High-mass Dimuon Resonances in Pb-Pb Collisions at 5.5 TeV in CMS

1
High-mass Dimuon Resonances in Pb-Pb Collisions
at 5.5 TeV in CMS

• Dipanwita Dutta
• BARC, India
• On behalf of the CMS Collaboration

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Outline
Physics Motivation Dimuons from Quarkonia and
Z0 CMS Experimental Setup Simulation for
Dimuons Results Summary
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Dimuons From SPS, RHIC to LHC

• LHC Factor 30-45 increase in energy compared
  to RHIC

SPS 17 GeV RHIC 200 GeV LHC 5.5 TeV
initial T 200 MeV 300 MeV gt 600 MeV
volume 103 fm3 104 fm3 105 fm3
lifetime lt 2 fm/c 2-4 fm/c gt 10 fm/c

• Heavy Ion Physics at LHC
• Plasma Hotter, Bigger and Longer life time
• Access to lower x and higher Q2
• Unprecedented gluon Density
• Availability of new Probes (Y,Y',Y")
• Z0 with large cross-section

?20
High Mass Dimuon Resonances at LHC
J/?, Y,Y',Y", Z0
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Dimuons Probe of Dense QCD Medium
Dissociation of Qnia (Debye Screening) Hot QCD
Thermometer

• Z0 Weak production and decay-- No final state
  effect
• Baseline for Quarkonium Suppression

5
Dimuons Probe of Initial State

• state in a novel Bjorken-x range (10-3-10-5)
• nuclear shadowing,
• high-density saturated gluon distribution.

108 106 104 102 100
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CMS Detector for Heavy Ions

• Muon system
• Drift Tubes (DT) in central barrel region
• Cathode Strip Chambers (CSC) in endcap region
• Resistive Plate Chambers (RPC) in barrel and
  endcap

precise measurement of position (momentum)
fast info for LVL-1 trigger

• Excellent coverage
• 5 units of rapidity and 2?
• Strongest magnetic field
• 4 T, 2 T (return yoke)
• Tag from muon stations,
• momentum resolution from
• Silicon tracker
• 2 of momentum
• resolution for tracks with
• pT lt100 GeV
• EcalHcalCoil absorbs hadrons

Coil
HCAL
Tracker
ECAL
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Dimuon Sources at LHC Signal and Background

• Signal Dimuon Resonances
• Quarkonia J/? (BR 5.9), ? (BR 2.5)
• Z0 (BR 3.4)

• Background Dimuons
• Decays from open c and b
• Decays from ?, K
• Decays from W
• Mixed muon pairs

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Simulation of Quarkonia
Marc Bedjidian, Olga Kodolova, CMS NOTE-2006/089
Resonance cross-section (?b)
J/? ?' ? ?' ?"
B???prod 48930 879 304 78.8 44.4

• Signal (J/?,?) CEM, NLO-pp, (CTEQ5MEKS98
  PDF),TAA scaled
• Background Uncorrelated Muon Pairs from ?/K
  decays
• Two scenarios for the multiplicity of charged
  particles
• dNch/d? 2500 at ?0
• dNch/d? 5000 at ?0
• Only ? and K are considered ( 90 of charged
  particles multiplicity)
• Kaon/pion 11 (HIJING)
• pT and ? distributions of pions and kaons
  according to HIJING
• Background Muons from Open Heavy Quark (b,c)
• NLO pp, CTEQ5MEKS98 PDF, TAA scaled

b0
5 c.c.
min.bias.
N(cc) w/o shadowing
226
206
51

w/ shadowing
150
135
33
b0
5 c.c.
min.bias.
N(bb) w/o shadowing
6
5.5
1.4

w/ shadowing
5
4.7
1.2
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Dimuon reconstruction algorithm for Quarkonia
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Dimuon High Level Trigger performance for Heavy
Ions
Two Different Level 1 Trigger (single muon
trigger) L1 optimised for
High luminosity pp run OL1
low quality muon candidates optimised for HI L2
and L3 run on online farm Trigger Conditions
Two L1 or L2 opposite sign L3 (cut on loose)
J/y trigger efficiency 0.97 (OL1-L2 chain)

0.44 (L1-L2 chain)
? trigger efficiency 21 (OL1-L2 chain)

16.5 (L1-L2 chain)
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Dimuon efficiency purity vs dNch/dy
Y is embedded in PbPb events Efficiency Eff
Efftrk-1 x Efftrk-2 x Effvtx gt 80 for all
multiplicity (barrel) gt 65 for all
multiplicity (barrelendcap) Purity true
Y reco/all vtx reco gt 90 (all
multiplicities)
realistic LHC multiplicity range
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J/y mass spectra (like-sign subtraction)
sJ/y 35 MeV/c2 in (barrelendcap), Both muons
with ?lt2.4
S/B1.2
S/B0.6
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? mass spectra (like-sign subtraction)
Excellent Mass Resolution at LHC
sY 54 MeV/c2 in (barrel) and ?? 90 MeV/c2 in
(barrelendcap)
S/B0.97
Barrel Both muons with hlt0.8
Barrel endcap Both muons with hlt2.4
S/B0.12
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pT and ? reach of Quarkonia (1 Pb-Pb run)
For 1 month LHC run, L int 0.5 nb-1
? of J/?
? of ?
Very Large Statistics
N(J/?)105
N(?)104
pT of ?
pT of J/?
pT reach 40 GeV (without suppression)
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Simulation for Z0???- Gen. level
D. Dutta et. al
Expected No. for one month LHC run, Lint0.5 nb-1
Processes Cross-section ?pp(Z0) Pythia6.409 CTEQ5M Cross-section ?PbPb(Z0) TAA? ?pp(Z0) ?BR 0-10 cent. (MB) No. of Z0 for 0-10 cent. (MB) collisions NPbPbLint? ?PbPb(Z0) ?Acc.(0.55)
Z0,Z0jet (MSUB1,15,30) 60 nb 30.6 (77)?b 8.2?103 (2.0?104)
BR in Z0???- 3.4
CMS Muon Acceptance pT (?) gt 3.5 GeV,
?(?)lt2.4 Acceptance of Z055
qq(bar)?Z0(Z0jet)
Total
qg?(Z0jet)
Dominant Contribution for Z0 prod qq(bar)
annihilation?Study of Quark PDF Shadowing
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Simulation for Z0 ???-

• Dimuons
• bb(bar) fragmentation
• dominant contribution
• Combinatorial background
• b and ?,K 16
• ?,K and charm decay 5-6
• Signal from Z0 Clear peak
• 11,000 events in
• MZ10 GeV/c2,
• Less than 5 background

DY
CMS Physics TDR Addendum to High Density QCD
with Heavy Ions, J. Phys. G, Nucl. Part. Phys.
34 (2007) 2304
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?- ,Z- jet tagging ?

• CMS can also calibrate jet-energy loss with
  back-to-back Z and/or virtual ? (large
  cross-sections, good detection capabilities)
• Dominant (heavy-Q) dimuon backgd.
• removable via secondary-vtx. cut

D. Dutta, C.Mironov et al.
Dimuon trigger
NZ-jet103
Z0 / g
q/g
Away side
Associated Hadrons
pT gt25 GeV/c
sr50 mm sj20 mm
3s vtx. cut
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Summary

• J/?,? and Z0 Prominent probe of QCD media in
  PbPb collisions
• Stepwise melting Thermometer of QGP
• Quarkonia production via gg fusion
• probe of low x QCD
• Z0 production via qqbar annihilation
• Probe of Nuclear shadowing of quark PDF
• Simulation Studies of J/?,?
• Acceptance J/?15 (at high pT) and ?26
• Dimuon Efficiency 80 and purity 90
• Mass Resolutions at LHC
• s1 MQQ (barrelendcap), sJ/?35 MeV/c2
  (barrelendcap)
• s?54 MeV/c2 (barrel alone)
• Signal/Background 5(1), 1(0.1) for J/?,? in
  barrel (endcaps)
• High rate expected (per year)
• J/? 180 kevents, Y 25 kevents,
  Y 7 kevents, Y 4 kevents
• High pT reach 40 GeV
• Generator Studies of Z0
• Aceeptance Z055
• No. of Z0 103(104) for 10 central
  (Minbias) within CMS acceptance

Thank you
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• Back Up Slides

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Quarkonia production kinematical spectra
pT and h according to Yellow Report,
CERN-2004-009, hep-ph/0311048
J/y
Y
J/y
Y
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Heavy quark pairs production kinematical spectra
pT and h according to Yellow Report,
CERN-2004-009, hep-ph/0311048
bbbar
ccbar
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J/y and Y trigger strategy
L1 Trigger single muon trigger with no momentum
cuts optimized for HI run
conditions L2 and L3 run on online farm L2
trigger condition either opposite(like)
sign dimuon candidate at L1 trigger or
opposite(like) sign dimuon candidate at L2
trigger L3 includes regional track finder
starting from the muon stations, primary
vertex finder with pixel detectors and dimuon
vertex constraints
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Dissociation (Color Screening) Hot QCD
Thermometer
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Quarkonia rates and S/B ratio at CMS
Signal-to-background ratio and expected quarkonia
yields in one month of PbPb running (0.5 nb-1
integrated luminosity) for two multiplicity
scenarios and two h windows
dNch/d???0, ?? S/B N(J/?) S/B N(?) N(?) N(?)
2500, ???lt2.4 1.2 184000 0.12 26000 7300 4400
2500, ???lt0.8 4.5 11600 0.97 6400 2000 1200
5000, ???lt2.4 0.6 146000 0.07 20,300 5900 3500
5000, ???lt2.4 2.8 12600 0.52 6000 1800 1100
No of J/? 105 and No. of ? 104 in Minbias
Event
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Dimuon Sources at LHC Signal and Background

• Signal Dimuon Resonances
• Quarkonia J/? (BR 5.9), ? (BR 2.5)
• Z0 (BR 3.4)

• Background Dimuons
• Decays from open c and b
• Decays from ?, K
• Decays from W
• Mixed muon pairs

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Cross-sections for Z0
Processes Cross-section ?pp(Z0) Pythia6.409 CTEQ5M Cross-section ?PbPb(Z0) TAA? ?pp(Z0) ?BR 0-10 cent. (MB) No. of Z0 for 0-10 cent. (MB)l collisions NPbPbLint? ?PbPb(Z0) ?Acc.(0.55) No. of Z0 0-10 Cent. (MB) MRST HO PDF, with shadowing R. Vogt PRC64, 044901(2001)
Z0,Z0jet (MSUB1,15,30) 60 nb 30.6 (77)?b 8.2?103 (2.0?104) 3.8?103 (9.6?103) (using 15 nb with CMS acc.)
(mZ-5)GeV M??(mZ5)GeV 25.4 nb 12.9 (32.7) ?b 3.5?103 (8.8 ?103) 3.8?103 (9.6?103) (using 15 nb with CMS acc.)