and roll back to a previous version if any problems are encountered There is nothing more damaging to a public web service than faulty operation 6 Implementing a new event generator In this section we provide guidelines for adding a new generator to the MCPLOTS framework An up to date set of instructions is maintained in the MCPLOTS documentation files The guidelines are accompanied by concrete examples and comments drawn from the experience obtained by the implementation of the ALPGEN generator in the framework When adding a new generator one should note that the MCPLOTS framework relies on the libraries with the code needed for the event generation being available in the format and with configurations as used by the GENSER project The generator libraries are accessed from the CERN based AF
21. d new generators and tunes to the event generation machinery will be explained in section 5 16 generator_name tune_nam tune name in the tune name section of the configuration file Furthermore a line style for this particular tune has to be defined in the format generator_name tune_name ColR ColG ColB lineStyle lineWidth markerStyle markerSiz where we have used the character to imply line continuation and the available options for the style settings are documented in the ROOT web documentation Once multiple generator tunes have been named tune subgroups can be defined For this add lines in the format generator_group_name subgroup_name tune_l tune_2 tune_3 at the tune group section of mcplots conf As an example let us look at the HERWIG vs SHERPA tune group which is part of the HERWIG generator group menu The necessary defini tions to construct this tune group are Tune names herwigt default Herwig sherpa default Sherpa Generator names herwig Herwig sherpa Sherpa Tune line styles herwigt default 0 6 0 3 0 0 2 15 24 1 25 sherpa default 1 0 0 0 0 0 3 135 33 1 4 Tune group Herwigt Herwigt vs Sherpa herwigt default sherpa default This concludes the discussion of manipulations of the configuration file mcplots conf 5 Updating the MCPLOTS site The pre
22. d to non perturbative QCD a long standing and unsolved problem In the absence of such a solution MC generators apply a divide and conquer strategy factorizing the problem into many simpler pieces and treating each one at a level of approximation dictated by our understanding of the corresponding parts of the underlying fundamental theory A central question when a disagreement is found between simulation and data is thus whether the discrepancy is within the intrinsic uncertainty allowed by the inaccuracy of the calculation or not This accuracy depends both on the sophistication of the simulation itself driven by the development and implementation of new theoretical ideas but it also depends crucially on the available constraints on the free parameters of the model Using existing data to constrain these is referred to as tuning Useful discussions of tuning can be found e g in 1 2 4 10 Typically experimental studies include comparisons of specific models and tunes to the data in their publications Such comparisons are useful both as immediate tests of commonly used models and to illustrate the current amount of theoretical uncertainty surrounding a particular distribution They also provide a set of well defined theoretical reference curves that can be useful as benchmarks for future studies However many physics distributions in particular those that are infrared IR sensitive often represent a complicated cocktail of phy
23. e been measured up to large high pr jet multiplicities by the LHC experiments 47 54 The multi leg generators such as ALPGEN 20 HELAC 55 MADGRAPH 56 57 SHERPA 26 and WHIZARD 58 are well suited for the physics case For ALPGEN and MADGRAPH the efficient population of phase space needed for prediction of high extra jet multiplicities is frequently obtained by producing separate 23 runs with fixed number of extra partons from the matrix element Np that are passed through the parton shower and hadronization In this way the high Np sub samples which are more probable to populate the high extra jet bins in the physics events can be produced with larger integrated luminosity than the low Np respectively A concrete example is the measurement of W jets by the ATLAS collaborating 47 where the cross section decreases by an order of magnitude per extra jet while the differential measurement is available for up to gt 4 extra jets Another example requiring the second pass of the merging code is also a combine the physics distributions from generator runs that populate different regions of phase space using generator level cuts or filters This is a possible scenario for any generator The merging code and the histogram structure described in section 3 1 is suited to address such use cases In figure 11 the event generation branches in which the histograms hO h1 h2 are produced correspond to the production of the sub samples with 0
24. e cuts within which to restrict the hard process kinematics These optional settings can be provided by changing the optional pTMin mMax columns above in our example such cuts are not desired which is indicated by the symbol Note that such cuts must be applied with extreme care since they refer to the hard partonic subprocess not the final physical final state and hence there is always the risk that bremsstrahlung or other corrections e g underlying event can cause events to migrate across cut thresholds In the end only the speed with which the results are obtained should depend on these cuts not the final physical distributions themselves any such de pendence is a sign that looser cuts are required We would like to point out that a separate generator run is required for each set of MC cuts Hence it is useful to choose as small a set of different cuts as possible The following is an excerpt from rivet histograms map which concerns a CDF analy sis of differential jet shapes 44 in which two different generator level p cuts are invoked to ensure adequate population of a much larger number of jet p bins here ranging from 37 to 112 GeV MC Initialization and Cuts in GeV 9 Rivet mcplots beam process Ecm pTMin Max mMin Max RivetAnalysis_Hist Obs Cut ppbar jets 1960 17 CDF_2005_S6217184_d01 x01 y01 js_diff cdf3 037 ppbar jets 1960 17 CDF_2005_S6217184_d01 x01 y02 js_diff cdf3 045 ppbar jet
25. e since Dec 2010 and is nearing a trillion generated events in total 900 billion as of June 2013 This paper is intended to give an overview of what is available on the site and how to use it In particular section 2 contains a brief user guide for the site explaining its features and contents in simple terms how to navigate through the site and how to extract plots and information about how they were made from it As a reference for further additions and updates and for the benefit of future developers sections 3 6 then describe the more concrete details of the technical structure and implementation of the site which the ordinary user would not need to be familiar with Section 3 describes the architecture of the site and the thinking behind it It currently relies on the following basic prerequisites e The HEPDATA database 13 of experimental results e The RIVET Monte Carlo analysis tool 14 which contains a large code library for comparing the output of MC generators to distributions from HEPDATA RIVET in turn relies on the HEPMC universal event record format 15 on the FASTJET package for jet clustering 16 17 and on the LHAPDF library for parton densities 18 19 e Monte Carlo event generators Currently implemented generators include ALPGEN 20 EPOS 21 HERWIG 22 PHOJET 23 PYTHIA 6 24 PYTHIA 8 25 SHERPA 26 and VINCIA 27 Some of these in turn use the Les Houches Event File LHEF format 28
26. eflect your choice as you can verify by checking the explicit version numbers written at the bottom of each plot You can return to the Generator Versions page at any time to modify your choice After making your choice click on the Front Page button to exit the Generator Versions view The Generator Validation link changes the page layout and content from the Front Page one to one in which different generator versions can be compared both globally via y values and individually on each distribution This view will be discussed in more detail in section 2 4 The Update History link simply takes you to a page on which you can see what the most recent changes and additions to the site were and its previous history As an experimental social feature we have added a like button to the bottom of the front page which you can use to express if you are happy with the MCPLOTS site 2 2 The Analysis Filter Immediately below the main menu we have collected a few options to control and organize which analyses you want to see displayed on the site under the subheading Analysis Filter illustrated in figure 2 Analysis filter Analysis filter ALL pp ppbar ALL pp ppbar gt ALL ee gt ALL ee Specific analysis Specific analysis i gt Latest analyses ATLAS 2012 11183818 i _ CDF 1990 S2089246 a Analysis Filter Normal View b Analysis Filter Dropdown Menu Figure 2 The analysis filter submenu normal view le
27. ets and extraction of the cross section for the electroweak production of a Z with two jets in pp collisions at sqrt s 7 TeV 1305 7389 55 A Cafarella C G Papadopoulos and M Worek Helac Phegas A Generator for all parton level processes Comput Phys Commun 180 2009 1941 1955 0710 2427 56 J Alwall P Demin S de Visscher R Frederix M Herquet et al MadGraph MadEvent v4 The New Web Generation JHEP 0709 2007 028 0706 2334 57 J Alwall M Herquet F Maltoni O Mattelaer and T Stelzer MadGraph 5 Going Beyond JHEP 1106 2011 128 1106 0522 58 W Kilian T Ohl and J Reuter WHIZARD Simulating Multi Particle Processes at LHC and ILC Eur Phys J C71 2011 1742 0708 4233 30
28. example mkdir SHOME release 2000 epos cd HOME release 2000 epos cp myResults info txt find myResults tgz xargs t L 1 tar zxf NNN wn Now the new results are stored in the directory SHOME release 2000 epos dat To display these and only these new histograms on meplots dev cern ch re point and update the database by cd WWW In sf SHOME release 2000 epos dat SSCRIPTS updatedb sh For example by running SCRIPTS mcprod runAll sh lxbatch 100k epos 19 These actions update the database and the new plots will be visible on the meplots dev cern ch pages Updating the development web pages is a fairly common task while working on mcplots Updating the official web pages mcplots cern ch should of course only be done with great cau tion For completeness we here briefly describe the procedure The contents of a specific revision of the development web page can be transferred to the official site by executing a simple script For this log into mcplots dev cern ch and execute SSCRIPTS updateServer sh r revision d path to dir dat where revision is the SVN revision number of the mcplots code that you want to update the server to and path to dir dat is the full path to the plot data that you would like to display on the web page Either of the arguments can be omitted and at least one argument is necessary For backward compatibility we advise to display plot data that has been stored on m
29. ft and after clicking on the Specific Analysis dropdown menu right At the time of writing the main choice you have here is between ALL pp ppbar for hadron col lisions and ALL ee for fragmentation in electron positron collisions The default is ALL pp ppbar so if you are interested in seeing all hadron collider analyses you will not have to make any changes here Using the Specific Analysis dropdown menu you can also select to see only the plots from one particular RIVET analysis The latter currently requires that you know the RIVET ID of the analysis you are interested in The ID is typically formed from the experiment name the year and the inSPIRE ID or SPIRES ID for older analyses of the paper containing the original analysis as illustrated in figure 2b the numbers beginning with I are inSPIRE codes while ones beginning with S are SPIRES ones You can also find this information in the RIVET user manual 14 and or on the RIVET web pages Finally if you click on Latest Analyses only those analyses that were added in the last update of the site will be shown This can be useful to get a quick overview of what is new on the site for instance to check for new distributions that are relevant to you and that you may not have been able to 4 see on your last visit to the site More options may of course be added in the future in particular as the number of observables added to the pp ppbar set grows 2 3 Selecting Ob
30. g a new RIVET analyses see 14 which also includes ready made templates and examples that form convenient starting points For comparisons to experimental data see the comments in section 4 1 above on ensuring an apples to apples comparison between data and Monte Carlo output 4 3 Event generation Given a RIVET analysis inclusion into the production machinery and display of MCPLOTS can be achieved by editing a small number of steering files We illustrate the procedure with the concrete example of an OPAL analysis of charged hadron momentum spectra in hadronic Z decays 43 for which a RIVET analysis indeed already exists called OPAL_1998_S3780481 First input cards for the MC generator runs must be provided which specify the hard process and any additional settings pertaining to the desired runs Note that random number seeds are handled automatically by the MCPLOTS machinery and should not be modified by the user One such card gt Corrections to full phase space 4m coverage without any tracking or calorimeter thresholds are only useful to the extent the actual measured acceptance region is reasonably close to full phase space in the first place and should be avoided otherwise to avoid possible inflation of errors by introducing model dependent extrapolations 12 must be provided for each MC generator for which one wishes results to be displayed on the site Several cards are already available in the following directory C
31. ges between successive versions thus allowing you to look for any significant changes that may have resulted from improvements in the modelling tuning reflected by decreasing x values or mistunings bugs reflected by increasing x values The largest and smallest individual x values and changes in the relevant data set are also shown in smaller fonts above and below the average values To aid the eye values smaller than 1 are shaded green eins 70 005 0769 e wp o Process Summary click on numbers to see individual observables lt Ay gt incl 5 theory uncertainty on all points 0 71 ee Z hadronic 0 01 0 0 030 0 59 0 45 Color codes GREEN lt 1 ORANGE 1 4 RED gt 4 Figure 7 Generator Validation example showing an excerpt of the validation view for default settings of the PYTHIA 8 generator corresponding to less than lo average deviation from the data values between 1 and 4 are shaded orange corresponding to less than 2c deviation and values greater than 4 are shaded red following the spirit of the Les Houches tune killing exercise reported on in 10 In the example shown in figure 7 the changes are less than a few per cent indicative of no significant overall change Bear in mind that the statistical precision of the MC sample plays a role hence small fluctuations in these numbers are to be expected depending on the available numbers of generated events for each versi
32. gher resolution and or in vector graphics formats Currently pdf eps and png formats are available For publications or presentations we strongly recommend using these high resolution versions rather than the web optimized ones displayed on the page to avoid undesirable pixelation effects Soft QCD mb diff fwd Multiplicity Distributions Generator Group Herwig Pythia6 Pythia8 Sherpa Epos Phojet Custom Subgroup GPMCs Only LHC Tunes Tevatron Tunes Diffraction pp 7000 GeV ALICE INEL gt 0 ATLAS Nch gt 1pT gt 2 5 Soft QCD mb diff fwd Soft QCD mb diff fwd gt 0 In lt 1 0 allp_ Charged multiptcity N gt 1 p gt 2 5 Geavic 3 4M events gt 3 4M events 1 6 doldN an ALICE ATLAS Epos a 1 Epos gt Heewig 4a o gt Heewige Phojet 10 Phojet Pythia 6 Pythia 6 Pythia 8 Pythia 8 10 Sherpa F a aa a o ds 10 Py t Pa na pa i l E 10 20 N ch Non Figure 4 The plot page The generator and tune group selections are at the top followed by the available plots for the chosen observable ordered by CM energy and subordered alphabetically pdf eps png show details gt pdf eps png hide details ALICE reference Epos param Herwig param Phojet param Pythia 6 param Pythia 8 param Sherpa param steer a The Ratio Pane b After clicking on show details Figure 5 The
33. h represent the x distributions with x defined as momentum divided by half the centre of mass energy in light flavor and c tagged events respectively and the distribu tions d05 x01 y01 and d07 x01 y01 which represent the ln x distributions in light flavor and b tagged events respectively The new analysis is added to the MCPLOTS production machinery by adding one line to the file SCARDS rivet histograms map for each new observable In the case of the OPAL analysis we could add the following lines MC Initialization and Cuts in GeV Rivet mcplots beam process Ecm pTMin Max mMin Max RivetAnalysis_Hist Obs Cut ee zhad 91 2 OPAL_1998_S3780481_d01 x01 y01 x opal 1998 uds ee zhad OAs OPAL_1998_S3780481_d02 x01 y01 X opal 1998 c ee zhad OF 32 OPAL_1998_S3780481_d05 x01 y01 xin opal 1998 uds ee zhad 912 OPAL_1998_S3780481_d06 x01 y01 xin opal 1998 c If several different analyses include the same observable or approximately the same e g with dif ferent cuts we recommend to assign them the same consistent name in the Obs column such as x and 1nx above This will cause the corresponding plots to be displayed on one and the same page on the MCPLOTS web pages rather than on separate ones with Cut giving a further labelling of the individual distributions on each page As an option to optimize the MC production rivet histograms map allows the specifica 13 tion of a set of phase spac
34. hich observables actually changed and how Also in this view you can click on the numbers in the table Doing so takes you to the final level of validation detail which is a plot showing the two generator versions compared on the given observable In the example of figure 8 clicking on the value 0 29 in the third row will produce the plot shown in figure 9 As usual you can use the links below the plot to download it in various formats or obtain all the numerical information that was used to make it 3Garbage In Garbage Out pp ppbar Underlying Event Observable Cut __ Eneray x 0 165 IS lt pT gt vs Nch AWAY ATLAS pT gt 0 5 ATLAS pT gt 0 5 lt pT gt vs Nch TRNS ATLAS pT gt 0 5 ATLAS pT gt 0 5 Figure 8 Generator Validation example showing an excerpt of the detailed observable by observable validation view for default settings of the PYTHIA 8 generator comparing two different versions 7000 GeV pp Underlying Event Average Pp vs Nj TRNS In lt 2 5 P gt 0 5 GeV c P k N ee ee ATLAS 8 165 4 8 108 p1 p_ GeV gt 2 2M events Rivet 1 8 2 0 8 0 6 ATLAS_2010_ 8894728 Pythia 8 0 4 L L L L L L 10 20 30 N chg is Ratio to ATLAS mcplots cern ch os 10 20 30 Figure 9 Generator Validation example showing the plot produced by clicking on the number 0 29 in the x table shown in figure 8
35. in position contents and uncertainties with the following specific formats for each section type HISTOGRAM xLo xMid xHi yValu rror rror HISTOSTATS xLo xMid xHi entries sumW sumW2 sumXW sumx2W PROFILESTATS xLo xMid xHi entries sumW sumW2 sumXW sumX2W sumYW sumY2W sumY2W2 where e xLo xHi bin edges low and high positions e xMid bin centre position e yValue bin value e error error bin negative and positive errors 10 e entries number of bin fills e sum sums of various quantities accumulated during bin fills weight weight weight X weight X X weight Y weight Y Y weight Y Y weight weight As mentioned above the sum type quantities provide the additional statistical information needed to combine histograms from different runs 3 2 Directory Structure The MCPLOTS site is structured as a directory tree with separate subdirectories for WWW content MC production scripts etc In the following we assume that this structure has been installed in a global home directory which we denote SHOME home mcplots MCPLOTS home directory where the location home mcplots corresponds to the current implementation on the meplots cern ch server There are five important subdirectories in the home directory SDOC SHOME doc Documentation and Help SPLOTTER SHOME plotter Source code for ROOT based plotting t
36. ing the lines Process names zhad Z hadronic Z Hadronic Observable names x Scaled momentum Scaled momentum xin Log of scaled momentum Log of scaled momentum Cut names opal 1998 uds OPAL u d s events OPAL u d s events opal 1998 c OPAL c events OPAL c events to the configuration file SWWW mcplots conf These steps include a new analysis into the MCPLOTS display framework so that new plots will be visible after the next update of the database Before discussing how to update the MCPLOTS framework to produce MC runs for the new analysis and display the corresponding plots section 5 we will discuss some advanced display possibilities that are steered by mcplots conf 4 4 1 Tune groups MCPLOTS further allows for each one observable to manipulate which of the available generator runs should be displayed together in one plot This is possible by defining tune groups inmcplots conf Tune groups will be displayed as Generator groups between the black observable label bar and the grey collider information bar The definition of tune groups requires three steps To begin with a correspondence between the internal generator name and the public name has to be defined by including a line in the format generator_name generator name in the same section of mcplots conf as other generator names This should be followed by the definition of the tune name through a line like How to include ad
37. irst virtualization based volunteer cloud The basic procedure to include a new measurement on MCPLOTS is first to provide the relevant experimental data points to HEPDATA second to provide a RIVET routine for the corresponding anal ysis and lastly to provide a very small additional amount of information to MCPLOTS essentially specifying the placement of the observable in the MCPLOTS menus and summarizing the cuts applied in a LaTeX string as e g exemplified by the already existing analyses on the site This is described in more detail in section 4 To update MCPLOTS with a new version of an existing generator the first step is to check whether it is already available in the standard CERN Generator Services GENSER repository 38 and if not announce the new version to the GENSER team The MCPLOTS steering scripts should then be updated to run jobs for the new version as described in section 5 To add a new generator to MCPLOTS the first step is to check that it can run within CERNVM CERNVM provides a standardized Scientific Linux environment that should be appropriate for most high energy physics HEP applications including several commonly used auxiliary packages such as the GNU Scientific Library GSL the C BOOST libraries and many others A standalone version of CERNVM can be downloaded from 34 for testing purposes To the extent that dependencies require additional packages to be installed these should be communicated to the MCP
38. llestrero P Bartalini S Belov E Boos et al A Standard format for Les Houches event files Comput Phys Commun 176 2007 300 304 hep ph 0609017 30 LHC home 2 0 http lhcathome2 cern ch 31 B Segal P Buncic D G Quintas C Aguado Sanchez J Blomer et al LHC cloud computing with CernVM PoS ACAT2010 2010 004 32 C Aguado Sanchez J Blomer P Buncic G Chen J Ellis et al Volunteer Clouds and citizen cyberscience for LHC physics J Phys Conf Ser 331 2011 062022 33 D Lombrafia Gonzalez F Grey J Blomer P Buncic A Harutyunyan et al Virtual machines amp volunteer computing Experience from LHC Home Test4Theory project PoS ISGC2012 2012 036 34 P Buncic C Aguado Sanchez J Blomer L Franco A Harutyunian et al CernVM A virtual software appliance for LHC applications J Phys Conf Ser 219 2010 042003 http cernvm cern ch 35 A Harutyunyan J Blomer P Buncic I Charalampidis F Grey et al CernVM Co Pilot An extensible framework for building scalable computing infrastructures on the cloud J Phys Conf Ser 396 2012 032054 36 A Harutyunyan C Aguado Sanchez J Blomer and P Buncic CernVM Co Pilot A framework for orchestrating virtual machines running applications of LHC experiments on the cloud J Phys Conf Ser 331 2011 062013 37 The Test4Theory Project http Ihcathome2 cern ch about test4theory
39. ly The ALPGEN event record can be written in HEPMC format either by invoking AGILE using the unweighted events as inputs or by using dedicated inter face code following the ALPGEN internal parton shower interface code examples and adopting the standard HEPEVT to HEPMC conversion utilities The implementation of the FORTRAN generators in the AGILE framework in order to obtain the events in the HEPMC format is not a prerequisite for running in the MCPLOTS framework It should however be noted that using AGILE simplifies running of RIVET in step 3 in figure 11 It is therefore preferred over dedicated interfaces AGILE allows by setting an input flag to pass parton level events in LHEF format 29 to the supported General Purpose Event Generators We thus anticipate that when showering events in LHEF format with FORTRAN event generators such as PYTHIA and HERWIG no dedicated code will be necessary for the steps 2 and 3 in figure figure 11 6 2 Steps 4 1 4 2 from single run histograms to Physical Distributions After the analysis run in step 3 in figure 11 the MCPLOTS framework merges the single run histograms with the rest of the compatible analysis runs preceding it steps 4 1 and 4 2 In some cases the single run histograms already correspond to Physical Distributions and the merging is done in order to improve the statistical precision In other cases several single run histograms need to be combined in order to obtain the Physical Distributions
40. necessary to update the 1ist_runs function To include for example version 2 7 0 of HERWIG with a tune called default the line echo Smode Sconf herwigt 2 7 0 default Snevt Sseed has to be added Please note that the list_runs function of runAll sh groups the runs of generators into blocks e g all HERWIG runs follow after the comment Herwigt This order should be maintained The necessary changes of list _runs are slightly different depending on if we want to include a completely new generator version or simply a new tune for an existing generator version The above line is appropriate for the former For the latter let us imagine we want to add HERWIG v 2 7 0 with two tunes called default and myTune Then we should add the string mul Smode Sconf herwigt 2 7 0 Snevt Sseed default myTune to the HERWIG block of runAll1 sh After this it is necessary to include the novel generator versions and tunes in the file SCARDS generator_name tunes map where generator_name is the name of the MC generator to be updated For our second example the addition of the lines default 22 1 20 2 7 0 myTune to SCARDS herwig tunes map is necessary Depending on how tunes are implemented in the MC generator it might also be necessary to include a new file with the tune parameters into the SCARDS directory Currently this is the case for HERWIG tunes and non supported tune variations
41. ng the distribution of MC generator runs If mode is set to list the script simple returns a list of all possible generator runs dryrun will set up the event generation machinery but not execute the generation local will queue all desired runs on the current desktop while xbatch distributes jobs on the lxplus cluster at CERN nevt The number of MC events per run filter Optional filter of the MC runs For instance if filter herwig runAll sh will only produce HERWIG results queue Queue to be used on the Ixplus cluster The runAll sh script executes the event generation and analysis steering script SSCRIPTS mcprod runRivet sh for all the desired input settings It is in principle also possible to run this script separately 5 3 Updating the MCPLOTS database To display the results of new MC runs it is necessary to update the database with the new histograms MCPLOTS has both a development area with plots shown on meplots dev cern ch and an official release area with plots shown on meplots cern ch The development pages are updated as follows Let us assume that we have produced new EPOS results and these new results are stored in myResults Then log into mcplot s dev by ssh myUserName lxplus cern ch ssh mcplots dev Then copy the new information and to the directory SHOME release on this machine It is encour aged to include the mcplots revision number e g 2000 into the directory name For
42. o aim to provide event generator authors with a pre release validation service in which a would be new version of a generator or tune parameter card can be uploaded securely and a private version of the site made available on which the corresponding results can be compared with the standard set of generators and tunes Plans for future developments of TEST4THEORY include minimizing the size of the downloadable CERNVM image for TEST4THEORY WCERNVM a new delivery method for TEST4THEORY that would allow one to download install and run TEST4THEORY directly from a web browser TEST4THEORY Direct and the development of a new interactive citizen science application based on the TEST4THEORY framework Note to users of MCPLOTS we are of course very grateful if a reference to this work is included 25 when using content from MCPLOTS but even more importantly we ask our users to please acknowl edge the original sources for the data analyses physics models and computer codes that are displayed on MCPLOTS We have tried to make this as easy as possible by including links to the original ex perimental papers together with each plot Other references that may be appropriate depending on the context include HEPDATA 13 RIVET 14 MC generator manuals 20 26 and relevant physics and or tuning papers As an example of good practice and to ensure maximal clarity and reproducibility all plots on MCPLOTS include explicit generator names and version
43. on Note to make these numbers more physically meaningful the MC predictions are assigned a flat 5 theory uncertainty as a baseline sanity limit for the achievable theoretical accuracy with present day MC models A few clear cases of GIGO are excluded from the x calculation but some problematic cases remain Thus e g if a calculation returns a too small cross section for a dimen sionful quantity the corresponding x value will be large even though the shape of the distribution may be well described It could be argued how this should be treated how much uncertainty should be allowed for each observable whether it is reasonable to include observables that a given model is not supposed to describe etc These are questions that we do not believe can be meaningfully or reliably addressed by a fully automated site containing tens of thousands of model observable combinations In the end the interpretation of the information we display is up to you the user That is also why at least for the time being we do not display any direct comparisons between different MC generators To see the values for all of the individual distributions that enter a given process type click on any of the x values in the table Or to see a comparison between two successive versions click on any of the A x values The result of doing the latter is illustrated in figure 8 You can now scroll down the list of observables to get a more detailed view of w
44. on to RIVET histograms Before running the event generation in step 1 of figure 11 the generator configuration scripts should be set up As discussed in section 4 3 the physics process configuration files for each event generator 21 should reside in the directory SSCRIPTS mcprod configuration See also the discussion of tune groups in section 4 4 1 The location of the SCRIPTS directory was defined in section 3 2 Additional generator specific files may be needed Examples are linking against the generator libraries of the GENSER project parsing the generator configuration scripts or providing generator level event filters used by some of the analyses in order to enable efficient filling of the histograms Some concrete examples are given below Such generator specific files should be put into a dedicated directory SSCRIPTS mcprod generator Using ALPGEN as an example the ALPGEN specific files reside in the directory SSCRIPTS mcprod alpgen The process specific files are passed in text format using the standard MCPLOTS naming conven tion generator process params for example alpgenherwigjimmy winclusive params alpgenpythia6 jets params The parameters in these params files are grouped into sections responsible for for various steps of event generation parameters in sections genwgt and genuwgt are used for the generation of the weighted and unweighted events accordingly the parameters
45. ool SPOOL SHOME pool Output from BOINC cluster SRELEASE SHOME releas Collection of generated MC data SSCRIPTS SHOME scripts Production and update scripts WWW SHOME www Front of house WWW pages and content The Doc directory contains documentation and help content that extends and updates this write up and should be consulted by future developers The SPLOTTER directory contains the C source code and Makefile for the small plotting utility used to generate the plots on the mcplots web pages It only depends on ROOT and takes histogram data files in the format used on the mcplots site as input It can be copied and or modified for personal use if desired as e g in 42 Any changes to the code located in the PLOTTER directory itself on the MCPLOTS server will be reflected in the plots appearing on the site after the plotter has been recompiled and the browser cache is refreshed The SPOOL directory contains the MC data sets generated by the Test4Theory BOINC cluster The SRELEASE directory contains MC data sets generated manually and combinations of data sets so called releases For example typically the data visible on the public site meplots cern ch is a combination of BOINC data sets which have large statistics and a number of manually generated data sets applied on top for distributions that cannot be run on the BOINC infrastructure or to add new versions of generators which were not yet available at the time of gene
46. ormat tomcplots conf Itis not necessary to follow a predefined ordering when adding observable name correspondences Figure 10 illustrates how parts of the declaration lines ctm Transverse Minor Central Transverse Minor gapfr vs dy fb Jets Veto Gap fraction vs amp Delta y FB Gap fraction vs Deltay FB 15 are related to the web page layout The HTML submenu name e g Jets Veto i e the text in the solid black box will appear as a link on a grey field The HTML name of the displayed plot Transverse Minor i e the text in solid green boxes enters both in the menu and on top of the page while in the LaTeX observable name Central Transverse Minor i e the text in the dashed green box is printed directly onto the plot Finally cut names have to be translated as well This is achieved by expanding mcplots conf with cut declaration lines in the format cut_name HTML name plot label in LaTeX format The features resulting from adding the line cmsl pt090 CMS 90 lt pT lt 125 90 lt p_ perp lt 125 are shown encased in magenta boxes in figure 10 Again the plot label 90 lt py lt 125 i e the text in the dashed magenta box is included in the plot in parentheses and after the observable label After translating the internal process observable and cut names the display on MCPLOTS is fixed For the sample OPAL analysis discussed in section 4 3 the current layout would be obtained by add
47. ratio pane before a and after b clicking on the show details link The example corresponds to the left hand plot shown in figure 4 Additional information about the plot such as data tables references and run cards can be ac cessed by clicking on the show details dropdown menu illustrated in figure 5b In this example clicking on ALICE gives you a text file containing a table of the experimental data points along with additional information from RIVET about the plot Clicking on reference sends you to the inSPIRE page for the experimental paper in which the measurement was presented Clicking on a generator name will give you a text file containing a table of the results obtained with that generator together with additional technical information from MCPLOTS including an additional table which is used by MCPLOTS to combine the results of several different runs You can use or ignore the addi tional information in these files as you wish Clicking on param gives you the exact generator run card that was used to make the plot so that you can see precisely how the results were generated These cards can also be useful as examples to start generating your own standalone results or to check that you can reproduce ours Finally the steer link contains the steering card used by the ROOT based tool that makes the actual plots you see Though this tool is not yet publicly accessible on the site just contact us if you would like a copy e g to
48. ration of the BOINC data set The SCRIPTS directory contains various scripts used to organize and run generator jobs and to update the contents of the www directory which contains all the HTML and PHP source code together with style and configuration files for the meplots cern ch front end of the site 4 Implementing a new analysis In this section we describe how to implement additional analyses in the MCPLOTS generation ma chinery so that the results will be displayed on the mcplots cern ch web page The default SVN repository resides at https svn cern ch reps mcplots trunk It can also be ac cessed using a web browser via TRAC at https svnweb cern ch trac mcplots browser trunk 11 The implementation of new analyses relies on four main steps the first of which only concerns comparisons to experimental data it is not needed for pure MC comparisons Furthermore both the first and second steps are becoming standard practice for modern experimental analyses minimizing the remaining burden The steps are described in sections 4 1 4 4 4 1 HEPDATA First the relevant set of experimentally measured data points must be provided in the Durham HEP DATA repository which both RIVET and MCPLOTS rely on see 13 for instructions on this step Important aspects to consider is whether the data points and error bars are all physically meaningful e g no negative values for a positive definite quan
49. s 1960 37 CDF_2005_S6217184_d02 x01 y02 js_diff cdf3 073 ppbar jets 1960 37 CDF_2005_S6217184_d02 x01 y03 js_diff cdf3 084 After changing rivet histograms map it is necessary to run the available MC generators in order to produce the new histograms and then update the MCPLOTS database in order to display the results We will describe how to include new generator tunes run the generators and update the database in section 5 For now we will assume that the results of MC runs are already available and continue by discussing how to translate the language of rivet histograms map into the labels that are displayed on the meplots cern ch pages 4 4 Displaying the results on MCPLOTS The next step after implementing a new analysis is to define a correspondence between the internal names as declared in the rivet histograms map file and the names that will be displayed on the web page and on plots Correspondence definitions are collected in the configuration file SWWW mcplots conf All internal process observable and cut names defined by adding new lines to the histogram map should be defined in the configuration file Process names are translated by adding a line process_name HTML name plot label in LaTeX format to the list of processes at the beginning of mcplots conf Please note that the sequence of process name definitions in this file also determines the order of processes in the web page menu In figure 10 the Jets label
50. servables Below the Analysis Filter the list of processes and observables for the selected set of analyses is shown This is illustrated in figure 3 Jets FB Correlations gt Transverse Minor Identified Particles Y gt Transverse Thrust gt KOS gt Di jet x gt N gt Di jet Ao 5 gt Di jet mass Cross sections J l l 1 Identified Particles pT Gap fraction vs A P y Identified Particles Ratios HT a The Process and Observables List b An expanded dropdown menu J Figure 3 Illustrations of the process and observables list normal view left and after clicking on a shaded dropdown menu right in this case Identified Particles Y Clicking on any blue link below one of the process headers e g below the Jets header fig ure 3a or any blue link in the shaded drop down menus figure 3b will open the plot page for that observable in the right hand part of the page At the top of the plot page figure 4 you can select which generators and tune combinations you want to see on the page By default you are shown the results obtained with default settings of the available generators but the links for each generator give you access to see results for different tune and model variations Use the Custom link to specify your own set of generators and tunes The available plots for the chosen settings are shown starting with the highest CM energies at the top of the page and for each CM energy cascading
51. sics effects The conclusions that can be drawn from comparisons on individual distributions are therefore limited They also gradually become outdated as new models and tunes supersede the old ones In the long term the real aim is not to study one distribution in detail for which a simple fit would in principle suffice but to study the degree of simultaneous agreement or disagreement over many mutually complementary distributions This is also a prerequisite to extend the concept of tuning to more rigorous consistency tests of the underlying physics model for instance as proposed in 8 The effort involved in making simultaneous comparisons to large numbers of experimental distri butions and to keep those up to date previously meant that this kind of exercise was restricted to a small set of people mostly Monte Carlo authors and dedicated experimental tuning groups The aim with the mcplots cern ch MCPLOTS web site is to provide a simple browsable repository of such comparisons so that anyone can quickly get an idea of how well a particular model describes various data sets Simultaneously we also aim to make all generated data parameter cards source codes ex perimental references etc freely and directly available in as useful forms as possible for anyone who wishes to reproduce re plot or otherwise make use of the results and tools that we have developed The MCPLOTS web site is now at a mature and stable stage It has been onlin
52. te the value of the quantity for the in dividual sub sample Hence merging the Np0 Np1 Np2 sub samples in ALPGEN_FIXED mode would result in the following METADATA for X crosssection in pb crosssection 25554 1 samples_crosssection 20831 403148 4285 7315005 436 96532523 It should be noted that the merging in the MCPLOTS needs to proceed on the fly as the new samples are produced This makes the merging more challenging than in the experimental physics analysis case where the final statistics and cross sections of all the Np samples is known at the time of analysis and plot production While in the experimental physics analysis the Np samples can be normalized to the same integrated luminosity prior to the plot production the MCPLOTS machinery needs to deal with merging of the already produced plots In case the need arises further merging modes could be added to the merging structure For this it is however crucial that the information needed for consistent merging is available after the RIVET run and correctly transferred to the merging routine An example piece of such information is the cross section in the MLM matching applications where the final cross section is only known after the parton shower Hence in case the cross section is not correctly transferred from the matrix 24 0 0 Al i 8 0G 10G Frank 103G ksysju gsanco Toby B Igor Michae Ricky ChrisS Greeri Derv S NL Sunny1 Jay Po j
53. the Tevatron to the LHC hep ph 0605240 20 M L Mangano M Moretti F Piccinini R Pittau and A D Polosa ALPGEN a generator for hard multiparton processes in hadronic collisions JHEP 0307 2003 001 hep ph 0206293 21 K Werner I Karpenko T Pierog M Bleicher and K Mikhailov Event by Event Simulation of the Three Dimensional Hydrodynamic Evolution from Flux Tube Initial Conditions in Ultrarelativistic Heavy Ion Collisions Phys Rev C82 2010 044904 1004 0805 27 22 M Bahr S Gieseke M Gigg D Grellscheid K Hamilton et al Herwig Physics and Manual Eur Phys J C58 2008 639 707 0803 0883 23 F W Bopp R Engel and J Ranft Rapidity gaps and the PHOJET Monte Carlo hep ph 9803437 24 T Sjostrand S Mrenna and P Z Skands PYTHIA 6 4 Physics and Manual JHEP 0605 2006 026 hep ph 0603175 25 T Sj strand S Mrenna and P Skands A brief introduction to PYTHIA 8 1 Comput Phys Commun 178 2008 852 867 0710 3820 26 T Gleisberg S H che F Krauss M Schonherr S Schumann et al Event generation with SHERPA 1 1 JHEP 0902 2009 007 0811 4622 27 W T Giele D A Kosower and P Z Skands Higher Order Corrections to Timelike Jets 1102 2126 28 E Boos M Dobbs W Giele I Hinchliffe J Huston et al Generic user process interface for event generators hep ph 0109068 29 J Alwall A Ba
54. tity and whether a detector simulation is required to compare MC generators to them or not If a detector simulation is needed detector level data it may not be possible to complete the following steps unless some form of parametrized response or smearing function is available that can bring MC output into a form that can be compared directly to the measured data For this reason data corrected for detector effects within a phase space region corresponding roughly to the sensitive acceptance of the apparatus particle level with a specific set of cuts defining the acceptance is normally preferred For data corrected to the particle level the precise definition of the particle level including defi nitions of stable particle lifetimes phase space cuts thresholds and any other corrections applied to the data must be carefully noted so that exactly the same definitions can be applied to the MC output in the following step 4 2 RIVET A RIVET analysis must be provided that codifies the observable definition on MC generator output As already mentioned this is becoming standard practice for an increasing number of SM analyses at the LHC a trend we strongly encourage and hope will continue in the future RIVET analyses already available to MCPLOTS can e g be found in the analyses html documentation file of the RIVET installation used by MCPLOTS located in the RIVET installation directory For instructions on implementin
55. use it to make your own standalone plots outside of MCPLOTS 2 4 The Generator Validation View Clicking on Generator Validation see the main MCPLOTS menu in figure 1 opens the validation view You can click on Front Page to get back to the default view at any time In this view instead of the Analysis Filter you will see a list of event generators beneath the main MCPLOTS menu You can click on each generator to see a list of the available tunes and model variations for that generator This is illustrated in figure 6 Generator Tune alpgenpythia6 epos herwig herwig powheg phojet pythia6 650 Sail ore ed Figure 6 Generator Validation View excerpt of the generator tune selection menu As an example clicking on pythia8 default will show the validation view for default settings of the PYTHIA 8 generator in the right hand side of the page illustrated in figure 7 In this view no plots are shown immediately Instead you are presented with a table of x values averaged over all measurements within each process category Note that we use a slightly modified definition of x discussed below At the top of the page you can select which versions of the generator you want to include in the table Click the Display button to refresh the table after making modifications Below the line labelled Process Summary we show the main table of x values for the versions you have selected as well as the relative chan
56. vious section described how to add new processes and new analyses to the MCPLOTS frame work and how to modify their organization and labelling on the web site After a new analysis has been implemented or when updating the site with new tunes generators or RIVET versions the next step is to update the database with new MC generator runs In this section we will briefly discuss how to update existing MC generators by including new generator versions and tunes How to implement a completely new event generator is described separately in section 6 This is followed by a de scription of how to manually produce MC results and how to update the database of the development page mceplots dev cern ch which serves as a pre release testing server for MCPLOTS We finish by explaining how to make a public MCPLOTS release transferring the contents of the development page to the public one 5 1 Updating existing generators MCPLOTS takes generator codes from the GENSER repository which can be found in See http root cern ch specifically the pages on lineStyle and markerStyle A nice helping tool to create your own colour schemes is http colorschemedesigner com 17 afs cern ch sw lcg external MCGenerators Only generator versions in this repository can be added to the MCPLOTS event generation machinery To introduce a new generator version on MCPLOTS changes of the file SSCRIPTS mcprod runAll sh are required Specifically it is
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