Yichun Xu, 2011/07/18 QCD phase transition and RHIC 1

Investigating jet chemistry at RHIC through identified hadron compositions from p+p to Au+AuYichun Xu (许依春 ) for the STAR Collaboration Center for Particle Physics and Technology

University of Science and Technology of China

Yichun Xu, 2011/07/18 QCD phase transition and RHIC 2

Outline Motivation

In p+p, extend identified hadron spectra up to higher pT. Good constraints to pQCD calculation. Baseline for study of nuclear modification factor in HIC.

In Au+Au, study of nuclear modification factor (RAA) Color charge effect, Jet conversion, Jet hadrochemistry

Data analysis Identify charged , K, p(p) by ionization energy loss (dE/dx) Reconstruct 0

S with one triggered pion

Results & Summary

Yichun Xu, 2011/07/18 QCD phase transition and RHIC 3

Good constraints to pQCD calculation

Ng(i)/ (Ng(i) + Nq(i)); i = , K, p…

Large gluon contribution (~ 90%) to produced baryons @ high pT;Substantial quark contribution (~ 40%) to produced mesons @ high pT.J. Adams et al. Phys. Lett. B 637:161-169, 2006; Z. Xu (for STAR) arXiv:0806.0200AKK: S.Albino, B. A. Kniehl, G. Kramer, NPB 725 (2005) 181;KKP: Bernd A. Kniehl, G. Kramer, and B. Potter, Nucl. Phys. B597:337-369, 2001;EPOS: K.Werner, F. Liu and T. Pierog, hep-ph/0506232;

Yichun Xu, 2011/07/18 QCD phase transition and RHIC 4

Baseline for study of RAA in HIC

Color charge effect of parton energy loss

ddpdddpNd

NRT

ppT

AB

binAB /

/12

2

Eg

Eq~ 9/4In pQCD:

hardparton

path length L

Quark

Quark

RAA(p)<RAA()STAR: PRL97,152301(2006)

Yichun Xu, 2011/07/18 QCD phase transition and RHIC 5

Jet Conversion & Enhanced parton splitting

W. Liu, R.J. Fries, Phys. Rev. C77 (2008) 054902 W. Liu, C.M. Ko, B.W. Zhang, Phys. Rev. C 75, 051901 (2007)

S.Sapeta and U.A. Wiedemann, Eur.Phys.J.C55:293-302,2008

Jet parton scatters on medium parton and changes flavor.

q + qbar g + g

q(qbar) + g g + q(qbar)

Enhanced parton splitting in medium

Enhance p/ and K/ ratios in A+A jets for LHC energy.

<1

Yichun Xu, 2011/07/18 QCD phase transition and RHIC 6

Experiment and Data set

Time Projection Chamber (TPC) Electro-Magnetic Calorimeter (EMC)

Data set:EMC Triggers in run5 pp @ 200GeV Jet Patch trigger: ETtot > 6.4 GeVHigh Tower trigger: ET > 2.5 GeV ET > 3.6 GeV

0.05rad()x0.05()

Near-side

Away-side

Yichun Xu, 2011/07/18 QCD phase transition and RHIC 7

±/K±/p(pbar) with dE/dx (away-side)

Where Bπ is the expected mean dE/dx of from Bichsel function of ionization energy loss in TPC.

pT>3GeV

)/)/log(( BdxdEn XX

STAR preliminary

- +

Nucl. Instru. & Meth. A 614 (2010) 28–33Nucl. Instr. & Meth. A 558 (2006) 419

Yichun Xu, 2011/07/18 QCD phase transition and RHIC 8

Triggered K0S at high pT (near-side)K0

S→(trigger)

Barrel Electro-Magnetic Calorimeter

K0S

Triggered by tower

STAR preliminary

Given pT=5 GeV/c, ~5.6M HT1 triggered events are equivalent to

L(0.64 pb-1)*(30mb)*effTrg(3%)/effTrk(90%) ~600M minimum bias events.

A factor of 100 enhancement

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Comparison of K0S signal

STAR preliminary

RunII 10.26M minimum bias eventsRunV 5.6M EMC trigger events

From Mark Heinz thesis

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Constraint for pQCD calculation (I)

[1] S.Albino, B. A. Kniehl, G. Kramer, Nucl.Phys.B803:42-104,2008 [2] Daniel de Florian, Rodolfo Sassot and Marco Stratmann, arXiv: 0707.1506 [hep-ph]; Phys.Rev.D76:074033,2007. DSS Fragmentation Functions –provided by W. Vogelsang

First extend particle spectra up to 15 GeV/c in p+p collisions.pQCD NLO calculations are consistent with charged pion spectraOur data can provide a better constraint on Fragmentation Function

STAR preliminary

Yichun Xu, 2011/07/18 QCD phase transition and RHIC 11

Constraint for pQCD calculation (II)

J. Adams et al. Phys. Lett. B 637:161-169, 2006

Compare to published data:(Consistent with published data)1. +, pbar/p,K-/K+

decrease with increasing pT indicates relatively higher valence quark contribution to +, K+, p than to -, K-, pbar.

2. p/ ~0.2, pbar/~0.13. K±/±~ K0

S/± no trigger biasCompare to models:1. Both can describe +, b

ut deviate other ratios2. DSS over-predicts pbar, K-

relative to p, K+ and 3. AKK over-predicts proton

under-predicts pbar.

STAR preliminary

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RAA for , K±+p(pbar), K0S and 0

1. RAA()~RAA(K0S)~ RAA(0) despite the

differences in quark flavor composition and mass at high pT .

2. RAA(K++p)~ RAA(K-+pbar) despite the different contributions from gluon and quark jets and the effect of the Casimir factor on jet energy loss

3. Jet conversion’s RAA(K0S) > measure

kaon spectra in p+p w/ FF in model Original RAA(K0

S) w/o jet conversion was assumed to be equal to RAA().

4. Enhanced parton splitting RAA(0)~R

AA()5. Require Quantitative modeling and c

alculations incorporating 3D hydrodynamics in an expanding medium and the proper FFs.W. Liu, R.J. Fries, Phys. Rev. C77 (2008) 054902; W. Liu, C.M. Ko, B.W. Zhang, Phys. Rev. C 75, 051901 (2007)

STAR preliminary

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Summaryp+p collisions: Extend identified hadron spectra up to 15 GeV/c in p+p. Anti-particle/particle indicates relatively higher valence quark contribut

ion to +, K+, p than to -, K-, pbar. Provide constraints for Fragmentation Function.

Au+Au collisions: Color charge effect can not explain RAA(K++p)~ RAA(K-+pbar) and RAA

()~RAA(K0S)~ RAA(0)

The prediction of RAA(K0S) with Jet Conversion in central Au+Au collisio

ns is higher than our measurements. Enhanced parton splitting can not explain RAA(0)~RAA(). Require Quantitative modeling and calculations incorporating 3D hydrody

namics in an expanding medium and the proper FFs.

Thanks for your attention!