Heavy flavor production in STAR. What can charm and beauty tell us about matter in heavy ion collisions? Manuel Calderón de la Barca Sánchez UC Davis for the STAR collaboration DIS 2006 Tsukuba, Japan 21/April/2006

21/April/2006Manuel Calderón de la Barca 2 Light quark sector highlights Inclusive yields and back-to-back di-hadron correlations are very similar in p+p and d+Au collisions Both are strongly suppressed in central Au+Au collisions at 200 GeV Large energy loss of light quarks in the formed nuclear matter Phys. Rev. Lett. 91, (2003). Pedestal&flow subtracted STAR Jet quenching Hadron suppression in central AuAu

21/April/2006Manuel Calderón de la Barca 3 Heavy quarks in a hot medium Quenching weights, more recent way to study energy loss of heavy quarks in a dense medium. Quenching weights, more recent way to study energy loss of heavy quarks in a dense medium. Armesto et al. hep- ph/ Armesto et al. hep- ph/ Energy loss depends on properties of medium (gluon densities, size) depends on properties of probe (color charge, mass) c, b D, B 1) production 2) quark energy loss 3) fragmentation D,B spectra are affected by energy loss, and might be more sensitive to medium properties than light quarks. Heavy quark has less dE/dx due to suppression of small angle gluon radiation Dead Cone effect Y. Dokshitzer & D. Kharzeev PLB 519(2001)199 Elastic energy loss for heavy quarks? Might have an effect. M.G.Mustafa Phys. Rev C 72 (2005)

21/April/2006Manuel Calderón de la Barca 4 Measuring heavy flavors Hadronic decay channels: D 0 K, D * D 0, D +/- K Hadronic decay channels: D 0 K, D * D 0, D +/- K Non-photonic electrons: Non-photonic electrons: Semileptonic channels: Semileptonic channels: c e + + anything (B.R.: 9.6%) c e + + anything (B.R.: 9.6%) D 0 e + + anything(B.R.: 6.87%) D 0 e + + anything(B.R.: 6.87%) D e + anything(B.R.: 17.2%) D e + anything(B.R.: 17.2%) b e + + anything(B.R.: 10.9%) b e + + anything(B.R.: 10.9%) B e + anything(B.R.: 10.2%) B e + anything(B.R.: 10.2%) Drell-Yan Drell-Yan (small contribution for p T < 10 GeV/c at RHIC) (small contribution for p T < 10 GeV/c at RHIC) Photonic electron background: Photonic electron background: conversions ( e + e - ) conversions ( e + e - ) Dalitz decays Dalitz decays … decays (small) … decays (small) K e3 decays (small) K e3 decays (small)

21/April/2006Manuel Calderón de la Barca 5 Charm reconstruction via hadronic decays nucl-ex/ D0D0 STAR Phys. Rev. Lett. 94 (2005) dAu: (stat.) 0.4(sys.) mb AuAu: (stat.) 0.42(sys.) mb Total charm cross section per NN interaction Assumes Binary scaling dAu to AuAu Charm produced in initial collisions. Systematics and statistics limited (only 3 p T bins in Au+Au).

21/April/2006Manuel Calderón de la Barca 6 Charm reconstruction via muons Use dE/dx at low p. Use dE/dx at low p. Add TOF information (limited acceptance) Add TOF information (limited acceptance) e 0.15<pT<0.25 GeV/c, DCA<3cm All particle After de/dx cut STAR Preliminary 1) Data 2) Primary track 3) B.G. (K, decay) 4) Sum of 2),3) c at low p T (no photonic/Dalitz backgrounds) only limited to very low p T.

21/April/2006Manuel Calderón de la Barca 7 dNg/dy=1000 small suppression R AA ~ 0.7 for c+b Predictions of electron nuclear modification factor R AA Beauty predicted to dominate above 4-5 GeV/c Single e- from NLO/FONLL scaled to M. Cacciari et al., hep-ph/ dNg/dy=3500 medium suppression R AA ~ 0.5 for c+b q=14 GeV 2 /fm medium suppression R AA ~ 0.4 for c+b ^ Two different theories: Theory I: Djordjevic et al.: Theory II: Armesto et al.:

21/April/2006Manuel Calderón de la Barca 8 Electrons at p T 5-10 GeV. Use trigger detectors: TPC: tracking, PID | |<1.3 =2 BEMC (tower, SMD): PID 0< <1 =2 TOF patch good for low pT, acc. small, no trigger Run2003/2004 min. bias. 6.7M events with half field high tower trigger 2.6M events with full field (45% of all) 10% central 4.2M events (15% of all ) Preliminary results from: HighTower trigger: Only events with high tower E T >3 GeV/c 2 Enhancement of high p T

21/April/2006Manuel Calderón de la Barca 9 hadrons electrons Electron ID in STAR – EMC 1.TPC: dE/dx for p > 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 2.EMC: a)Tower E & p/E b)Shower Max Detector (SMD) Hadrons/Electron shower develop different shape Use # hits in Shower Max to discriminate 85-90% purity of electrons (p T dependent) h discrimination power ~ electrons Kp d hadronselectrons 8

21/April/2006Manuel Calderón de la Barca 10 Electron background Inclusive electron spectra: Inclusive electron spectra: Signal Signal Heavy quarks semi-leptonic decays Heavy quarks semi-leptonic decays Dominant background Dominant background Instrumental: Instrumental: - γ conversion – Hadronic decays: - Dalitz decays (π 0, η) - Dalitz decays (π 0, η) Rejection strategy: For every electron candidate Combinations with all TPC electron candidates M e+e- <0.14 GeV/c 2 flagged photonic Correct for primary electrons misidentified as background Correct for background rejection efficiency Background rejection efficiency central Au+Au M e+e- <0.14 GeV/c 2 red likesign

21/April/2006Manuel Calderón de la Barca 11 Electrons, muons, D0 results At low pt, consistent with binary scaling At low pt, consistent with binary scaling Large errors still for D0 measurement. Large errors still for D0 measurement. Higher pt, begin to see suppression… Higher pt, begin to see suppression…

21/April/2006Manuel Calderón de la Barca 12 Non-photonic electron spectra at higher p T pp,dAu,AuAu s NN = 200 GeV Photonic electrons subtracted Excess over photonic electrons observed Corrected for 10-15% hadron contamination Beauty contribution, can it be disentangled? pQCD calculations can give a range from 2-10 GeV for the c-b crossover in the e spectra.

21/April/2006Manuel Calderón de la Barca 13 R AA nuclear modification factor Suppression up to ~ observed in 40-80% centrality ~ in centrality % Strong suppression up to ~ 0.2 observed at high p T in 0-5% Maximum of suppression at p T ~ 5-6 GeV/c Theories currently do not describe the data Curves with c-only match R AA but, of course, not the p+p spectra Armesto et al. hep-th/ van Hess et al. hep-th/ Wicks et al. hep-th/

21/April/2006Manuel Calderón de la Barca 14 Large electron suppression is a PUZZLE Large suppression => large dE/dx of heavy quarks (NOT EXPECTED) Maybe higher at pT? Where is b contribution? Elastic energy loss? Important, helps, but not enough! Not enough, R AA saturates! Armesto et al. hep-ph/ The low end of c-b overlap The high end of c-b overlap Wicks et al nucl-th/ Recent study on 3 body cqq elastic scattering in QGP No beauty included! Liu&Ko nucl-th/ Large dN g /dx~ 3500,

21/April/2006Manuel Calderón de la Barca 15Summary Non-photonic electrons from heavy flavor decays were measured in s = 200 GeV p+p, d+Au and Au+Au collisions by STAR up to pT~10 GeV/c Expected to be sensitive to both charm and beauty Strong suppression of non-photonic electrons has been observed in Au+Au increasing with centrality Suggests large energy loss for heavy quarks (similar to light quarks ) Theoretical attempts to explain suppression fail if b+c are included What is the contribution of b? Are there other/different contributions to energy loss? It is desirable to separate contribution b+c experimentally direct reconstruction of other detector upgrades displaced vertex in heavy ion environment?! Large acceptance TOF (Ds and c, 2009) e-h correlations