An Tai Aug.9-14, 2004, CCAST Workshop, Beijing 1 Open charm and charmonium production at RHIC (1) Motivations (2) Results from STAR and PHENIX (3) Conclusions

An Tai Aug.9-14, 2004, CCAST Workshop, Beijing 1

Open charm and charmonium production at RHIC

(1) Motivations(2) Results from STAR and PHENIX(3) Conclusions and outlook

An Tai


J/D

K*Kpd, HBT

vv22 saturatessaturates

TT saturatessaturates

Q2

time

Heavy flavor probing the matter properties at early stage in heavy ion collisions, gluon structure function in nucleus.

1410*3.2

)2.0

5.0*5.05.1*5.114.3(

)exp(22

sc mmtorpenaltyfac

J/ψ( ) D( )

mc=1.2-1.5 GeV/c2

uccc


Geometry of Nucleus-Nucleus Collisions

Number of Participants

Impact Parameter

Npart – No of participant nucleonsNbinary – No of binary nucleon-nucleon collisions

pddnN

pddn

pddAB

pdd

pp

binary

AB

D

J

ppAB

33

/

33

1

93.0

)(


Heavy flavor production is a crucial probe of a QGP

TrV Dreq Dr /1,)( /

4

J/psi dissociation in QGP ?

QGP

Debye Screening

D < Size of J/ψ, a bound state can not exist J/ψ suppression

ccc

ccc

cc

However, J/ψ may be formed through coalescence at RHIC J/ψ enhancement

! New lattice QCDJ/ψ survives up to 1.6 Tc


c-quark energy loss testing the dead-cone effect

M. Djordjevic and M. Gyulassy QM04

D. Kharzeev, PLB 519 (2001) 199-206

qq

Another stringent test of jet energy loss in a QGP


Is the charm quark hadronization modified by the thermal medium ?

StatisticalCalescene Model

0.229

0.504

0.190

0.075

0.214

Statistical model: A. Andronic etc. nucl-th/0209035 and private communication


STAR --- TPC, TOF, EMCal -- large acceptancePHENIX--- Drift chamber, RICH, EMCal, two-arm muon detector -- small acceptance, high rate capability

pp, dAu, AuAu, √s=130 GeV,200 GeV

PHENIX

4.2||2.1:

35.0||:

e STAR

1||:,,, pKe


(9.1%)

we also measure D from its semi-leptonic decay to electrons, D eX

KD

%)8.3(%),68( 00* KDDD s

)(00 KD

%)8.3(0 KD

Decay channels used to construct open charm

(6.2%)

About 15 M dAu minbias events are used in the analysis


Mass plots from dAu data using event-mixing technique


Results--- D spectrum and Ratios

Open symbol D+/D0Solid symbol D*/D0

dAu minbias at √s=200 GeV


Phenix measured open charm through D eX at √s=130 and 200 GeV in Au+Au collisions

NNcc

NNcc

NNcc

central

peripheral

No significant charm enhancement in Au+Au over pp binary scaling is observed for pT(D)>1 GeV/c


A combined fit using D0 and the electron data leads =1.44± 0.20 ± 0.44 mb

Compare measurements of open charms with background-subtracted electron data in STAR

NNcc

The band is obtained from D decay based on the power-law fit to the measured open charm spectrum.


pQCD calculations of charm cross section

LO

NLO


Charm cross section vs NLO calculations

PHENIX and STAR data are consistent within uncertainties.

STAR measured charm cross section is higher than the NLO predictions by factor of 3-5.

cc=709b±85(stat) (sys)+332

-281

√s=130 GeV

cc=420b±33(stat)±250(sys)

√s=200 GeV

STAR

cc=1400b±200(stat)±400 (sys)

PHENIX


Fragmentation of a c-quark

γp


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


Charm quark hadronization at RHIC


PHENIX: J/e+e- and +- from pp

pT and rapidity shape are consistent with COM over phenix coverage.


Cross section and <pT> from pp

= 3.99 +/- 0.61(stat) +/- 0.58(sys) +/- 0.40(abs) b <pT>=1.80+0.23(stat.)+0.16(syst.


Predicted Gluon Shadowing in d+Au

J/ in dAu collisions at RHIC

From Eskola, Kolhinen, VogtNucl. Phys. A696 (2001) 729-746.

d Au

x


J/ψ production via coalescence ?

R. L. Thews, M. Schroedter, J. Rafelski, Phys Rev C 63, 054905Plasma 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

PHENIX

Disfavor models with enhancement over binary collision scaling.

Ncc ~ 7 in central Au+Au, may be possible.cc


Conclusions Open charm and J/ψ are measured at RHIC in pp, dAu and

Au+Au collisions. =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 bare-quark distribution from the NLO calculation.

The measured J/ψ pT and rapidity distributions are consistent with Color Octet Model.

NNcc


(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 DsKKπ

Detector upgrade is essential !

Challenge and solution of STAR open charm study in heavy ion collisions

Outlook


TOF upgrade will greatly enhance STAR open charm study by providing better particle identification


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 DCA daughter

D0

Decaylength

K-

+

DCA between daughters


Study heavy flavor with the Vertex detector Goals --- study matter properties created at

RHIC Heavy flavor energy loss

Precise D spectra Charm flow

D v2

Charm thermalization Yield of D+, Ds

+, c+

mVertex allows the same measurement 100 times faster than TPC+SVT

Charm quark must go through a thermalized partonic medium

Yes


END




NLO pQCD predictions are provided by R. Vogt, hep-ph/0203151

bare c-quark spectrum, normalized to measured dn/dy

MRST HO

Peterson’s function ε=0.06

c quark

=4,3,2,1 (GeV)^22Tk

After and fragmentationTk

Higher order pQCD is in need or charm hadronization through fragmentation+recombination (R. Rapp and E. Shuryak hep-ph/0301245 ?


Mass plots from dAu data using event-mixing technique


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 flow

Charm thermalization Yield of D+, Ds

+, c+

J/ψ suppression or enhancement

Yes

Outlook

Charm quark must go

through a partonic medium




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




MRST HO

Peterson’s function ε=0.06

c quark

=4,3,2,1 (GeV)^22Tk

After and fragmentation

Tk

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


J/ψ production via coalescence ?

R. L. Thews, M. Schroedter, J. Rafelski, Phys Rev C 63, 054905Plasma 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

PHENIX

Disfavor models with enhancement over binary collision scaling.

Ncc ~ 7 in central Au+Au, may be possible.cc


Open charm spectrum is hard !

Phenix: Phys. Rev. Lett. 88, 192303(2002)

D. Kharzeev,hep-ph/0310358


c-quark energy loss and the dead-cone effect


D. Kharzeev, PLB 519 (2001) 199-206



ratios -- consistent with other experiments

)/( 0DD

Open symbol D+/D0Solid symbol D*/D0

0* /DD

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.


Fragmentation of a c-quarkγp

Charm hdronization


Is the fragmentation universal ?

Bare c-quark spectrumTkAfter and fragmentation

ε=0.06 π+A scattering at 350 GeV/c

momentum degradation due to fragmentation can be counter-balanced by initial Tk


x2~ 0.1

x2~ 0.003

x2~ 0.01

Parton initial state multiple scattering leads to broadening of J/ pT

distribution

Broadening comparable to lower energy (s = 39 GeV in E866)

Cronin Effect: pT broadening )1972( ppdA


STAR D spectrum and single electron data are consistent

dAu minbias at √s=200 GeV dσcc/dy=0.30±0.04(stat.)±0.09(syst.) mb


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 p2

T 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 p2

T 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.”

NLO c-quark XF distribution coincides with open charm XF distribution


Is the fragmentation universal ?Bare c-quark spectrum

TkAfter and fragmentation

ε=0.06 π+A scattering at 350 GeV/c

momentum degradation due to fragmentation can be counter-balanced by initial Tk


c-quark energy loss and the dead-cone effect


D. Kharzeev, PLB 519 (2001) 199-206



FONLL and CDF data

Documents

An Tai Aug.9-14, 2004, CCAST Workshop, Beijing 1 Open charm and charmonium production at RHIC (1) Motivations (2) Results from STAR and PHENIX (3) Conclusions