1 Introduction 2 Your Project - UChicago High Energy Physics
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1. CMS Studies of jet production with cms in pp collisions at s 7 tev arX1v 1106 38860v1 June 2011 CMS W z jets production with cms detector arXiv 1111 3015v1 November 2011 Les Houches Conference The qcd sm working group Summary report arXiv 0204316v1 April 2002 J Alwall et al Madgraph 5 Going beyond arXiv 1106 0522v1 June 2011 D Miller for ATLAS Studies of the internal properties of jets and jet substruc ture with the atlas detector arXiv 1110 5995v1 October 2011 M Schwartz J Gallicchio Quark and gluon tagging at the lhe arXiv 1106 8076v1 October 2011 K Van Tilburg J Thaler jidentifying boosted objects with n subjettiness arXiv 1011 2268v3 January 2011 G Salam M Cacciari and G Soyez The anti kt jet clustering algorithm arXiv 0802 1189v2 April 2008 C Vermillion S Ellis and J Walsh Recombination algorithms and jet sub structure Pruning as a tool for heavy particle searches arXiv 0912 0083v1 December 2009 S Mrenna T Sjostrand and P Skands Pythia 6 4 physics and manual arX1v 0608175v2 May 2006 152. e NTupleMaker cc The main nTupler This is the piece of the code that will be compiled into an executable and do the conversion of the file from ExRootSTDHEPConverter output into an analyzeable Root TTree If you want to add any new routines or variables to output this is the file you will use to incorporate these changes e ProcessFile sh Bash script that can be run as prompt MadGraph Process gt source ProcessFile sh in hep out root to convert a hep file from MadGraph to a analyzeable output file in one line The Makefile here includes a directive that includes the FastJet libraries by point ing to the fastjet install directory FASTJET Users meehan work fast jet install To work on your machine change the path to point the directory in which you created fastjet install earlier Now use the Makefile to compile the nTupler Jet Clustering by executing prompt MadGraph Process gt make 13 which will produce the executeable NTupler which can be run on an input file in root that was previously produced by ExRootSTDHEPConverter to pro duce the output nTuple out root by executing prompt MadGraph Process gt NTupler in root out root If you have set up all components correctly this should produce the file out root which is in the correct format to be analyzed as a Root TTree using the procedure that was previously outlined in the Standalone ROOT nTuple Analysis If you have done enough Root tutorials and looked at e
3. You will most like not have to deal with such things right away but having the ability to do so will help you convert your analysis code into something that can more easily be used to do ATLAS analysis ROOTCFLAGS shell root config cflags ROOTLIBS shell root config libs 1Minuit 1EG CXX g CXXFLAGS 0 Wall fPIC ROOTCFLAGS OBJS Physics o Physics OBJS CXX o OBJS CXXFLAGS ROOTLIBS CC 0 CXX c CXXFLAGS lt clean rm f 0 Note that in this code the lines indented must be indented using a tab and not a string of spaces or the Makefile will not run properly This file will compile the source code scripts into executables and can be run by executing prompt gt make Now make a new textfile called input txt and copy the name of the test dataset files to it as below Make a line break after each dataset file Note that these datasets can reside in any location and you must just provide the entire path to the dataset if they are not in the same directory as your analysis code If the file resides in the same directory as your analysis code they you use ZZWZ_l1qq_10000events_ntuple_01 root but if it does not then you would use datasets mysets montecarlo signal ZZWZ_1lqq_10000events_ntuple_01 root if they reside in the directory datasets mysets montecarlo signal And as before if you have multiple files you want to string together and run in the same analysis
4. and then a corre sponding link to a specific process one can see all the tree level Feynman diagrams NOTE There are no loop diagrams this is because MadGraph only generates diagrams at tree level can you guess what this means However for our purposes 11 you care about the Results and Events Database link Go into this link and you will see a number of files that can be downloaded as in Fig B Results for p p gt e ve 1 in the sm Available Results Events Cross section pb Parton level LHE rootfile Hadron level results banner Pythia Reco Objects PGS STDHEP LHE rootfile LHE 61811E 04 Pp 7000 x 7000 GeV LHCO rootfile Main Page Figure 2 What the MadGraph page should look like with all the appropriate output if you have installed everything correctly Download the STDHEP file corresponding to the process you just generated which is a zipped file ending in the suffix hep Unzip it and place the and place the hep file into a new directory call it Process that will be dedicated to converting and nTupling the files into the format you previously analyzed with Root 3 2 2 ExRootSTDHEPConverter Usage If you succesfully installed all the utilities then in the MadGraph directory there should appear an ExRootAnalysis directory which contains multiple executable files Copy the ExRootSTDHEPConverter to the Process di
5. elements Figure 1 Hard scatter by MadGraph on left with subsequent phenomenological showering by Pythia on right There are many different ways to use it and the procedures presented here are only one path that can be followed and only uses a fraction of its functionality It is based on using MadGraph to produce something called STDHEP files which calculate the kinematics of a hard process as shown in Fig 1 which is then showered using Pythia as in Fig This showering procedure produces hundreds of final state particles each of which is represented by a Lorentz 4 vector and would be representative of the particles entering the ATLAS detector Because there are so many particles in this final state these files are formatted in accordance with the Les Houches accord 8 such that they conform to standards of the particle physics community and there is well developed software that can read them and put them in terms of a root file that you now know how to analyze from the previous section There are two main stages to this conversion In the first step the STDHEP files are transformed to Root readable files using ExRootSTDHEPConverter which creates a Root readable file that can then be sent through an nTupler program to perform the organization of physics objects such as electrons muons MET Missing Transverse Energy and jets In the following you will learn how to perform each of these steps and how to modify them
6. histograms of different variables with different kinematic selections to investigate the different aspects of the physics in which you are interested Some things you may want to consider adding to your code at this point to allow for more flexibility if you have not done so already are e The ability to pass the executable arguments look up how to do this in the c reference This will allow you to pass it a char argument that specifies which set of input files to run over so that it can be made to analyze signal or background You can also specify the name of the output root file this same way so the output is different for signal or background e A loop that runs over all events in the data file e A section it could be an external function or class if you know how to do this that selects electrons muon and or jets that pass certain kinematic or quality requirements like el_pt gt at i gt 30 0 GeV This would have to be run for each event e A conditional statement that only selects events that have exactly two good as defined above oppositely charged leptons and combines their four vectors into a single four vector representative of a dilepton Z boson in some cases system Try exploring the TLorentzVector class in Root to do this 3 2 MadGraph Setup MadGraph_ 9 is one of many different types of Monte Carlo physics generators that can simulate particle physics events based on the analysis of Feynman diagrams matrix
7. then you can include their paths as new lines in this file However do not mix physics processes One should only need to link together multiple files when they are limited by the number of events that can be stored in a single file for a single process 3 1 6 Compile and Run for First Time After making the previous files you are ready to run your analysis code To compile the code type prompt gt source cppmake sh Be patient this may take a while and will take longer if you have an involved code or you are including multiple external libraries Chances are you will have bugs in your code and you will need to fix these However once the code is com pileable this will produce an output executable Physics that can be run by typing prompt gt Physics This will run your analysis code creating and filling any histograms you have spec ified it to and printing out any messages you have specified it to print It should produce the output file Physics_output root that you told it to above As you should know from the Root tutorials this file and its contents can be viewed by running root root 0 new TBrowser If you have done everything correctly then this file should contain some histograms of various things you have specified You re job now is to figure out if these his tograms are correct Are they filled Do they have the right shape Do they have too many bins Too few and then elaborate on your code to produce
8. to suit your needs 3 2 1 MadGraph Setup and Usage Unless MadGraph is already set up on your machine you will need to download and install it yourself To do so go to the MadGraph site http madgraph hep uiuc edu register yourself as a new user and go to Downloads to download the latest tarball Place it in a working directory and untar it with prompt gt tar xzvf MadGraphd_v _ _ Now go into the MadGraph working directory you just created NOTE for running MadGraph you will need a Fortran compiler g77 a c compiler gcc and Python v2 6 or later installed on your machine first If you do not have these installed then install them as necessary for your machine Once you have successfully installed the software start MadGraph and install all four packages as follows prompt MadGraph gt bin mg5 If Python2 6 is not the default version of python for your machine then modify the first line of the bin mg 5 file from usr bin env python to usr bin env python26 This will ensure that MadGraph will use the Python2 6 version each time you start it Once MadGraph is started execute mg5 gt help install syntax install pythia pgs Delphes MadAnalysis ExRootAnalysis Download the last version of the program and install it localy in the current Madgraph version In order to have a sucessfull instalation you will need to have up to date F77 and or C and Root compiler mg5 gt install pythia pgs and then insta
9. Standalone ATLAS Analysis Project Sam Mechan The University of Chicago High Energy Physics 1 Introduction Presently the LHC is delivering luminosity to ATLAS at a rate of approximately 35 x 10cm s This luminosity translates into 10 collisions per second That s a lot of collisions However most of these collisions will not be interesting the def inition of which is left up to you So it is the job of physicists to develop clever ways to sort through these events and determine interesting signatures that can distinguish the haystack from the needle unless of course you are looking at the haystack in which case you have a different set of challenges However because of the scale of the ATLAS experiment the computing infras tructure can take a considerable amount of work to understand and is in such a constant state of flux that it can be more of a hinderance when working on some thing like a BA thesis or a summer project However thanks to the work of a lot of smart people there are analysis tools that can be used to approximate and they do a pretty good job the physics that goes on at the LHC using ATLAS And the great thing is these tools can be used on your personal laptop so you can do LHC physics anywhere This project will introduce you to those tools help you set them up on your computer 2 Your Project Within ATLAS heavy particles like W and Z bosons are created in numerous different ways So
10. TCollection fc gt GetList std cout lt lt Total number of entries in chain all files lt lt chain gt GetEntries lt lt std endl Init chain Replace void Physics Init TTree tree By void Physics Init TChain tree Replace virtual void Init TTree tree By virtual void Init TChain tree 3 1 4 Modify Physics C Start by including the basic headers one needs to do analysis with the Root tools include the headers you need for your analysis include include include include include include include include include include include include lt TROOT h gt lt TChain h gt lt TFile h gt lt TH1 h gt TApplication h mandatory lt stdio h gt lt stdlib h gt lt iostream gt lt fstream gt lt math h gt lt vector gt lt list gt include lt string gt Include the following function just below the include statements Note that the input txt file contains a newline separated list of the ntuple files over which you want to run the analysis code You will create this file with a sample nTuple path later int main int argc char argv Physics a input txt instance a of Physics with input txt files a Loop execute code in Loop function of a The main part of the analysis will be done in the Physics Loop function From what you know from doing the root tutorials you will be able to implement things as below Start by removing al
11. Z gt 1 1 j 1 add process pp gt Z gt 1 1 j j 2 add process pp gt Z gt 1 1 j j j 3 This indicates that you want to generate three different process the production of a Z boson and subsequent decay to t47 pair in association with 0 1 and 2 jets Now modify the run_card dat file This file controls many different param eters of events you will generate but to begin with only change the input beam energies from 7000 GeV to 3500 GeV to correctly simulate the current LHC beams You are now ready to simulate events Go into the Zjets directory and execute prompt MadGraph Zjets gt bin new_process_mg5 which will draw all of the corresponding Feynman diagrams for the interaction you specified in the proc_card mg5 dat file Now execute prompt MadGraph Zjets gt bin generate_events entering 0 to run the event generation in serial and then a descriptive title for the run This can be expediated and later more easily implemented in bash by executing something like prompt MadGraph Zjets gt bin generate_events 0 Zplus0123jets_10000events After MadGraph has finished producing all of the events and the prompt reap pears check the output by executing prompt MadGraph Zjets gt open index html which will bring you to a web browser and you can view different information about your events Explore this page to see what information MadGraph automatically generates For instance by clicking the Process Information link
12. ader file folling the define line include the following lines include lt iostream gt include TFileCollection h using namespace std Replace TTree fChain pointer to the analyzed TTree or TChain By TChain fChain pointer to the analyzed TTree or TChain Replace Physics TTree tree 0 By TChain chain Physics const char fileName Note that this is where one can include the declarations of extra functions you need in your C file e g int elec_selection int ielec for selecting a sub set of good electrons It is alright if you don t have any of these yet however if you don t know how to declare functions in c you may want to go back to your c tutorials and review how to do this at this point Replace the constructor another c word you should know associated to classes Physics Physics TTree tree if parameter tree is not specified or zero connect the file used to generate this class and read the Tree if tree 0 TFile f TFile gROOT gt GetListOfFiles gt FindObject ZZWZ_11qq_ 10000events_ntuple_01 root at f f new TFile ZZWZ_11lqq_10000events ntuple_01 root tree TTree gDirectory gt Get physics Init tree By the constructor Physics Physics const char inputFile TChain chain new TChain Physics TFileCollection fc new TFileCollection mylist mylist inputFile chain gt AddFileInfoList
13. f AntiKt4 jets and one for Cambridge Aachen jets If these terms seem foreign to you then go back to FastJet and work through some of the tutorials they will help explain the nuts and bolts of how to get FastJet to do different things And then ask someone what these different jets are 4 Encouraging Words When doing data analysis there seem two be to main hurdles that you encounter 1 Why doesn t anything work 2 Why is this so damn hard 14 Hopefully this short guide has helped to adress the first and allow you to concentrate more on the second over the coming days weeks and months Good luck References 1 2 10 11 12 13 14 15 ATLAS confinement arXiv November 2009 ATLAS Measurement of inclusive jet and dijet cross sections in proton proton collisions at 7 tev centre of mass energy with the atlas detector arXiv 1009 5908v2 September 2010 ATLAS Study of jet shapes in inclusive jet production in pp collisions at sqrt s 7 tev using the atlas detector arXiv 1101 0070v1 December 2010 ATLAS Measurement of the production cross section for w bosons in asso ciation with jets in pp collisions at sqrt s 7 tev with the atlas detector arXtv 1012 5382 February 2011 ATLAS Measurement of the production cross section for z gamma in as sociation with jets in pp collisions at sqrt s 7 tev with the atlas detector arXwv 1111 2690 November 2011
14. l the comment lines and replace the remaining code with the modified code below TH1F hi new TH1F hi electron pt 1000 0 1000 if fChain 0 return Long64_t nentries fChain gt GetEntriesFast Long64_t nbytes 0 nb 0 for Long64_t jentry 0 jentry lt nentries jentry Long64 t ientry LoadTree jentry if ientry lt 0 break nb fChain gt GetEntry jentry nbytes nb if el_n gt 0 hi gt Fill el_pt gt at 0 TFile outputfile Physics_output root RECREATE hi gt Write outputfile Close This is only a brief example and fills the histogram with the pr of only the first electron in each event Over time your analysis will grow by adding things like this After adding a few basic things to 1 create 2 fill and 3 writeout histograms for various variables move on to the next section 3 1 5 Make Compiling Tools In the directory you have been working to create your analysis code make a new textfile called Makefile and copy the following lines to it This is your Makefile something you have hopefully learned about from your exploration of c This is used to compile your analysis into an executable file and link to this any external libraries necessary to do complicated things like scaling measured electron energies to account for detector defects or calculating reweighting factors that account for something called pileup if you don t know what this is ask someone
15. ll Delphes MadAnalysis and ExRootAnalysis in the same way Wait for each to successfully complete because having each of these is important to be able to output STDHEP files from MadGraph Next in the main MadGraph di rectory copy the Template directory to a new directory call it Zjets Go into the Zjets Cards directory and make sure that all the proper cards are copied as needed To get the required STDHEP output one only needs to copy the pythia card as prompt MadGraph Zjets Cards gt cp pythia_card_default dat pythia_card dat But it is also good to have access to other outputs from MadGraph if your analysis needs them in the future so copy the other cards as prompt MadGraph Zjets Cards gt cp delphes_card_ATLAS dat delphes_card dat prompt MadGraph Zjets Cards gt cp delphes trigger ATLAS dat delphes trigger dat prompt MadGraph Zjets Cards gt cp param card default dat param _card dat 10 prompt MadGraph Zjets Cards gt cp pgs_card_ATLAS dat pgs_card dat prompt MadGraph Zjets Cards gt cp proc_card_mg5 dat proc_card dat Now that you have all the necessary setup finished go to your Zjets Cards di rectory and modify the proc_card_mg5 dat file This is the card that determines the specific physics process Feynman diagram that will be calculated and simu lated Replace the lines generate pp gt e ve 1 add process p p gt e ve j 2 add process pp gt tt 3 with generate p p gt Z gt 1 1 0 add process pp gt
16. mething called the TSelector class which can be run within Root to perform a set of event selections However in this framework you will create a class Physics to analyze ntuples that can be used as a standalone compileable program that draws upon functionality from Root and FastJet 3 1 1 Initial Setup Before analysis follow these steps to get c and Root set up on your machine This is easier to do for Linux or Mac machines If you have a Windows machine we reccomend that you partition your hard drive and install Linux on part of your hard drive This way you can use the Linux part of you machine to boot into the environment that can be used for analysis If you are working on a UChicago HEP computer these utilities are likely setup for you already e If you do not know how to program in c start by performing a few basic tutorials to learn how to write compileable programs and use Makefiles Such tutorials can be found on http www cplusplus com doc tutorial e If you do not already have Root set up on your machine and or do not know how to use it then start by downloading and installing the latest version of Root on your machine This is described on http root cern ch drupal content downloading root 4The steps presented here are adapted from the tutorial https wiki physik uni muenchen de etp index php ROOT_grid_analysis e After installing Root go ahead and try to work through as many of the exam ples on http ro
17. metimes they may be created from interesting physics qq gt H ZZ and sometimes they may be created from standard model processes qq gt Zqq But what comes into the ATLAS detector is the decay products of these W and Z bosons These decay products can be leptons or partons and we can use the measurements we make of the kinematics of these decay products to reconstruct the W and Z bosons Much work has been done to understand the kinematics of leptonically decaying W and Z bosons A 7 but those that decay hadronically are more difficult to understand This is because the quarks coming from Z gt qq do not interact with the detector in the same way In fact they cannot even stay as single quarks because of something called confinement I This confinement causes the quarks to hadronize and produce a shower of particles that enter into the ATLAS detector calorimeters These showers of particles are what we measure and are called jets 6 13 In contrast to reconstructing a leptonic decay 1 The author can be contacted at meehan uchicago edu This is as of 19 December 2011 with current running conditions found at hitp op webtools web cern ch op webtools vistar vistars php usr LHC1 3If you are a student of UC HEP then work on the local machine mjolz2 This has been configured with proper setups for some of the tools such as Root python and the compilers you will need in this project from clean well measured electrons or m
18. nough examples you should know the basics of how a Root TTree is structured and how to read write from it If you do not know these at this point go back and do so as it will be absolutely necessary if you wish to be able to use this code to investigate new and different kinematics and variables than it currently provides Knowing these basics the best way to understand the code it to read through it line by line and understand what is happenning at each step Do this and see if you can identify the following pieces of code and expound on the code by doing the following e Identifying where the program load an event from the input TTree into memory Identifying where the program loops through all the particles in a given event Identifying where the program determines if the particle is a final state particle based on PID infromation Identifying where the program creates and fill block corresponding to electrons muons and photons These two things may happen in two different locations e Where MET Missing Transverse Energy is calculated Does this calculation make sense What does the nTupler do with the leftover particles that are identified as being in the final state but not idenitified as electrons photons or muons FastJet is invoked here to create variable blocks corresponding to different jet collections Currently there are blocks corresponding AntiKt7 and Antikt10 jets see if you can create a block with the same structure o
19. nts where the decay is semileptonic meaning that the Z decays to pair and the other boson decays to a pair of jets Analyze both samples in the same way only selecting events where a good dilepton pair has a mass close to that of the Z boson 91 GeV and on the same set of axes overlay the invariant mass plot of the two highest pr jets be sure to scale each sample to the corresponding process cross section and luminosity If you had data collected from ATLAS would it be easy to distinguish an excess above the Z jets background due to the inclusion of the ZZ WZ diboson physics Is it possible by making certain kinematic requirements on different physics objects for instance pr Z gt 100GeV that make it easier to distinguish such an excess Play around with different kinematic variables to see how good you can do How can you tell if a cut is beneficial or not Think Poisson statistics and if this hint is not illuminating ask someone After working with kinematics as much as possible you will start to go beyond by using an aspect of jet substructure Thinking about the decay of your signal process W Z jj it is evident that these jets can onlybe produced by quarks so if we could have some way to discriminate quark jets from gluon jets we could use it to select these jets only Take a look at some of these papers to learn more about We don t know much about this yet You re job is to learn what you can about this topic incorp
20. on but you probably won t worry about this to begin with To do this you need to start by setting up Fast Jet which can be found on the web to download at http fastjet fr After you have downloaded and unpacked the tarball of the FastJet version you plan to use I recommend installing version 3 or later to have access to features such as pruning merging etc Now download the user manual and follw the quickstart section of the manual following through until you are able to successfully run the simple example includ ing in the manual If you can do this everything is set up properly Note that in the quickstart section of the manual the main hangup that caused for confusion when trying to compile a program using the FastJet libraries and namespace were that to include the fastjet install directory one must be sure to use the key in the upper left of the keyboard instead of an apostrophe 3 2 4 nTuple Creation After having set up FastJet successfully go to the site http hep uchicago edu mee han StandaloneAnalysis Tutorial and download the following files e MakeFile For compiling the nTupler e NTupleMaker h The main header file for the nTupler containing all the in formation about the variables in the TTree produced from ExRoot STDHEPConverter and the TTree that will be output from this nTupler in addition to any other variables class or function definition you need for any procedures you write
21. orate it into your analysis and then teach us what you know 3 Tools As previously mentioned the tools used to do official ATLAS analysis with data from the LHC can for some purposes be more combersome than useful For this project such is the case However there are two tools used in ATLAS analyses that are fully open source and can be used by you to investigate things that if useful can be incorporated into an official ATLAS analysis These are e ROOT The main analysis package used by the high energy physics com munity ROOT is a derivative of c so if you already know that coding language great If not then you will have to do some additional homework e MadGraph MadGraph is a tool used to generate Monte Carlo physics events and can be used to generate pseudo data that looks just like what you would see from ATLAS This pseudo data can then be analyzed using ROOT to get results that can be used to draw conclusions about the physics you are investigating 3 1 Standalone ROOT nTuple Analysis To perform standalone analysis you will be using the c coding language One of the main websites with directions on how to use different features of this language is http www cplusplus com The official root website can be found at http root cern ch drupal This contains documentation that will be useful as you progress and want to use more complicatted tools from Root The conventional way to do analysis with root is to use so
22. ot cern ch root html tutorials as you can stand The more examples you do here the better e After you are comfortable with Root you will use an automatic Root utility to create a standalone class you should know what this is in c speak that can be compiled and run to analyze an ntuple This is described in the next section 3 1 2 Generate Class Start by obtaining a Root ntuple that has the structure of a TTree a Root class One such example of an nTuple can be found at http hep uchicago edu mee han StandaloneAnalysisTutorial with the suffix of root This is the same format of nTuple as you will be producing in the next section of this tutorial using MadGraph Download this and put it in a directory of your own called it MyAna Open root and use it to create the Physics h and Physics C class files root 1 TFile f new TFile ZZWZ_1lqq_10000events_ntuple_01 root root 2 TTree t TTree f gt Get Physics root 3 t gt MakeClass Physics Info in lt TTreePlayer MakeClass gt Files Physics h and Physics C generated from TTree Physics Int_t 0 3 1 3 Modify Physics h Now that you have created the basic analysis class using root you must modify the necessary sections to make it a program that can be compiled as a standalone pro gram and used to analyze the ntuple or any ntuple with the same structure without Root The first piece you will modify is the header file Physics h At the top of the he
23. rectory you created ear lier Run the STDHEP file through this processor as prompt Process gt ExRootSTDHEPConverter file_in hep file_out root to output the Root readable pythia file file_out root Open this file with a TBrowser and look at its contents to see what information is currently there Note though that during the showering process not all the particles whose kinematics are contained in this file make it to the final state determined by looking at their Gen Particle Status and enter into the ATLAS detector However all of this information is contained in this file you just produced Furthermore this file contains informa tion on electrons muon and photons all of which we can measure 4 vectors for but also on many other species of particles identified by their GenParticle PID that cannot be measured as cleanly but will be clustered into jets using FastJet This process of organizing the Root file you just created into a file that can be easily analyzed as you previously did is the topic of the next section 3 2 3 FastJet Setup The last step in creating an analyzeable ntuple from MadGraph is to transform the showered particle file output from the ExRootSTDHEP Converter into a Root file 12 containing a TTree that event by event contains separate banks for the various particle types their respective 4 vectors and any other measurement information that may be useful in analysis e g detector quality informati
24. uons reconstructing a hadronic decay from jets is a much messier business For this reason we are interested in investigating techniques that can be used to extract the most information we can from a jet This is a field of study that is called jet substructure 14 To start with once you have set up the analysis tools described in the following sections try to do the following to start your analysis You ve got a bunch of leptons electrons and muons in your ntuple you ll know what this is later do all of them fall within the ATLAS detector think polar angle Do they all have enough energy to be detected Put some cuts on kinematic variables to select good leptons The signal Monte Carlo that you are working with has the processes Z amp By selecting only events with two good leptons can you reconstruct the invariant mass of the dilepton system and see the leptonically decaying Z boson peak The signal Monte Carlo that you are working with also has the processes Z qq By selecting only events with two good jets can you reconstruct their invariant mass and see the hadronically decaying Z boson Which one of these two resonant peaks would be easy to distinguish from a background Why NOTE the answer is the leptonically decaying Z peak If you don t see this then ask With MadGraph produce a large set 1 million Z jets events to simulate your background and a large set of ZZ WZ eve
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