2010/04/18 Yichun Xu@HEP8th-Nanchang 1

Measurements of identified hadron production at high pT in p+p and Au+Au collisions at RHIC-STAR许依春 (Yichun Xu)Center for Particle Physics and Technolo

gyUniversity of Science and Technology of

China

2010/04/18 Yichun Xu@HEP8th-Nanchang 2

Outline Motivation

In p+p, extend identified hadron spectra study up to pT~15 GeV/c 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 and pbar by dE/dx Reconstruct K0

S with one triggered daughter

Results & Summary

2010/04/18 Yichun Xu@HEP8th-Nanchang 3

Extend Charged hadron spectra in p+p

Proton spectra was limited to 7GeV/c with current statistics from minbias p+p @ STAR.[1]

In Au+Au, it has been extended to 12GeV/c. [2][1] Phys. Lett. B 637 (2006) 161 [2] Phys. Rev. Lett. 97 (2006) 152301

2010/04/18 Yichun Xu@HEP8th-Nanchang 4

Energy loss and QCD

Color charge effect of parton energy loss

ddpdddpNd

NR

Tpp

TAB

binAB /

/12

2

Eg

Eq

~ 9/4In pQCD:

hardparton

path length L

Quark

Quark

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

2010/04/18 Yichun Xu@HEP8th-Nanchang 5

Jet Conversion

hardparton

path length L

Quark

gluon

W. Liu, R.J. Fries, Phys. Rev. C77 (2008) 054902

q + qbar g + g

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

W. Liu, C.M. Ko, B.W. Zhang, Phys. Rev. C 75, 051901 (2007).

2010/04/18 Yichun Xu@HEP8th-Nanchang 6

Jet hadrochemistry

Enhanced parton splitting in medium calculation for LHC. Mechanism may lead to higher p/ and K/ ratios in A+A jets.

S.Sapeta and U.A. Wiedemann, arXiv:0707.3494

2010/04/18 Yichun Xu@HEP8th-Nanchang 7

±/K±/p(p) with dE/dx

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

2010/04/18 Yichun Xu@HEP8th-Nanchang 8

K0S with triggered

K0S→(trg)

Barrel Electro-Magnetic Calorimeter

K0S

Triggered by tower

STAR preliminary

STAR preliminary

2010/04/18 Yichun Xu@HEP8th-Nanchang 9

Kaon in p+p collisions

Charged and neutral kaons are extended up to 15 GeV/c in p+p collisions.

Charged and neutral kaons are consistent.

Phys. Rev. C 75 (2007) 64901

STAR preliminary STAR preliminary

AKK: S. Albino, B. A. Kniehl, and G. Kramer, arXiv: 0803.2768v2DSS: Daniel de Florian, Werner Vogelsang, and Federico Wagner, arXiv: 0708.3060v3

2010/04/18 Yichun Xu@HEP8th-Nanchang 10

Constraint for pQCD calculation

[1] arXiv:0803.2768 , [2] Phys. Rev. Lett. 98, 252001 (2007)

Simon, private communication

Our data will provide a better constraint on Fragmentation Function!

2010/04/18 Yichun Xu@HEP8th-Nanchang 11

Particles Ratios in p+p collisions

Experimental data:(Consistent with published data)1. +, p/p: decrease with p

T indicates a significant quark jet contribution not only to meson but also to baryon.

2. p/ and p/: p/~0.2, and p/~0.1

Compare to models:1. PYTHIA(v6.205) describe

ratios reasonably.2. DSS over-predicts anti-pr

otons relative to pions and protons.

PLB 637 (2006) 161

STAR preliminary

2010/04/18 Yichun Xu@HEP8th-Nanchang 12

RAA for , K and p1. RAA(proton)>RAA(pion)@ high pT

Which is in contrast to the prediction of color charge dependence of Energy Loss.

How the gluon jet/quark jet interact with the medium created in Au+Au collisions?

2. RAA(K) ~ 0.4 at high pT > 5.0 GeV/c

Consistent with the prediction of jet conversion by interaction with the medium in Au+Au.

3. RAA() ~ RAA() at high pT

Light quark mesons have no mass effect

pT (GeV/c)

STAR preliminary

2010/04/18 Yichun Xu@HEP8th-Nanchang 13

RAA vs Npart

Integral RAA at pT>5.5 GeV/c, <pT

>~6.2 GeV/c

RAA for kaon and pion are suppressed more in central collisions.

RAA for kaon > RAA for pion, even in peripheral collisions.

=> Does jet chemistry change in small system?

2010/04/18 Yichun Xu@HEP8th-Nanchang 14

Summary

p+p collisions: Extend identified hadron spectra up to 15 GeV/c in p+p. Provide constraints for Fragmentation Function. Indicates a significant quark jet contribution to baryon from

decrease of pbar/p with pT .

Au+Au collisions: No mass effect from RAA() ~ RAA()

Color charge effect cannot explain RAA(p) > RAA().

RAA(K)~0.4 in central Au+Au collisions is consistent with the prediction of Jet Conversion in the medium.

Thanks for your attention!

2010/04/18 Yichun Xu@HEP8th-Nanchang 15

2010/04/18 Yichun Xu@HEP8th-Nanchang 16

with triggered p

can be extended up to 10 GeV/c in p+p collisions with the triggered data sample, which will provide additional probe for the jet conversion.

_

7<pT<8 GeV/c

STAR preliminary

2010/04/18 Yichun Xu@HEP8th-Nanchang 17

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 GeV High Tower trigger: ET>2.5 GeV ET>3.6 GeV Central trigger in run4 AuAu@200GeV

2010/04/18 Yichun Xu@HEP8th-Nanchang 18

Triggered and enhancement factor

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 minibias evts.

A factor of 100 enhancement