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Xin Dong University of Science & Technology of China Lawrence Berkeley National Laboratory. Open Charm Measurements from STAR. Many Thanks to Dr. Gerd Kunde!. H. Huang, H. Ritter, L. Ruan, K. Schweda, P. Sorensen, A. Tai, N. Xu, Z. Xu, H. Zhang L. Grandchamp, J. Raufeisen, R. Vogt. - PowerPoint PPT Presentation
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Feb. 2nd, 05, LANL X.Dong, USTC/LBNL 1
Open Charm Measurements from STAR
Xin Dong University of Science & Technology of China
Lawrence Berkeley National Laboratory
H. Huang, H. Ritter, L. Ruan, K. Schweda, P. Sorensen, A. Tai, N. Xu, Z. Xu, H. Zhang
L. Grandchamp, J. Raufeisen, R. Vogt
Many Thanks to Dr. Gerd Kunde!
X.Dong, USTC/LBNL 2Feb. 2nd, 05, LANL
Outline
Introduction & Motivation
Direct charm reconstruction
Indirect electron measurements
Discussions
Conclusions & outlook
X.Dong, USTC/LBNL 3Feb. 2nd, 05, LANL
Heavy flavor in pQCD
D mesons
, ’,
Large Q value needed (>≈3GeV)
pQCD should work better!
π0 measurements are consistent with NLO pQCD calculation!
Charm should be better!!
PHENIX, PRL 91, 241803(2003) STAR, PRL 92, 171801(2004)
X.Dong, USTC/LBNL 4Feb. 2nd, 05, LANL
(p)QCD Test
Total cross section measurement --- not depend on the fragmentation models A powerful test of QCD calculations !
Charm spectrum measurement --- fragmentation test for theory predictions.
X.Dong, USTC/LBNL 5Feb. 2nd, 05, LANL
Heavy flavors – a unique probe to QGP
J/D
K*
K
p
d
TT
saturatessaturates
Q2
time
Charm quark mostly produced from the initial fusion of partons (mostly gluons)
Z. Lin & M. Gyulassy, PRC 51 (1995) 2177
sensitive to Initial Nuclear Effects
Z. Lin & M. Gyulassy, PRL 77 (1996) 1222
dN
/dM
dy
rati
o (S
h/n
o S
h)
X.Dong, USTC/LBNL 6Feb. 2nd, 05, LANL
Heavy quark energy loss
M. Djordevic & M. Gyulassy QM04, nucl-th/0404006
● 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
22
Y. Dokshitzer &D. Kharzeev PLB 519(2001)199
J. Adams et. al, PRL 91(2003)072304
X.Dong, USTC/LBNL 7Feb. 2nd, 05, LANL
J/ψ production: suppression/enhancement?
J/ψ suppression scenario in QGP ! --- Debye screening
A. Andronic et. al. PLB 571,36(2003)
Statistical model: Large ccbar yield in one heavy ion collision recombination production J/ψ possible J/ψ enhancement
Statistical model
Total charm yield from pQCD calculations!
X.Dong, USTC/LBNL 8Feb. 2nd, 05, LANL
Charm quark flow
Charm quark flows -> Strong indication of thermalization of light quarks
V. Greco, C.M. Ko, R. Rapp, PLB 595(2004)202 Coalescence approach
X.Dong, USTC/LBNL 9Feb. 2nd, 05, LANL
Single electrons Open charm v2
X. Dong et. al, PLB597, 328(2004).
At pT > 2.5 GeV/c:
1) D-meson spectrum is ‘hard’, yields of pion will be small, measure D-decayed electron to infer the open charm v2
2) D-meson flow indication of light flavor thermal equilibrium.
X.Dong, USTC/LBNL 10Feb. 2nd, 05, LANL
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
CDF, PRL 91, 241804 (2003)
X.Dong, USTC/LBNL 11Feb. 2nd, 05, LANL
Measurements in heavy ion collisions
PHENIX Au+Au@130GeV Phys. Rev. Lett. 88, 192303 (2002)
Nbin scaling for open charm spectrum Total cross section consistent with NLO pQCD calculation
X.Dong, USTC/LBNL 12Feb. 2nd, 05, LANL
STAR detector
MagnetMagnet
CoilsCoils
Central Central TriggerTriggerBarrel Barrel (CTB)(CTB)
ZCalZCal
Time Time Projection Projection
ChamberChamber(TPC)(TPC)
Year 2000Year 2000
Barrel EM Cal Barrel EM Cal (BEMC)(BEMC)
Silicon Vertex Silicon Vertex Tracker (SVT)Tracker (SVT)Silicon Strip Silicon Strip Detector (SSD)Detector (SSD)
FTPCFTPCEndcap EM CalEndcap EM CalFPDFPD
TOFp, TOFrTOFp, TOFr
Year 2001+Year 2001+
X.Dong, USTC/LBNL 13Feb. 2nd, 05, LANL
D0 direct reconstruction
Event mixing technique
KD0 ( Br. 3.83%)
First Direct Open CharmReconstruction at RHIC
STAR PRL, in print
X.Dong, USTC/LBNL 14Feb. 2nd, 05, LANL
%)2.9(KD
%)8.3(%),68( 00* KDDD s
%)2.6)((00 KD
%)8.3(0 KD
D mesons measured at STAR
STAR Preliminary
X.Dong, USTC/LBNL 15Feb. 2nd, 05, LANL
Open charm spectrum
STAR Preliminary
1) D*/D0 ratio is consistent with other experiments and models2) Power-law describes the spectrum well up to ~11GeV/c
X.Dong, USTC/LBNL 16Feb. 2nd, 05, LANL
Hadron identification: STAR Collaboration, nucl-ex/0309012
Indirect measurement D→e+X
STAR PRL, in print
electrons
Electron identification: TOFr |1/ß-1| < 0.03 TPC dE/dx electrons!!!
X.Dong, USTC/LBNL 17Feb. 2nd, 05, LANL
Inclusive electrons
1. With TOF and dEdx, electrons can be identified well from ~0.3GeV/c up to ~3GeV/c!
2. Select electrons (e-) using dE/dx only (2-4GeV)
Hadron contamination was corrected for ~ 5-30% pT 2-4 GeV/c
STAR Preliminary
X.Dong, USTC/LBNL 18Feb. 2nd, 05, LANL
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
X.Dong, USTC/LBNL 19Feb. 2nd, 05, LANL
Background subtraction
a) Data: background spectrakinematical selection of the conversion and 0 Dalitz decay pairs in TPC
b) MC: conversion and 0 Dalitz decay reconstruction efficiency ~60%
c) MCMC: relative contributions of different sources: determined from PYTHIA/HIJING
+ detector simulations
conversion and 0 Dalitz decay reconstruction efficiency :~60% at pT>1.0 GeV/c
Invariant Mass Square
Rejected
Signal
STAR Preliminary
STAR Preliminary
X.Dong, USTC/LBNL 20Feb. 2nd, 05, LANL
Background contribution
An increasing excess found at higher pT region, pT > 1.0 GeV/c, → expected to be contribution of semileptonic decay from heavy flavor hadrons
STAR PRL, in print
X.Dong, USTC/LBNL 21Feb. 2nd, 05, LANL
Combining fit
1) Good agreement between D0 and electrons spectra2) d+Au and p+p do not show significant nuclear effect
STA
R P
RL,
in p
rint
Combined fit forD0 and electrons
PYTHIA: MSEL = 1, CTEQ5M1
X.Dong, USTC/LBNL 22Feb. 2nd, 05, LANL
Charm yields
Assumption for the combining fit: 1. D0 spectrum follows the power law function 2. only normalization scale between different D meson pT spectrum 3. All the background subtracted electrons are from D decay
p+p and d+Au electron spectra show approximately binary scaling
.)(3.0.)(3.03.1 sysstatRedAu 1<pT<4GeV/c
X.Dong, USTC/LBNL 23Feb. 2nd, 05, LANL
Charm production at mid-rapidity
Color Dipole: Phys. Rev. D67 (2003) 054008
R.Vogt, A. Tai, private communicationsHSD: Phys. Rev. C67 (2003) 054905
STAR Preliminary
X.Dong, USTC/LBNL 24Feb. 2nd, 05, LANL
Charm total cross-section
1) NLO pQCD calculations under predict the total charm production cross section at RHIC
2) Scales (muR or muF) may be energy dependent
Mid-rapidity → Full rapidity 4.7 ± 0.7
STAR PRL, in print
X.Dong, USTC/LBNL 25Feb. 2nd, 05, LANL
J/ψ production
PHENIX J/psi in AuAu, PRC 69 (2004) 014901
This upper limit invalidates the expectation from large open charm cross section!
1) Statistical model prediction implies possible J/psi enhancement
2) But with STAR ccbar cross section (from d+Au) , a much larger enhancement (~3-10) for J/psi production in central Au+Au collisions.
X.Dong, USTC/LBNL 26Feb. 2nd, 05, LANL
Directly reconstructed D mesons
D and electron spectra are consistent!
Electrons from D decay
Consistency check
STAR PreliminarySTAR Preliminary
X.Dong, USTC/LBNL 27Feb. 2nd, 05, LANL
Open charm spectrum is harder !
Phenix: PRL. 88, 92303(2002)
D. Kharzeev, hep-ph/0310358
D0, D*, D
A. Tai, A. Suaide, QM04STAR Preliminary
B decay dominated region
STAR Preliminary
X.Dong, USTC/LBNL 28Feb. 2nd, 05, LANL
Charm quark hadronization at RHIC
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 broadening and fragmentation
Tk
A. Tai QM04
STAR Preliminary
R. Vogt, hep-ph/0203151
1) Higher order processes needed2) Charm hadronization through fragmentation + recombination?
X.Dong, USTC/LBNL 29Feb. 2nd, 05, LANL
Non-photonic electron v2
STAR: 0-80% (F.Laue SQM04) PHENIX: Minimum bias statistical error only HSD: E. Bratkovskaya et al., hep-ph/0409071 X. Dong, S. Esumi, et al., Phys. Lett. B597, 328(2004).
corrected for e± from decay M. Kaneta et al, J.Phys. G30, S1217(04)
Systematic errors are important!
X.Dong, USTC/LBNL 30Feb. 2nd, 05, LANL
Conclusions
1) Both direct open charm reconstruction and indirect charm semi-leptonic decay electrons are measured at STAR in d+Au collisions. They provide consistent results.
2) Total charm cross section from this measurement is higher than NLO pQCD calculations.
3) Preliminary D meson spectrum appears to imply a unusual hard fragmentation function for charm quarks.
4) Study open charm v2 and J/ yields to address thermalization issues at RHIC. The run-IV data will just do that.
X.Dong, USTC/LBNL 31Feb. 2nd, 05, LANL
Upgrade at STAR
STAR MRPC - TOF STAR Heavy Flavor Tracker
1) Full open charm measurements2) Full resonance measurements with both hadron and
lepton decays
X.Dong, USTC/LBNL 36Feb. 2nd, 05, LANL