Quarkonia and heavy flavor – recent results from STAR

Quarkonia and heavy Quarkonia and heavy flavor flavor – recent results from – recent results from

STARSTAR

Workshop: Hot and Dense Matter in the RHIC-LHC Era, Tata Institute of Fundamental Research, Mumbai, 12–14 February 2008

André Mischke for the STAR Collaboration

Amsterdam

2

Outline

• Charm production cross-section in heavy-ion collisions

Au+Au and Cu+Cu data (new)

• Heavy quark energy loss in the medium

Non-photonic electron spectra

• Experimental access to charm and bottom contributions

e-h correlations

e-D0 correlations (new)

• Quarkonia production in QCD matter

J/ at high-pT (new)

in Au+Au (new)

3

central RAA data

K.J. Eskola et al., Nucl. Phys. A747 (2005) 511

increasing density

• Jet quenching of light quarks well described by energy loss models medium is extremely opaque

• Surface bias effectively leads to saturation of RAA with density

• Limited sensitivity to the region of highest energy density

• Need: - insensitive trigger particles: Prompt photons - more penetrating probes: Heavy quarks

?

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2

2

4ˆ ˆtransport coefficient: ,

1S C

mediumC

Nq xG x qL c

N

light hadrons

Limitations of RAA

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Heavy quark energy loss

• Due to their large mass heavy quarks are believed to be primarily produced by gluon fusion M. Gyulassy and Z. Lin, PRC 51, 2177 (1995)

- production rates calculated by pQCD

- sensitivity to initial state gluon distribution

Does it hold for heavy-ion collisions?

• Heavy quarks

- are ”grey probes”

- lose less energy due to suppression of small angle gluon radiation (dead-cone effect) Dokshitzer & Kharzeev, PLB 519, 199 (2001)

• Radiative and collisional energy loss

M.G. Mustafa, PRC72, 014905A.K. Dutt-Mazumder et al., PRD71, 094016 (2005)

parton

hot and dense medium

Wicks et al, NPA784, 426 (2007)

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The STAR experiment

Centrality & trigger - - ZDCZDC

- - CTB+BEMCCTB+BEMC

Tracking and PID - - MagnetMagnet

• 0.5 Tesla - - TPCTPC

• || < 1.5 • p/p = 2-4%• dE/dx/dEdx = 8%

- ToF- ToF• 60ps resolution

- SVT- SVT

Energy measurement - - Barrel EMCBarrel EMC

• fully installed and operational, || < 1• Pb/scintillator (21 X0)

• dE/E ~16%/E• Shower maximum detector

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Heavy flavour measurements: hadronic

decay channel • D0 K(B.R.: 3.83%)

• D* D0(B.R.: 61.9%)

• D K(B.R.: 9.51%)

Direct clean probe: signal in invariant mass distribution

Difficulty: large combinatoric background; especially in high multiplicity environments

Event-mixing

Vertex tracker

- charm c ~ 100-200 m

- bottom c ~ 400-500 m

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Heavy flavour measurements: semi-

leptonic decay channels • c ℓ+ + X (B.R.: 9.6%) ℓ = e or

D0 ℓ+ + X (B.R.: 6.87%)

D ℓ + X (B.R.: 17.2%)

• b ℓ- + X (B.R.: 10.9%)

B ℓ + X (B.R.: 10.2%)

Single (non-photonic) electrons sensitiveto charm and bottom

Robust electron trigger

Photonic electron background

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Au+Au and Cu+Cu data




e-h correlations

e-D0 correlations


J/ at high-pT

in Au+Au

9

Electron identification - ToF

electrons

• ToF patch (prototype)

- /30

- 0 > > -1

• Electron ID

- |1/ß-1| < 0.03

- TPC dE/dx

• Momentum range:

- pT < 4 GeV/c

pK

e

10

Muon identification - ToF

• Low-pT (< 0.25 GeV/c) muons can be measured with TPC + ToF

• Separate different muon contributions using MC simulations:

- K and decay

- charm decay

- DCA (distance of closest approach) distribution is very different

0.17 < pT < 0.21 GeV/c

0-12% Au+Au

minv2 (GeV2/c4)

Inclusive from charm from / K (simu.)Signal+bg. fit to data

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Open charm reconstruction - TPC• Hadronic decay channel: D0 → K + (B.R. 3.8%)

- PID in TPC using dE/dx- pT < ~3 GeV/c

• No reconstruction of displaced vertex up to now• Background description using mixed event technique (details in PRC 71, 064902 (2005))

after background subtraction

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Charm cross section in Au+Au

±

e±

D0

• Combined fit covers ~95% of cross section

• NNcc = 1.40 ± 0.11 ± 0.39 mb in 12% most central Au+Au

• NNcc agrees with NLO calculation

progress in determining theoretical uncertainties, R. Vogt, hep/ph: 0709.2531

• More data points needed to constraint models

STAR p+p and d+Au data, PRL 94, 062301 (2005)

STAR preliminary

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• dNNcc/dy follows binary collision scaling

→ charm is exclusively produced in initial state; as expected

→ no room for thermal production

STAR preliminary

Open charm in Cu+Cu

Cu+Cu minbiasRun 5

1.30 0.25 ( .) NNcc stat mb

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e-h correlations

e-D0 correlations


J/ at high-pT

in Au+Au

hadrons electrons

1. TPC: dE/dx for pT > 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 SMD to discriminate

• 85-90% purity of electrons (pT dependent)

• hadron discrimination power ~103-104

electrons

K p d

hadrons

electrons

Electron identification - EMCAdvantage: triggering to enrich high-pT particle sample

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mass (GeV/c2)

Photonic electron background

– unlike-sign pairs– like-sign pairs

• Most of the electrons in the final state are originating from other sources than heavy-flavor decays

• Dominant photonic contribution

- gamma conversions

- 0 and Dalitz decays

• Exclude electrons with low invariant mass minv < 150 MeV/c2

Non-photonic electron excess at high-pT

• 70% photonic background rejection efficiency

e-

e+

e-

(assigned as primary track)

(global track)

(primary track)dca

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RAA for non-photonic electrons

• Surprise in central Au+Au: Electrons from D and B decays are strongly suppressed; not expected due to dead-cone effect

• Smoothly decreases from peripheral to central Au+Au

• Models implying D and B energy loss are inconclusive yet

Phys. Rev. Lett. 98, 192301 (2007)

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D/B crossing point

M. Cacciari et al., PRL95, 122001 (2005)

• Large uncertainty in D/B crossing point: pT = 3-10 GeV/c

• Goal

- access to underlying production mechanisms

- separate D and B contribution experimentally

• Approach: Two heavy-flavor particle correlations

D/B crossing point in FONLL

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e-h correlations

e-D0 correlations


J/ at high-pT

in Au+Au

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Electron-hadron correlations

• Azimuthal e-h correlations

- Exploit different fragmentation of associated jets

• e-h correlations

- B much heavier than D

subleading electrons get larger kick from B (decay kinematics)

near-side e-h correlation is broadened

• Extract relative B contribution using PYTHIA simulations

B e (PYTHIA)D e (PYTHIA)D+B fit to data

1measured B DR R

p+p 200 GeV

Run 5 p+p, L 3 pb-1

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• Access to underlying production mechanism

• Identification and separation of charm and bottom production events using their decay topology and azimuthal angular correlation of their decay products

- electrons from D/B decays are used to trigger on charm or bottom quark pairs

- associate D0 mesons are reconstructed via their hadronic decay channel (probe)

Electron-D0 correlations

charm production

trigger side

probe side3.

83%

5

4%

~

10%

c

c

g

g

flavor creation (LO) gluon splitting (NLO)

g

g

g

g

c

c 0

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LO PYTHIA simulations

• Near-side- B decays (dominant)

• Away-side- charm flavor creation (dominant)- small B contribution

• Away-side- B decays (dominant)- small charm contribution

like-sign e-K pairs unlike-sign e-K pairs

LO PYTHIA

3<pTtrg<7 GeV/c

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K invariant mass distribution w/o electron trigger

combinatorial background is evaluated using like-sign pairs

STAR preliminary

dn/dm

• D0 reconstruction: dE/dx cut (±3) around Kaon band

• Significant suppression of combinatorial background: factor 200

• S/B = 14% and signal significance = 3.7

D0+D0

w/ non-photonic electron trigger

position: 1892 ± 0.005 GeV/c2

width: 16.2 ± 4.7 MeV/c2

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like-sign e-K pairs

Relative Be contribution

• Model uncertainties not included yet

• Good agreement between different analyses

• Data consistent with FONLL within errors• Small gluon splitting contribution

• Comparable D and B contributions

Au+Au: suggests significant suppression of non-photonic electrons from bottom in medium

essentially from B decays only

75% from charm25% from beauty

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e-h correlations

e-D0 correlations


J/ at high-pT

in Au+Au

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Quarkonia production in QCD matter

H. Satz, HP2006

• “Melting” of Quarkonia states in QGP- color screening of static potential between heavy quarks: J/suppression: Matsui and Satz, Phys. Lett. B 178 (1986) 416

- suppression states is determined by TC and their binding energy QCD thermometer

• Sequential disappearance of states- color screening deconfinement

- QCD thermometer access to properties of QGP

• Lattice QCD: Evaluation of spectral functions

RHICRHIC

Charmonia: J/, ’, c Bottomonia: (1S), (2S), (3S)

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J/ production at high-pT

J/

/c

H. Liu, K. Rajagopal and U.A. WiedemannPRL 98, 182301(2007) and hep-ph/0607062

• Data consistent with no suppression at high pT: RAA(pT > 5 GeV/c) = 0.9 ± 0.2

• While at low-pT RAA = 0.5-0.6 (PHENIX)

• Indicates RAA increase from low pT to high pT

• But, most models expect a decrease RAA at high pT

- two component approach by X. Zhao and R. Rapp, hep-ph/07122407

- AdS/CFT by H. Liu, K. Rajagopal and U.A. Wiedemann, PRL 98, 182301(2007) and hep-ph/0607062

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• STAR detector can resolve individual states

• Low statistics currently yield is extracted from combined ++ states

• FWHM ≈ 400 MeV/c2

mass resolution in STAR

e+e-

• RHIC II with 20 nb-1 will definitely allow separation of 1S, 2S and 3S states• Measurement will greatly benefit from the future Muon Telescope Detector upgrade

simulation with inner tracker (X/X0 6%)

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(1s+2s+3s) signal in p+p

• unlike-sign pairs— like-sign pairs

background subtracted

• (1s+2s+3s) d/dy at y=0

• Peak width consistent with expected mass resolution

preliminary

preliminary

Run 6 p+p, L 9 pb-1

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Mid-rapidity (1s+2s+3s) cross-section

STAR preliminaryp+p 200 GeV

y

d/d

y (n

b)

Cou

nts

• Integrated yield at mid-rapidity: |y|<0.5

• (1s+2s+3s) e+e-:

BRee d/dy = 91 ± 28(stat.) ± 22(sys.) pb

• Consistent with NLO pQCD calculations and world data trend

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Sample -triggered event• e+e-

• mee = 9.5 GeV/c2 (offline mass)• cosθ = -0.77 (offline opening angle)• E1 = 6.6 GeV (online cluster energy hardware trigger)• E2 = 3.2 GeV (online cluster energy software trigger)

charged tracks

electron m

omentum > 3 GeV/c

in Au+Au (Run 7)

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signal in Au+AuRun 7 Au+Au, L 300 b-1

• First measurement in nucleus-nucleus collisions

• 4 signal

• These data should provide a first measurement of RAA after corrections for efficiency are completed

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• Charm production cross-section- follows binary collision scaling no room for thermal production

- agrees with FONLL within errors

• Non-photonic electron spectra - energy loss in heavy-ion collision is much larger than expected

- models invoking radiative + collisional energy loss get closest to data

• Electron-D0 azimuthal correlations- first heavy-flavor particle correlation measurement at RHIC

- B and D contributions similar at pT > 5 GeV/c; consistent with FONLL

- STAR data + MC@NLO simulations: Small gluon-splitting contribution

• Quarkonia- cross-section in pp consistent with pQCD and world data trend

- first signal in Au+Au

- Next: absolute cross-section in p+p, d+Au (Run 8) and Au+Au and RAA

Summary

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• More exciting results are about to come with the STAR detector upgrades

- Heavy Flavor Tracker

- Full barrel Time-of-Flight

Outlook

SSD

HFT

e

• improved D → K reconstruction• excellent electron ID(J/ range 0.2<p<4 GeV/c)• J/ trigger in Au+Au

• low-pT muon ID (0.2 GeV/c)

• active pixel sensor technology

• 2 layers CMOS Active Pixel sensors

• pixel dimension: 30 m 30 m

• resolution: ~10 m

ToFToF

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The STAR collaboration

52 institutes from 12 countries, 582 collaborators52 institutes from 12 countries, 582 collaborators

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Backup

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Compilation: Charm cross section at RHIC

Yifei Zhang, QM2008

38

R

f

Ndy

dNCuCu

bin

ppinel

CuCu

DNNcc

0

Extraction of charm cross-section

mbstat

NNR

f

N

dydN

NNcc

ccD

ppinel

CuCubinary

D

.)( 25.030.1

05.054.0/

7.07.4

mb 0.6 -/+ 41.8

2.9-1.051.5

(stat.) 0.035 -/ 0.18/

0

0

Inelastic cross section in p+p (UA5)

Conversion to full rapidity

Ratio obtained from e+e- collisions

Number of binary collisions (Glauber)

39

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 = 41.8 0.6 mb

Nbin = 7.5 0.4 (Glauber) |y|<0.5 to 4: f = 4.70.7 (PYTHIA) RdAu = 1.3 0.3 0.3 PRL 94, 062301 (2005)

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• FONLL calculation factor of about 5 lower than p+p data

• Spectra shape of p+p spectrum is well described

• Large uncertainty over where Be dominates over De.

p+p at sNN = 200 GeVPhys. Rev. Lett. 98, 192301 (2007)

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Latest efforts to describe the data

• Radiative energy loss with typical gluon densities is not enoughDjordjevic et al., PLB 632 (2006) 81

• Models involving a very opaque medium agree betterArmesto et al., PLB 637 (2006) 362

• Collisional energy loss / resonant elastic scatteringWicks et al., nucl-th/0512076 andvan Hees and Rapp, PRC 73 (2006) 034913

• Heavy quark fragmentation and dissociation in the medium → strong suppression for c and bAdil and Vitev, hep-ph/0611109

Comparisons to models

• Theoretical explanations are inconclusive• Is it possible to determine B contribution experimentally?

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K-

b

b

B-

D*0

D0

+

e

e-

B+

-

K+

D0

Electron tagged correlations:bottom production

Near- and away-side correlation peak expected for B production

like-sign pairslike-sign pairs near-side correlationnear-side correlation

unlike-sign pairsunlike-sign pairs away-side correlationaway-side correlation

Charge-sign requirement on trigger electron and decay Kaon gives additional constraint on production process

43

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NLO Process: Gluon splitting

• FONLL/NLO calculations only give single inclusive distribution no correlations

• PYTHIAPYTHIA is not really adequate for NLO predictions

• STAR measurement of D* in jet access to charm content in jets

• Gluon splitting rate consistent with pQCD calculation

Small contribution from gluon splitting at top RHIC energy

PYTHIAPYTHIAcharm production

E.

Nor

rbin

& T

. S

jost

rand

, E

ur.

Phy

s. J

. C

17,

137

(200

0)

STAR Preliminary

Mue

ller

& N

ason

PLB

157

(19

85)

226

P29: X. Dong, Charm Content in Jets

45

Δ(

c,c)

Δ(e,D0)

• NLO QCD computations with a realistic parton shower model

Remarkable agreement of the away-side peak shape between LO PYTHIA and MC@NLO

Gluon-splitting contribution is small

- S. Frixione, B.R. Webber, JHEP 0206 (2002) 029- S. Frixione, P. Nason, and B.R. Webber, JHEP 0308 (2003) 007 - private code version for charm production

MC@NLO

LO PYTHIA

like-sign e-K pairs

3<pT<7 GeV/c

MC@NLO predictions for charm production

46

trigger in STAR

Real Data, p+p Run V• Large acceptance

• Fast L0 trigger (hardware) - Select events with at least one

high energy EMC cell (E~4 GeV)

• L2 trigger (software)- EMC cell clustering

- Using topology (cosθ) and mass reconstruction in real time

• Very clean to trigger up to central Au+Au

• Trigger efficiency ~80%

• Offline: Match TPC tracks to triggered EMC cells

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= geo×L0×L2×2(e)×mass

cross section and uncertainties

0

ee

y

NdBR

dy dy dt

L

geometrical acceptance geo 0.263±0.019

efficiency L0 trigger L0 0.928±0.049

efficiency L2 trigger L2 0.855±0.048

efficiency of e reconstr. 2(e) 0.47±0.07

efficiency of mass cut mass 0.96±0.04

0.094±0.018

Ldt = (5.6±0.8) pb-1N = 48±15(stat.)

Documents

Quarkonia and heavy flavor – recent results from STAR