Measurements of neutral and charged kaon production at high pT up to 15 GeV/c at STARYichun Xu

(for the STAR collaboration)University of Science and Technology of China

Brookhaven National Laboratory

----as a probe for Jet Conversion at RHIC

Yichun Xu (USTC/BNL) March 30th-April 4th, QM09, Knoxville, TN 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) March 30th-April 4th, QM09, Knoxville, TN 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) March 30th-April 4th, QM09, Knoxville, TN 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

NRT

ppT

AB

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) March 30th-April 4th, QM09, Knoxville, TN 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) March 30th-April 4th, QM09, Knoxville, TN 6

K± 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) March 30th-April 4th, QM09, Knoxville, TN 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) March 30th-April 4th, QM09, Knoxville, TN 8

Kaon in p+p

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) March 30th-April 4th, QM09, Knoxville, TN 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) March 30th-April 4th, QM09, Knoxville, TN 10

Particles Ratios in p+p collisionsExperimental 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) March 30th-April 4th, QM09, Knoxville, TN 11

Ratios in p+p, d+Au and A+A

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

QM08STAR preliminary

STAR preliminary

Yichun Xu (USTC/BNL) March 30th-April 4th, QM09, Knoxville, TN 12

K/ ratio in p+p and A+A

STAR preliminary

pT (GeV/c)

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

Yichun Xu (USTC/BNL) March 30th-April 4th, QM09, Knoxville, TN 13

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) March 30th-April 4th, QM09, Knoxville, TN 14

with triggered pbar

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/cSTAR preliminary

Yichun Xu (USTC/BNL) March 30th-April 4th, QM09, Knoxville, TN 15

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.

Thanks !

Yichun Xu (USTC/BNL) March 30th-April 4th, QM09, Knoxville, TN 16

2)(xC

BAxf

arXiv:0807.4303v1