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[email protected] Quarks 2006

Suppression of high-pT non-photonic electrons in Au+Au collisions at √sNN = 200 GeV

HOT QUARKS 2006

Jaroslav BielcikYale University/BNL


• Inclusive yields are strongly suppressed in central Au+Au collisions at 200 GeV

Hadron suppression in central AuAuHadron suppression in central AuAu

STARSTAR

Hadron suppression in central AuAu

• Large energy loss of light quarks in the formed nuclear matter

Energy loss depends on properties of medium (gluon densities, size) depends on properties of “probe” (color charge, mass)

Probing the medium with heavy quarks => need to measure heavy quark mesons p+p (d+Au) and Au+Au


Measuring charm and beauty Measuring charm and beauty

Hadronic decay channels: D0K, D*D0, D+/-

K

(Haibin’s talk) 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)

Photonic electron background: conversions ( e+e- ) ’ Dalitz decays … decays (small) Ke3 decays (small)


Heavy flavor electrons from FONLLHeavy flavor electrons from FONLL

Beauty predicted to dominate above 4-5 GeV/c

heavy flavor e- from FONLL

scaled to

Cacciari, Nason, Vogt, Phys.Rev.Lett 95 (2005)

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


Energy loss of heavy quarksEnergy loss of heavy quarks

D, B (electrons)

1)

production

in hard scattering

c, b

2)

quark energy loss

3)

fragmentation

• 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 BDMPS case

Heavy quark energy loss BDMPS case

2

ˆTk

q BDMPS: Armesto, Salgado, Wiedemann, PRD 69 (2004) 114003

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

•Model: pQCD + E loss probability (quenching weights) + Glauber collision geometry

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

0.4

0.1

hep-ph/0510284

0.20.3

light

heavy

=14 GeV2/fm

RAA ~ 0.2 light mesons

RAA ~ 0.4 for electrons from c+b

q̂


Heavy quark energy loss DGLV caseHeavy quark energy loss DGLV case

Wicks et al nucl-th/0512076

ignore the data for the moment

DGLV: 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

heavy

RAA ~ 0.2 light mesonsRAA ~ 0.4-0.6 for electrons from c+b

Djordjevic et al. Phys.Lett B 632, 81 (2006)


STAR Detector and Data SampleSTAR Detector and Data Sample

Electrons in STAR: TPC: tracking, PID ||<1.3 =2 BEMC (tower, SMD): PID 0<<1 =2 TOF patch (Haibin talk)

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 )

Preliminary results from:

HighTower trigger: Only events with high tower ET>3 GeV/c2

Enhancement of high pT

Hot Quarks 2006

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

• Use # hits cuts

85-90% purity of electrons (pT dependent)h discrimination power ~ 103-

104

electrons

K p d


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 AuAu

M e+e-<0.14 GeV/c2

red likesign

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

Inclusive/Photonic:


STAR non-photonic electron spectra pp, dAu, AuAu sNN = 200 GeV

STAR non-photonic electron spectra pp, dAu, AuAu sNN = 200 GeV

pp, dAu: up to 10 GeV/c AuAu: 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


pp

AA

AAAA

dpd

T

dpNd

R

3

3

3

3

RAA nuclear modification factorRAA 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


RECENT ELECTRON RAA BY D. TEANEYRECENT ELECTRON RAA BY D. TEANEY

D.Teaney (Moriond 2006) Input: spectrum of c+b from Cacciari et. al.

Weak coupling Boltzmann-Langevin Model Phys.Rev.C71;064904 (2005)

Only collisional energy loss Neglect radiative energy loss (v<6) Hadronization: according to measured fragmentation functions

diffusion coefficientD=3/2T corresponds to dNg/dy~2000


Large electrons suppression is a PUZZLELarge electrons suppression is a PUZZLE

Large suppression => large dE/dx of heavy quarks (NOT EXPECTED)

Maybe higher at pT? Where b starts to play a role?

Elastic energy loss? Important, helps, but not enough!

Not enough, RAA saturates! Large dNg/dy~ 3500, q ~14 GeV2/fm ?^

Armesto et al. hep-ph/0511257

Recent study on 3 body cqq elastic scattering in QGP

No beauty included!


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

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?

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

Hot Quarks 2006

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/Eb) Shower Max Detector

(SMD)• Hadrons/Electron

shower develop different shape

• Use # hits cuts

85-90% purity of electrons (pT dependent)h discrimination power ~ 103-

104

electrons

K p d

hadrons

electrons


Charm Total Cross Section

1.13 0.09(stat.) 0.42(sys.) mb in 200GeV minbias Au+Au collsions

1.4 0.2(stat.) 0.4(sys.) mb in 200GeV minbias d+Au collisions

Charm total cross section per NN interaction

Charm total cross section follows roughly Nbin scaling from d+Au to Au+Au considering errors

Indication of charm production in initial collisions


What is v2?What is v2?

Non-central Au-Au collisions azimuthally anisotropic source of matter in coordinate space azimuthally anisotropic (isotropic) of particles in momentum space, given enough particle interactions Non-zero (zero) v2

v2 is built up at the early stage of the collision so it is a nice probe of the hot and dense medium created at RHIC energy!

)](2cos[

)](cos[212

1

2

1

2

3

3

r

nrn

tt

v

nvdydpp

Nd

dp

NdE


1 2 3

4 5

1: inclusive

2: OSLM

3: SSLM

4: 2-3

5: 1-(2-3)/eff

OSLM: Opposite Sign Low Invariant Mass; SSLM: Same Sign Low Invariant Mass

Charm electron v2 determination

AFTER SUBTRACTING BACKGOUND CONTRIBUTION – LARGE SYSTEMATIC ERRORS


The detector material in STAR caused too much photonic background, which caused huge systematic and statistical uncertainties. Our result is not sensitive enough to make any conclusion about heavy quark v2 so far.

Electron v2 with new method – large systematic errors


Charm energy lossCharm energy loss

Strong suppression observed! Indicates charm energy loss in medium.

For D0 RAA, stat. error only.

STAR Preliminary


Hadron contamination p/E methodHadron contamination p/E method


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


Two fake conversion points reconstructed

(picking one closer to primary vertex)


Trigger biasTrigger bias

MB/HT ratio (0-5%)


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!


Electron/Hadron ratioElectron/Hadron ratio



P/E in momentum binsP/E in momentum bins

momentum [GeV/c]

a.u

.


dEdx for pt bins dEdx for pt bins


Inclusive electron spectra AuAu sNN = 200 GeV

Inclusive electron spectra AuAu sNN = 200 GeV

High tower trigger allows STAR to extend electron spectra up to 10 GeV/c

3 centrality bins: 0-5%

10-40%

40-80%

Corrected for hadron contamination ~10-15%


STAR non-photonic electron spectra pp,dAu,AuAu sNN = 200 GeV


Photonic electrons subtractedExcess over photonic electrons observedConsistent with STAR TOF spectra

Beauty is expected to give an important contribution above 5 GeV/c


pp

AA

AAAA

dpd

T

dpNd

R

3

3

3

3

RAA nuclear modification factorRAA nuclear modification factor

Suppression up to ~ 0.4-0.6 observed in 40-80% centrality

~ 0.3 -0.4 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


Inclusive electron spectra sNN = 200 GeVInclusive electron spectra sNN = 200 GeV

TOF electrons

STAR Preliminary

Excess of electrons over photonic background in all centralities and systems Corrected for 10-15% hadron contamination




Photonic electrons subtracted

Consistent with STAR TOF spectra

Consistent with PHENIX

Beauty is expected to give an important contribution above 5 GeV/c

STAR Preliminary



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


for the collaboration