Open charm and charmonium
production at RHIC
An Tai
(1) Motivations
(2) Results from STAR and PHENIX
(3) Conclusions and outlook
An Tai
Aug.9-14, 2004, CCAST Workshop, Beijing
1
Heavy flavor probing the matter properties at early stage in
heavy ion collisions, gluon structure function in nucleus.
J/ψ( cc ) D( cu )
Q2
mc=1.2-1.5 GeV/c2
J/y, D
W
f
v2 saturates
X
L, K*
penaltyfactor  exp( p
p, K
1 .5 * 1 .5  0 . 5 * 0 .5
 (3.14
)
0 .2
 2.3 *10 14
D, p
time
d, HBT
An Tai
bT saturates
Aug.9-14, 2004, CCAST Workshop, Beijing
mc2  ms2

)
2
Geometry of Nucleus-Nucleus Collisions
Number of Participants
Impact Parameter
Npart – No of participant nucleons
Nbinary – No of binary nucleon-nucleon collisions
pp
d AB
d



(
AB
)
d3p
d3p
 J /y  0.93
dn AB
dn pp
 D  1  3  N binary 3
d p
d p
An Tai
Aug.9-14, 2004, CCAST Workshop, Beijing
3
Heavy flavor production is a crucial probe
of a QGP
QGP
Debye Screening
V (r ) 
q e  r / D
4p
r
, D  1 / T
D< Size of J/ψ, a bound
state can not exist  J/ψ
suppression
However, J/ψ may be formed through
coalescence at RHIC  J/ψ enhancement
J/psi dissociation in QGP ?
c c c
cc 
cc c
! New lattice QCDJ/ψ survives up to 1.6 Tc
An Tai
Aug.9-14, 2004, CCAST Workshop, Beijing
4
c-quark energy loss testing the dead-cone effect
D. Kharzeev, PLB 519 (2001) 199-206
q
q
M. Djordjevic and M. Gyulassy QM04
Another stringent test of jet energy
loss in a QGP
An Tai
Aug.9-14, 2004, CCAST Workshop, Beijing
5
Is the charm quark hadronization modified by
the thermal medium ?
Statistical
Calescene
Model
0.229
0.504
0.190
0.075
0.214
Statistical model: A. Andronic etc. nucl-th/0209035 and private communication
An Tai
Aug.9-14, 2004, CCAST Workshop, Beijing
6
e  : |  | 0.35
STAR
  : 1.2 |  | 2.4
e, p , K , p : |  | 1
PHENIX
STAR --- TPC, TOF, EMCal -- large acceptance
PHENIX--- Drift chamber, RICH, EMCal, two-arm muon detector -- small
acceptance, high rate capability
pp, dAu, AuAu, √s=130 GeV,200 GeV
An Tai
Aug.9-14, 2004, CCAST Workshop, Beijing
7
Decay channels used to construct open charm
D  K p (3.8%)
0


D 0  K p   0 (p p  )
D   Kpp
(6.2%)
(9.1%)
D  D p s (68%), D  Kp (3.8%)
*
0
0
About 15 M dAu minbias events are used in the analysis
we also measure D from its semi-leptonic decay to
electrons, D eX
An Tai
Aug.9-14, 2004, CCAST Workshop, Beijing
8
Mass plots from dAu data using eventmixing technique
An Tai
Aug.9-14, 2004, CCAST Workshop, Beijing
9
Results--- D spectrum and Ratios
dAu minbias at √s=200 GeV
Open symbol
D+/D0
Solid symbol
D*/D0
An Tai
Aug.9-14, 2004, CCAST Workshop, Beijing
10
Phenix measured open charm through D eX at √s=130
and 200 GeV in Au+Au collisions
No significant charm enhancement in Au+Au over pp binary scaling is
observed for pT(D)>1 GeV/c
 cNN
c
 cNN
c
central
 cNN
c
peripheral
An Tai
Aug.9-14, 2004, CCAST Workshop, Beijing
11
Compare measurements of open charms with
background-subtracted electron data in STAR
A combined fit using D0 and
the electron data leads
 cNN
c =1.44± 0.20 ± 0.44 mb
The band is obtained
from D decay based
on the power-law fit
to the measured open
charm spectrum.
An Tai
Aug.9-14, 2004, CCAST Workshop, Beijing
12
pQCD calculations of charm cross section
LO
NLO
An Tai
Aug.9-14, 2004, CCAST Workshop, Beijing
13
Charm cross section vs NLO calculations
√s=130 GeV
cc=420b±33(stat)±250(sys)
√s=200 GeV
STAR
cc=1400b±200(stat)±400 (sys)
PHENIX
cc=709b±85(stat)
+332
-281
(sys)
PHENIX and STAR data are consistent within uncertainties.
STAR measured charm cross section is higher than the NLO
predictions by factor of 3-5.
An Tai
Aug.9-14, 2004, CCAST Workshop, Beijing
14
Fragmentation of a c-quark
γp
An Tai
Aug.9-14, 2004, CCAST Workshop, Beijing
15
Is the fragmentation function universal ?
Bare c-quark distribution from NLO coincides with D spectrum ---- Peterson’s
Function is too soft for charm hadronization in hadron-hadron collisions.
π+A scattering
An Tai
Aug.9-14, 2004, CCAST Workshop, Beijing
16
Charm quark hadronization at RHIC
An Tai
Aug.9-14, 2004, CCAST Workshop, Beijing
17
PHENIX: J/e+e- and +- from pp
pT and rapidity shape
are consistent with
COM over phenix
coverage.
An Tai
Aug.9-14, 2004, CCAST Workshop, Beijing
18
Cross section and <pT> from pp
 = 3.99 +/- 0.61(stat) +/- 0.58(sys) +/- 0.40(abs) b
An Tai
<pT>=1.80+0.23(stat.)+0.16(syst.
Aug.9-14, 2004, CCAST Workshop, Beijing
19
J/y in dAu collisions at RHIC
x
Predicted Gluon Shadowing in d+Au
From Eskola, Kolhinen, Vogt
Nucl. Phys. A696 (2001) 729-746.
An Tai
d
Aug.9-14, 2004, CCAST Workshop, Beijing
Au
20
J/ψ production via coalescence ?
Ncc ~ 7 in central Au+Au,
PHENIX
cc 
may be possible.
R. L. Thews, M. Schroedter, J.
Rafelski, Phys Rev C 63,
054905
Plasma Coalescence Model
Binary Scaling
Absorption (Nuclear + QGP) +
final-state coalescence
Absorption (Nuclear + QGP)
L. Grandchamp, R. Rapp, Nucl
Phys A709, 415; Phys Lett B
523, 60
Disfavor models with enhancement over binary collision scaling.
An Tai
Aug.9-14, 2004, CCAST Workshop, Beijing
21
Conclusions




Open charm and J/ψ are measured at RHIC in pp, dAu and
NN

c
Au+Au collisions. c =0.709-1.4 mb, σNNJ/ψ=3.99 +/0.61(stat) +/- 0.58(sys) +/- 0.40(abs) µb.
The STAR measured charm cross section for NN collisions
is larger than the NLO predictions. No significant charm
enhancement is observed in AuAu collisions.
The measured D pt spectrum shape coincides with the barequark distribution from the NLO calculation.
The measured J/ψ pT and rapidity distributions are
consistent with Color Octet Model.
An Tai
Aug.9-14, 2004, CCAST Workshop, Beijing
22
Outlook
Challenge and solution of STAR open charm
study in heavy ion collisions
(1) Test dead-cone effect of open charm energy loss, we
need to measure RAA (Rcp) with an experimental
uncertainty under 20%
(2) v2 measurement of open charm in AA is also difficult
due to large combinatorial background
(3) Test charm thermalization, need to measure DsKKπ
Detector upgrade is essential !
An Tai
Aug.9-14, 2004, CCAST Workshop, Beijing
23
TOF upgrade will greatly enhance STAR open charm study
by providing better particle identification
An Tai
Aug.9-14, 2004, CCAST Workshop, Beijing
24
STAR Vertex Detector will provide precision
needed for our physics goals

Two layers



1.5 cm radius
4 cm radius
24 ladders




2 cm by 20 cm each
< 0.2% X0 to limit
multiple scattering
~ 100 Million Pixels
Position resolution < 10 µm,
D0 cτ = 124 µm
An Tai
K-
Decay
length
p+
DCA between
D0 daughters
DCA daughter
Aug.9-14, 2004, CCAST Workshop, Beijing
25
Study heavy flavor with the Vertex detector

Goals --- study matter properties created at
RHIC

Heavy flavor energy loss


Charm flow Yes Charm quark must go through a thermalized


Precise D spectra
D v2
partonic medium
Charm thermalization

Yield of D+, Ds+, Lc+
mVertex allows the same measurement 100
times faster than TPC+SVT
An Tai
Aug.9-14, 2004, CCAST Workshop, Beijing
26
END
An Tai
Aug.9-14, 2004, CCAST Workshop, Beijing
27
An Tai
Aug.9-14, 2004, CCAST Workshop, Beijing
28
Charm quark hadronization at RHIC
Higher order pQCD is in need or charm hadronization through
fragmentation+recombination (R. Rapp and E. Shuryak hep-ph/0301245 ?
bare c-quark spectrum,
normalized to measured dn/dy
After kT and fragmentation
MRST HO
Peterson’s function
ε=0.06
c quark
kT2=4,3,2,1 (GeV)^2
NLO pQCD predictions are provided by R. Vogt, hep-ph/0203151
An Tai
Aug.9-14, 2004, CCAST Workshop, Beijing
29
Mass plots from dAu data using eventmixing technique
An Tai
Aug.9-14, 2004, CCAST Workshop, Beijing
30
Outlook
With the 10-20 more data in run4 and future detector upgrade (TOF, new
vertex detectors), heavy flavor program will address the many
outstanding issues related the matter properties formed at RHIC

Heavy flavor energy loss

Precise D spectra
Charm quark must go

Charm flow

Charm thermalization


Yes
through a partonic
medium
Yield of D+, Ds+, Lc+
J/ψ suppression or enhancement
An Tai
Aug.9-14, 2004, CCAST Workshop, Beijing
31
Charm quark hadronization at RHIC
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
bare c-quark spectrum,
normalized to measured dn/dy
An Tai
Aug.9-14, 2004, CCAST Workshop, Beijing
32
Charm quark hadronization at RHIC
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
bare c-quark spectrum,
normalized to measured dn/dy
After kTand
fragmentation
MRST HO
Peterson’s
function ε=0.06
c quark
kT2 =4,3,2,1 (GeV)^2
An Tai
Aug.9-14, 2004, CCAST Workshop, Beijing
33
J/ψ production via coalescence ?
Ncc ~ 7 in central Au+Au,
PHENIX
cc 
may be possible.
R. L. Thews, M. Schroedter, J.
Rafelski, Phys Rev C 63,
054905
Plasma Coalescence Model
Binary Scaling
Absorption (Nuclear + QGP) +
final-state coalescence
Absorption (Nuclear + QGP)
L. Grandchamp, R. Rapp, Nucl
Phys A709, 415; Phys Lett B
523, 60
Disfavor models with enhancement over binary collision scaling.
An Tai
Aug.9-14, 2004, CCAST Workshop, Beijing
34
Open charm spectrum is hard !
Phenix: Phys. Rev. Lett. 88,
192303(2002)
D. Kharzeev,hep-ph/0310358
An Tai
Aug.9-14, 2004, CCAST Workshop, Beijing
35
c-quark energy loss and the dead-cone effect
D. Kharzeev, PLB 519 (2001) 199-206
M. Djordjevic and M. Gyulassy QM04
Another stringent test of jet energy loss in a QGP
An Tai
Aug.9-14, 2004, CCAST Workshop, Beijing
36
D * / D 0 ( D  / D0 )
ratios -- consistent with other experiments
Open symbol D+/D0
Solid symbol D*/D0
CDF: hep-ex/0307080
HERA: www-h1.de/h1/www/publications/conf_list.html
e+e-: hep-ph/0312054
Statistical model: A. Andronic etc. nucl-th/0209035 and private
communication.
An Tai
Aug.9-14, 2004, CCAST Workshop, Beijing
37
Charm hdronization
Fragmentation of a c-quark
γp
An Tai
Aug.9-14, 2004, CCAST Workshop, Beijing
38
Is the fragmentation universal ?
momentum degradation due to fragmentation can be counter-balanced by initial
kT
Bare c-quark spectrum
After
π+A scattering at 350 GeV/c
An Tai
kT and fragmentation
ε=0.06
Aug.9-14, 2004, CCAST Workshop, Beijing
39
Cronin Effect: pT broadening
 dA   pp (2 197)
x2~ 0.003
Parton initial state
multiple scattering leads
to broadening of J/y pT
distribution
x2~ 0.01
x2~ 0.1
An Tai
Broadening
comparable to lower
energy (s = 39 GeV
in E866)
Aug.9-14, 2004, CCAST Workshop, Beijing
40
STAR D spectrum and single electron data are consistent
dAu minbias at √s=200 GeV
An Tai
dσcc/dy=0.30±0.04(stat.)±0.09(syst.) mb
Aug.9-14, 2004, CCAST Workshop, Beijing
41
NLO c-quark XF distribution coincides with open charm XF distribution
S. Frixione, M. Mangano and P. Nason (hep-ph/9702287) in
their summary paper of heavy quark production:
“ We conclude that, when using the central value of the charm
mass, mc =1.5 GeV, favored by the total cross section
measurements, the theoretical results for the p2T spectrum can
describe the data well, only if a large kT kick is applied to the
fragmented curve. Therefore, there seems to be a potential
discrepancy between theory and experiments in the p2T
spectrum in charm hadroproduction. From a different point of
view, however, the discrepancy may be interpreted as the
signal that some of the other theoretical assumptions are not
totally sound. For example, the Peterson fragmentation
function may not be suitable to describe the hadronization
process in hadronic collisions; the data would suggest a
function more peaked towards the x≃ 1 region. Moreover,
higher-order perturbative corrections may also play a role.”
An Tai
Aug.9-14, 2004, CCAST Workshop, Beijing
42
Is the fragmentation universal ?
momentum degradation due to fragmentation can be counter-balanced by initial
kT
Bare c-quark spectrum
After
π+A scattering at 350 GeV/c
An Tai
kT and fragmentation
ε=0.06
Aug.9-14, 2004, CCAST Workshop, Beijing
43
c-quark energy loss and the dead-cone effect
D. Kharzeev, PLB 519 (2001) 199-206
M. Djordjevic and M. Gyulassy QM04
Another stringent test of jet energy loss in a QGP
An Tai
Aug.9-14, 2004, CCAST Workshop, Beijing
44
FONLL and CDF data
An Tai
Aug.9-14, 2004, CCAST Workshop, Beijing
45