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Manuel Calder ón de la Barca S ánchez UC Davis for the STAR collaboration DIS 2006

Heavy flavor production in STAR. What can charm and beauty tell us about matter in heavy ion collisions?. Manuel Calder ón de la Barca S ánchez UC Davis for the STAR collaboration DIS 2006 Tsukuba, Japan 21/April/2006. Light quark sector highlights. STAR. Pedestal&flow subtracted.

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Manuel Calder ón de la Barca S ánchez UC Davis for the STAR collaboration DIS 2006

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  1. 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

  2. Light quark sector highlights STAR Pedestal&flow subtracted Hadron suppression in central AuAu Jet quenching • 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, 072304 (2003). Manuel Calderón de la Barca

  3. Heavy quarks in a hot medium D, B c, b 1) production 2) quark energy loss 3) fragmentation Energy loss depends on properties of medium (gluon densities, size) depends on properties of “probe” (color charge, mass) • Quenching weights, more recent way to study energy loss of heavy quarks in a dense medium. • Armesto et al. hep-ph/0501225 • 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) • D,B spectra are affected by energy loss, and might be more sensitive to medium properties than light quarks. Manuel Calderón de la Barca

  4. Measuring heavy flavors • Hadronic decay channels:D0Kp, D*D0p, D+/-Kpp • Non-photonic electrons: • Semileptonic channels: • c  e+ + anything (B.R.: 9.6%) • D0  e+ + anything(B.R.: 6.87%) • D e + anything(B.R.: 17.2%) • b  e+ + anything (B.R.: 10.9%) • B e + anything(B.R.: 10.2%) • Drell-Yan • (small contribution for pT < 10 GeV/c at RHIC) • Photonic electron background: • gconversions (p0 gg; g e+e- ) • p0, h, h’ Dalitz decays • r, f … decays (small) • Ke3decays (small) Manuel Calderón de la Barca

  5. Charm reconstruction via hadronic decays D0 STAR Phys. Rev. Lett. 94 (2005) nucl-ex/0510063 Total charm cross section per NN interaction dAu: 1.4  0.2(stat.)  0.4(sys.) mb AuAu: 1.11 0.08(stat.)  0.42(sys.) mb Assumes Binary scaling dAu to AuAu  Charm produced in initial collisions . Systematics and statistics limited (only 3 pT bins in Au+Au). Manuel Calderón de la Barca

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

  7. ^ q=14 GeV2/fm medium suppression RAA ~ 0.4 for c+b Predictions of electron nuclear modification factor RAA Two different theories: Single e- from NLO/FONLL scaled to M. Cacciari et al., hep-ph/0502203 Theory I: Djordjevic et al.: • Beauty predicted to dominate above 4-5 GeV/c dNg/dy=1000 small suppression RAA ~ 0.7for c+b dNg/dy=3500 medium suppression RAA ~ 0.5 for c+b Theory II: Armesto et al.: Manuel Calderón de la Barca

  8. Electrons at pT 5-10 GeV. HighTower trigger: • Only events with high tower ET>3 GeV/c2 • Enhancement of high pT • Use trigger detectors: • TPC: tracking, PID |h|<1.3 f=2p • BEMC (tower, SMD): PID 0<h<1 f=2p • TOF patch good for low pT, acc. small, no trigger Preliminary results from: 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 ) Manuel Calderón de la Barca

  9. electrons hadrons Electron ID in STAR – EMC d K p p electrons electrons hadrons • 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 • EMC: • Tower E & p/E • Shower Max Detector (SMD) • Hadrons/Electron shower develop different shape • Use # hits in Shower Max to discriminate • 85-90% purity of electrons • (pT dependent) • h discrimination power ~ 103-104 Manuel Calderón de la Barca 8

  10. Electron background M e+e-<0.14 GeV/c2 red likesign Background rejection efficiency central Au+Au • Inclusive electron spectra: Signal • Heavy quarks semi-leptonic decays Dominantbackground • Instrumental: - γ conversion • Hadronic decays: - Dalitz decays (π0, η) • Rejection strategy: For every electron candidate • Combinations with all TPC electron candidates • Me+e-<0.14 GeV/c2 flagged photonic • Correct for primary electrons misidentified as background • Correct for background rejectionefficiency Manuel Calderón de la Barca

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

  12. Non-photonic electron spectra at higher pTpp,dAu,AuAu sNN = 200 GeV • Photonic electrons subtracted • Excess over photonic electrons observed • Corrected for 10-15% hadron contamination • Beautycontribution, can it be disentangled? • pQCD calculations can give a range from 2-10 GeV for the c-b crossover in the e spectra. Manuel Calderón de la Barca

  13. RAA nuclear modification factor Armesto et al. hep-th/0511257 van Hess et al. hep-th/0508055 Wickset al.hep-th/0512076 Suppression up to ~ 0.5-0.6 observed in 40-80% centrality ~ 0.5 -0.6 in centrality 10-40% Strong suppression up to ~ 0.2 observed at high pTin 0-5% Maximum of suppression at pT ~ 5-6 GeV/c Theories currently do not describe the data Curves with c-only match RAA but, of course, not the p+p spectra Manuel Calderón de la Barca

  14. Large electron suppression is a PUZZLE • Large dNg/dx~ 3500, The low end of c-b overlap The high end of c-b overlap Armesto et al. hep-ph/0511257 Wicks et al nucl-th/0512076 Liu&Ko nucl-th/0603004 • Large suppression => large dE/dx of heavy quarks (NOT EXPECTED) Not enough, RAA saturates! • Where is b contribution? Maybe higher at pT? • Elastic energy loss? Important, helps, but not enough! • Recent study on 3 body cqq elastic scattering in QGP No beauty included! Manuel Calderón de la Barca

  15. Summary • 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+cexperimentally • direct reconstruction of other • detector upgrades • displaced vertex in heavy ion environment?! • Large acceptance TOF (Ds and Lc, 2009) • e-h correlations Manuel Calderón de la Barca

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