Transcript Document

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 Technology
University of Science and Technology of China
2010/04/18
Yichun Xu@HEP8th-Nanchang
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Outline
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Motivation
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In p+p, extend identified hadron spectra study up to pT~15 GeV/c
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In Au+Au, study of nuclear modification factor (RAA)
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Color charge effect, Jet conversion, Jet hadrochemistry
Data analysis
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Good constraints to pQCD calculation.
Baseline for study of nuclear modification factor in HIC.
Identify charged p, K, p and pbar by dE/dx
Reconstruct K0S with one triggered daughter
Results & Summary
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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
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[2] Phys. Rev. Lett. 97 (2006) 152301
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Energy loss and QCD
d 2 N AB / dpT d h
d 2  pp / dpT d h
1
= N
bin
RAB
path length L
hard
parton
Quark
Quark
Color charge effect of parton energy loss
E g
In pQCD:
E q
~ 9/4
STAR: PRL97,152301(2006)
RAA(p)<RAA(p)
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Jet Conversion
path length L
gluon
hard Quark
parton
q(qbar) + g  g + q(qbar)
W. Liu, R.J. Fries, Phys. Rev. C77 (2008) 054902
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q + qbar  g + g
W. Liu, C.M. Ko, B.W. Zhang, Phys. Rev. C 75, 051901 (2007).
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Jet hadrochemistry
S.Sapeta and U.A. Wiedemann, arXiv:0707.3494
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Enhanced parton splitting in medium calculation for LHC.
Mechanism may lead to higher p/p and K/p ratios in A+A jets.
2010/04/18
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p±/K±/p(p) with dE/dx
STAR preliminary
-
+
pT>3GeV
n p =
X
log(( dE / dx) X / Bp )
p
Where Bπ is the expected mean dE/dx of p from
Bichsel function of ionization energy loss in TPC.
Nucl. Instr. & Meth. A 558 (2006) 419
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Nucl. Instru. & Meth. A 614 (2010) 28–33
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K0S with triggered p
Triggered by tower
p
K0S→p++p-(trg)
K0S
STAR preliminary
STAR preliminary
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Kaon in p+p collisions
STAR preliminary
STAR preliminary
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
2010/04/18
AKK: S. Albino, B. A. Kniehl, and G. Kramer, arXiv: 0803.2768v2
DSS: Daniel de Florian, Werner Vogelsang, and Federico Wagner,
arXiv: 0708.3060v3
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Constraint for pQCD calculation
Simon, private
communication
Our data will provide a better constraint on Fragmentation Function!
[1] arXiv:0803.2768 , [2] Phys. Rev. Lett. 98, 252001 (2007)
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Particles Ratios in p+p collisions
Experimental data:
(Consistent with published data)
1. p-/p+, p/p: decrease with
pT indicates a significant
quark jet contribution not
only to meson but also to
baryon.
2. p/p and p/p: p/p+ ~0.2,
and p/p-~0.1
Compare to models:
1. PYTHIA(v6.205) describe
ratios reasonably.
2. DSS over-predicts antiprotons relative to pions
and protons.
STAR preliminary
PLB 637 (2006) 161
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RAA for p, K and p
1. 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(p) ~ RAA(r0) at high pT
STAR preliminary
Light quark mesons have no mass effect
pT (GeV/c)
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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?
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Summary
Thanks for your attention!
p+p collisions:
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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:
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No mass effect from RAA(p) ~ RAA(r)
Color charge effect cannot explain RAA(p) > RAA(p).
RAA(K)~0.4 in central Au+Au collisions is consistent with the
prediction of Jet Conversion in the medium.
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L with triggered p
7<pT<8 GeV/c
STAR preliminary
L 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.
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Experiment and Data set
Data set:
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Time Projection Chamber (TPC)
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Electro-Magnetic Calorimeter (EMC)
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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
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Triggered p and enhancement factor
STAR preliminary
A factor of 100 enhancement
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.
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