Quarkonia and heavy flavor – recent results from STAR

Amsterdam Quarkonia and heavy flavor – recent results from STAR André Mischke for the STAR Collaboration Workshop: Hot and Dense Matter in the RHIC-LHC Era, Tata Institute of Fundamental Research, Mumbai, 12–14 February 2008

Outline • Charm production cross-section in heavy-ion collisions • Au+Au and Cu+Cu data (new) • Heavy quark energy loss in the medium • Non-photonic electron spectra • Experimental access to charm and bottom contributions • e-h correlations • e-D0 correlations (new) • Quarkonia production in QCD matter • J/ at high-pT (new) •  in Au+Au (new)

Jet quenching of light quarks well described by energy loss models  medium is extremely opaque Surface bias effectively leads to saturation of RAA with density Limited sensitivity to the region of highest energy density Need: - insensitive trigger particles: Prompt photons - more penetrating probes: Heavy quarks ? Limitations of RAA K.J. Eskola et al., Nucl. Phys. A747 (2005) 511 light hadrons central RAA data increasing density

parton hot and dense medium Heavy quark energy loss • Due to their large mass heavy quarks are believed to be primarily produced by gluon fusion M. Gyulassy and Z. Lin, PRC 51, 2177 (1995) - production rates calculated by pQCD - sensitivity to initial state gluon distribution •  Does it hold for heavy-ion collisions? • Heavy quarks • - are ”grey probes” • - lose less energy due to suppression of small angle gluon radiation (dead-cone effect)Dokshitzer & Kharzeev, PLB 519, 199 (2001) • Radiative and collisional energy loss • M.G. Mustafa, PRC72, 014905 A.K. Dutt-Mazumder et al., PRD71, 094016 (2005) Wicks et al, NPA784, 426 (2007)

The STAR experiment • Energy measurement • - Barrel EMC • fully installed and operational, || < 1 • Pb/scintillator (21 X0) • dE/E ~16%/E • Shower maximum detector • Tracking and PID • - Magnet • 0.5 Tesla • - TPC • || < 1.5 • p/p = 2-4% • dE/dx/dEdx = 8% • - ToF • 60ps resolution • - SVT Centrality & trigger - ZDC - CTB+BEMC

Heavy flavour measurements: hadronic decay channel • D0 Kp (B.R.: 3.83%) • D* D0p (B.R.: 61.9%) • D Kpp (B.R.: 9.51%) • Direct clean probe: signal in invariant mass distribution • Difficulty: large combinatoric background; especially in high multiplicity environments • Event-mixing • Vertex tracker • charm c ~ 100-200 m • - bottom c ~ 400-500 m

Heavy flavour measurements: semi-leptonic decay channels • c ℓ+ + X(B.R.: 9.6%) ℓ = e or  • D0  ℓ+ + X(B.R.: 6.87%) • D ℓ + X(B.R.: 17.2%) • b  ℓ- + X(B.R.: 10.9%) • B ℓ + X(B.R.: 10.2%) • Single (non-photonic) electrons sensitiveto charm and bottom • Robust electron trigger • Photonic electron background

Charm production cross-section in heavy-ion collisions • Au+Au and Cu+Cu data • Heavy quark energy loss in the medium • Non-photonic electron spectra • Experimental access to charm and bottom contributions • e-h correlations • e-D0 correlations • Quarkonia production in QCD matter • J/ at high-pT •  in Au+Au

Electron identification - ToF • ToF patch (prototype) • -  /30 • - 0 >  > -1 • Electron ID • |1/ß-1| < 0.03 • TPC dE/dx • Momentum range: • - pT < 4 GeV/c p K e  electrons

Muon identification - ToF 0.17 < pT < 0.21 GeV/c 0-12% Au+Au • Low-pT (< 0.25 GeV/c) muons can be measured with TPC + ToF • Separate different muon contributions using MC simulations: • K and  decay • charm decay • DCA (distance of closest approach) distribution is very different   minv2 (GeV2/c4) Inclusive   from charm  from  / K (simu.) Signal+bg. fit to data

Open charm reconstruction - TPC • Hadronic decay channel: D0 → K +  (B.R. 3.8%) • PID in TPC using dE/dx- pT < ~3 GeV/c • No reconstruction of displaced vertex up to now • Background description using mixed event technique (details in PRC 71, 064902 (2005)) after background subtraction

STAR preliminary Charm cross section in Au+Au D0 ± e± STAR p+p and d+Au data, PRL 94, 062301 (2005) • Combined fit covers ~95% of cross section • NNcc= 1.40 ± 0.11 ± 0.39 mb in 12% most central Au+Au • NNcc agrees with NLO calculation progress in determining theoretical uncertainties, R. Vogt, hep/ph: 0709.2531 • More data points needed to constraint models

Cu+Cu minbiasRun 5 Open charm in Cu+Cu STAR preliminary • dNNcc/dy follows binary collision scaling • → charm is exclusively produced in initial state; as expected • → no room for thermal production

electrons hadrons d K p p electrons electrons hadrons Electron identification - EMC Advantage: triggering to enrich high-pT particle sample • TPC: dE/dx for pT > 1.5 GeV/c • only primary tracks • (reduces effective radiation length) • electrons can be discriminated well from hadrons up to 8 GeV/c • allows to determine the remaining hadron contamination after EMC • EMC: • tower E & p/E • shower Max Detector (SMD) • hadrons/Electron shower develop different shape • use # hits in SMD to discriminate • 85-90% purity of electrons (pT dependent) • hadron discrimination power ~103-104

e+ (global track) e- (assigned as primary track) e- (primary track) dca  Photonic electron background • Most of the electrons in the final state are originating from other sources than heavy-flavor decays • Dominant photonic contribution • gammaconversions • 0 and  Dalitz decays • Exclude electrons with low invariant mass minv< 150 MeV/c2 •  Non-photonic electron excess at high-pT • 70% photonic background rejection efficiency – unlike-sign pairs – like-sign pairs mass (GeV/c2)

RAA for non-photonic electrons Phys. Rev. Lett. 98, 192301 (2007) • Surprise in central Au+Au: Electrons from D and B decays are strongly suppressed; not expected due to dead-cone effect • Smoothly decreases from peripheral to central Au+Au • Models implying D and B energy loss are inconclusive yet

D/B crossing point in FONLL M. Cacciari et al., PRL95, 122001 (2005) D/B crossing point • Large uncertainty in D/B crossing point: pT = 3-10 GeV/c • Goal • - access to underlying production mechanisms • separate D and B contribution experimentally • Approach: Two heavy-flavor particle correlations

Electron-hadron correlations Run 5 p+p, L3pb-1 • Azimuthal e-h correlations • - Exploit different fragmentation of associated jets • e-h correlations • - B much heavier than D • subleading electrons get larger kick from B (decay kinematics)  near-side e-h correlation is broadened • Extract relative B contribution using PYTHIA simulations p+p 200 GeV B e (PYTHIA) D  e (PYTHIA) D+B fit to data

trigger side c g g c 3.83% 54% ~10% charm production c  0 c g g g g probe side flavor creation (LO) gluon splitting (NLO) Electron-D0 correlations • Access to underlying production mechanism • Identification and separation of charm and bottom production events using their decay topology and azimuthal angular correlation of their decay products • electrons from D/B decays are used to trigger on charm or bottom quark pairs • associate D0 mesons are reconstructed via their hadronic decay channel (probe)

like-sign e-K pairs unlike-sign e-K pairs LO PYTHIA 3<pTtrg<7 GeV/c LO PYTHIA simulations • Near-side • B decays (dominant) • Away-side • charm flavor creation (dominant) • small B contribution • Away-side • B decays (dominant) • small charm contribution

w/o electron trigger w/ non-photonic electron trigger STAR preliminary dn/dm combinatorial background is evaluated using like-sign pairs position: 1892 ± 0.005 GeV/c2 width: 16.2 ± 4.7 MeV/c2 K invariant mass distribution D0+D0 • D0 reconstruction: dE/dx cut (±3) around Kaon band • Significant suppression of combinatorial background: factor 200 • S/B = 14% and signal significance = 3.7

like-sign e-K pairs Relative Be contribution essentially from B decays only 75% from charm 25% from beauty • Model uncertainties not included yet • Good agreement between different analyses • Data consistent with FONLL within errors • Small gluon splitting contribution • Comparable D and B contributions •  Au+Au: suggests significant suppression of non-photonic electrons from bottom in medium

Quarkonia production in QCD matter Charmonia:J/, ’, cBottomonia:(1S), (2S), (3S)‏ • “Melting” of Quarkonia states in QGP • color screening of static potential between heavy quarks:J/suppression: Matsui and Satz, Phys. Lett. B 178 (1986) 416 • suppression states is determined by TC and their binding energy  QCD thermometer • Sequential disappearance of states • color screening  deconfinement • QCD thermometer  access to properties of QGP • Lattice QCD: Evaluation of spectral functions H. Satz, HP2006 RHIC

J/y /c • Data consistent with no suppression at high pT: RAA(pT > 5 GeV/c) = 0.9 ± 0.2 • While at low-pT RAA = 0.5-0.6 (PHENIX) • Indicates RAA increase from low pT to high pT • But, most models expect a decrease RAA at high pT • two component approach by X. Zhao and R. Rapp, hep-ph/07122407 • AdS/CFT by H. Liu, K. Rajagopal and U.A. Wiedemann, PRL 98, 182301(2007) and hep-ph/0607062 J/ production at high-pT H. Liu, K. Rajagopal and U.A. Wiedemann PRL 98, 182301(2007) and hep-ph/0607062

 mass resolution in STAR simulation with inner tracker (X/X06%) • STAR detector can resolve individual  states • Low statistics currently  yield is extracted from combined ++ states • FWHM ≈ 400 MeV/c2  e+e- • RHIC II with 20 nb-1 will definitely allow separation of 1S, 2S and 3S states • Measurement will greatly benefit from the future Muon Telescope Detector upgrade

preliminary preliminary (1s+2s+3s) signal in p+p Run 6 p+p, L9 pb-1 • unlike-sign pairs • like-sign pairs background subtracted • (1s+2s+3s) d/dy at y=0 • Peak width consistent with expected mass resolution

STAR preliminary p+p 200 GeV Counts d/dy (nb) y Mid-rapidity (1s+2s+3s) cross-section • Integrated yield at mid-rapidity: |y|<0.5 • (1s+2s+3s)  e+e-: • BRee d/dy = 91 ± 28(stat.) ± 22(sys.) pb • Consistent with NLO pQCD calculations and world data trend

in Au+Au (Run 7) Sample -triggered event •   e+e- • mee = 9.5 GeV/c2 (offline mass)‏ • cosθ = -0.77 (offline opening angle)‏ • E1 = 6.6 GeV (online cluster energy hardware trigger)‏ • E2 = 3.2 GeV (online cluster energy software trigger)‏ electron momentum > 3 GeV/c charged tracks

signal in Au+Au Run 7 Au+Au, L300 b-1 • First  measurement in nucleus-nucleus collisions • 4signal • These data should provide a first measurement of RAA after corrections for efficiency are completed

Summary • Charm production cross-section • follows binary collision scaling  no room for thermal production • agrees with FONLL within errors • Non-photonic electron spectra • energy loss in heavy-ion collision is much larger than expected • models invoking radiative + collisional energy loss get closest to data • Electron-D0 azimuthal correlations • first heavy-flavor particle correlation measurement at RHIC • B and D contributions similar at pT > 5 GeV/c; consistent with FONLL • STAR data + MC@NLO simulations: Small gluon-splitting contribution • Quarkonia •  cross-section in pp consistent with pQCD and world data trend • first  signal in Au+Au • Next: absolute cross-section in p+p, d+Au (Run 8) and Au+Au and RAA

improved D → Kreconstruction excellent electron ID(J/ range 0.2<p<4 GeV/c) J/ trigger in Au+Au low-pTmuon ID (0.2 GeV/c) p e m Outlook • More exciting results are about to come with the STAR detector upgrades • Heavy Flavor Tracker • Full barrel Time-of-Flight SSD ToF HFT • active pixel sensor technology • 2 layers CMOS Active Pixel sensors • pixel dimension: 30 m  30 m • resolution: ~10 mm

The STAR collaboration 52 institutes from 12 countries, 582 collaborators

Backup

Compilation: Charm cross section at RHIC Yifei Zhang, QM2008

Extraction of charm cross-section Number of binary collisions (Glauber) Inelastic cross section in p+p (UA5) Conversion to full rapidity Ratio obtained from e+e- collisions

Obtaining the Charm Cross-Section scc • From D0 mesons alone: • ND0/Ncc ~ 0.540.05 • Fit function from exponential fit to mT spectra • Combined fit: • Assume D0 spectrum follows a power law function • Generate electron spectrum using particle composition from PDG • Decay via routines from PYTHIA • Assume: dN/dpT(D0, D*, D, …) have same shape only normalization • In both cases for d+Au  p+p: • sppinel = 41.8  0.6 mb • Nbin = 7.5  0.4 (Glauber) • |y|<0.5 to 4p: f = 4.70.7 (PYTHIA) • RdAu = 1.3  0.3  0.3 PRL 94, 062301 (2005)

Non-photonic electron spectra p+p at sNN = 200 GeV Phys. Rev. Lett. 98, 192301 (2007) • FONLL calculation factor of about 5 lower than p+p data • Spectra shape of p+p spectrum is well described • Large uncertainty over where Be dominates over De.

Comparisons to models Latest efforts to describe the data • Radiative energy loss with typical gluon densities is not enoughDjordjevic et al., PLB 632 (2006) 81 • Models involving a very opaque medium agree betterArmesto et al., PLB 637 (2006) 362 • Collisional energy loss / resonant elastic scatteringWicks et al., nucl-th/0512076 andvan Hees and Rapp, PRC 73 (2006) 034913 • Heavy quark fragmentation and dissociation in the medium → strong suppression for c and bAdil and Vitev, hep-ph/0611109 • Theoretical explanations are inconclusive • Is it possible to determine B contribution experimentally?

+ e- K- e D0 D*0 B- unlike-sign pairs  away-side correlation like-sign pairs  near-side correlation b b B+ D0 Near- and away-side correlation peak expected for B production - K+ Electron tagged correlations:bottom production Charge-sign requirement on trigger electron and decay Kaon gives additional constraint on production process

PYTHIAcharm production STAR Preliminary NLO Process: Gluon splitting • FONLL/NLO calculations only give single inclusive distribution  no correlations • PYTHIA is not really adequate for NLO predictions • STAR measurement of D* in jet  access to charm content in jets • Gluon splitting rate consistent with pQCD calculation •  Small contribution from gluon splitting at top RHIC energy E. Norrbin & T. Sjostrand, Eur. Phys. J. C17, 137 (2000) Mueller & Nason PLB 157 (1985) 226 P29: X. Dong, Charm Content in Jets

MC@NLO LO PYTHIA like-sign e-K pairs 3<pT<7 GeV/c Δ(c,c) Δ(e,D0) MC@NLO predictions for charm production • NLO QCD computations with a realistic parton shower model •  Remarkable agreement of the away-side peak shapebetween LO PYTHIA and MC@NLO •  Gluon-splitting contribution is small • S. Frixione, B.R. Webber, JHEP 0206 (2002) 029 • S. Frixione, P. Nason, and B.R. Webber, JHEP 0308 (2003) 007 • private code version for charm production

 trigger in STAR • Large acceptance • Fast L0 trigger (hardware) - Select events with at least one high energy EMC cell (E~4 GeV) • L2 trigger (software) • EMC cell clustering • Using topology (cosθ) and mass reconstruction in real time • Very clean to trigger up to central Au+Au • Trigger efficiency ~80% • Offline: Match TPC tracks to triggered EMC cells Real Data, p+p Run V

 cross section and uncertainties Ldt = (5.6±0.8) pb-1 N = 48±15(stat.)  = geo×L0×L2×2(e)×mass

Quarkonia and heavy flavor – recent results from STAR