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Open heavy flavor at RHIC. Jaroslav Biel čí k Czech Technical University Prague. High-p T physics at LHC , March 2008 , Tokaj. Outline. Motivation for heavy flavor physics Spectra: Charm mesons: D 0 Non-photonic electrons Heavy flavor e + e - pairs Flow/Energy loss

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Jaroslav biel k czech technical university prague

Open heavy flavor at RHIC

Jaroslav Bielčík

Czech Technical University


High-pT physics at LHC , March 2008, Tokaj


  • 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)

[email protected]




hot and dense medium

M.Djordjevic PRL 94 (2004)

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 extractproperties of the medium

dead-cone effect:

[email protected]

Dokshitzer and Kharzeev, PLB 519, 199 (2001)

Open heavy flavor
Open heavy flavor

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 muons

  • c  + + anything (B.R.: 9.5%)

[email protected]

Charm measurements at rhic
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

[email protected]

Direct d meson reconstruction at star


Phys. Rev. Lett. 94 (2005)

Direct D-meson reconstruction at STAR

STAR Preliminary

  • 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

[email protected]

Direct d meson reconstruction at phenix

PHENIX Preliminary

Year5 pp 200 GeV

Direct D-meson reconstruction at PHENIX

  • p+p 200 GeV/c:

  •  D0K+p-p0 decay channel

  • p0 identified via p0 gg 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 position

[email protected]

Leptons from hf decay at star
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-section

[email protected]

Leptons from hf decay at phenix
Leptons from HF decay at PHENIX

PHENIX PRL, 98, 172301 (2007)

p+p 200GeV/c

PHENIX Preliminary

  • 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

[email protected]

Star high p t np electrons


STAR high pT NP electrons

  • High-tower EMC trigger

  • => high pT electrons

  • FONLL scaled by ~5,

  • describes shape of p+p spectra well

  • suggesting bottomcontribution

STARPhys. Rev. Lett. 98 (2007) 192301

Phys. Rev. Lett. 98 (2007) 192301

PHENIX Phys. Rev. Lett. 97 (2006) 252002

[email protected]

Heavy quarks in p p from e e at phenix

c dominant

b dominant

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

After subtraction of Cocktail -

Fit to a*charm+ b*bottom (with PYTHIA shape)

Extracted cross sections in good agreement with single e result.


[email protected]

Charm cross section
Charm cross-section

PRL 94 (2005)

Total cross-section with large theoretical uncertainty.

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

[email protected]

Elliptic flow v 2 npe from hf decays
Elliptic flow v2 – NPE from HF decays


PRL, 98, 172301 (2007)

  • Non-zero elliptic flow for electron from heavy flavor decays

  • → indicatesnon-zero D v2,partonic level collective motion.

  • Strongly interact with the dense medium at early stage of HI collisions

  • Light flavor thermalization

[email protected]

R aa from d au to central au au

STARPhys. Rev. Lett. 98 (2007) 192301

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

STAR hadrons pT> 6 GeV/c

d+Au: no suppression expected 

slight enhancement

expected (Cronin effect)

Peripheral Au+Au:

no suppression expected

Central Au+Au:

little suppression expected ?!

Semi-Central Au+Au:

very little suppression expected

RAA from d+Au to central Au+Au

Nuclear modification factor

Non-photonic electrons suppression

similar to hadrons

pT (NPE) < pT (D NPE)

[email protected]

Nuclear modification factor r aa

PRL 98, 172301 (2007)

e± from heavy flavor

Nuclear Modification Factor RAA

  • very similar to light hadron RAA

    • careful:

      • 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(p0) ~ RAA(h)

  • crucial to understand:

  • what is the bottom contribution?

  • ideal:

  • RAA of identified charm and bottom hadrons

Radiative energy loss

STARPhys. Rev. Lett. 98 (2007) 192301

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

Radiative energy loss

  • parameters of medium in

  • models extracted from hadron data

  • Radiative energyloss alone

  • in medium with reasonable

  • parametersdoes not describe

  • the data

  • What are the other sources

  • of energy loss ?

  • Djordjevic, Phys. Lett. B632 81 (2006)

  • Armesto, Phys. Lett. B637 362 (2006)

[email protected]

Role of collisional energy loss

STARPhys. Rev. Lett. 98 (2007) 192301

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

Role of collisional energy loss

  • Collisional/elastic energy loss may

  • be importantfor heavy quarks

  • Still not good agreement at high-pT

  • Wicks, nucl-th/0512076

  • van Hess, Phys. Rev. C73 034913 (2006)

[email protected]

Charm alone

STARPhys. Rev. Lett. 98 (2007) 192301

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

Charm alone?

  • Since the suppression of

  • b quark electrons is smaller

  • charm alone agrees better

  • What is b contribution?

[email protected]

Bottom contribution to npe
Bottom contribution to NPE


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

  • Data shows non-zero B contribution

  • Good agreement among different analyses.

  • Data consistent with FONLL.


  • 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

[email protected]

Estimating h s

PRL 98, 172301 (2007)

Estimating h/s

  • transport models

    • Rapp & van Hees (PRC 71, 034907 (2005))

      • diffusion coefficient required for simultaneous fit of RAA and v2

        • DHQx2pT ~ 4-6

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

    • difficulties to describe RAA and v2 simultaneously

    • calculate perturbatively (and argue that plausible also non-perturbatively)

      • DHQ/ (h/(e+P)) ~ 6 (for Nf = 3)

  • at mB = 0

    • e + P = Ts

  • then

    • h/s = (1.3-2.0)/4p

Comparison with other estimates

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

S. Gavin and M. Abdel-Aziz:

PRL 97:162302, 2006

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

pTfluctuations STAR




conjectured quantum limit

Comparison with other estimates

  • estimates of h/s based on flow and fluctuation data

    • indicate small value as well

    • close to conjectured limit

    • significantly below h/s of helium (4ph/s ~ 9)

Uncertainty 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

[email protected]

Muon measurement

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

  • 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



(STAR), Hard Probes 2006

[email protected]

Conversion from dn dy to cross section
Conversion from dN/dy to Cross-Section

p+p inelastic cross section

number of binary collisions

conversion to full rapidity

ratio from e+e- collider data

*Systematic error measurement for dN/dy in progress.

[email protected]

Electron id in star emc








Electron ID in STAR – EMC

  • 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

  • EMC:

    • Tower E ⇒ p/E~1 for e-

    • Shower Max Detector

      • Hadrons/Electron shower develop different shape

  • 85-90% purity of electrons

  • (pT dependent)


p>1.5 GeV/c2



[email protected]

Photonic electrons background


  • Excess over photonic electrons observed

    for all system and centralities

    => non-photonic signal

Photonic electrons background

  • Background:Mainly from g conv and p0,h 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 rejectionefficiency

      ~50-60% for central Au+Au

[email protected]

S cc comparison with other measurements
sCC: comparison with other measurements

[email protected]

Combined Fit

D0, e , combined fit

Power-law function with parameters

dN/dy, <pT> and n to describe the D0


Generate D0e 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

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

Advantage: D0 and  constrain low pT

e constrains higher pT