High-p T identified particle spectra in p+p collisions at 200 GeV

High-pT identified particle spectra in p+p collisions at 200 GeV

Yichun Xu (for the STAR collaboration) Outline:

Motivation

Analysis

Preliminary results

Future work & Summary

Yichun Xu(USTC/BNL) 8/17/2008, Hot Quark, Colorado 2

MotivationExtend the identified hadron spectra study to higher pT range and test the applicability of pQCD in p+p collisions.

Baseline for study of color charge effect of parton energy loss in heavy ion collisions.Proton spectra in STAR is limited to 7GeV/c with current statistics from minimum bias p+p collisions.[1]

In Au+Au, it can be extended to 12GeV/c now. [2]

[1] Phys. Lett. B 637 (2006) 161 [2] Phys. Rev. Lett. 97 (2006) 152301


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

TPC Cuts:

pT>0.2 GeV/c, || < 0.5, Azimuthal

angle |∆φ|>π/2

∆φ

∆φ trigger


dE/dx re-calibration, why?

)/)/log(( BdxdEn XX

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

STAR preliminary

STAR preliminary 4.0<pT<4.5GeV/c

w/ EMC cut


Raw Yield

Peak positions of charged particles are fixed by parameters from re-calibration.

STAR preliminary

= 0.87

STAR preliminary


Results (1)—pion spectra

PYTHIA (V6.205, MSEL=1) and GEANT are used to get trigger enhancement to correct spectra in triggered events.

STAR preliminarySTAR preliminary


Results (2)—proton spectra

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

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

STAR preliminary

Simon, private communication

Our data will provide the best constraint on Fragmentation Functi

on!


Results(3)--Comparison with NLO

DSS, KKP and AKK2008 predict pionspectra very well, but PYTHIA under-predict pion production.

Only DSS can describe proton production.

STAR preliminary STAR preliminary


Results(4)--Ratios

PYTHIA describe all ratios very well, DSS over-predicts anti-proton, and AKK2008 over-predicts proton and under-predicts anti-proton.


Results(5)—compare with d+A, A+A

-/+ : isospin conservation

Pbar/p: are similar in three systems.

p(+-)/at intermediate pT: are consistent with coalescence prediction.

p (+-)/ at high pT: indicate more quark jet contribution to proton in p+p than in A+A.


Future work: EMC as hadron trigger detector

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

L(0.64 pb-1)*(30mb) * effTrg(3%)/effTrk(90%) ~ 0.6B events.

STAR preliminary

A factor of 100 enhancementSTAR preliminary

EMC module


Reconstruct KS with triggered pion

It can reach 10 GeV/c while it only arrive 5 GeV/c in minimum bias events .

Constrain K/ ratio and check hadron yields.

Good method to reconstruct resonance at high pT.

STAR preliminary

KS->


Summary

Extend pion and proton spectra to pT ~15 GeV/c.

-/+, pbar/p & p(pbar)/+(-) ratios are consistent with results from minimum-bias events within error.

DSS, KKP and AKK2008 describe pion yields very well, but only DSS predictions are consistent with proton production.

-/+ and pbar/p ratios are consistent with PYTHIA, which under-predicts the individual yields of + and -.

Decrease of pbar/p ratio indicates a significant quark jet contribution to baryon.


Thanks!


Backup


V0 (KS&) -- p&dE/dx

STAR preliminarySTAR preliminary

Ms(0.485,0.505)

M(1.112,1.118)

STAR preliminary


Re-calibration

STAR preliminary

2)(

xC

BAxf

Fit

function:No obvious color charge effect of parton energy loss in heavy ion collision.


NLO differences

KKP: e+e- data, no charge difference AKK: derived from KKP, including p,n,KS, etc. AKK2008: including STAR data, and constrained b

y including BRAHMS pbar/p ratio. DSS: e+e- data, including STAR data points.

EMC & SMD cuts: 0.3<p/E<1.5,n>=2,n>=2, |zdist|<2, |dist|<0.01


STAR preliminary

STAR preliminary

Documents

High-p T identified particle spectra in p+p collisions at 200 GeV