suppression of high-p t non-photonic electrons in au+au collisions at √s nn = 200 gev

[email protected] 1Hard Probes 2006

Suppression of high-pT non-photonic electrons in Au+Au collisionsat √sNN = 200 GeV Jaroslav BielcikYale University/BNL


Why measure non-photonic electrons?Why measure non-photonic electrons?

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%)

Non-photonic electrons indirect way to study heavy quarks

p+p – d+Au – Au+Au how heavy quarks interact with medium

Direct way: Hadronic decay channels: e.g. D0K

RAA


Charm quark productionCharm 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

Nbin scaling from p+p to Au+Au

Observed binary scaling d+Au => Au+Au

STAR cc


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 FONLLHeavy 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


• FONLL: Large uncertainty on c/b crossing point in pT: from scales/masses variation it changes from 3 to 9 GeV/c

Uncertainty of c/b contributionUncertainty of c/b contribution

set PDF,,,mm

m FR varying


Energy loss of quarks in mediumEnergy 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)

tpp

tAA

colltAA dpdN

dpdN

NpR

/

/1)(

nuclear modification factor:

RAA 1 … signal of medium effects

RAA hadrons … light quarks and gluons

RAA D,electrons … heavy quarks: c,b


Energy loss of heavy quarksEnergy 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) 199Armesto, Salgado, Wiedemann PRD 69 (2004) 114003

•Effect of collisional energy loss for heavy quarks M.G.Mustafa Phys. Rev C 72 (2005) M.Djordjevic nucl-th/0630066


Heavy quark energy loss ASW caseHeavy quark energy loss ASW case

2

ˆTk

q

ASW: Armesto, Salgado, Wiedemann, PRD 69 (2004) 114003

Dainese, Loizides, Paic, EPJC 38 (2005) 461.

/fmGeV 144ˆ 2q Density ( ) “tuned” to match RAA in central Au+Au at 200 GeV

q̂

light

=14 GeV2/fm

RAA ~ 0.2 light mesons

q̂

time averaged momentum transferquark-medium per unit lenght

2 ˆ LqCE Rs

0.4

0.1

hep-ph/0510284

0.20.3

heavy

RAA ~ 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.


Heavy quark energy loss DVGL caseHeavy 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/0512076)

light

RAA ~ 0.2 light mesons

RAA ~ 0.4-0.6 for electrons from c+b

heavy


STAR Detector 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 ET>3 GeV/c2

Enhancement of high pT


hadrons electrons

Electron ID in STAR – EMCElectron 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 (pT dependent) h discrimination power ~ 103-

104

electrons

K p d

allp>1.5 GeV/c2

p/E

SMD


Photonic electrons backgroundPhotonic electrons background Background: Mainly from conv and Dalitz 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 rejection efficiency ~50-60% for central Au+Au

M e+e-<0.14 GeV/c2

red likesign

Inclusive/Photonic:

Excess over photonic electrons observed for all system and centralities => non-photonic signal


STAR non-photonic electron spectra p+p, d+Au, Au+Au sNN = 200 GeV

STAR non-photonic electron spectra p+p, d+Au, Au+Au sNN = 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 importantcontribution above 5 GeV/c

JB QM2005 nucl-ex/0511005


STAR preliminary

Electrons from p+p x FONLL pQCDElectrons 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 ~ pT: both charm and beauty are needed to get shape both charm and beauty are off in FONLL

STARcc/FONLL


Electron RAA nuclear modification factorElectron RAA nuclear modification factor

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 pT in 0-5%

Maximum of suppression at pT ~ 5-6 GeV/c Theories currently do not describe the data well

Only c contribution would be consistent with the RAA but not the p+p spectra

Armesto et al. hep-th/0511257van Hess et al. Phys. Rev. C 73, 034913 (2006)Wicks et al. (DVGL) hep-th/0512076

JB QM2005 nucl-ex/0511005


SummarySummary 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 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 ( RAA 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


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 CollaborationSTAR Collaboration


STAR emc x tof x PHENIXSTAR emc x tof x PHENIX


EMC electronsEMC electrons

electrons

hadrons


Electron reconstruction efficiencyElectron reconstruction efficiency

AuAu200GeV the central collisions

determined from electron embedding in real events

the data are corrected for this effect


Part of the primary electrons is flaged as background

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


Dalitz Decays: ee versus eeDalitz Decays: ee versus ee

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 pT>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!


P/E in momentum binsP/E in momentum bins

momentum [GeV/c]

a.u

.


dEdx for pt bins dEdx for pt bins


Hadron suppressionHadron suppression


Au+Au

Systematical uncertainity

d+Au and p+p 40-80% 10-40% 0-5% Notes

electron id and track efficiency

(including dE/dx cut efficiency)

0.25 + 0.05 (2 GeV/c)

0.50 + 0.05(8 GeV/c)

0.16 + 0.05 (2 GeV/c)

0.47 + 0.05(8 GeV/c)

0.14 + 0.05 (2 GeV/c)

0.47 + 0.05(8 GeV/c)

0.13 + 0.05 (2 GeV/c)

0.45 + 0.05(8 GeV/c)

Obtained from embedding, using different cluster finder and

electron cuts.See a plot here of the efficiency variationsfor 0-5% most central Au-Au

Hadronic contamination

(0.50 + 0.03)% (2 GeV/c)

(20 + 4)% (8 GeV/c)

(2.0 + 0.1)%(2 GeV/c)

(20 + 4)%(8 GeV/c)

(2.0 + 0.1)%(2 GeV/c)

(20 + 4)%(8 GeV/c)

(2.0 + 0.1)%(2 GeV/c)

(22 + 5)%(8 GeV/c)

Obtained from changing dE/dx fit parameters

Background finding efficiency

0.65 + 0.06 0.67 + 0.06 0.62 + 0.06 0.56 + 0.06From different photon weigthfunctions and systematical

differences between Alex/Jaro/Yifei/Weijiang and Frank analysis

Bremsstrahlung

0.86 + 0.14 (2 GeV/c)

1.05 + 0.05 (8 GeV/c)

0.9 + 0.1 (2 GeV/c)

1.1 + 0.1(8 GeV/c)

0.9 + 0.1 (2 GeV/c)

1.1 + 0.1(8 GeV/c)

0.9 + 0.1 (2 GeV/c)

1.1 + 0.1(8 GeV/c)

Use the size of the correction as suggested by Jamie

Acceptance 0.84 + 0.050.75 + 0.15 0.75 + 0.15 0.75 + 0.15

from the EMC database tables

Click here for details

Trigger bias uncertainty 8% 6% 6% 5%

From the trigger bias fit parameters

Normalization uncertainty 14% for p+p Overall normalization for p+p


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suppression of high-p t non-photonic electrons in au+au collisions at √s nn = 200 gev

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