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Prospects for the observation of quarkonia in heavy ion

Prospects for the observation of quarkonia in heavy ion collisions with CMS detector at LHC. Olga Kodolova, SINP MSU ( for CMS Collaboration ).    +  - , Pb-Pb, dNch/d h = 3500.

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Prospects for the observation of quarkonia in heavy ion

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  1. Prospects for the observation of quarkonia in heavy ion collisions with CMS detector at LHC Olga Kodolova, SINP MSU (for CMS Collaboration) +-, Pb-Pb, dNch/dh = 3500 CMS HI groups: Adana, Athens, Basel, Budapest, CERN, Demokritos, Dubna, Ioannina, Kiev, Krakow, Los Alamos, Lyon, MIT, Moscow, Mumbai, N. Zealand, Protvino, PSI, Rice, Sofia, Strasbourg, U Kansas, Tbilisi, UC Davis, UI Chicago, U. Iowa, U. Minnesota, Yerevan, Vanderbilt, Warsaw, Zagreb

  2. Quarkonia: from SPS and RHIC to LHC  LHC RHIC Vogt, hep-ph/0205330 PbPb @ √sNN=5.5 TeV, pPb @ √sNN=8.8 TeV • Factor 30-45 increase in energy compared to AuAu, dAu @RHIC 30-45 times lower Bjorken x=2 mT / sqrt(s) • Larger cross-section • Larger luminosity LHC J/y RHIC Heavy-ion physics at LHC: Plasma hotter, longer-lived than @ RHIC Access to lower x, higher Q2 Unprecedented gluon densities Availability of new probes (Y,Y',Y'') Vogt,hep-ph/0205330

  3. CMS detector 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 <100 GeV Ecal+Hcal+Coil – absorbs hadrons Coil HCAL Tracker Tracker system: Silicon pixel layers (3 in barrel, 2 in endcap) Silicon strips layers (10 in barrel, 12 in endcap) ECAL

  4. Signal and background simulation Resonance cross-section (mb): J/y y' Y Y' Y” Bmmsprod 48930 879 304 78.8 44.4 Yellow Report, CERN-2004-009, hep-ph/0311048: CEM, NLO-pp, shadowing effect (CTEQ5M+EKS98 PDF) no additional absorption effects Values are averaged over impact parameter. Pb-Pb cross-section – 7.8 barn Main background sources: uncorrelated muon pairs from p/K decays muons from b- c- quark production 4 orders of magnitude between Y and Pb-Pb cross-section → need accurate fast Monte-Carlo

  5. I. Muon background sources: pions and kaons We have considered two scenarios for the multiplicity of charged particles in the most central collisions (5% of total cross-section): dNch/dh = 2500 at h=0 dNch/dh = 5000 at h=0 In fast Monte-Carlo, only pions and kaons are considered, which represent 90% of charged particles multiplicity. Kaon/pion = 11% (HIJING) pT and h distributions of pions and kaons according to HIJING

  6. II. Muon background sources:heavy quark production The number of ccbar and bbbar pairs per event The number of pairs produced in PbPb as a function of impact parameter N(QQ) = s(QQ) x TAA(b), where nuclear overlap TAA(b) = 30.4/mb Probability of n-muons in c and b quark decays

  7. 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

  8. Comparison of pp and HI HLT trigger performance for J/y and Y (detailed simulation) • Total Ytrigger efficiency:21% (OL1-L2 chain) 16.5% (L1-L2 chain) • L1 : optimized for high luminosity pp • OL1 : low quality muon candidate (used in HI) • J/y • Y • J/y • Y • Total J/y trigger efficiency: 0.97% (OL1-L2 chain) 0.44% (L1-L2 chain) • Total Pb-Pb events trigger efficiency: 1.6% HIJING with ccbar and bbar, OL1-L2 chain

  9. Z = 190m Dimuon reconstruction algorithm for J/y and Y Primary vertex determination select pairs of pixel hits with df giving 0.5<pT<5 GeV/c extrapolate each pair in RZ to the beam line Track finding start from the track candidate in muon stations extrapolate inwards from plane to plane using vertex constraints Track selection by cuts: fit quality (c2) vertex constraint -stations Si layers Si pixels -track

  10. Dimuon reconstruction efficiency & purity vs dNch/dy (detailed simulation) Y is embedded in PbPb events Efficiency: Eff = Efftrk-1 x Efftrk-2 x Effvtx > 80% for all multiplicity (barrel) > 65% for all multiplicity (barrel+endcap) Purity = [true Y reco]/[all vtx reco] > 90% (all multiplicities) “realistic” LHC multiplicity range • Total Pb-Pb events reconstruction efficiency: 31% HIJING with ccbar and bbar, 0.5% of Pb-Pb events survive after OL1/L2/tracker reconstruction chain.

  11. Dimuon mass resolution (detailed simulation) • Y • J/y Both muons with |h|<2.4 Both muons with |h|<2.4 sJ/y= 35 MeV/c2 in (barrel+endcap) • Y sY = 54 MeV/c2 in (barrel). Both muons with |h|<0.8 90 MeV/c2 in (barrel+endcap) Both muons with |h|<2.4 Both muons with |h|<0.8

  12. Fast Monte-Carlo method L1 and L2 trigger efficiency tables were generated for single pions, kaons, muons, b- and c- hadrons in (h, pT) bins with detailed CMS simulation dimuon reconstruction efficiency and purity dependence on the multiplicity was generated in (h, pT) bins with detailed CMS simulation dimuon mass resolution was obtained with detailed CMS simulation Each Pb Pb event is characterized by its impact parameter; 5 resonances states are mixed with the pions+kaons and muons coming from heavy-quark pairs Comparison of the detailed simulation with fast MC with the same generator input: HIJING 500 Kevents Each “dimuon” with p>2.8 and |h|<2.6 is summed with weight: W12 = Worigin12x W12trig xW12reco; Worigin12 = Worigin1 xWorigin2; Worigin1 =1 (for bg) or = s(quarkonium)/s(PbPb) (for signal) Worigin2 = the same Black squares – fast MC open circles – detailed CMS simulation

  13. J/y and Y L1/L2 trigger acceptance with fast MC J/y's are accepted above pT ~ 2 GeV/c. High pT acceptance is ~15% Y's are accepted (~35%) down to pT=0 GeV/c. High pT acceptance is ~15% Single muons acceptance is ~90% starting from p=4 GeV/c in |h|<2.4 Muon pair: ~80% Single kaons acceptance is ~1% starting from p=3 GeV/c in |h|<2.4 Kaon pair: 0.01% Single pions acceptance is ~0.5% starting from p=3 GeV/c in |h|<2.4 Pion pair: 0.0025%

  14. Dimuon mass spectra (signal+ background) with fast MC PbPb, dNch/dh = 5000, L=0.5 nb-1 Background: p/K (90% of Nch)->mX (probability to decay 99.98% / 63%) Background: c-,b- hadrons->m+X (probability to have at least 1 m in ccbar/bbar decays ~18% / 38% ) Combinatorial background: mixed sources 1  from /K + 1  from J/ 1  from b/c + 1  from /K J/y, y' peaks seen (S/B~0.6) All 3 Y peaks seen (S/B=0.07) Fast MC gives systematical error of 20%-25% in mass spectra

  15. Dimuon mass spectra (signal+ background) with fast MC PbPb, dNch/dh = 2500, L=0.5 nb-1 Background: p/K (90% of Nch)->mX (probability to decay 99.98% / 63%) Background: c-,b- hadrons->m+X (probability to have at least 1 m in ccbar/bbar decays ~18% / 38% ) Combinatorial background: mixed sources 1  from /K + 1  from J/ 1  from b/c + 1  from /K J/y, y' peaks seen (S/B~1.2) All 3 Y peaks seen (S/B=0.12)

  16. “high” multiplicity dNch/dηh|hη=0 = 5000 “low” multiplicity dNch/dh|ηh=0 = 2500 J/y mass spectra (like-sign background subtraction) with fast MC sJ/y= 35 MeV/c2 in (barrel+endcap). Both muons with |h|<2.4

  17. “high” multiplicity dNch/dhη|hη=0 = 5000 Y mass spectra (like-sign background subtraction) with fast MC sY = 54 MeV/c2 in (barrel). Both muons with |h|<0.8 90 MeV/c2 in (barrel+endcap) Both muons with |h|<2.4 Barrel: Both muons with |h|<0.8 Barrel+endcap: Both muons with |h|<2.4

  18. QQbar rates at CMS (1 nominal PbPb run) 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

  19. Differential QQbar spectra (1 nominal PbPb run)

  20. Summary J/y and Y are excellent probes of QCD media in A+A: Step-wise “melting” pattern is the QGP thermometer Production via gg fusion allows probing of low-x QCD structure and evolution Simulation studies of J/y and Y ->mm in CMS (PbPb @ √s=5.5 TeV/nn) Geometrical acceptance ~15% (at high pT) Dimuon efficiency ~80% and purity above 90% for all multiplicities sY=~1% MQQ (barrel+endcap), sJ/y=35 MeV/c2 (barrel+endcap) sY=54 MeV/c2 (barrel alone) Full separation of Y family is possible Signal/Background:~5(1), 1(0.1) for J/y and Y in barrel(+endcaps) High rate expected (per year): J/y ~ 180 kevents, Y ~ 25 kevents, Y’ ~ 7 kevents,Y’’ ~ 4 kevents Detailed differential studies of QCD matter are possible

  21. Quarkonia production: kinematical spectra pT and h according to Yellow Report, CERN-2004-009, hep-ph/0311048 J/y Y J/y Y

  22. 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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