Dimuon Measurements in Pb+Pb Collisions with the ATLAS Detector at LHC
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Transcript of Dimuon Measurements in Pb+Pb Collisions with the ATLAS Detector at LHC
Dimuon MeasurementsDimuon Measurementsin Pb+Pb Collisionsin Pb+Pb Collisions
with the ATLAS Detector at LHCwith the ATLAS Detector at LHC
Marzia RosatiMarzia Rosati
Iowa State UniversityIowa State University
forfor
the ATLAS Collaborationthe ATLAS Collaboration
Quark Matter 2009 Knoxville, Tennessee
March 30th - April 4th, 2009
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OutlineOutline
ATLAS Muon SpectrometerATLAS Muon Spectrometer Quarkonia measurementQuarkonia measurement
J/J/’s’sUpsilon’sUpsilon’s
Z boson measurementZ boson measurement
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The ATLAS Muon SpectrometerThe ATLAS Muon Spectrometer
ttoroidal magnetic fieldoroidal magnetic field: <B> = 4 : <B> = 4 TmTm
high phigh pTT resolution resolution independent of theindependent of the polar anglepolar angle
air-core coils to minimize the multiple scatteringair-core coils to minimize the multiple scattering
3 detector stations3 detector stations cylindrical in barrelcylindrical in barrel wheels in end capswheels in end caps
Clean in Pb+Pb central collisionsClean in Pb+Pb central collisions
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Muon Chambers:Muon Chambers: Trigger ChambersTrigger Chambers
Resistive Plate Chambers (RPC) in BarrelResistive Plate Chambers (RPC) in Barrel Thin Gap Chambers (TGC) in the EndcapsThin Gap Chambers (TGC) in the Endcaps
Momentum measurement chambersMomentum measurement chambers Monitored Drift tubes (MDT) in most of the solid angleMonitored Drift tubes (MDT) in most of the solid angle Cathode Strip Chambers (CSC) in the forward Endcap Cathode Strip Chambers (CSC) in the forward Endcap
regionregion
ATLAS Muon ATLAS Muon SpectrometerSpectrometer
CoverageCoverage::
||| < 2.7 | < 2.7
p>3GeV/cp>3GeV/c
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Muon Reconstruction Muon Reconstruction AlgorithmsAlgorithms
Muon reconstruction and identification combines Muon reconstruction and identification combines the the Muon SpectrometerMuon Spectrometer information with the information with the information from the information from the Inner DetectorsInner Detectors (Si pixels (Si pixels and microstrips covering |and microstrips covering ||<2.5)|<2.5) Combined Algorithms:
I. Reconstruct standalone muons by finding tracks in the muon spectrometer and then extrapolating these to the beam line.
II. Muons are found by matching standalone muons to nearby inner detector tracks and then combining the measurements from the two systems.
Tagging Algorithms: Inner detector tracks are tagged as muons
if a matching track segment in the first station of the muon spectrometer is found.
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Single Muon Performance in p+p Single Muon Performance in p+p CollisionsCollisions
Reconstruction efficiency >90% for pReconstruction efficiency >90% for pTT>6GeV/c>6GeV/c Spectrometer Momentum resolution ~5% at Spectrometer Momentum resolution ~5% at
ppTT=10GeV/c=10GeV/c Momentum resolutionMomentum resolution
Combined algorithm
Combined
Combined+Tag
Expected Performance of the ATLAS Experiment arXiv:0901.0512
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Using Dimuons to Probe Nuclear Using Dimuons to Probe Nuclear MatterMatter
ATLAS performance in Pb+Pb collisions to measure quarkonium and Z via di-muon channel was studied by merging single J/ and Z into Hijing Pb+Pb collisions at 5.5 TeV energy.
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-Z
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J
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LLattice QCD makes a clear prediction for the onset of deconfinement, different quarkonia states test the degree of color screening
ATLAS has good capabilities to measure several and states to probe quarkonia deconfinement and other phenomena like dissociation by gluon and regeneration from heavy pairs
Probing Deconfinement with Probing Deconfinement with QuarkoniaQuarkonia
cc
Color Screening
cc
Lattice QCD calculation
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bb
cc
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J/J/ Acceptance and Invariant Mass Acceptance and Invariant Mass DistributionDistribution
Using the Combined+tag algorithms with pUsing the Combined+tag algorithms with pTT>1.5 GeV:>1.5 GeV: Acceptance x Reconstruction Efficiency= 0.53%Acceptance x Reconstruction Efficiency= 0.53% J/J/ mass resolution ~ 70 MeV mass resolution ~ 70 MeV Signal/Background 3:20Signal/Background 3:20
Combined pT >3.0 GeVCombined+tag pT >3.0 GeVCombined+tag pT >1.5GeV
Combined+tag pT >1.5 GeV
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Acceptance and Mass Acceptance and Mass ResolutionResolution
Muons from Muons from decays are more energetic and decays are more energetic and they can be reconstructed over a large they can be reconstructed over a large kinematic rangekinematic range
Acceptance x Reconstruction Efficiency=13%Acceptance x Reconstruction Efficiency=13% mass resolution 120-160 MeVmass resolution 120-160 MeV
Single Single + Hijing
ATLASPRELIMINARY
ATLASPRELIMINARY
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Upsilon Invariant MassUpsilon Invariant Mass
Invariant Mass Spectra are calculated assuming that both high pT muons and scale with number of binary collisions : Use PYTHIA to get muons from charm/beauty leptonic
decays Run full simulation on single pions and kaons to extract
muon spectrum from hadron decays from hadron decays Add Add ’s ’s |y|<1: Barrel Only
Mass Resolution 120 MeVMass Resolution 120 MeVSignal/Background 4:10Signal/Background 4:10
ATLAS PRELIMINARY
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Quarkonia Performace and Quarkonia Performace and RatesRates
Rates calculated for one month running at nominal Rates calculated for one month running at nominal luminosity with 50% machine+experiment efficiency luminosity with 50% machine+experiment efficiency equivalent to an integrated luminosity of 0.5nbequivalent to an integrated luminosity of 0.5nb-1-1..
J/J/ (|y|(|y|<1)<1)
Acceptance x Acceptance x EfficiencyEfficiency
0.53%0.53% 12.5 12.5 %%
4.7%4.7%
Mass Resolution Mass Resolution (MeV)(MeV)
6868 160160 120120
Signal:BackgroundSignal:Background 3:203:20 3:103:10 4:104:10
Rate/monthRate/month 130,00130,0000
18,7518,7500
7,1007,100
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Probing PDF’s with Z BosonProbing PDF’s with Z Boson
Z production rate in p+p can be accurately calculated in NNLO Z production rate in p+p can be accurately calculated in NNLO pQCD therefore measuring production in Pb+Pb will provide a pQCD therefore measuring production in Pb+Pb will provide a precise measurement of PDF’sprecise measurement of PDF’s We can determine x dependence of shadowing while measuring Z as We can determine x dependence of shadowing while measuring Z as
a function of rapiditya function of rapidity Study centrality dependence while dividing into rapidity bins to Study centrality dependence while dividing into rapidity bins to
restrict the x coveragerestrict the x coverage Use Z as a reference for quarkonium suppressionUse Z as a reference for quarkonium suppression
C. Anastasiou et al., Phys.Rev.D69:094008,2004
R.Vogt, Phys.Rev.C64:044901,2001
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Z Boson AcceptanceZ Boson Acceptance
Acceptance for Z boson was estimated by Acceptance for Z boson was estimated by generating Z’s with flat rapidity and generating Z’s with flat rapidity and transverse momentum distributionstransverse momentum distributions
Weighting the calculated acceptance with Weighting the calculated acceptance with kinematic distributions predicted by NLO we kinematic distributions predicted by NLO we derive:derive: Acceptance x Reconstruction Efficiency=60%Acceptance x Reconstruction Efficiency=60%
Acc
epta
nceATLASPRELIMINARY
ATLASPRELIMINARY
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Z Mass ResolutionZ Mass Resolution
p+p Pb+Pb
Acceptance x EfficiencyAcceptance x Efficiency 60%60%
Mass ResolutionMass Resolution 2.2 GeV2.2 GeV
Rate/yearRate/year 8,0008,000
Rates calculated for one month running at nominal luminosity with Rates calculated for one month running at nominal luminosity with 50% machine+experiment efficiency equivalent to an integrated 50% machine+experiment efficiency equivalent to an integrated luminosity of 0.5nbluminosity of 0.5nb-1-1, using NLO kinematic distributions., using NLO kinematic distributions.
ATLASPRELIMINARY
ATLASPRELIMINARY
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ConclusionsConclusions
ATLAS will make interesting measurements in dimuon ATLAS will make interesting measurements in dimuon channel probing Hot and Cold Nuclear Matter effects channel probing Hot and Cold Nuclear Matter effects in Pb+Pb Collisionsin Pb+Pb Collisions
Excellent capability to measureExcellent capability to measure1.1. J/J/’s’s2.2. ’’ss3.3.ZZ00’s’s
Mass resolution is almost unaffected in PbPb collisions
Mass resolution is good enough to separate different states in the barrel region
We should be able to see and J/ peaks in a few weeks of running
Currently studying the feasibility of e+e- channel
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END
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The ATLAS DetectorThe ATLAS Detector
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Contributions to Muon Momentum Contributions to Muon Momentum ResolutionResolution
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Single Muon PerformanceSingle Muon Performance
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ATLAS Muon SpectrometerATLAS Muon Spectrometer