Centrality dependence of heavy flavor
production from single electron
measurements
Jaroslav Bielcik
Yale University/BNL
for the
collaboration
 Motivation
 STAR and electron ID
 Analysis
 Results: p+p, d+Au, and Au+Au at sNN = 200 GeV
 Summary
QM2005 Budapest
Jaroslav Bielcik
Heavy quark production at RHIC
 Can we learn something from the difference between heavy and
light quarks?
 How do heavy quarks interact with the medium?
– Thermalization, suppression?
ENERGY LOSS
D,
B
c,
b
light
1)
2)
3)
production
medium energy loss
fragmentation
Important test of transport properties
of sQGP
Heavy quark energy loss is expected
to be smaller because of dead cone
D,B spectra are affected by energy loss
(M.Djordjevic PRL 94 (2004))
QM2005 Budapest
Jaroslav Bielcik
2
Detecting charm/beauty via semileptonic D/B decays
 Hadronic decay channels: D0Kp, D*D0p, D+/-Kpp
See H.Zhang talk 5c
 Non-photonic electrons:
 Semileptonic channels:
 c  e+ + anything
– D0  e+ + anything
– D  e + anything
 b  e+ + anything
– B  e + anything
(B.R.: 9.6%)
(B.R.: 6.87%)
(B.R.: 17.2%)
(B.R.: 10.9%)
(B.R.: 10.2%)
 Drell-Yan (small contribution for pT < 10 GeV/c)
 Photonic electron background:




g conversions (p0  gg; g  e+e- )
p0, h, h’ Dalitz decays
r, f … decays (small)
Ke3 decays (small)
QM2005 Budapest
Jaroslav Bielcik
3
Electrons and nuclear modification factor RAA
Single e- from NLO/FONLL
scaled to
M. Cacciari et al.,
hep-ph/0502203
prediction:
electron suppression up to 2
 Beauty predicted to dominate
above 4-5 GeV/c
prediction:
large electron suppression of ~ 5 for c only
medium suppression of ~ 2.5 for c+b
QM2005 Budapest
Jaroslav Bielcik
4
STAR Detector and Data Sample
Electrons in STAR:
 TPC: tracking, PID
|h|<1.3 f=2p
 BEMC (tower, SMD): PID 0<h<1 f=2p
 TOF patch
HighTower trigger:
 Only events with high tower
ET>3 GeV/c2
 Enhancement of high pT
Processed:
Run2003/2004 min. bias.
high tower trigger
10% central
QM2005 Budapest
6.7M events with half field
2.6M events with full field (45% of all)
4.2M events (15% of all )
Jaroslav Bielcik
5
Electron ID in STAR – EMC
1. TPC: dE/dx for p > 1.5 GeV/c
•
Only primary tracks
•
Electrons can be discriminated
well from hadrons up to 8
GeV/c
Allows to determine the
remaining hadron contamination
after EMC
•
(reduces effective radiation length)
hadrons
electrons
K
p
d
p
electrons
2. EMC:
a) Tower E ⇒ p/E
b) Shower Max Detector (SMD)
• Hadrons/Electron shower
develop different shape
• Use # hits cuts
85-90% purity of electrons
(pT dependent)
h discrimination power ~ 104-105
QM2005 Budapest
hadrons
electrons
Electron background
 Inclusive electron spectra:
Signal
M e+e-<0.14 GeV/c2
– Heavy quarks semi-leptonic decays
Dominant background
− Instrumental:
red likesign
– γ conversion
– Hadronic decays:
- Dalitz decays (π0, η)
 Rejection strategy:
Background rejection efficiency central Au+Au
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 rejection
efficiency
QM2005 Budapest
Jaroslav Bielcik
7
Inclusive electron spectra AuAu sNN = 200 GeV
 3 centrality bins: 0-5%
10-40%
40-80%
 High tower trigger allows
STAR to extend electron
spectra up to 10 GeV/c
 Corrected for hadron
contamination ~10-15%
 Remaining problem:
charge exchange reaction
in EMC at high pT:
p±  p0  gg
(still under study)
QM2005 Budapest
Jaroslav Bielcik
8
STAR non-photonic electron spectra
pp,dAu,AuAu sNN = 200 GeV
 Photonic electrons
subtracted
 Excess over photonic
electrons observed
 Consistent with STAR
TOF spectra
See H.Zhang talk 5c
Beauty is expected to give an important
contribution above 5 GeV/c
QM2005 Budapest
Jaroslav Bielcik
9
RAA nuclear modification factor
 d 3N 
 3 
dp  AA
RAA  
 d 3 
TAA   3 
 dp  pp
Suppression up to ~ 0.4-0.6
observed in 40-80% centrality
~ 0.3 -0.4 in centrality 10-40%
Strong suppression up to ~ 0.2
observed at high pT in 0-5%
Maximum of suppression at pT
~ 5-6 GeV/c
QM2005 Budapest
Jaroslav Bielcik
10
Summary
 Non-photonic electrons from heavy flavor decays were
measured in s = 200 GeV p+p, d+Au and Au+Au
collisions by STAR up to pT~10GeV/c
 Strong suppression of non-photonic electrons has
been observed in Au+Au increasing with centrality
RAA ~ 0.2-0.3 for pT> 3 GeV/c
 suggests large energy loss of heavy quarks
 Need more detailed theory (incl. b suppression and
centrality dependence)
 Still more data on tape …
More stat at central
e-e correlation (what happens with the other D?)
e-h correlation (heavy flavor tagged jets)
QM2005 Budapest
Jaroslav Bielcik
11
STAR Collaboration
545 Collaborators from 51 Institutions
in 12 countries
Argonne National Laboratory
Institute of High Energy Physics - Beijing
University of Bern
University of Birmingham
Brookhaven National Laboratory
California Institute of Technology
University of California, Berkeley
University of California - Davis
University of California - Los Angeles
Carnegie Mellon University
Creighton University
Nuclear Physics Inst., Academy of Sciences
Laboratory of High Energy Physics - Dubna
Particle Physics Laboratory - Dubna
University of Frankfurt
Institute of Physics. Bhubaneswar
Indian Institute of Technology. Mumbai
Indiana University Cyclotron Facility
Institut de Recherches Subatomiques de Strasbourg
University of Jammu
Kent State University
Institute of Modern Physics. Lanzhou
Lawrence Berkeley National Laboratory
Massachusetts Institute of Technology
Max-Planck-Institut fuer Physics
Michigan State University
Moscow Engineering Physics Institute
QM2005 Budapest
Jaroslav Bielcik
City College of New York NIKHEF
Ohio State University
Panjab University
Pennsylvania State University
Institute of High Energy Physics - Protvino
Purdue University
Pusan University
University of Rajasthan
Rice University
Instituto de Fisica da
Universidade de Sao Paulo
University of Science and Technology of China USTC
Shanghai Institue of Applied Physics - SINAP
SUBATECH
Texas A&M University
University of Texas - Austin
Tsinghua University
Valparaiso University
Variable Energy Cyclotron Centre. Kolkata
Warsaw University of Technology
University of Washington
Wayne State University
Institute of Particle Physics
Yale University
University of Zagreb
12