Heavy flavor Heavy flavor production in production in

STAR.STAR.

What can charm and What can charm and beauty tell us about beauty tell us about matter in heavy ion matter in heavy ion

collisions?collisions?Manuel Calderón de la Barca SánchezUC Davisfor the STAR collaboration

DIS 2006Tsukuba, Japan 21/April/2006

21/April/2006 Manuel Calderón de la Barca2

Light quark sector Light quark sector highlightshighlights

Inclusive yields and back-to-back di-hadron correlations are very similar in p+p and d+Au collisions

Both are strongly suppressed in central Au+Au collisions at 200 GeV

Large energy loss of light quarks in the formed nuclear matter

Phys. Rev. Lett. 91, 072304 (2003).

Pedestal&flow subtracted

STARSTAR

Jet quenching Hadron suppression in central AuAu

21/April/2006 Manuel Calderón de la Barca3

Heavy quarks in a hot Heavy quarks in a hot mediummedium

Quenching weights, more Quenching weights, more recent way to study energy recent way to study energy loss of heavy quarks in a loss of heavy quarks in a dense medium.dense medium.

Armesto et al. Armesto et al. hep-ph/0501225hep-ph/0501225

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

c, b D, B

1)

production

2)

quark energy loss

3)

fragmentation

• D,B spectra are affected by energy loss, and might be more sensitive to medium properties than light quarks.

• Heavy quark has less dE/dx due to suppression of small angle gluon radiation

“Dead Cone” effectY. Dokshitzer & D. Kharzeev PLB 519(2001)199

Elastic energy loss for heavy quarks? Might have an effect. M.G.Mustafa Phys. Rev C 72 (2005)

21/April/2006 Manuel Calderón de la Barca4

Measuring heavy flavorsMeasuring heavy flavors

Hadronic decay channels:Hadronic decay channels: DD00KK, D, D**DD00, D, D+/-+/-KK

Non-photonicNon-photonic electrons: electrons: Semileptonic channels:Semileptonic channels:

c c e e++ + anything + anything (B.R.: 9.6%(B.R.: 9.6%)) DD0 0 e e++ + anything + anything (B.R.: 6.87%(B.R.: 6.87%) ) DD e e + anything + anything (B.R.: 17.2%(B.R.: 17.2%))

b b e e++ + anything + anything (B.R.: 10.9%(B.R.: 10.9%)) BB e e + anything + anything (B.R.: 10.2%(B.R.: 10.2%))

Drell-Yan Drell-Yan (small contribution for p(small contribution for pTT < 10 GeV/c at RHIC) < 10 GeV/c at RHIC)

PhotonicPhotonic electron background: electron background: conversionsconversions ( ( e e++ee-- ) ) ’ ’ Dalitz decaysDalitz decays … … decays (small)decays (small) KKe3e3 decays (small)decays (small)

21/April/2006 Manuel Calderón de la Barca5

Charm reconstruction via hadronic Charm reconstruction via hadronic decaysdecays

nucl-ex/0510063

D0

STAR Phys. Rev. Lett. 94 (2005)

dAu: 1.4 0.2(stat.) 0.4(sys.) mbAuAu: 1.11 0.08(stat.) 0.42(sys.) mb

Total charm cross section per NN interaction

Assumes Binary scaling dAu to AuAu Charm produced in initial collisions . Systematics and statistics limited (only 3 pT bins in Au+Au).

21/April/2006 Manuel Calderón de la Barca6

Charm reconstruction via Charm reconstruction via muonsmuons

Use dE/dx at low p.Use dE/dx at low p. Add TOF information Add TOF information

(limited acceptance)(limited acceptance)

e

0.15<pT<0.25 GeV/c, DCA<3cm

All particle

After de/dx cutSTAR Preliminary

1) Data

2) Primary track

3) B.G. (K, decay)

4) Sum of 2),3)

c→ at low pT (no photonic/Dalitz backgrounds)

only limited to very low pT.

21/April/2006 Manuel Calderón de la Barca7

dNg/dy=1000 small suppression RAA ~ 0.7 for c+b

Predictions of electron nuclear modification factor Predictions of electron nuclear modification factor RRAAAA

Beauty predicted to dominate above 4-5 GeV/c

Single e- from NLO/FONLL

scaled to

M. Cacciari et al., hep-ph/0502203

dNg/dy=3500 medium suppression RAA ~ 0.5 for c+b

q=14 GeV2/fm medium suppression RAA ~ 0.4 for c+b ^

Two different theories:

Theory I: Djordjevic et al.:

Theory II: Armesto et al.:

21/April/2006 Manuel Calderón de la Barca8

Electrons at pElectrons at pTT 5-10 GeV. 5-10 GeV.Use trigger detectors:

TPC: tracking, PID ||<1.3 =2 BEMC (tower, SMD): PID 0<<1 =2 TOF patch good for low pT, acc. small, no trigger

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

21/April/2006 Manuel Calderón de la Barca9

hadrons electrons

Electron ID in STAR – EMCElectron ID in STAR – EMC1. 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 in Shower Max to discriminate

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

104

electrons

K p d

hadrons

electrons

8

21/April/2006 Manuel Calderón de la Barca10

Electron backgroundElectron background Inclusive electron spectra:Inclusive electron spectra: Signal Signal

− HHeavy quarkeavy quarkss semi-leptonic semi-leptonic decaydecayss

DominantDominant backgroundbackground− Instrumental:Instrumental:

- - γγ conversion conversion– Hadronic decays:Hadronic decays:

- Dalitz decays (- Dalitz decays (ππ00, , ηη) )

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

Background rejection efficiency central Au+Au

M e+e-<0.14 GeV/c2

red likesign

21/April/2006 Manuel Calderón de la Barca11

Electrons, muons, D0 Electrons, muons, D0 resultsresults

At low pt, consistent with binary scalingAt low pt, consistent with binary scaling Large errors still for D0 measurement.Large errors still for D0 measurement.

Higher pt, begin to see suppression…Higher pt, begin to see suppression…

21/April/2006 Manuel Calderón de la Barca12

Non-photonic electron spectra at higher pNon-photonic electron spectra at higher pTT pp,dAu,AuAu pp,dAu,AuAu ssNNNN = 200 GeV = 200 GeV

Photonic electrons subtracted

Excess over photonic electrons observed

Corrected for 10-15% hadron contamination

Beauty contribution, can it be disentangled? pQCD calculations can give a range from 2-10 GeV for the c-b crossover in the e spectra.

21/April/2006 Manuel Calderón de la Barca13

pp

AA

AAAA

dpd

T

dpNd

R

3

3

3

3

RRAAAA nuclear modification factor 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

Curves with c-only match RAA but, of course, not the p+p spectra

Armesto et al. hep-th/0511257van Hess et al. hep-th/0508055Wicks et al. hep-th/0512076

21/April/2006 Manuel Calderón de la Barca14

Large electron suppression is a Large electron suppression is a PUZZLEPUZZLE

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

Maybe higher at pT? Where is b contribution?

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

Not enough, RAA saturates!

Armesto et al. hep-ph/0511257

The low end of c-b overlap

The high end of c-b overlap

Wicks et al nucl-th/0512076

Recent study on 3 body cqq elastic scattering in QGP

No beauty included!

Liu&Ko nucl-th/0603004

Large dNg/dx~ 3500, 2ˆ ~ 14GeV /q fm

21/April/2006 Manuel Calderón de la Barca15

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 be sensitive to 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

(similar to light quarks )

Theoretical attempts to explain suppression fail if 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 direct reconstruction of other detector upgrades

displaced vertex in heavy ion environment?! Large acceptance TOF (Ds and c, 2009)

e-h correlations