Charm and Electrons in Thomas Ullrich, STAR/BNL International Workshop on Electromagnetic Probes of Hot and Dense Matter ECT, Trento June 8, 2005

2 Outline  STAR’s Heavy Flavor Program l Detector capabilities l Experimental techniques  Open Charm (and Beauty) Production l Non-photonic electrons §p+p: the reference §d+Au: cold nuclear matter effects §Au+Au: (  QM’05) l D mesons §d+Au: charm cross-section §Au+Au: (  QM’05)  Thermalization of heavy quarks ? l Au+Au: v 2 of non-photonic electrons  Quarkonia: J/  and   Summary and Outlook

3 Detecting D-Mesons via Hadronic Decays Hadronic Channels:  D 0  K  (B.R.: 3.8%)  D   K  p(B.R.: 9.1%)  D *±  D 0 π(B.R.: 68%  3.8% (D 0  K  ) = 2.6%  )  D 0  K  (B.R.: 6.2%  100% (     ) = 6.2%)   c  p K  (B.R.: 5%)

4 Detecting D-Mesons via Hadronic Decays Hadrons in STAR:  TPC: tracking, PID  SVT: vertex’ing, PID  ZDC/CTB: centrality/trigger TPC:  High tracking efficiency for tracking hadrons (~90%)   p/p ~ 1% at 1 GeV/c  large acceptance |  |<1  PID (dE/dx) limits: l p up to 1 GeV/c K,  up to 0.7 GeV/c SVT:  current vertex’ing performance not sufficient to resolve typical charm secondary vertices (c  ~ 120(D 0 ) - 315(D  )  m)  background   Current analyses are based on TPC alone

5 General Techniques for D Reconstruction 1.Identify charged daughter tracks through energy loss in TPC 2.Alternatively at high p T use h  and assign referring mass (depends on analysis) 3.Produce invariant mass spectrum in same event 4.Obtain background spectrum via mixed event 5.Subtract background and get D spectrum 6.Often residual background to be eliminated by fit in region around the resonance Exception D*: search for peak around m(D*)-m(D 0 ) = GeV/c 2 D0D0 D0D0 D*D*

6 Detecting Charm/Beauty via Semileptonic D/B Decays Semileptonic Channels:  c  e + + anything (B.R.: 9.6%) D 0  e + + anything(B.R.: 6.87%) l D   e  + anything(B.R.: 17.2%)  b  e + + anything(B.R.: 10.9%) l B   e  + anything(B.R.: 10.2%)  single “non-photonic” electron continuum “Photonic” Single Electron Background:   conversions (  0   )   0,  ’ Dalitz decays  , , … decays (small)  Ke3 decays (small)

7 Detecting Charm/Beauty via Semileptonic D/B Decays Electrons in STAR:  TPC: tracking, PID  BEMC (tower, SMD): PID  EEMC (tower, SMD): PID  ToF patch: PID

8 Electron ID in STAR – EMC 1.TPC for p and dE/dx ●e/h ~ 500 (p T dependent) 2.Tower E  p/E ●e/h ~ 100 (p T dependent) 3.Shower Max Detector (SMD) shape to reject hadrons ●e/h ~ 20 4.e/h discrimination power ~ 10 5 Works for p T > 1.5 GeV/c electronshadrons

9 Electron ID in STAR – ToF Patch Electron identification: TOF |1/ß-1| < 0.03 TPC dE/dx electrons electrons MRPC – ToF (prototype):  /30 

10 Inclusive Single Electrons p+p/d+Au Inclusive  non-photonic spectra : How to assess photonic background? PHENIX 1: cocktail method PHENIX 2: converter method STAR: measurement of main background sources ToF + TPC: 0.3 GeV/c < p T < 3 GeV/c TPC only: 2 < p T < 3.5 GeV/c EMC + TPC: p T > 1.5 GeV/c

11 Photonic Single Electron Background Subtraction in pp and dAu Method: 1.Select an primary electron/positron (tag it) 2.Loop over opposite sign tracks anywhere in TPC 3.Reject tagged track when m < m cut ~ 0.1 – 0.15 MeV/c 2 4.Cross-check with like-sign Rejection Efficiency: Simulation/Embedding background flat in p T weight with measured  0 spectra (PHENIX)  conversion and  0 Dalitz decay reconstruction efficiency ~60% Relative contributions of remaining sources: PYTHIA/HIJING + detector simulations Invariant Mass Square Rejected Signal Opening Angle  conversion and  0 Dalitz decay reconstruction efficiency : ~60% at p T >1.0 GeV/c

12 Photonic Single Electron Background Subtraction p T dependent hadron contamination (5-30%) subtracted Excess over background

13 Non-Photonic Single Electron Spectra in p+p and d+Au

14 Nuclear Effects R dAu ? Nuclear Modification Factor: Within errors compatible with R dAu = 1 … … but also with R dAu (h  ) NOTE: R dAu for a given p T comes from heavy mesons from a wide p T range  p(D)  >  p(e)  (~  1.5-3)  makes interpretation difficult hadrons

15 D 0 Mesons in d+Au Mass and Width consistent with PDG values considering detector effects: mass=1.867±0.006 GeV/c 2 ; mass(PDG)=1.8645±0.005 GeV/c 2 mass(MC)=1.865 GeV/c 2 width=13.7±6.8 MeV width(MC)=14.5 MeV

16 Obtaining the Charm Cross-Section   cc From D 0 mesons alone:  N D0 /N cc ~ 0.54  0.05  Fit function from exponential fit to m T spectra Combined fit:  Assume D 0 spectrum follows a power law function  Generate electron spectrum using particle composition from PDG  Decay via routines from PYTHIA  Assume: dN/dp T (D 0, D*, D , …) have same shape only normalization In both cases for d+Au  p+p:   pp inel = 42 mb  N bin = 7.5  0.4 (Glauber)  |y|<0.5 to 4  : f = 4.7  0.7 (PYTHIA)  R dAu = 1.3  0.3  0.3

17 Charm Cross-Section   cc pp Charm Cross-Section From D 0 alone:  cc = 1.3  0.2  0.4 mb From combined fit:  cc = 1.4  0.2  0.4 mb

18 Discrepancy between STAR and PHENIX ? STAR from d+Au:  cc = 1.4  0.2  0.4 mb (PRL94,062301) PHENIX from p+p (preliminary):  cc =  (+0.332,  0.281) mb PHENIX from min. bias Au+Au:  cc =   mb (PRL94,082301) Reality check: 1.4  mb and 0.71  mb are not so bad given the currently available statistics (soon be more!) pp pp SPS, FNAL (fixed target) and ISR (collider) experiments

19 Discrepancy between STAR and PHENIX ? 90% 15% Combined fit of STAR D 0 and PHENIX electrons: No discrepancy:  cc =1.1  0.1  0.3 mb STAR: PRL 94, (2005) PHENIX p+p (QM04): S. Kelly et al. JPG30(2004) S1189

20 Statistical model (e.g. A. Andronic et. al. PLB 571,36(2003)) : Large  cc yield in heavy ion collisions  J/  production through recombination  possible J/  enhancement Consequences of High Cross-Section: J/  Recombination  In stat models:  cc typically from pQCD calculations (~390  b)  STAR  cc  much larger enhancement (~3-4) for J/  production in central Au+Au collisions  PHENIX’s upper limit would invalidate the expectation from large  cc ?! Δy = 1 Δy = 2 Δy = 3 Δy = 4

21 NLO/FONLL Recent calculations in NLO (e.g. R. Vogt et al. hep-ph/ )  Calculations depend on: l quark mass m c factorization scale  F (typically  F = m c or 2 m c ) renormalization scale  R (typically  R =  F ) l parton density functions (PDF)  Hard to obtain large  with  R =  F (which is used in PDF fits) Fixed-Order plus Next-to-Leading-Log (FONLL)  designed to cure large logs for p T >> m c where mass is not relevant K factor (NLO  NNLO) ? from hep-ph/

22 NLO/FONLL  For p T spectra    m T 2 for  calculations  2  m 2  p T integrated  < direct calculated   FONLL higher over most p T than NLO  Choice of FF plays big role  Uncertainty bands: reflect uncertainties in  and m c

23 Charm Total Cross Section Can we confirm or rule out Cosmic Ray experiments? (Pamir, Muon, Tian Shan) under similar conditions? NPB (Proc. Suppl.) 122 (2003) 353 Nuovo Ciment. 24C (2001) 557 X. Dong USTC  NLO calculations under-predict current  cc at RHIC  More precise data is needed  high statistics D mesons in pp PHENIX,STAR: stat. error only

24 Comparison: Non-Photonic Electrons with NLO FONLL calculations: Charm: scaled by  STAR /  FONLL Bottom: Can be estimated from fit of sum to data (numbers soon) Errors used: data + FONLL uncertainty bands Plenty of room for bottom !!!

25 High-p T D 0 -Meson Spectra in d+Au How is it done ?  Assumptions: same shape of D 0, D*, D  spectra  D 0  K  defines low p T points  D 0  K   defines one high-p T point  Combined allow power law fit  Allows to move D* and D  spectra into place  Cross-check with known ratios Problem: D*/D 0 and D  / D 0 not well known (p T,  s dependent ?) Note: spectrum depends on one point: D 0  K  

26 High-p T D-Meson Spectra in d+Au Headache: Spectra very hard (too hard)  NLO: fragmentation function   function (Peterson FF needs  c =  b ) ?  Yield at 10 GeV/c only factor 3 below CDF (LO/NLO ~ 10) ? Intensive systematic studies of D 0  K   of many people over many month …

27 High-p T D-Meson Spectra in d+Au Until we found the problem …  subtle effect  after correction no significant signal D 0  K     “combined” low to high-p T D 0 spectra is gone Upper limits from D 0  K  (90% CL) Note: D* itself is still valid!!! Now a “standalone” spectra. Doesn’t affect possibility of studying R AA in Au+Au

28 Strong Elliptic Flow at RHIC Strong elliptic flow at RHIC (consistent with hydro limit ?)  Scaling with Number of Constituent Quarks (NCQ) l partonic degrees of freedom !?  (v 2 /n) vs. (p T /n) shows no mass and flavor dependence  Strong argument for partonic phase with thermalized light quarks What’s about charm?  Naïve kinematical argument: need M q /T ~ 7 times more collisions to thermalize  v 2 of charm closely related to R AA

29 Charm Elliptic Flow from the Langevin Model  Diffusion coefficient in QGP: D = T/M  momentum drag coefficient)  Langevin model for evolution of heavy quark spectrum in hot matter  Numerical solution from hydrodynamic simulations  pQCD gives D  (2  T)  6(0.5/  s ) 2 AMPT: (C.M. Ko) ←  =10 mb ←  =3 mb

30 Charm Elliptic Flow through Resonance Effects Van Hees & Rapp, PRC 71, (2005)  Assumption: survival of resonances in the QGP  Introducing resonant heavy-light quark scattering  heavy particle in heat bath of light particles (QGP) + fireball evolution time-evolved c p T spectra in local rest frame “Nearly” thermal: T ~ 290 MeV Including scalar, pseudoscalar, vector, and axial vector D-like-mesons gives: σ cq→cq (s 1/2 =m D )≈6 mb Cross-section is isotropic  the transport cross section is 6 mb, about 4 times larger than from pQCD t-channel diagrams

31 How to Measure Charm v 2 Best: D mesons  need large statistics, high background  not yet Alternative: Measure v 2 of electrons from semileptonic charm decays  Emission angles are well preserved above p = 2 GeV/c  2-3 GeV Electrons correspond to ≈3-5 GeV D-Mesons

32 Analysis: v 2 of Non-Photonic Electrons  Same procedures as for single electrons (incl. background subtraction) l But much harder cuts (plenty of statistics) l Special emphasis on anti-deuteron removal l γ-conversions, π 0 -Dalitz electrons removed via invariant mass  Remaining 37% photonic electron background subtracted with v 2 max =17%  Reaction plane resolution  res ~ 0.7  Consistency check: PYTHIA + MEVSIM (v 2 generator) + analysis chain  OK v 2 = cos(2[Φ-Ψ]) / Ψ res

Phenix : Min. Bias Star: 0-80% STAR: stat. errors only Phenix: nucl-ex/ (QM2004) nucl-ex/ (submitted to PRC) Star: J. Phys. G (Hot Quarks 2004) J. Phys. G (SQM 2004) v 2 of Non-Photonic Electrons  Indication of strong non-photonic electron v 2  consistent with v 2 (c) = v 2 (light quark)  smoothly extending from PHENIX results  Teany/Moor  D (2  T) = 1.5 (  s = 1?)  expect substantial suppression R AA  Greco/Ko  Coalescence model (shown above) appears to work well

34 Quarkonia in STAR STAR:  Large acceptance |  |<1  High tracking efficiency (90%)  J/  acceptance  efficiency (p T e > 1.2 GeV/c) ~ 10%   : Acceptance  efficiency (p T e > 3.5 GeV/c) ~ 14%  Without Trigger (min. bias running): Min bias (100 Hz): 18 J/  and 0.02  per hour running  Signal-to-Background Ratios l S/B > 1: 1 for  S/B = 1:25 – 1:100 for J/   S eff = S/(2(B/S)+1)  significance close to that of J/   STAR needs quarkonia triggers

35 Quarkonia Trigger in STAR J/  e + e   :  L0-trigger: 2 EMC tower with E > 1.2 GeV (~60° apart)  L2-trigger (software): veto , better E, 2.5 < M inv < 3.5 GeV/c 2  Efficiency currently too low in Au+Au (pp only)  need full ToF  e + e   :  L0-trigger: 1 EMC tower with E > 3.5 GeV  L2-trigger (software): M inv > 7 GeV/c 2  High Efficiency (80%) – works in Au+Au  Tests in Au+Au show it works  small background  counts = expectations  Need full EMC for that l 2004 ½ barrel EMC l 2005 ½ - ¾ barrel EMC trigger threshold No N ++ +N -- subtracted

36 Summary and Outlook Heavy Flavor Production in RHI is the next big topic that needs to be addressed  STAR has solid baseline measurements in pp and d+Au l D 0 in d+Au from p T = GeV/c l D* in d+Au mesons from p T = 1.5 – 6 GeV/c l Non-photonic single electrons in p+p and d+Au from 1.5 – 10 GeV/c  Measurements indicate a large  cc in pp at RHIC d  /dy| y=0 = 0.30  0.04(stat)  0.09(sys) mb l NLO pQCD calculations under predict this value (~ a factor of 3-5) Large  cc appear to rule out expectation of J/ψ enhancement from some charm coalescence and statistical models  Preliminary results on v 2 of non-photonic electrons indicate substantial elliptic flow of charm in Au+Au collisions at RHIC l consistent with v 2c = v 2light-q theory calculations l consistent (smoothly extending) with PHENIX results l try to extend to higher p T range (possibly b dominated)  First Results on J/  and  soon

37 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