Zhangbu Xu, BNLJuly 28 th, ISMD2004 1 Open Charm Production at RHIC Zhangbu Xu BNL Outline Why Open...

1Zhangbu Xu, BNLJuly 28th, ISMD2004

Open Charm Production at RHIC

Zhangbu XuBNL

OutlineWhy Open CharmMeasurements:

Direct/semileptonic p+p, d+Au, Au+Au

What issues addressedConclusions


How much do we know?PHENIX, PRL 91, 241803(2003)

STAR, PRL 92, 171801(2004)

π0 measurements are consistent with NLO pQCD calculation!Charm should be better!!

D mesons

, ’,

Q>3GeV down to low pT

pQCD?

PDF?

FF?

Total Cross Section is Insensitive to FF!


Initial Charm Production in A+A

sensitive to Initial Nuclear Effects

Z. Lin & M. Gyulassy, PRL 77 (1996) 1222

dN

/dM

dy

rati

o (S

h/n

o S

h)

Charm quark mostly produced from the initial fusion of partons (mostly gluons)

Z. Lin & M. Gyulassy, PRC 51 (1995) 2177


Heavy Quark as Unique Probe in A+A Collisions

M. Djordevic & M. Gyulassy QM04, nucl-th/0404006

V. Greco, C.M. Ko, R. Rapp, nucl-th/0312100

● Heavy Quark Flow Effects● Heavy Quark has less dE/dx due to suppression of small angle gluon radiation

k

E

M

dP

k

dkkdCdP Fs

,

)/1()(

0

2220

022

022

22Y. Dokshitzer &D. Kharzeev PLB519(199)2001


“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


J/ψ production: suppression/enhancement?

A. Andronic et. al. PLB 571,36(2003)R.L. Thews et. al. PRC 63, 054905(2003)

Charm input from pQCD


Why Open Charm?

What creates Heavy Quarks?

Which Nuclear Effect dominates production?

How Heavy Quarks fragment?

Do Heavy Quarks thermalize in QGP?

Whether Heavy Quark and Light Quark Energy Losses are the same?

Total Cross Section

pT spectra

p+p

p+A (d+A)

A+A

Energy/rapidity


Previous Experiments

Low-energy fixed target – direct D measurement

Fermilab E769, PRL 77, 2388 (1996)

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

CDF directy D measurement -- high pT

hep-ex/0307080

CHARM is hard to get!


D0 direct reconstruction

Event mixing technique

KD0( Br. 3.83%)

C. Adler et al., Phys. Rev. C 66, 061901(R)(2002)H. Zhang, J. Phys. G 30, S577(2004)

First Direct Open CharmReconstruction at RHIC

STAR Preliminary

L. Ruan QM04H. Zhang DNP03


Hadron identification: STAR Collaboration, nucl-ex/0309012

A New Hadron-Blind Detector

Electron identification: TOFr |1/ß-1| < 0.03 TPC dE/dx electrons!!!

electrons

L. Ruan QM04


Measurements of electron background

Background Topology:• TOFr tagged e+/e-

• Large 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

γ conversionπ0 , η Dalitz decaysKaon decaysρ ω Φ vector meson decaysheavy quark semi-leptonic decayothers

Single ElectronsSpectra

γ conversion and π0 Dalitz decays are the dominant sources at low pt region.

background

signal

L. Ruan QM04X. Dong BNL Seminar


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



Direct/semilepton Spectra

Combined fit forD0 and electrons

PYTHIA: MSEL = 1, CTEQ5M1

Good agreement between D0 and electrons spectra!d+Au and p+p do not show significant nuclear effect

STAR Preliminary



Charm production cross-section

NLO pQCD calculation under-predict the ccbarproduction cross sectionat RHIC

Power law for ccbar productionCross section from SPS->RHIC n = 1.9 +- 0.2

( 0.3 for charged multiplicity)



Electron Spectra


Open charm spectrum is hard !

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

D. Kharzeev,hep-ph/0310358

B decay dominated region

D0, D*, D

A. Tai, A. Suaide, QM04


Charm quark hadronization at RHIC

NLO pQCD predictions: 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 fragmentation

Tk

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

A. Tai QM04


PHENIX Ability to Study Charm

-- electron and muon measurement

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 ID and Trk.

• Open charm.

• flow of charm.

• J/’

• Upsilon

High rate capability

X. Wei for PHENIX (RHIC/AGS Users’ Meeting)


Charm semileptonic decay in PHENIX

Subtraction of “photonic” sources.

• conversion of photons from hadron decays in material

• Dalitz decays of light mesons ()

Converter method

• Comparison of e+/- spectra with and without converter allows separation of photonic and non-photonic sources of single electrons.

measurement via -e coincidences

• Yield of -e in vicinity of mass with mixed event subtraction

-e invariant mass

γ

e+

e-ConverterAu

Au



Are Things Consistent?

cc=709b±85(stat) (sys)+332

-281

PYTHIA ISR

NLO pQCD (M. Mangano et al., NPB405(1993)507)

PHENIX PRELIMINARY

PHENIX data is consistent with the prediction of NLO pQCD calculation and PYTHIA prediction.

--X. Wei for PHENIX (RHIC/AGS Users’ Meeting)

Most of the recent calculation indicates cc300 b with reasonable parameters


Scaling of Electron Spectra Au-Au s = 200 GeV

1/T A

A

1/T A

A

1/T A

A

1/T A

A

1/T A

A

1/T

ABE

dN/d

p3 [m

b G

eV-2]

1/T

ABE

dN/d

p3 [m

b G

eV-2]

1/T

ABE

dN/d

p3 [m

b G

eV-2]

1/T

ABE

dN/d

p3 [m

b G

eV-2]

1/T

ABE

dN/d

p3 [m

b G

eV-2]

1/T

ABE

dN/d

p3 [m

b G

eV-2]

• data seems to scale with Ncoll in all the centrality bins

Yellow band represents the set of alpha values consistent with the data at 90% Confidence Level

dN/dy = A (Ncoll)

0.906 < < 1.042



Charm Flow

PHENIX PRELIMINARY

PHENIX RUN2 data can not distinguish different scenario due to low statistics.

From RUN4, both STAR and PHENIX can do better in charm v2 measurements

STAR charm scaled up to Au+Au with thermal model for J/

M. Kaneta QM04


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)

Charm production seems to scale with Nbin collisions

Hard Charm Spectra is observed.

Data from run4 Au+Au will address the medium effects


Consistency between electron data sets

STAR systematically (slightly) above PHENIX beware: error bars are meant to be taken seriously!

Zhangbu Xu, BNLJuly 28 th, ISMD2004 1 Open Charm Production at RHIC Zhangbu Xu BNL Outline Why Open...

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