Transcript Identified particle prod at high transverse

Identified Particle
Production at High
Transverse Momentum
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at RHIC
Vlad Pantuev, Stony Brook University
Moriond QCD 2005
Motivation – Based on the Questions:
•What kind of medium produced at RHIC?
•How do we measure properties of this medium?
•What is the origin of baryon-meson anomaly:
Is it medium effect?
Modification of fragmentation function?
Somehow, just mass effect?
Will try to answer some questions by measuring
identified particle production at high pt:
Other hadrons. Wider momentum range.
In p+p collisions, establishes the elementary hadronic
reference. From RCP to RAuAu .
In d+Au collisions, establishes the size of initial state
nuclear matter effects. Detailed study of the Cronin effect
for mesons and baryons.
Moriond QCD, 2005
In Au+Au collisions at lower energies, 62.4 GeV,
absence or presence of the baryon anomaly ?
What is the magnitude at lower energies ?
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Some history of the problem, jet quenching
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Strong suppression of p0
yields above pT ~ 2 GeV/c at
200 GeV central Au+Au
collisions at RHIC, but no
suppression for proton and
antiproton at intermediate pT
~ (2-5 GeV/c): “Baryon
anomaly at RHIC”
Moriond QCD, 2005
“Anomalous”
proton to pion ratios at 200 GeV
central Au+Au collisions at RHIC.
PHENIX: PRL 91, 172301 (2003), PRC 69, 034909 (2004)
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Au+Au collisions at sNN = 200 GeV
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Other hadrons:
In nuclear modification factor all baryons
follow the same tendency
Mesons are suppressed regardless of its
mass
PS. Please remember, R_AA and Rcp
have different definition but close to each
other
PHENIX, AuAu @ 200 GeV
GLV RAA
dNg/dy = 1100
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“Controlled” d+Au collisions
Old data: 38.8 GeV p+W vs. p+Be
Cronin effect
No suppression as in central AuAu.
Larger Cronin effect for baryons, but
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Can’t explain factor 4-5 difference in AuAu
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Au+Au, lower energy, 62.4 GeV
charged
0-10%
p0
charged
Still significant pion suppression, but less.
Proton/pion >1, this explains Raa for charged.
10-30%
p0
What about other observable, FLOW, at 62.4?
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Elliptic flow at 62 GeV vs 200 GeV Au+Au
dN
 1  2v2 ( pT ) cos[ 2(  R )]
d
Preliminary
STAR
Upper curves: v2 {2-particle}
Lower curves: v2 {4-particle}
Solid points: 62 GeV
Open points: 200 GeV
Charged hadrons.
v2(pT) for 62 GeV is close to 200 GeV
Moriond QCD, 2005
In many aspects 62.4 GeV and
200 GeV data look similar 7
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Description of baryon production at high pt is tough task for theorists.
Yet crude, but very interesting idea is used in quark recombination model.
One of the demonstrations how simple
quark counting works is explanation of the
elliptic flow for mesons and baryons by
quark coalescence model, D.Molnar and
S.Voloshin:
V2_meson(pt) = 2 V2_q(pt/2)
V2_baryon(pt) = 3 V2_q(pt/3)
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So, recombination model:
• Two competing processes for
hadron production:
• ede
• Jet-Fragmentation in the
vacuum
• Recombination of 3 quarks or a
quark/anti-quark pair in a
densely populated phase space
• Fries et al.
• In case of thermalized partons
at RHIC, fragmentation wins
over recombination only above
pT = 5 GeV/c
• This explains p/p ratio
Fries, et al, nucl-th/0301087
• Cronin effect could also be
explained by recombination of
Thermal and Shower partons in
the final state.
Also, Greco, Ko, Levai, nucl-th/0301093
Also, R.C. Hwa and C.B.Yang, Phys.Rev.Lett. 93 (2004) 082302
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Predictive power of the model is at
moderate to high pt through the TS
and TT term for mesons.
Proton term will have:
TTT+TTS+TSS+SSS
The result that recombination model can
nicely describe Au+Au AND d+Au is
puzzling for me personally. – I can imagine
“quark bath” in AuAu, but how the same is
true for cold dAu collisions, especially for
“quark thermal part” ?
What about difference in Baryon- and
Meson-triggered jets?
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STAR vs PHENIX  correlations in Au+Au. 2particle correlation with identified hadron
PHENIX nucl-ex/0408007
|η|<0.7
|η|<0.35
STAR preliminary
meson – π, K
baryon – p, p
Difference in STAR/PHENIX yields due to various |η| windows.
Meson and Baryon “jets” are very similar!
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Conclusions
•In central Au+Au collisions in the intermediate pt region, baryons are not
suppressed, unlike mesons.
•The nature of the difference is probably in the number of constituent quarks, not
mass.
•At high pt > 5 GeV/c, there is also visible baryon suppression.
•In d+Au at midrapidity we see enhancement, even larger for baryons. Cronin effect.
•At 62.4 GeV Au+Au collisions there is suppressions of pions and ratio proton/pion>1.
Evidence of smooth sqrt(s) energy dependense.
•Proton enhancement and elliptic flow exibits a pattern suggestive of the relevance of
constituent quark degree of freedom. But is it proof of de-confinement?
•Intermediate pt region baryons possess jet-like characteristics.
Baryon/meson ratio in central Au+Au is still a puzzle!
There are many other observations that particle and
jet production is modified in Dense Medium created in
central heavy ion collisions at RHIC. Strong_QGP ?
Moriond QCD, 2005
Much more coming soon from the last very high
statistics Au+Au run and just finished Cu+Cu run
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STAR Preliminary, particle spectra in
jets
Near
PHENIX, preliminary, h-h azimuthal correlations
in Au+Au, background subtracted
Away
Very soon it will be possible to draw
identified hadrons in plots like that…
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