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Measurements of identified meson and baryon production at high p T in p+p and Au+Au collisions at STAR. Yichun Xu University of Science and Technology of China Brookhaven National Laboratory. Outline. Motivation In p+p, extend identified spectra study up to p T ~15 GeV/c - PowerPoint PPT Presentation
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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