Drell-Yan analysis Procedure
This twiki represents a review of all the most important parts of the Drell-Yan cross section measurement. It is intended to familiarize you with the technical aspects of the analysis procedure. At the end of each section there is a set of questions and exercises. Note, the software and samples evolve very frequently so some parts of the page will get obsolete very soon!
- MC samples change frequently (usually we have a new generation of MC samples every season). Even though GEN level stays the same reconstruction keeps getting improved from release to release, so it is recommnded to use the most up-to-date MC. Another things that constantly changes is the vertex information (tuned to data) and pile up.
- MC: 311X Monte Carlo samples (this list shows all the signals and backgrounds we consider, but it is already superseded by Summer11 42X samples)
- DY tautau
- Current latest MC generation is 42X Summer11
- We use SingleMu and DoubleMu PDs, PromptReco (and ReReco when it becomes available)
- JSONs are constantly updated in this directory as we certify more and more data:
- "Golden" */afs/cern.ch/cms/CAF/CMSCOMM/COMM_DQM/certification/Collisions11/7TeV/*Prompt/Cert_160404-161312_7TeV_PromptReco_Collisions11_JSON.txt
- Calo-free /afs/cern.ch/cms/CAF/CMSCOMM/COMM_DQM/certification/Collisions11/7TeV/Prompt/Cert_160404-161312_7TeV_PromptReco_Collisions11_JSON_MuonPhys.txt
- Use DBS tool to retrieve info about the most up-to-date MC and DATA samples
- Relevant software: CMSSW_4_1_3: see the twiki page to get the information about CMSSW releases used for data taking as they evolve
- Global tag
- Data: GR_R_311_V2 for reprocessing and GR_P_V14 for prompt reco
- MC: MC_311_V2, START311_v2
- ElectroWeakAnalysis/Skimming, ElectroWeakAnalysis/DYskimming, UserCode
- Global tag
- how to run: PATtuple production: see the corresponding twiki, note, a lot of code in CVS is outdated (we keep updating it)
Q1: Do you think the list of signal and background samples mentioned above is complete for the Drell-Yan cross section measurement in the region 15-600 GeV invariant mass? (You need to think not only about physics processes but also about kinematic region of the sample generated)
Q2: Using the DBS tool mentioned above or a command line equivalent find all the MC samples relevant for the Drell-Yan cross-section measurement for Summer11 production, example:
Q3. (might be advanced, if you fails ask me) Port the above skimming code to 42X: you need this, because 41X and 42X releases are incompatible
Q4: Produce a PAT-tuple
More PAT-tuples can be found here: /store/user/asvyatko/DYstudy/dataAnalysis11//PATtuple/ (you can use signal and Data only for now)
Since the event size even for PAT is quite big, we usually perform one more skimming step and store our data in form of ntuples. The input for ntuple-maker is PAT tuple (however, with some gymnastics you can run on GEN-SIM-RECO or AODSIM)
Q1: Try to produce ntuple
Hint: spot all the errors, they might be related to global tag, REDIGI version (for MC)
Q2: Find the invariant mass branch and inspect it
step3: Event Selection
Once the ntuples are ready, one can proceed to the actual physics analysis. The first step of every analysis is the event selection. Currently, we use the so-called cut-based approach to discriminate between signal and background. For more on event selection please read chapter 3 in the analysis note CMS-AN-11-013. Before starting to run a macro, set up the working area:
Before running the macros, we need to fix few things which are changing frequently for our analysis:
- Mass range and binning:
for the early stage of 2011 analysis we keep the 2010 binning [15,20,30,40,50,60,76,86,96,106,120,150,200,600]
- Trigger selection:
- See the presentation on event selection for 2011
- Thus, for 2011 we consider a combination of Double muon trigger and a combination of single isolated muon triggers can be used as a cross-check. Use three following combinations:
- HLT_Mu15, HLT_Mu24, HLT_Mu30
- HLT_IsoMu15, HLT_IsoMu17, HLT_IsoMu24
- DoubleMu6, DoubleMu7, Mu13_Mu8
- Offline selection: Baseline event selection has not changed compared to 2010 analysis, see
- we will consider moving to PF muons and PF isolation: this study is in progress right now
- Relevant software: ROOT macros for control plots and invariant mass plot are here: UserCode/Purdue/DYAnalysis/AnalysisMacros/ControlPlots, check it out as usually
- When you have produced the ntuples, you need to set the up:
To produce the invariant mass plot do:
To produce dimuon kinematic distributions run
To produce other control plot (for all the evnet selection variables used in the analysis, as documented in the note), use:
Q1: Check data/MC agreement for each plot, look for discrepancies.
Another constituent of the cross-section measurement is the acceptance.
- Acceptance is determined using GEN level information, so that the generation of MC is not crucial
- Use the acceptance numbers documented in the note to save time: CMS-AN-11-013
Below are some additional details on the acceptance calculation which might be necessary if the procedure will change.
We use POWHEG NLO acceptance, see all the relevant formulas in this talk (the updated version), see slide18 for acceptance definitions and refer to earlier talks. Di\ue to the intrinsic discrepancies in the modeling between the POWHEG and FEWZ we correct the Z kinematics. For that, we extract the weight maps from POWHEG at NLO and from FEWZ at NNLO (to be more specific it is at NNLO below 40 GeV and NLO otherwise, as the effect of higher order corrections is negligible at the higher masses). The weight map is essentially the ratio of double inclusive cross-sections extracted from POWHEG and FEWZ per PT-Y bin (PT, Y refer to Z kinematics, which is identical here to dimuon kinematics, our final aim). Details on the re-weighting technique are also in the linked presentation.
How to run: The code makes use of mostly Adam's tools. Current working area is here: /home/ba01/u115/asvyatko/PATAdam/CMSSW_3_8_7/src
To setup area do:
Not yet tested under CMSSW 4XY, because there was no need - GEN level info did not change. Follow README to calculate weights, which also calculates the 1D acceptance in mass bins.
Weight map producer uses the FEWZ acceptance as the input, find all the macros here: /UserCode/ASvyatkovskiy/FEWZ_scripts,
to work one needs to do*:*
To run you use whatever config you need
to get the output of the jobs use corresponding get-output scripts:
The details on the factorization and the application of correction factors are documented here , and can be found in this talk. With the current factorization scheme we measure four following efficiencies:
- Trigger, Reconstruction+ID, isoloation, tracking:
- We use the officiela TagAndProbe package
- How to run (on top of CMSSW 414):
- The procedure goes in two steps:
- T&P tree production -> rerun seldom (ideally once), it depends only on the definitions of the tag and probe
- fitting: separate job for trigger and all the muonID related efficiencies -> reran frequently and usually interactively (change binning, definitions)
- All the latest macros/configs can be found here: UserCode/ASvyatkovskiy/TagAndProbe
- Isolation: RandomCone - currently, code is private and not possible to use.
After familiarizing yourself with the TagAndProbe package, you need to produce the muon efficiencies as a function of pT and eta. You do not need this in the analysis, but rather to understand if everything you are doing is correct. After you are done with that, produce the 2D efficiency pT-eta map (it is alredy produced in one go when running fiMuonID.py).
The final step here is to produce the efficiency as function of invariant mass and the efficiency correction factor as a function of invariant mass.
step6: Background estimation
There are various methods employed to estimate the QCD background in a data-driven way (QCD is currently the only background estimated not from MC). The most important are:
- The template method
- Isolation variable has distinct shape for signal and background
- Create templates for shapes using data
- Same sign events for background
- Signal from opposite sign events in the Z peak region with one muon highly isolated (shape taken from second muon)
- Extract estimate of background contamination in signal region using the fit results
- Weight map method
- Produce pT-Y weight map
And you can always ask me: firstname.lastname@example.org