Z0 measurement in first year heavy ion data

Heavy Ion Collision at LHC will explore the region of energy and particle density significantly beyond those reachable at RHIC. This gives rise to addition of qualitatively new probes that become accessible in detail only at LHC energies. The factor 30 increase in energy between RHIC (200 GeV) and LHC ( 2.76 TeV) decreases the x values from 0.02 to 6 ~ 7 X 10 ^-4 . The low x region can be effectively probed in the perturbative regime up to Q² > m ² _Z0 at LHC only. At this high collision energies of LHC, the cross-section for the processes with Q ² > (50GeV ) ² are large enough for detailed systematic studies. Massive gauge boson Z0 production proceeds predominantly through the q q channel. Hence Z0 boson provides a unique opportunity to study the modifications of quark distributions in the nucleus at high Q ² = m ² _Z0 in LHC. The CMS detector at LHC is designed to identify and precisely measure muons over a large energy and rapidity range and is well suited to study the Z0 boson in their muon decay channel.

Another importance of Z0 channel in CMS Heavy Ion Physics lies in the fact that, it is considered to be the alternative baseline for the quarkonium physics. The baseline for quarkonium suppression at RHIC is dilepton continuum which is mostly produced by Drell-Yan like processes. AT LHC energy, the dilepton continuum will be over shadowed by the contribution from semileptonic charm and beauty decays, whose cross-sections are not only having uncertainties but also suffer from nuclear effects. Z0, with very little final state interaction, is thus a potential candidate for baseline of quarkonium suppression.

MinimumBiasedJpsiMeasurement

Z0FromJulyExercise2010

Common AnalysisCode For Z0 measurement

Working on

Todo list :
- Finalise Z0 Filters and categories Comments from others required Done
-
A- later
-
-Test the algorithms for Z0 embedded inHydjet minimum biased Heavy ion
events
A- can use the files from february (details here
https://twiki.cern.ch/twiki/bin/viewauth/CMS/HImuonReco#Hi_offline_reco):
for MinBias : /castor/cern.ch/user/s/silvest/rootfiles/HI/Z/root/RECO
for b-0 : /castor/cern.ch/user/s/silvest/rootfiles/central/Z0/root/RECO

Code development for Heavy Ion

We started to finalize analysis frame work for Z0 measurement. Heavy ion reconstructed data will have reconstructed muons in reco::Muons collection. Reconstructed muons collection will have three type of muons

1. Global Muons

2. StandAlone Muons

Tracker Muons Global Muons are best quality muons which are reconstructed in muon chamber and then matched to tracks in tracker by a combine fit using Kalman Fitting. StandAlone muons are tracklets reconstructed in muons chambers which does not matched from any track in tracker. Also Tracker Muons are low energy muons which does not reach up to muon chambers due to high magnetic field, and being reconstructed in tracker only by their property on minimum energy disposition in tracker. In heavy ion collisions track density will be very high in tracker so tracker muons will not be very suitable for Z0 reconstruction in heavy ion collisions. We make filters for good Global Muons and good Stanalone Muons which select good muons from muon collection on the basis of their pT and pseudorapidity .We started to make Physics Analysis Toolkit (PAT) objects from reco::Muons. PAT is a collection of standard reconstructed objects like (Muon, Electron, Charged Hadrons, neutral hadrons) which are finalized by various Physics Analysis Groups in CMS

Three categories for Z0 are formed

1. DiMuons Global Global

2. DiMuons Global Standalone

3. DiMuons Standalone Standalone

common analyzer : ZToMuMu

• MuSkim_cfg.py: Uses heavy ion reconstructed files and select events with muons, makes pat muons from reco::muons, selects goodSTAmuons and goodGlobalmuons.
• ZToMuMuSkim_cfg.py: Can take output of MuSkim _cfg.py OR Z0Ana/JulyExercise10/pythons/muonSkimPatRecoTemplate_cfg.py, Makes exclusive Z0 categories. Can be modified to use patMuons insted of reco::muons.
  
• ZToMuMuPlot_cfg.py: Takes output of ZToMuMuSkim _cfg.py and plots Z0 and daughter muons kinematical distributions.
• Z0MassFit.C: Fits Z0 mass peak with RBW+Pol2 and calculates efficiency for MC and Yeild for data.
• New 2D plots are included in ZToMuMuPlot_cfg.py. They are Inv mass Vs pT, rapidity, centrality so that one can do Yield vs Centrality, pT, and rapidity study.
• Centrality is included in analysis. No event selection based on centrality.
• code is updated on CVS and one can test it

Plots with pT bins:

MC data :/castor/cern.ch/user/d/dmoon/cms370/Hydjet_MinBias_2.76TeV_Z0_Emb_Reco 20 K events

Global Global Muons 20000 Z0 embadded in HYDJET 3 pT bins [0,4,8,20]

Yield vs pT

Global STA Muons 20000 Z0 embadded in HYDJET 3 pT bins [0, 4, 8, 20]

Yield Vs pT Global STA

STA STA Muons 20000 Z0 embadded in HYDJET 3 pT bins [0,4,8,20]

Yield vs pT for STA STA

Glb Glb Muons 20000 Z0 embadded in HYDJET 3 Y bins [- 2.4,-0.8] [- 0.8,0.8] [ 0.8,2.4]

Glb Glb Muons Yield 20000 Z0 embadded in HYDJET 3 rapidity bins [- 2.4,-0.8] [- 0.8,0.8] [ 0.8,2.4]

Glb Sta Muons 20000 Z0 embadded in HYDJET 3 Y bins [- 2.4,-0.8] [- 0.8,0.8] [ 0.8,2.4]

Glb STA Muons Yield 20000 Z0 embadded in HYDJET 3 rapidity bins [- 2.4,-0.8] [- 0.8,0.8] [ 0.8,2.4]

STA STA Muons 20000 Z0 embadded in HYDJET 3 Y bins [- 2.4,-0.8] [- 0.8,0.8] [ 0.8,2.4]

STA STA yield

Global Global Muons 20000 Z0 embadded in HYDJET 3 centrality bins [0,13,26,40]

Global Global Muons Yield 20000 Z0 embadded in HYDJET 3 centrality bins [0,13,26,40]

Global STA Muons mass 20000 Z0 embadded in HYDJET 3 centrality bins [0,13,26,40]

Global STA Muons yield 20000 Z0 embadded in HYDJET 3 centrality bins [0,13,26,40]

STA STA Muons mass 20000 Z0 embadded in HYDJET 3 centrality bins [0,13,26,40]

STA STA Muons yield 20000 Z0 embadded in HYDJET 3 centrality bins [0,13,26,40]

Data Samples: Outdated

'rfio:/castor/cern.ch/user/k/kumarv/Z0/Zmumu_HIReco_PtYGunFlat2000.root'

# 1000 Z0 reconstructed using heavy ion reconstruction algorithm including HI_HLT. ( raw data rfio:///castor/cern.ch/user/j/jrobles/MuonPtYGunFlat/Z0/ZmumuPtYGunFlat2000.root )


'rfio:/castor/cern.ch/user/k/kumarv/Z0/Z0_pp_Reco_1_10.root', # 5000 pythia events reconstructed with pp algorithm (pp HLT included)

'rfio:/castor/cern.ch/user/k/kumarv/Z0/Z0_pp_Reco_11_20.root' # 5000 pythia events reconstructed with pp algorithm (pp HLT included)

Details of code

code is avilbale on CVS

http://cmssw.cvs.cern.ch/cgi-bin/cmssw.cgi/UserCode/CmsHi/Z0Ana/

ZToMuMu/test/ZToMuMuSkim_cfg.py run on reco::Muons make PAT objects and then three Z0 categories.

ZToMuMu/test/ZToMuMuPlots_cfg.py run on output of Skim file and make all the histograms for Z0 kinematical quantities for all three categories.

in ZToMuMu/test : * MuSkim _cfg.py: Uses heavy ion reconstructed files and select events with muons, makes pat muons from reco::muons, selects goodSTAmuons and goodGlobalmuons. * ZToMuMuSkim _cfg.py: Can take output of MuSkim _cfg.py OR Z0Ana/JulyExercise10/pythons/muonSkimPatRecoTemplate_cfg.py, Makes exclusive Z0 categories. Can be modified to use patMuons insted of reco::muons. * ZToMuMuPlot _cfg.py: Takes output of ZToMuMuSkim _cfg.py and plots Z0 and daughter muons kinematical distributions. * Z0MassFit.C: Fits Z0 mass peak with RBW+Pol2 and calculates efficiency for MC and Yeild for data.

More information

http://indico.cern.ch/getFile.py/access?contribId=0&resId=0&materialId=slides&confId=93737

Clues from Z0 measurement in pp Electroweak group:

Strategy in EWK group

Electroweak group strategy start from reconstructed MC data in DBS. This MC data is reconstructed in two steps

1. GEN,SIM,DIGI,L1,DIGI2RAW,HLT,RAW2DIGI,L1Reco
2. RAW2DIGI,L1Reco,RECO

To start We check out

CMSSW/ ElectroWeakAnalysis/ Skimming/

CMSSW/ ElectroWeakAnalysis/ ZMuMu/

These are the two main dir containing everythingh which in done for Z0 in Electroweak group.