Jaroslav BielčíkCzech Technical

University

Prague

High-pT physics at LHC , March 2008, Tokaj

Open heavy flavor at RHIC

jaroslav.bielcik@fjfi.cvut.cz 2

Outline

• Motivation for heavy flavor physics• Spectra:

– Charm mesons: D0

– Non-photonic electrons

– Heavy flavor e+e- pairs

• Flow/Energy loss• Summary

QM 2008: Y.Zhang (overview), A. Shabetai (STAR), D. Hornback(PHENIX) R. Averbeck (PHENIX),  Y. Morino (PHENIX) 

 

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Heavy quarks as a probe• p+p data: baseline of heavy ion measurements test of pQCD calculations

• Due to their large mass heavy quarks are primarily produced by gluon fusion in early stage of collision production rates calculable by pQCDM. Gyulassy and Z. Lin, PRC 51, 2177 (1995)

•heavy ion data:

• Studying flow of heavy quarks understanding of thermalization

• Studying energy loss of heavy quarks independent way to extract properties of the medium

parton

hot and dense medium

light

M.Djordjevic PRL 94 (2004)

ENERGY LOSS

dead-cone effect:

Dokshitzer and Kharzeev, PLB 519, 199 (2001)

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Open heavy flavor

%07.080.3..

,, 00

RB

KDKD Direct: reconstruction of all decay products

Indirect: charm and beauty via electrons

c e+ + anything (B.R.: 9.6%)b e+ + anything (B.R.: 10.9%)issue of photonic background

charm (and beauty) via muonsc + + anything (B.R.: 9.5%)

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Charm measurements at RHIC

STAR measurements:

Signal/Spectra

D0 K c + X (y=0, low pT) c,b e + X

Flow & energy loss

RAA from NPE

PHENIX measurements:

Signal/Spectra

D0 K-+0 c + X (<y>=1.65, pT>1 GeV/c) c,b e + X e+e-

Flow & energy loss

Elliptic flow from NPE

RAA from NPE

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SPECTRA

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STAR Preliminary

Direct D-meson reconstruction at STAR

D0

Phys. Rev. Lett. 94 (2005)

• K invariant mass distribution in d+Au, Au+Au minbias, Cu+Cu minbias at 200 GeV collisions

• No displaced vertex used => only pT<3.3 GeV/c

7.4~/ NS

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PHENIX Preliminary

Year5 pp 200 GeV

Direct D-meson reconstruction at PHENIX

• p+p 200 GeV/c: D0K+ - 0 decay channel0 identified via 0 decay Only visible signal in 5<pT<15 GeV/c No visible signal below 5 GeV/c and above 15 GeV/c

peak is not at right positionjaroslav.bielcik@fjfi.cvut.cz

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Leptons from HF decay at STAR

STAR Preliminary

• STAR charm cross section: combined fit of muons, D0 and low pT electrons

90% of total kinematic range covered

• New Cu+Cu D0 spectrum agree with Au+Au after number of binary scaled

• Low pT muon constrains charm cross-sectionjaroslav.bielcik@fjfi.cvut.cz

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Leptons from HF decay at PHENIX

PHENIX Preliminary

PHENIX PRL, 98, 172301 (2007)

• Electron spectrum is harder than muon spectrum, within errors they are consistent at intermediate pT

• Systematically higher than FONLL calculation (up to factor ~ 4)

• Integral e yield follows binary scaling, high pT strong suppression at central AuAu collisions

p+p 200GeV/c

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• High-tower EMC trigger => high pT electrons

• FONLL scaled by ~5, describes shape of p+p spectra well suggesting bottom contribution

STAR high pT NP electrons

STAR

Phys. Rev. Lett. 98 (2007) 192301 STAR Phys. Rev. Lett. 98 (2007) 192301 PHENIX Phys. Rev. Lett. 97 (2006) 252002

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Heavy quarks in p+p from e+e- at PHENIX

c dominant

b dominant

After subtraction of Cocktail -Fit to a*charm+ b*bottom (with PYTHIA shape)

Extracted cross sections in good agreement with single e result.arXiv:0802.0050

jaroslav.bielcik@fjfi.cvut.cz

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Charm cross-section

PRL 94 (2005)

Both STAR and PHENIX are self-consistent

observation of binary scaling

STAR results ~ 2 times larger than PHENIX

Consistent with NLO calculation

however error bands are huge

Total cross-section with large theoretical uncertainty.

ENERGY LOSS/FLOW

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Elliptic flow v2 – NPE from HF decays

• Non-zero elliptic flow for electron from heavy flavor decays → indicates non-zero D v2, partonic level collective motion.• Strongly interact with the dense medium at early stage of HI collisions• Light flavor thermalization

PHENIX Run4

PRL, 98, 172301 (2007)

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d+Au: no suppression expected slight enhancement

expected (Cronin effect) Peripheral Au+Au:

no suppression expected Semi-Central Au+Au: very little suppression expected

RAA from d+Au to central Au+Au

STAR hadrons pT> 6 GeV/c

Central Au+Au: little suppression expected ?!

tpp

tAA

colltAA dpdN

dpdN

NpR

/

/1)(

Nuclear modification factor

STAR Phys. Rev. Lett. 98 (2007) 192301 PHENIX Phys.Rev.Lett.98 (2007) 172301

Non-photonic electrons suppressionsimilar to hadrons

pT (NPE) < pT (D NPE)

PRL 98, 172301 (2007)

e± from heavy flavor

Nuclear Modification Factor RAA

very similar to light hadron RAAcareful:

– decay kinematics!– pT(e±) < pT(D)

intermediate pT

– indication for quark mass hierarchy as expected for radiative energy loss

(Dokshitzer and Kharzeev, PLB 519(2001)199)highest pT

– RAA(e±) ~ RAA(0) ~ RAA()

crucial to understand:

what is the bottom contribution? ideal:

RAA of identified charm and bottom hadrons

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Radiative energy loss

• Radiative energy loss alone in medium with reasonable parameters does not describe the data

Djordjevic, Phys. Lett. B632 81 (2006)

Armesto, Phys. Lett. B637 362 (2006)

• What are the other sources of energy loss ?

• parameters of medium in models extracted from hadron data

STAR Phys. Rev. Lett. 98 (2007) 192301 PHENIX Phys.Rev.Lett.98 (2007) 172301

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Role of collisional energy loss

Wicks, nucl-th/0512076van Hess, Phys. Rev. C73 034913 (2006)

• Collisional/elastic energy loss may be important for heavy quarks

• Still not good agreement at high-pT

STAR Phys. Rev. Lett. 98 (2007) 192301 PHENIX Phys.Rev.Lett.98 (2007) 172301

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Charm alone?

• Since the suppression of b quark electrons is smaller – charm alone agrees better

• What is b contribution?

STAR Phys. Rev. Lett. 98 (2007) 192301 PHENIX Phys.Rev.Lett.98 (2007) 172301

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Bottom contribution to NPE

• Good agreement among different analyses. • Data consistent with FONLL.

(b

e)/(

ce+

b

e)

• Difficult to interpret suppression without the knowledge of charm/bottom

• Data shows non-zero B contribution

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Conclusions

• Heavy flavor is an important tool to understand HI physics at RHIC• RHIC results are interesting and challenging charm cross section

• Binary scaling in charm production produced in initial phase• Differences between STAR and PHENIX will be addressed • NLO is consistent with data

non-photonic electrons• strong high-pT suppression in Au+Au large energy loss of c+b• heavy quark energy loss not understood

• b relative contribution consistent with FONLL

important b contribution • none zero charm flow is observed at RHIC energy

does b also flow?

large uncertainties

PRL 98, 172301 (2007)

at B = 0 + P = Ts

then /s = (1.3-2.0)/4

transport modelsRapp & van Hees (PRC 71, 034907 (2005))

– diffusion coefficient required for simultaneous fit of RAA and v2

– DHQx2T ~ 4-6

Estimating /s

Moore & Teaney (PRC 71, 064904 (2005))

– difficulties to describe RAA and v2 simultaneously– calculate perturbatively (and argue that plausible

also non-perturbatively)

– DHQ/ (/(+P)) ~ 6 (for Nf = 3)

4/)8.30.1(/ s

S. Gavin and M. Abdel-Aziz: PRL 97:162302, 2006

pTfluctuations STAR

Comparison with other estimates 4/)2.12.01.1(/ s

R. Lacey et al.: PRL 98:092301, 2007

v2 PHENIX & STAR

4/)4.24.1(/ s

H.-J. Drescher et al.: arXiv:0704.3553

v2 PHOBOS

conjectured quantum limit

estimates of /s based on flow and fluctuation data

indicate small value as well close to conjectured limit significantly below /s of helium (s

~ 9)

Charm ~ y

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Uncertainty of c/b relative contributionUncertainty of c/b relative contribution

• FONLL: Large uncertainty on c/b crossing 3 to 9 GeV/c

Beauty predicted to be significant above 4-5 GeV/c

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

- this helps to constrain charm cross-section

• Separate different muon contributions using MC simulations:

- K and decay

- charm decay

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

minv2 (GeV2/c4)

0.17 < pT < 0.21 GeV/c

0-12% Au+Au

Muon measurementT

PC

+T

OF

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

(STAR), Hard Probes 2006

m2=(p//)2

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Conversion from dN/dy to Cross-Section

mbstat

NNR

f

N

mb

dydN

NNcc

ccD

CuCubinary

ppinel

D

.)(18.094.0

05.054.0/

7.07.4

2.87-1.0451.52

42

(stat.) 0.025 -/ 0.132/

0

0

RfNdydN CuCubin

ppinel

CuCu

D

NNcc ///0

p+p inelastic cross section

conversion to full rapidity

ratio from e+e- collider data

number of binary collisions

mb 18.017.0 conversion dy todN fromerror sys. *Systematic error measurement for dN/dy in progress.

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hadrons electrons

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)

electrons

K p d

all

p>1.5 GeV/c2

p/ESMD

Electron ID in STAR – EMC

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Photonic 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

Inclusive/Photonic:

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

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CC: comparison with other measurements

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Power-law function with parameters dN/dy, <pT> and n to describe the D0 spectrum

D0, e , combined fit

Generate D0e decay kinematics according to the above parameters

Vary (dN/dy, <pT>, n) to get the min. 2 by comparing power-law to D0 data and the decayed e shape to e and data

Advantage: D0 and constrain low pT

e constrains higher pT

Spectra difference between e and ~5% (included into sys. error)

Combined Fit