Transcript Document

Open Charm Production at RHIC
Zhangbu Xu
BNL
Outline
Why Open Charm
Measurements:
Direct/semileptonic
p+p, d+Au, Au+Au
What issues addressed
Conclusions
July 28th, ISMD2004
Zhangbu Xu, BNL
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How much do we know?
PHENIX, PRL 91, 241803(2003)
D mesons
, Y’, c
PDF?
pQCD?
Q>3GeV down to low pT
STAR, PRL 92, 171801(2004)
FF?
Total Cross Section is
Insensitive to FF!
π0 measurements are consistent with NLO pQCD calculation!
Charm should be better!!
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Initial Charm Production in A+A
dN/dMdy ratio (Sh/no Sh)
sensitive to Initial Nuclear Effects
Z. Lin & M. Gyulassy, PRL 77 (1996) 1222
Charm quark mostly produced
from the initial fusion of partons
(mostly gluons)
Z. Lin & M. Gyulassy, PRC 51 (1995) 2177
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Heavy Quark as Unique Probe in A+A Collisions
● Heavy Quark has less dE/dx due to
● Heavy Quark Flow Effects
suppression of small angle gluon radiation
V. Greco, C.M. Ko, R. Rapp, nucl-th/0312100
Y. Dokshitzer &D. Kharzeev PLB519(199)2001
dP 
0 
 sC F d 

M
E
2
2
k  dk 
 (k    0 )
2
, 
2
2
2

dP0
(1   0 /  )
2
2
2
k

M. Djordevic & M. Gyulassy QM04, nucl-th/0404006
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“Dead Cone”-- Conclusions
The upcoming D meson data for 200 GeV D-Au
and Au-Au results will soon become available.
According to our results, charm quark
suppression should be small ~ 0.6-0.8. Therefore,
this suppression should be definitely much smaller
than the already observed pion suppression (0.2).
If this result is confirmed, then Jet Tomography of
QGP will pass another stringent test. On the other
hand, if the prediction is falsified, then either the
tomographic or the QGP paradigm will have to be
revised or abandoned.
Magdalena Djordjevic and Miklos Gyulassy, QM04
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J/ψ production: suppression/enhancement?
Charm input from pQCD
R.L. Thews et. al. PRC 63, 054905(2003)
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A. Andronic et. al. PLB 571,36(2003)
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Why Open Charm?
 What creates Heavy Quarks?
 Total Cross Section
 Which Nuclear Effect dominates
production?
 pT spectra
 How Heavy Quarks fragment?
 Do Heavy Quarks thermalize in
QGP?
 Whether Heavy Quark and Light
Quark Energy Losses are the
same?
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 p+p
 p+A (d+A)
 A+A
 Energy/rapidity
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Previous Experiments
Low-energy fixed target
– direct D measurement
CDF directy D measurement
-- high pT
hep-ex/0307080
Fermilab E769, PRL 77, 2388 (1996)
CHARM is hard to get!
ISR 52-63GeV – inconsistency, S.P.K. Tavernier Rep. Prog. Phys. 50, 1439 (1987)
UA2: 630 GeV p+pbar (two electron data points), O. Botner et al. PLB 236 (1990) 488
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D0 direct reconstruction


D  K  ( Br. 3.83%)
0
STAR Preliminary
First Direct Open Charm
Reconstruction at RHIC
Event mixing technique
C. Adler et al., Phys. Rev. C 66, 061901(R)(2002)
H. Zhang, J. Phys. G 30, S577(2004)
L. Ruan QM04
H. Zhang DNP03
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A New Hadron-Blind Detector
Hadron identification:
STAR Collaboration, nucl-ex/0309012
electrons
Electron identification:
TOFr |1/ß-1| < 0.03
TPC dE/dx
electrons!!!
L. Ruan QM04
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Measurements of electron background
Single
Electrons
Spectra
γ conversion
π0 , η Dalitz decays
Kaon decays
ρ ω Φ vector meson decays
heavy quark semi-leptonic decay
others
background
signal
γ conversion and π0 Dalitz decays are the dominant sources at low pt region.
Background Topology:
•
•
•
TOFr tagged e+/eLarge TPC acceptance
High efficiency of reconstructing
electron pair
TPC
For the γ conversion and π0 Dalitz decay, background
spectra are obtained from data using kinematical
selection of the pairs in TPC
L. Ruan QM04
X. Dong BNL Seminar
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Background contribution
STAR Preliminary
An increasing excess found at higher pT region, pT > 1.0 GeV/c,
as expected to be contribution of semileptonic decay from heavy
flavor hadrons
L. Ruan QM04
X. Dong BNL Seminar
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Direct/semilepton Spectra
STAR Preliminary
Combined fit for
D0 and electrons
Good agreement between
D0 and electrons spectra!
d+Au and p+p do not
show significant nuclear
effect
PYTHIA: MSEL = 1, CTEQ5M1
L. Ruan QM04
X. Dong BNL Seminar
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Charm production cross-section
NLO pQCD calculation
under-predict the ccbar
production cross section
at RHIC
Power law for ccbar production
Cross section from SPS->RHIC
n = 1.9 +- 0.2
( 0.3 for charged multiplicity)
L. Ruan QM04
X. Dong BNL Seminar
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Electron Spectra
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Open charm spectrum is hard !
D0, D*, D
A. Tai, A. Suaide, QM04
B decay dominated region
Phenix: Phys. Rev. Lett. 88,
192303(2002)
D. Kharzeev,hep-ph/0310358
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Charm quark hadronization at RHIC
bare c-quark spectrum,
normalized to measured dn/dy
After k T and
fragmentation
MRST HO
Peterson’s
function ε=0.06
c quark
2
k T =4,3,2,1 (GeV)^2
NLO pQCD predictions: R. Vogt, hep-ph/0203151
A. Tai QM04
Higher order pQCD is in need or charm hadronization through
fragmentation+recombination (R. Rapp and E. Shuryak hep-ph/0301245) ?
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PHENIX Ability to Study Charm
-- electron and muon measurement
X. Wei for PHENIX (RHIC/AGS Users’ Meeting)
 high resolution tracking and
momentum measurement from
Drift chamber.
Good electron identification from
Ring Imaging Cherenkov detector
(RICH) and Electromagnetic
Calorimeter (EMCal).
Good momentum resolution and
muon identification from mID and
mTrk.
High rate capability
•
•
•
•
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Open charm.
flow of charm.
J/y, y’
Upsilon
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Charm semileptonic decay in PHENIX
Subtraction of “photonic” sources.
•
conversion of photons from hadron decays in material
•
Dalitz decays of light mesons (0, h, , h,, f)
γ
Converter method
•
e+/- spectra
Comparison of
with and without converter Au
allows separation of photonic and non-photonic sources
of single electrons.
e-
Converter
-e invariant mass
measurement via -e coincidences
•
e+
Au
Yield of -e in vicinity of  mass with mixed event
subtraction
X. Wei for PHENIX (RHIC/AGS Users’ Meeting)
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Are Things Consistent?
PHENIX PRELIMINARY
NLO pQCD (M. Mangano et al.,
NPB405(1993)507)
PYTHIA
Most of the recent calculation indicates
cc300 mb with reasonable parameters
ISR
+332
cc=709mb±85(stat)-281 (sys)
PHENIX data is consistent with the prediction of
NLO pQCD calculation and PYTHIA prediction.
--X. Wei for PHENIX (RHIC/AGS Users’ Meeting)
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Scaling of Electron Spectra Au-Au s = 200 GeV
0.906 <  < 1.042
AA
3 [mb GeV-2]
1/TABEdN/dp
1/T
3 [mb GeV-2]
1/TAB1/T
EdN/dp
AA
3 [mb GeV
3 [mb
EdN/dp
GeV-2] -2]
1/T1/T
EdN/dp
ABAA
AB1/T
1/TAAABEdN/dp3 [mb GeV-2]
1/T
EdN/dp3 [mb GeV-2]
1/T1/T
AA AB
X. Wei for PHENIX (RHIC/AGS Users’ Meeting)
Yellow band represents the set of alpha
values consistent with the data at 90%
Confidence Level
dN/dy = A (Ncoll)
• data seems to scale with Ncoll in all the centrality bins
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Charm Flow
PHENIX PRELIMINARY
PHENIX RUN2 data
can not distinguish
different scenario due
to low statistics.
M. Kaneta QM04
STAR charm scaled up to Au+Au
with thermal model for J/y
From RUN4, both STAR
and PHENIX can do better
in charm v2 measurements
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Conclusions
Open charm yields were measured in d+Au collisions from both
direct reconstruction and charm decayed electrons.
These measurements indicate a large total charm production
cross-section at RHIC. (STAR>NLO, PHENIX=NLO)
 Hard Charm Spectra is observed.
 Charm production seems to scale with Nbin collisions
 Data from run4 Au+Au will address the medium effects
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Consistency between electron data sets
 STAR systematically (slightly) above PHENIX
 beware: error bars are meant to be taken seriously!
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