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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 (=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
  •  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
STARSTAR 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]

Combined Fit

D0, e , combined fit

Power-law function with parameters

dN/dy, and n to describe the D0


Generate D0e decay kinematics

according to the above parameters

Vary (dN/dy, , 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