Transcript Document

Medium effect on jet correlations in
Au+Au and Cu+Cu collisions at
sqrt(sNN) = 200GeV at RHIC-PHENIX
Hua Pei
Iowa State University
For the collaboration of PHENIX
7/18/2015
Hua Pei, Iowa State University on SQM2007 for PHENIX
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Outline
• Physics Scheme
– How parton-jet has been changed by the hot medium
created at RHIC?
– How this medium will make its own response to this
jet?
• In the Order of Slides
– Detector
– Analysis Method
– Histograms of Jet Shape and Yield, comparing AA to
p+p
7/18/2015
Hua Pei, Iowa State University on SQM2007 for PHENIX
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What are we looking at?
p+p
AA(AuAu or
CuCu)
leading
particle
(trigger)
vs.
hadrons
c
a
d
leading particle
suppressed
c
b
a
hadrons
Parton Distribution Functions
Hard-scattering cross-section
Fragmentation Function
d
b
hadrons
• Initial yields and pT distributions can be predicted from
p+p measurements + pQCD + collision geometry + cold
(initial) nuclear effects
– Critical to perform measurements in reference p+p
and p(d)+A systems
• In AA collision, observed deviations from reference
measurements can be attributed to the medium,
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Hua Pei, Iowa State University on SQM2007 for PHENIX
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What experiment do we use?
EMCAL --- measure energy deposit of electrons and
gammas
DC --- obtain momentum of charged particles
PC --- measure hit
position of charged
particles
• Tracking and
Matching (DC, PC)
• charged hadrons
EMCAL (PbSc + PbGl)


,
0
h+
h-
Ks

0


0

,0,Ks
PID -- TOF and EMCal
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Hua Pei, Iowa State University on SQM2007 for PHENIX
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What do we know from single
particle measurement?
See more details on
Monday’s talk from
Arkadij Taranenko
• Strong suppression (RAA ~ 0.2) is seen even at high pT
• Constant for pT>4GeV/c for all centralities
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Hua Pei, Iowa State University on SQM2007 for PHENIX
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Why we are not satisfied yet?
• Remember at the beginning we asked two
questions:
– How parton-jet has been changed by the hot
medium created at RHIC?
– How this medium will make its own response
to this jet?
• Single spectrum is the convolution of
these two effects. How do we identify them
from each other?
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Hua Pei, Iowa State University on SQM2007 for PHENIX
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What’s the “New” Tool?
p+p, PHENIX
PRD, 74 072202 (06).
Df
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What does the jet look like now?
vs.
Observation of particles produced
~1 radian away from back-to-back!
• Correlation survives high-multiplicity environment of A+A
• But in more than one way …
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Hua Pei, Iowa State University on SQM2007 for PHENIX
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How are jets modified then?
PHENIX nucl-ex/0611019
• We see in AA collisions the far-side peak not at Df =  as
they used to be at p+p. Need to quantify this change
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Hua Pei, Iowa State University on SQM2007 for PHENIX
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How shall we quantify this modified jet?
PHENIX nucl-ex/0611019
Fit away-side peak with double Gaussian, each centered at
Df =  ± D
• D scales with collision energy and system size!
• Emission consistent with strong medium response to
energy deposited by the traversing medium
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Hua Pei, Iowa State University on SQM2007 for PHENIX
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How do we quantify the change of
medium itself, then?
Au+Au / p+p s = 200 GeV
arXiv:0705.3238 [nucl-ex]
 Establish the punch-through jet
component (“Head Region”)
 and the medium-induced
component (“Shoulder Region”)
HR+SR (|Df-|<=/2) and HR (|Df|<=/6).
Per-trigger yield vs. Df
In next slide we show various trigger and partner (pAT  pBT),
arranged by increasing pair momentum (pAT + pBT)
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Hua Pei, Iowa State University on SQM2007 for PHENIX
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How is the medium changed itself?
Au+Au & p+p s = 200 GeV
• Evolves from flat 
concave  convex
• Do the side peaks
merge to form the
reappearance of “header”
peak? Or do the
header/side peaks
represent two different
physics mechanisms?
arXiv:0705.3238 [nucl-ex]
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Hua Pei, Iowa State University on SQM2007 for PHENIX
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How do we quantify this side-peak?
Analogous to RAA, but
describes jet yield
modification
• HR exhibits
early onset of
suppression,
relative to p+p
• H+S (entire
away side)
exhibits overall
enhancement
arXiv:0705.3238 [nucl-ex]
HR is suppressed due to jet quenching,
SR is enhanced, reflecting the response of medium to
deposited energy.
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What PHENIX see further:
Truncated mean-pT for 1<pTB< 5, vs. Npart
Near side: flat with Npart (>100), increase
with pTA.
Far side: shows a very different
centrality and pTA dependence of the
<pT> between HR and SR.
• HR smooth decrease with Npart up to
200, behaviors consistently with jet
quenching
• SR however, shows an universal
partner spectra shape, reflecting the
property of response of medium to lost
energy.
arXiv:0705.3238 [nucl-ex]
7/18/2015
Hua Pei, Iowa State University on SQM2007 for PHENIX
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How PID helps our jet analysis (1) ?
Trigger high-pT 0
Near side
We also observe jets broader in Near-side
Cu+Cu than p+p, showing the medium effects at
near-side as well.
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Hua Pei, Iowa State University on SQM2007 for PHENIX
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How associated PID helps our jet
analysis?
PHENIX Preliminary
Associated Charged
Baryon/Meson
Away side
Jet-pair distributions for associated mesons (squares) and baryons
(circles) for 1 < pTassoc < 1.3 GeV/c (top) and 1.6 < pTassoc < 2.0 (bottom).
Results are for a hadron trigger (2.5 < pT < 4.0 GeV/c) and centrality
selections of 0-20% and 20-40%.
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How associated PID helps our jet
analysis (con) ?
Associated Charged
Baryon/Meson
Near/Away side
There is a clear increase in the slope (for mesons, Fig. 3b) going from
peripheral to central, showing that medium affects particle ratio on
both near and away sides. The slope *parameter* aka 'temperature‘
also shows similar trend as inclusive p/ ratio going from central to
peripheral.
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How PID can do more on jet analysis?
 trigger jets
PHENIX Preliminary
Normal dijet (o-h):
Trigger bias: Ep < Ejet,
Possible surface bias
Direct  tagged jet:
No fragmentation: E ~ Ejet
No strong interaction, sensitive
Proposed in hep-ph/9605213
~10 years ago
 
0


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to the whole medium
But!
Trigger  is a mixture of direct
and hadron-decay photon. Need
hot dense medium
more effort to subtract decay
part.
Hua Pei, Iowa State University on SQM2007
for PHENIX
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Summary and Conclusion
• PHENIX physics program has steady progressed beyond
“discovery” stage, addressing next level of questions
mapping out properties of the plasma :
– How are jets affected by passage through the medium created
in RHIC collisions?
– How does the medium respond to the impact of a high-pT
probe?
• Answers include:
– splitting D universal with different systems => interaction of jet
and medium
– head-region decreases => suppression of jet
– shoulder region increases with lower pt, => consistence with
medium response
– jets modified near and far side, including baryon-rich at central
collision
• What shown here only scratch the surface of the methods
for studying the
medium
in PHENIX!
7/18/2015
Hua Pei,
Iowa State University
on SQM2007 for PHENIX
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Backup Slides
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What We had Expected
QCD “Phase Diagram”
F. Karsch, Prog. Theor. Phys. Suppl. 153, 106 (2004)
• Seeking the Quark Gluon Plasma (QGP)
– Existed early in the universe
– Expected to be created in RHIC collisions
• Lattice QCD predicts a transition to the QGP
– T ~ 170 MeV
– e ~ 1.0 GeV/fm3
• For QGP, strong interaction plays critical role
– Deconfinement of quarks and gluons
– Need properties
and
dynamics
of this
strongly
interacting system
7/18/2015
Hua Pei,
Iowa
State University
on SQM2007
for PHENIX
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What particle do we use?
• RHIC Run4 Au+Au data
• Sampled 241 mb-1
• 1972 x 241 mb-1 ~ 1 pb-1 p+p
equivalent
• 1.5 B events recorded
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RHIC Run5 Cu+Cu data
• Sampled 3 nb-1
• 632 x 3 nb-1 ~ 1 pb-1 p+p equivalent
• 2.2 B events sampled
– 59 M minimum bias events
– 1.9 M high-pT triggered
Hua Pei, Iowa State University on SQM2007 for PHENIX
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What particle do we use?
And we have a good spectrum
of identified particles at
PHENIX
(Phys. Rev. C 69, 034909 (2004)
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Hua Pei, Iowa State University on SQM2007 for PHENIX
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Where this CF tool has led us?
• Azimuthal correlation
functions show
~ complete absence of
“away-side” jet
– pT,trig: 4-6 or 3-4
– pT,assoc: 2 - pT,trig
Pedestal&flow subtracted
 Further evidence for surface emission only (?)
• That is, “partner” in hard scatter is absorbed in the dense
medium
• Question: where has the energy gone?
– (Partial) Answer: need to widen “search” in pT
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PHENIX nucl-ex/0611019
The measured correlation C(Df) (squares) and the (di)jet correlation
J(Df) (circles with boxes for point-to-point systematic errors) in
central Au+Au collisions at sqrt(NN) = 200 GeV/c.
The full line shows the background term and the dotted line shows a
C(Df) fit with Jet + Flow background.
The left axis shows the measured correlation amplitude and the
right axis shows the (di)jet correlation amplitude.
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Hua Pei, Iowa State University on SQM2007 for PHENIX
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arXiv:0705.3238 [nucl-ex]
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What’s your knowledge about “Ridge”
effect at RHIC?
relative ridge yield := ridge yield / Jet(D)
Au+Au 0-10%
STAR preliminary
3<pt,trigger<4 GeV
pt,assoc. > 2 GeV
dN /dpt  pt e- p t /T
“jet”
slope
ridge
slope
inclusiv
e slope
7/18/2015
STAR
preliminary
As STAR observed, the “ridge” is
much softer than “jet” in high-pT
trigger region (5-10GeV).
Do PHENIX also see that?
Hua Pei, Iowa State University on SQM2007 for PHENIX
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Centrality dependence of near-side yield
Jet + Ridge
Ridge
Jet
• steep increase of near-side yield with centrality in Au+Au
• ratio of yields in central Au+Au/d+Au ~ 4-5
-> “ridge” yield increases with centrality
ridge of K0S < ridge of Λ
-> “jet” yield is independent of centrality and agrees with d+Au
(effects of merged tracks under study)
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pTtrigger dependence of jet and ridge yields
Jet + Ridge
Ridge
Jet
• near-side associated yield is ridge dominated at intermediate pT
• jet yield:
- increases steeply with pTtrigger
- smaller for Λ-triggers than for K0S-triggers ?
- baryon jet is wider than meson jet
- effects of merged tracks under study
• jet/ridge ratio increases with pTtrigger
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Hua Pei, Iowa State University on SQM2007 for PHENIX
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pT-distribution of associated particles
J. Putschke (STAR), QM’06
“jet” slope
ridge slope
inclusive
slope
STAR preliminary
h-h correlations
pTassociated>2GeV/c
• Ridge spectra similar
Trigger particle
T(ridge) MeV
T (jet) MeV
h+/-
438 ± 4 (stat.)
478 ± 8
K0S
406 ± 20 (stat.)
530 ± 61
Λ
416 ± 11 (stat.)
445 ± 49
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to particles from the bulk
• Jet spectra are harder
(T increases steeply with pTtrig)
Hua Pei, Iowa State University on SQM2007 for PHENIX
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What PHENIX see:
Truncated mean-pT for 1<pTB< 5, vs. Npart
Intermediate pT: shows a very different
centrality and pTA dependence of the <pT>
between HR and SR.
• HR behavior consistent with jet quenching
• SR however, shows an universal partner
spectra shape, reflecting the property of
response of medium to lost energy.
• Nearside: flat with Npart
(>100), increase with pTA.
• S region: flat with Npart (>100)
and pTA.
• H region: smooth decrease
with Npart up to 200.
arXiv:0705.3238 [nucl-ex]
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PID dependent Jet-correlation
PHENIX Preliminary
Jet-pair distributions for associated mesons (red) and baryons (blue) for
1.3 < pTassoc < 1.6 GeV/c and hadron trigger (2.5 < pT < 4.0 GeV/c) and
centrality selections of 20-40% (top) and 70-90% (bottom).
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√s=200 GeV, p+p => x
NLO QCD agrees well with data
D. d’Enterria
nucl-ex/0611012
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Hua Pei, Iowa State University on SQM2007 for PHENIX
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