Hard Probes Suppression of high-p T non-photonic electrons in Au+Au collisions at √s NN = 200 GeV Jaroslav Bielcik Yale University/BNL

Hard Probes Why measure non-photonic electrons? Non-photonic electrons: Semileptonic channels: c  e + + anything (B.R.: 9.6%) D 0  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%) Non-photonic electrons indirect way to study heavy quarks p+p – d+Au – Au+Auhow heavy quarks interact with medium Direct way: Hadronic decay channels: e.g. D 0  K  R AA

Hard Probes Charm quark production Z. Lin & M. Gyulassy, PRC 51 (1995) 2177  Charm is dominantly produced in initial hard scattering via gluon fusion:  Charm total cross-section should follow N bin scaling from p+p to Au+Au Observed binary scaling d+Au => Au+Au STAR  cc

Hard Probes  Beauty predicted to dominate above 4-5 GeV/c heavy flavor e- from FONLL scaled to Cacciari, Nason, Vogt, Phys.Rev.Lett 95 (2005) Heavy flavor electrons in FONLL Due to mass of heavy quarks it’s production should be calculable in pQCD FONLL: extension of NLO pQCD Crossing point is important because of huge c,b mass difference => interactions can be different

Hard Probes FONLL: Large uncertainty on c/b crossing point in p T : from scales/masses variation it changes from 3 to 9 GeV/c Uncertainty of c/b contribution varying

Hard Probes Energy loss of quarks in medium Charm and beauty quarks probe the nuclear matter in Au+Au Energy loss depends on properties of medium (gluon densities, size) depends on properties of “probe” (color charge, mass) nuclear modification factor: R AA  1 … signal of medium effects R AA hadrons … light quarks and gluons R AA D,electrons … heavy quarks: c,b

Hard Probes Energy loss of heavy quarks D,B (electrons) spectra are affected by energy loss light M.Djordjevic PRL 94 (2004) ENERGY LOSS 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 Armesto, Salgado, Wiedemann PRD 69 (2004) Effect of collisional energy loss for heavy quarks M.G.Mustafa Phys. Rev C 72 (2005) M.Djordjevic nucl-th/

Hard Probes Heavy quark energy loss ASW case ASW: Armesto, Salgado, Wiedemann, PRD 69 (2004) Dainese, Loizides, Paic, EPJC 38 (2005) 461.  Density ( ) “tuned” to match R AA in central Au+Au at 200 GeV light =14 GeV 2 /fm R AA ~ 0.2 light mesons time averaged momentum transfer quark-medium per unit lenght hep-ph/ heavy R AA ~ 0.4 for electrons from c+b R.Baier, Yu.L.Dokshitzer, A.H.Mueller, S.Peigne' and D.Schiff, (BDMPS), Nucl. Phys. B483 (1997) 291.

Hard Probes Heavy quark energy loss DVGL case DVGL: Djordjevic, Guylassy Nucl.Phys. A 733, 265 (2004) dNg/dy=1000 gluon density of produced matter + Elastic energy loss ( Wicks et al nucl-th/ ) light R AA ~ 0.2 light mesons R AA ~ for electrons from c+b heavy

Hard Probes STAR Detector Electrons in STAR:  TPC: tracking, PID |  |<1.3  =2   BEMC (tower, SMD): PID 0<  <1  =2   TOF patch HighTower trigger:  Only events with high tower E T >3 GeV/c 2  Enhancement of high p T

Hard Probes 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~1 for e - b)Shower Max Detector Hadrons/Electron shower develop different shape 85-90% purity of electrons (p T dependent) h discrimination power ~ electrons  Kp d all p>1.5 GeV/c 2 p/E SMD

Hard Probes Photonic electrons background  Background : Mainly from  conv and    Dalitz  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 ~50-60% for central Au+Au M e+e- <0.14 GeV/c 2 red likesign Inclusive/Photonic:  Excess over photonic electrons observed for all system and centralities => non-photonic signal

Hard Probes STAR non-photonic electron spectra p+p, d+Au, Au+Au  s NN = 200 GeV  p+p, d+Au: up to 10 GeV/c  Au+Au: 0-5%, 10-40%, 40-80% up to 8 GeV/c  Photonic electrons subtracted  Corrected for 10-15% hadron contamination  Beauty is expected to give an important contribution above 5 GeV/c JB QM2005 nucl-ex/

Hard Probes STAR preliminary Electrons from p+p x FONLL pQCD 5.5  FONLL has to be scaled by factor ~5.5 to match the data  Ratio Data/FONLL is constant ~ p T : both charm and beauty are needed to get shape both charm and beauty are off in FONLL  STAR cc /  FONLL

Hard Probes Electron R AA nuclear modification factor Suppression up to ~ observed in 40-80% centrality ~ in centrality 10-40% 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 well Only c contribution would be consistent with the R AA but not the p+p spectra Armesto et al. hep-th/ van Hess et al. Phys. Rev. C 73, (2006) Wicks et al. (DVGL) hep-th/ JB QM2005 nucl-ex/

Hard Probes 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 p T ~10 GeV/c Expected to have contribution from both charm and beauty  FONLL underpredicts non-photonic electrons p+p electrons  Strong suppression of non-photonic electrons has been observed in Au+Au, increasing with centrality Suggests large energy loss for heavy quarks ( R AA similar to light quarks )  Theoretical attempts to explain it seem to fail if both b+c are included What is the contribution of b? Are there other/different contributions to energy loss? Collisional energy loss, multibody effects…  It is desirable to separate contribution b+c experimentally detector upgrades (displaced vertex) e-h correlations

Hard Probes Argonne National Laboratory Institute of High Energy Physics - Beijing University of Bern University of Birmingham Brookhaven National Laboratory California Institute of Technology University of California, Berkeley University of California - Davis University of California - Los Angeles Carnegie Mellon University Creighton University Nuclear Physics Inst., Academy of Sciences Laboratory of High Energy Physics - Dubna Particle Physics Laboratory - Dubna University of Frankfurt Institute of Physics. Bhubaneswar Indian Institute of Technology. Mumbai Indiana University Cyclotron Facility Institut de Recherches Subatomiques de Strasbourg University of Jammu Kent State University Institute of Modern Physics. Lanzhou Lawrence Berkeley National Laboratory Massachusetts Institute of Technology Max-Planck-Institut fuer Physics Michigan State University Moscow Engineering Physics Institute City College of New York NIKHEF Ohio State University Panjab University Pennsylvania State University Institute of High Energy Physics - Protvino Purdue University Pusan University University of Rajasthan Rice University Instituto de Fisica da Universidade de Sao Paulo University of Science and Technology of China - USTC Shanghai Institue of Applied Physics - SINAP SUBATECH Texas A&M University University of Texas - Austin Tsinghua University Valparaiso University Variable Energy Cyclotron Centre. Kolkata Warsaw University of Technology University of Washington Wayne State University Institute of Particle Physics Yale University University of Zagreb 545 Collaborators from 51 Institutions in 12 countries STAR Collaboration

Hard Probes STAR emc x tof x PHENIX

Hard Probes EMC electrons electronshadrons

Hard Probes Electron reconstruction efficiency AuAu200GeV the central collisions determined from electron embedding in real events the data are corrected for this effect

Hard Probes Part of the primary electrons is flaged as background AuAu200GeV the central collisions determined from electron embedding in real events the data are corrected for this effect

Hard Probes Dalitz Decays:     e  e  versus     e  e  The background efficiency for Dalitz electrons is evaluated by weighting with the  0 distribution but should be weighted by the true    distribution. Comparing the spectra of this both cases normalized to give the same integral for p T >1 GeV/c (cut-off for electron spectra) we see almost no deviation. The effect of under/over correction is on the few percent level!

Hard Probes P/E in momentum bins momentum [GeV/c] a.u.

Hard Probes dEdx for pt bins

Hard Probes Hadron suppression

Hard Probes Au+Au Systematical uncertainity d+Au and p+p40-80%10-40%0-5%Notes electron id and track efficiency (including dE/dx cut efficiency) (2 GeV/c) (8 GeV/c) (2 GeV/c) (8 GeV/c) (2 GeV/c) (8 GeV/c) (2 GeV/c) (8 GeV/c) Obtained from embedding, using different cluster finder and electron cuts. See a plot here of the efficiency variations for 0-5% most central Au-Au See a plot here of the efficiency variations for 0-5% most central Au-Au Hadronic contamination ( )% (2 GeV/c) (20 + 4)% (8 GeV/c) ( )% (2 GeV/c) (20 + 4)% (8 GeV/c) ( )% (2 GeV/c) (22 + 5)% (8 GeV/c) Obtained from changing dE/dx fit parameters Background finding efficiency From different photon weigth functions and systematical differences between Alex/Jaro/Yifei/Weijiang and Frank analysis Bremsstrahlung (2 GeV/c) (8 GeV/c) (2 GeV/c) (8 GeV/c) Use the size of the correction as suggested by Jamie Acceptance from the EMC database tables Click here for details Click here for details Trigger bias uncertainty8%6% 5% From the trigger bias fit parameters Normalization uncertainty14% for p+pOverall normalization for p+p

Hard Probes R.Vogt Slides

Hard Probes R.Vogt Slides

Hard Probes R.Vogt Slides

Hard Probes R.Vogt Slides