Charm and Electrons in

Thomas Ullrich, STAR/BNL

International Workshop onElectromagnetic Probes of

Hot and Dense MatterECT, Trento June 8, 2005

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Outline STAR’s Heavy Flavor Program

Detector capabilities Experimental techniques

Open Charm (and Beauty) Production Non-photonic electrons

p+p: the referenced+Au: cold nuclear matter effectsAu+Au: ( QM’05)

D mesonsd+Au: charm cross-sectionAu+Au: ( QM’05)

Thermalization of heavy quarks ? Au+Au: v2 of non-photonic electrons

Quarkonia: J/ and Summary and Outlook

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Detecting D-Mesons via Hadronic Decays

Hadronic Channels: D0 K (B.R.: 3.8%) D K p (B.R.: 9.1%) D*± D0π (B.R.: 68% 3.8% (D0 K ) = 2.6%) D0 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, PIDSVT: vertex’ing, PIDZDC/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:

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(D0) - 315(D) m) background

Current analyses are based on TPC alone

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General Techniques for D Reconstruction1. Identify charged daughter tracks through

energy loss in TPC

2. Alternatively at high pT 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 aroundm(D*)-m(D0) =0.1467 GeV/c2

D0

D0D*

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Detecting Charm/Beauty via Semileptonic D/B Decays

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%)

single “non-photonic” electron continuum

“Photonic” Single Electron Background: conversions (0 ) 0, ’ Dalitz decays , , … decays (small) Ke3 decays (small)

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Detecting Charm/Beauty via Semileptonic D/B Decays

Electrons in STAR:TPC: tracking, PIDBEMC (tower, SMD): PID

EEMC (tower, SMD): PIDToF patch: PID

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Electron ID in STAR – EMC

1. TPC for p and dE/dx● e/h ~ 500 (pT dependent)

2. Tower E p/E● e/h ~ 100 (pT dependent)

3. Shower Max Detector (SMD) shape to reject hadrons

● e/h ~ 20

4. e/h discrimination power ~ 105

Works for pT > 1.5 GeV/c

electrons

hadrons

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Electron ID in STAR – ToF Patch

Electron identification: TOF |1/ß-1| < 0.03 TPC dE/dx electrons

electrons

MRPC – ToF (prototype):/30

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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 < pT < 3 GeV/c

TPC only: 2 < pT < 3.5 GeV/c

EMC + TPC:pT > 1.5 GeV/c

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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 TPC3. Reject tagged track when m <

mcut ~ 0.1 – 0.15 MeV/c2

4. Cross-check with like-sign

Rejection Efficiency: • Simulation/Embedding

• background flat in pT

• 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 pT>1.0 GeV/c

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Photonic Single Electron Background Subtraction

pT dependent hadron contamination (5-30%) subtracted

Excess overbackground

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

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Nuclear Effects RdAu ?

Nuclear Modification Factor: inelpp

dAubindAu

TppdAu

TdAudAu NT

ddpdT

ddpNdR

/ where;/

/2

2

Within errors compatible with RdAu = 1 …

… but also with RdAu(h)

NOTE: RdAu for a given pT comes from heavy mesons from a wide pT range p(D) > p(e) (~ 1.5-3) makes interpretation difficult

hadrons

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D0 Mesons in d+Au

Mass and Width consistent with PDG values considering detector effects:• mass=1.867±0.006 GeV/c2;• mass(PDG)=1.8645±0.005 GeV/c2

• mass(MC)=1.865 GeV/c2

• width=13.7±6.8 MeV• width(MC)=14.5 MeV

cp

dy

dN

T

y

Aud

D

/GeV 08.032.1

008.0004.0028.00

0

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Obtaining the Charm Cross-Section cc

From D0 mesons alone: ND0/Ncc ~ 0.540.05

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: pp

inel = 42 mb

Nbin = 7.5 0.4 (Glauber) |y|<0.5 to 4: f = 4.70.7 (PYTHIA) RdAu = 1.3 0.3 0.3

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Charm Cross-Section cc

pp Charm Cross-Section

From D0 alone:

cc = 1.3 0.2 0.4 mb

From combined fit:

cc = 1.4 0.2 0.4 mb

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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 = 0.709 0.085 + (+0.332,0.281) mbPHENIX from min. bias Au+Au: cc = 0.622 0.057 0.160 mb (PRL94,082301)

Reality check: 1.4 0.447 mb and 0.71 0.343 mb are not so bad given thecurrently available statistics (soon be more!)

pp p

SPS, FNAL (fixed target) and ISR (collider) experiments

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Discrepancy between STAR and PHENIX ?

90%

15%

Combined fit of STAR D0 and PHENIX electrons:No discrepancy: cc=1.1 0.1 0.3 mb

STAR: PRL 94, 062301 (2005)PHENIX p+p (QM04): S. Kelly et al. JPG30(2004) S1189

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Statistical model (e.g. A. Andronic et. al. PLB 571,36(2003)) : Largecc 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

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NLO/FONLL

Recent calculations in NLO (e.g. R. Vogt et al. hep-ph/0502203) Calculations depend on:

quark mass mc

factorization scale F (typically F = mc or 2 mc)

renormalization scale R (typically R = F) 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 pT >> mc where mass is not relevant

K factor (NLO NNLO) ?

b

bb

FONLLbb

NLOcc

FONLLcc

99.067.0

381134

400146

87.1

244 ;256

from hep-ph/0502203

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NLO/FONLL

For pT spectra mT2

for calculations 2 m2

pT integrated < direct calculated FONLL higher over most pT than NLO Choice of FF plays big role Uncertainty bands:

reflect uncertainties in and mc

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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) 353Nuovo 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

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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 !!!

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High-pT D0-Meson Spectra in d+Au

How is it done ? Assumptions: same shape of D0,

D*, D spectra D0 K defines low pT points

D0 K defines one high-pT point

Combined allow power law fit Allows to move D* and D

spectra into place Cross-check with known ratios

Problem: D*/D0 and D/ D0 not well known (pT, s dependent ?)

Note: spectrum depends onone point: D0 K

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High-pT 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 D0 K of many people over many month …

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High-pT D-Meson Spectra in d+Au

Until we found the problem … subtle effect after correction no significant signal D0 K “combined” low to high-pT D0 spectra is gone

Upper limits from D0 K (90% CL)

Note: D* itself is still valid!!! Now a “standalone” spectra. Doesn’t affect possibility of studying RAA in Au+Au

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Strong Elliptic Flow at RHIC

Strong elliptic flow at RHIC (consistent with hydro limit ?) Scaling with Number of Constituent Quarks (NCQ)

partonic degrees of freedom !? (v2/n) vs. (pT/n) shows no mass and flavor dependence Strong argument for partonic phase with thermalized light quarks

What’s about charm? Naïve kinematical argument: need Mq/T ~ 7 times more collisions to thermalize v2 of charm closely related to RAA

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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(2T) 6(0.5/s)2

AMPT:(C.M. Ko)

← =10 mb

← =3 mb

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Charm Elliptic Flow through Resonance Effects

Van Hees & Rapp, PRC 71, 034907 (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 pT spectra in local rest frame

“Nearly” thermal: T ~ 290 MeV

Including scalar, pseudoscalar, vector, and axial vector D-like-mesons gives:

σcq→cq(s1/2=mD)≈6 mb

Cross-section is isotropic the transport cross section is 6 mb, about 4 times larger than from pQCD t-channel diagrams

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How to Measure Charm v2

Best: D mesons need large statistics, high background not yet

Alternative: Measure v2 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

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Analysis: v2 of Non-Photonic Electrons

Same procedures as for single electrons (incl. background subtraction) But much harder cuts (plenty of statistics) Special emphasis on anti-deuteron removal γ-conversions, π0-Dalitz electrons removed via invariant mass

Remaining 37% photonic electron background subtracted with v2max=17%

Reaction plane resolution res ~ 0.7 Consistency check: PYTHIA + MEVSIM (v2 generator) + analysis chain OK

v2 = cos(2[Φ-Ψ]) / Ψres

Phenix : Min. BiasStar: 0-80%STAR: stat. errors only

Phenix:nucl-ex/0404014 (QM2004)nucl-ex/0502009 (submitted to PRC)Star:J. Phys. G 190776 (Hot Quarks 2004)J. Phys. G 194867 (SQM 2004)

v2 of Non-Photonic Electrons

Indication of strong non-photonic electron v2

consistent with v2(c) = v2(light quark) smoothly extending from PHENIX results Teany/Moor D (2T) = 1.5 (s = 1?) expect substantial suppression RAA

Greco/Ko Coalescence model (shown above) appears to work well

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Quarkonia in STAR

STAR: Large acceptance ||<1 High tracking efficiency (90%) J/ acceptance efficiency (pT

e > 1.2 GeV/c) ~ 10%

: Acceptance efficiency (pTe > 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 S/B > 1: 1 for S/B = 1:25 – 1:100 for J/

Seff = S/(2(B/S)+1) significance close to that of J/

STAR needs quarkonia triggers

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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 < Minv < 3.5 GeV/c2

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): Minv > 7 GeV/c2

High Efficiency (80%) – works in Au+Au

Tests in Au+Au show it works small background counts = expectations Need full EMC for that

2004 ½ barrel EMC 2005 ½ - ¾ barrel EMC

triggerthreshold No N+++N--

subtracted

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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

D0 in d+Au from pT = 0 - 3 GeV/c

D* in d+Au mesons from pT = 1.5 – 6 GeV/c 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 = 0.300.04(stat)0.09(sys) mb 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 v2 of non-photonic electrons indicate substantial elliptic flow of charm in Au+Au collisions at RHIC consistent with v

2c = v

2light-q theory calculations

consistent (smoothly extending) with PHENIX results try to extend to higher pT range (possibly b dominated)

First Results on J/ and soon

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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 PhysicsMichigan 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 UniversityPusan 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 Institutionsin 12 countries

STAR Collaboration