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Open charm cross section and R_AA. Zhangbu Xu (BNL) for the STAR Collaboration. Charm Total Cross Sections Nuclear Effects Conclusions. M c ,b  1.5 GeV>> T c , L QCD , M uds M/E>>0. Hadron identification: STAR Collaboration, nucl-ex/0309012.

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Open charm cross section and r aa

Open charm cross section and R_AA

Zhangbu Xu (BNL)

for the STAR Collaboration

  • Charm Total Cross Sections

  • Nuclear Effects

  • Conclusions

Mc,b1.5 GeV>>Tc, LQCD, Muds


PANIC05, Zhangbu Xu (BNL)

Open charm cross section and r aa

Hadron identification:

STAR Collaboration, nucl-ex/0309012

Time Projection Chamber: 45 padrow, 2 meters (radius), s(dE/dx)8%, -1<<1

Multi-gap Resistive Plate Chamber TOFr: 1 tray (~1/200), s(t)=85ps

PANIC05, Zhangbu Xu (BNL)

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

    • Shower Max Detector (SMD)

      • Hadrons/Electron shower develop different shape

      • Use # hits cuts

  • h discrimination power ~ 103-105

Jaro Bielcik QM05

D 0 direct reconstruction

( Br. 3.83%)

D0 direct reconstruction

Direct Open Charm

Reconstruction at RHIC

Event mixing technique

C. Adler et al., Phys. Rev. C 66, 061901(R)(2002)

J. Adams et al., Phys. Rev. Lett. 94 (2005)062301

PANIC05, Zhangbu Xu (BNL)

D au charm total cross section
d+Au Charm Total Cross Section

Data provide reference for Au+Au data


Energy dependence mR and mF?

Need smaller errors to constrain pQCD and determine the effects

in Cosmic Ray Showers

X. Dong USTC

Can we confirm or rule out Cosmic Ray experiments

(Pamir, Muon, Tian Shan) under similar conditions?

Pamir, Nuovo Cim 24c (2001) 557; NPB 122(2003) 353c

PANIC05, Zhangbu Xu (BNL)

Open charm cross section and r aa

D0 Signal in Au+Au Collisions

Event-mixing background subtracted

invariant mass spectrum fit with

gaussian + Linear function

A 4.5 D0 signal observed at pT<3

GeV and |y|<1 from 14M Au+Au

minbias collision events

Three signals also seen in sub-pT ranges

with ~2.5 significances

Haibin Zhang QM05


PANIC05, Zhangbu Xu (BNL)

Open charm cross section and r aa

Dominant source at low pT

Mass(e+e-)<0.15 GeV/c2

Electron Spectrum

γ conversion

π0Dalitz decay

η Dalitz decay

Kaon decay

vector meson decays

  • Combinatorial background reconstructed by track rotating technique.

  • Invariant mass < 0.15 for photonic background.

Yifei Zhang


PANIC05, Zhangbu Xu (BNL)

Open charm cross section and r aa

Charm pT Spectra

D0 and e combined fit

<pT>=1.10  0.05(stat.) GeV/c in

minbias Au+Au

<pT>=1.32  0.08(stat.) GeV/c in d+Au

Haibin Zhang QM05


PANIC05, Zhangbu Xu (BNL)

Open charm cross section and r aa

Charm Total Cross Section

Charm total cross section per NN


STAR Preliminary

1.11 0.08(stat.)  0.42(sys.) mb in

200GeV minbias Au+Au collsions

1.4  0.2(stat.)  0.4(sys.) mb in

200GeV minbias d+Au collisions

Charm total cross section follows

roughly Nbin scaling from d+Au to

Au+Au considering errors

Indication of charm production in initial


Haibin Zhang, Xin Dong QM05

NLO pQCD from R. Vogt


PANIC05, Zhangbu Xu (BNL)

R aa of non photonic electrons
RAA of non-photonic electrons

STAR Highlight talk

  • Evidence of large heavy quark energy loss!

PANIC05, Zhangbu Xu (BNL)

Challenges to theory

M. Djordjevic, et. al. nucl-th/0507019

N. Armesto et. al. private comm.

any beauty?

Challenges to theory

Current energy loss mechanisms can only account for part of strong suppression of RAA for electrons.

PANIC05, Zhangbu Xu (BNL)

Photonic background

STAR Preliminary

STAR Preliminary

Photonic background

Photonic background matches with inclusive electrons.

→ Consistent with low charm yield at 62.4 GeV

PANIC05, Zhangbu Xu (BNL)

Muon id at low pt
Muon ID at low pT




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

PANIC05, Zhangbu Xu (BNL)


  • Charm cross sections measured in p+p, d+Au and Au+Au: binary scaling=> charm production at initial impact

  • Large suppression of HF->e spectra in Au+Au

  • Heavy Flavor measurements at RHIC, new challenges to theory.

  • Continue developments of new measurements and upgrades!

PANIC05, Zhangbu Xu (BNL)

Effects related to open charm
Effects related to Open Charm











  • Radiation Energy Loss

  • Collision Energy Loss

  • Dead Cone Effect

  • Ter-Mikayelian Effect

  • Transition Radiation

  • Flow (radial & elliptic)

  • (quark) Coalescence

  • Death of “dead cone”

  • Charm Resonance

  • CGC

    All these happen at intermediate pTEmphasize on experimental measurements

PANIC05, Zhangbu Xu (BNL)