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
Motivation
In p+p, extend identified hadron spectra study up to pT~15 GeV/c
In Au+Au, study of nuclear modification factor (RAA)
Color charge effect, Jet conversion, Jet hadrochemistry
Data analysis
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
Enhanced parton splitting in medium calculation for LHC.
Mechanism may lead to higher p/p and K/p ratios in A+A jets.
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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
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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:
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:
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:
Time Projection Chamber (TPC)
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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