Yichun Xu (USTC/BNL) April 27-29, Hangzhou, CHINA 1

Measurements of identified meson and baryon production at high pT in p+p and Au+Au collisions at STARYichun Xu

University of Science and Technology of China

Brookhaven National Laboratory

Yichun Xu (USTC/BNL) April 27-29, Hangzhou, CHINA 2

Outline

Motivation In p+p, extend identified spectra study up to pT~15 GeV/c

Good constraints to pQCD calculation Baseline for study of nuclear modification factor in heavy ion collisions.

In Au+Au, study of nuclear modification factor previous results (/p), color charge effect recent prediction (K), jet conversion

Data analysis Identify charge , K, p and pbar by dE/dx using re-calibration method Reconstruct neutral kaon with one triggered daughter

Results Summary

Yichun Xu (USTC/BNL) April 27-29, Hangzhou, CHINA 3

Motivation 1—high pT spectra in p+pExtend the identified hadron spectra study to higher pT in p+p collisions.

Test the applicability of pQCD in p+p collisions.

Provide baseline for Nuclear Modification Factor (RAB) in heavy ion collisions.

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

In Au+Au, it have been extended to 12GeV/c. [2]

[1] Phys. Lett. B 637 (2006) 161

[2] Phys. Rev. Lett. 97 (2006) 152301

Yichun Xu (USTC/BNL) April 27-29, Hangzhou, CHINA 4

Motivation 2—energy loss

A popular theoretical explanation RAA suppression—Energy Loss when jet pass the medium, which is characterized by (squared momentum transfer per collision and the mean free path .

Color charge effect of parton energy loss in heavy ion collisions.

ddpdddpNd

NR

Tpp

TAB

binAB /

/12

2

QM08

arXiv: 0804.4760

STAR preliminary

Eg

Eq

~ 9/4In pQCD:

Suppression for proton >

hardparton

path length L

Quark

Quark

Yichun Xu (USTC/BNL) April 27-29, Hangzhou, CHINA 5

Motivation 3—Jet Conversion

Another predictions recently, Jet Conversion:

The flavor of jet can be converted through the interaction with the medium.

Jet Conversion in heavy ion collisions.

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

hardparton

path length L

Quark

gluon

Yichun Xu (USTC/BNL) April 27-29, Hangzhou, CHINA 6

±/K±/p(p) with dE/dx

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

arXiv:nucl-ex/0505026v2

Focus

)/)/log(( BdxdEn XX

STAR preliminary

arXiv:0807.4303v1

- +

Yichun Xu (USTC/BNL) April 27-29, Hangzhou, CHINA 7

K0S with triggered

An independent way to reconstruct K0

S with one daughter triggered by the BEMC through K0

S→ for cross-checking credibility of PID in triggered events.

Barrel Electro-Magnetic Calorimeter

K0S

Triggered by tower

STAR preliminary

STAR preliminary

Yichun Xu (USTC/BNL) April 27-29, Hangzhou, CHINA 8

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

Yichun Xu (USTC/BNL) April 27-29, Hangzhou, CHINA 9

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!

AKK 2008 [1] is constrained by BRAHMS pbar/p ratio [2] (y=2.95, pT<5 GeV/c).

Yichun Xu (USTC/BNL) April 27-29, Hangzhou, CHINA 10

Particles Ratios in p+p collisions

Experimental data:(Consistent with published data)1. +: decrease with pT

2. p/p: decrease with pT indicates a significant quark jet contribution to baryon.

3. 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

Yichun Xu (USTC/BNL) April 27-29, Hangzhou, CHINA 11

Ratios in p+p and A+A

QM08STAR preliminarySTAR preliminary

p/ (Au+Au)>p/ (p+p & d+Au)p/p (Au+Au)>p/p (p+p & d+Au)

STAR preliminaryK/ (Au+Au) > K/ (p+p)

PRL 97, 152301 (2006)

Yichun Xu (USTC/BNL) April 27-29, Hangzhou, CHINA 12

RAA for , K and pRAA(proton)>RAA(pion) at 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.

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.

RAA() ~ RAA() at high pT

See more RAA Vs Npart in Anthony ’s talk in 6C session.pT (GeV/c)

STAR preliminary

Yichun Xu (USTC/BNL) April 27-29, Hangzhou, CHINA 13

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

Yichun Xu (USTC/BNL) April 27-29, Hangzhou, CHINA 14

Summary

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

m decrease of pbar/p with pT .

Color charge effect can’t explain suppression for pion and proton from RAA measurements.

RAA(K) ~ 0.4 shows consistence with the prediction of Jet Conversion in the medium created in Au+Au collisions.

Yichun Xu (USTC/BNL) April 27-29, Hangzhou, CHINA 15

Thanks!

Yichun Xu (USTC/BNL) April 27-29, Hangzhou, CHINA 16

Experiment and Data set

Time Projection Chamber (TPC) Electro-Magnetic Calorimeter (EMC) Shower Maximum Detector (SMD)

Data set:EMC Triggers in run5 pp @ 200GeV Jet Patch trigger: ETtot>7.8 GeV High Tower trigger: ETot>2.5 GeV ETot>3.6 GeV Central trigger in run4 AuAu@200GeV

Yichun Xu (USTC/BNL) April 27-29, Hangzhou, CHINA 17

dE/dx re-calibrationEMC cut: 0.3<p/E<1.5, n>=2, n>=2, |zdist|<2, |dist|<0.01

2)(

xC

BAxf

arXiv:0807.4303v1

STAR preliminary 4.0<pT<4.5GeV/c

w/ EMC cut

STAR preliminary