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

22

OutlineOutline

ATLAS Muon SpectrometerATLAS Muon Spectrometer Quarkonia measurementQuarkonia measurement

J/J/’s’sUpsilon’sUpsilon’s

Z boson measurementZ boson measurement

33

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

44

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

55

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.

66

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

77

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.

+-

+

-Z

+

-

J

88

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

T

bb

qq

cc

99

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

1010

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

1111

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

1212

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

1313

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

1414

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

1515

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

1616

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

1717

END

1818

The ATLAS DetectorThe ATLAS Detector

1919

Contributions to Muon Momentum Contributions to Muon Momentum ResolutionResolution

2020

Single Muon PerformanceSingle Muon Performance

2121

ATLAS Muon SpectrometerATLAS Muon Spectrometer