Haibin Zhang Brookhaven National Laboratory

1
Haibin ZhangBrookhaven National Laboratory
Open Charm Production at STAR
for
The STAR Collaboration
1
2
Outline
Motivations
D0, D, D open charm measurement in dAu
collisions
Single electron spectra in pp and dAu
collisions
Charm cross sections
Open charm pT spectrum and theoretical
comparisons
Summary
2
3
Motivation (I)
Through leptonic decay channel of open charm,
sensitive to shadowing
Charm quark mostly produced from the initial
fusion of partons (mostly gluons)
Z. Lin M. Gyulassy, PRL 77 (1996) 1222
dN/dMdy ratio (Sh/no Sh)
Z. Lin M. Gyulassy, PRC 51 (1995) 2177
3
4
Motivation (II)
Y.L. Dokshizer D.E. Kharzeev PLB 519 (2001) 199
enhancement of D0/? in HOT matter
4
5
Time Projection Chamber
TPC
TOFr
Event mixing technique
C. Adler et al., Phys. Rev. C 66,
061901(R)(2002) H. Zhang, J. Phys. G 30,
S577(2004)
5
6
D Mesons
dAu minbias collisions _at_ 200GeV
STAR Preliminary
6
7
Time of Flight
Hadron identification STAR Collaboration,
nucl-ex/0309012
Electron identification TOFr 1/ß-1 lt 0.03
TPC dE/dx electrons!!!
7
8
Electron Background
For the ? conversion and p0 Dalitz decay,
background spectra are obtained from data using
kinematical selection of the pairs in TPC
8
9
Electrons
STAR Preliminary
An increasing excess found at higher pT region,
pT gt 1.0 GeV/c, ?as expected to be contribution
of semi-leptonic decay from heavy flavor hadrons
9
10
Spectra
STAR Preliminary

• Good agreement between D0 and electrons
  spectra!
• dAu and pp do not show significant nuclear
  effect

10
11
Charm Cross Section
NLO pQCD calculation under-predict the
ccbar production cross section at RHIC
Power law for ccbar production Cross section from
SPS-gtRHIC n 1.9 - 0.2 ( 0.3 for charged
multiplicity)
11
12
Charm pT Spectrum
Charm pT spectrum can be fit well by the
power-law function Charm meson ratios consistent
with models and previous measurements
12
13
Charm pT Spectrum
Scaled to STAR measured cross section
The measured D pt spectrum shape coincides with
the bare-quark distribution from the NLO
calculation. Data favor a fragmentation function
peaked at x 1
NLO order calculation was done by R. Vogt and
FONLL code (fixed order NLO and resummations of
next-to-leading logs) was obtained from M.
Cacciaria and P. Nason, hep-ph0306212
13
14
Summary
14