Monte Calor Study of Hard and Soft Interactions:

1
Charm production at STAR
Yifei Zhang University of Science Technology of
China
10th Particle Physics Conference April 26-28,
Nanjing, China
Thanks to the conference organizers
2
Outline

• Introductions
• Signal/Spectra
• Flow energy loss
• Correlations
• Summary Outlook

3
Why measure charm?
Mb ? 4.8 GeV
gtgt Tc, LQCD, Muds
Mc ? 1.3 GeV

• Higgs mass electro-weak symmetry breaking.
  (current quark mass)
• QCD mass Chiral symmetry breaking. (constituent
  quark mass)
• Heavy quark masses are not modified by QCD
  vacuum. Strong interactions do not affect them.
• Important tool for studying properties of the
  hot-dense matter created at RHIC energy.

Muller nucl-th/0404015
4
Charm production cross-section

• Charm quarks are believed to be mainly produced
  at early stage by initial gluon fusions.
• Sensitive to initial parton distribution
  function.
• Nuclear and medium properties at initial stage.
• Precondition for light flavor thermalization if
  charm flow..
• Essential for recombination calculations of J/?
  production.

M. Gyulassy Z. Lin, PRC 51 (1995) 2177
Npart
L.Yan, P.Zhuang, N.Xu PRL 97 (2006) 232301
PHENIX data nucl-ex/0611020
5
Relativistic Heavy Ion Collider (RHIC)Brookhaven
National Laboratory (BNL), Upton, NY
6
Charm measurements at STAR

• STAR measurements
• Signal/Spectra
• D0 ? K?
• c ? ? X (y0, low pT)
• c ? e X
• Flow energy loss
• Radial flow from NPE
• RAA from NPE
• Correlations
• e-h, e-D0

7
Charm measurement at STAR

• Direct D0 reconstruction
• muon from charm semileptonic decay
• electron from heavy quark semileptonic decay

?-
semileptonic decay
c ? e anything (B.R. 10.3) c ? ? anything
(B.R. 8.2) c ? l anything (B.R. 9.6)
D0 ? K?, B.R. 3.83
8
Outline

• Introductions
• Signal/Spectra
• Flow energy loss
• Correlations
• Summary Outlook

9
Direct D-meson reconstructions at STAR
STAR Preliminary
A. Shabetai QM08
K? invariant mass distribution in dAu, AuAu
minbias, CuCu minbias at 200 GeV collisions.
10
D0 Lepton from HF decay at STAR
STAR Preliminary
New CuCu D0 spectrum agree with AuAu after
number of binary scaled. Low pT muon constrains
charm cross-section.
11
Charm cross-section
Total cross-section with large theoretical
uncertainty.
dAu PRL 94 (2005) CuCu A. Shabetai
QM08 AuAu Y. Zhang, JPG 32
(2006) S529
Both STAR and PHENIX are self-consistent. STAR
results 2 times larger than PHENIX Consistent
with NLO calculation.
12
Outline

• Introductions
• Signal/Spectra
• Flow energy loss
• Correlations
• Summary Outlook

13
Radial flow lepton from HF decays
D0 STAR Preliminary
STAR Preliminary
Tfo 220 MeV (best fit) freeze out ealier lt?tgt
0.23 (best fit), lt0.42 (1-?). favor moderate
or small radial flow. -- dense medium, light
flavor thermalization.
14
Charm energy loss, unsolved puzzle
No direct D-meson measurement at high pT. Heavy
flavor electron suppression was observed in
several experiments.
Radiative Collisional eloss calculations
describe data better. Question Partonic eloss
mechanism? Bottom contribution?
15
Outline

• Introductions
• Signal/Spectra
• Flow energy loss
• Correlations
• Summary Outlook

16
e-h correlations conical emission
Trigger on NPE from heavy quark decays.
Section XIII G. Wang
AuAu 200 GeV
CuCu 200 GeV
STAR Preliminary
Does heavy quark e-loss generate Mach Cone
emission?
17
e-h correlations bottom contribution
(b?e)/(c?eb?e)
e-h G. Wang, QM08 e-D0 A. Mischke, QM08
Simulation c?e, b?e, cb?e
Extract b/c ratio from the data/simulation
comparison
Good agreement among different analyses. Data
consistent with FONLL.
18
Does bottom affect charm X-sec?
STAR Preliminary
Before subtraction
(AuAu MB) (AuAu 0-12)
After bottom contribution subtraction
(AuAu MB) (AuAu 0-12)
Bottom contribution does NOT change charm
cross-section
(b?e)/(bc?e) upper limit of NLO is applied
19
Summary

• Charm cross-section is found to follow number of
  binary collisions scaling.
• None zero charm flow is observed at RHIC energy.
• Electron suppression is observed at RHIC but the
  energy loss mechanism is still NOT really
  understood.
• Abounding correlations related to heavy flavor
  are reported.

20
Outlook

• Currently
• W/o inner tracker, direct measurement of
  D-mesons through topology reconstruction is
  impossible due to insufficient track projection
  resolution close to the collision vertex.
• Heavy Flavor Tracker
• Single muon can not be measured at high pT at
  STAR.
• Muon Telescope Detector
• Single electron is always suffered from the
  amount of photonic background.
• Full barrel Time Of Flight Detector

Semileptonic decayed electron is not strongly
sensitive to D-mesons.