High pT particle production, hard
scattering and correlations from
the PHENIX Experiment
Vladislav Pantuev, INR Moscow
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Outline
Jet quenching. Current status
Inclusive yields. Reaction plane
dependence
Correlations. Two-particle, vs. reaction
plane
Conclusions
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Why hard scattering? Jet “tomography”
Capability to calculate in pQCD for p+p
Cross sections are small – should follow NN-collisions scaling
Process at very early stage of the collision. Can illuminate the whole AA collision in time
Direct photons can easy penetrate through color matter
Fragmentation functions could be parameterized
There is a believe that energy loss of colored parton in color medium could be calculated (?)
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Some questions remains from
RHIC to LHC
What are the energy loss mechanisms? Can we discriminate between them and quantify relevant parameters?
How does energy loss depend on quark mass?
How can we study the energy loss dependence on path length, pT, jet energy?
Is the medium modified by the probes?
How to extract properties of the colored medium from hard scattering observables?
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RAA energy scan, Cu+Cu
Transition happens at beam energy somewhere between 22
and 62 GeV.
LHC is well above – more clear signals. New features?
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Old question: Is Raa rising with pT ?
h extends pT range
Phys. Rev. C 82, 011902 (2010)
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RAA. Jet quenching. Current status
Current understanding of jet quenching faces several challenges
pQCD vs. AdS/CFT
Energy loss mechanisms ?
Large discrepancies among pQCD models for jet quenching
parameter:
GLV : 2.8 GeV2/fm
ASW: 10.0 GeV2/fm
HT : 2.3 GeV2/fm
AMY: 4.1 GeV2/fm
Need observables with more discriminating power
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Reaction plane – another “knob”
PHENIX has wide range of capabilities to
determine reaction plane
Beam-Beam counters, BBC
Zero degree calorimeters, ZDC
Reaction plane detectors, 3 rings, RXN
Muon Piston Calorimeters, MPC
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BBC
MPC
PbW04
2cm Pb converter
in front
RXN
(zero degree n calorimeter
ZDC/SMD /shower max detector)
(reaction plane detector)(muon piston
EM-calorimeter)
(beam-beam quartz-
Cherenkov detector)0 5-5 h
dN/dh
CNT
(PHENIX central tracking arm)
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So, “difficult” (to explain) result –
large anisotropy at high p T:
•v2 is non-zero at high pT
•v2 is flat above 6 GeV/cPhys. Rev. Lett. 105, 142301 (2010)
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RAA(Df):In many models, e-loss scales as:
radiative AdS/CFT
JJ and R. Wei, PRC82,024902,2010
Better scaling with m=2, Accidental? AdS/CFT is static, our
system is rapidly changing. Be aware!
Different colors and
sets correspond to
different centrality
and angles, PRC80
to=1.5-2
fm/c
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My non-PHENIX slide In previous slides with reference J.Jia and R.Wei PRC82,
024902(2010), where they use ~L3, there is an additional
parameter t0=1.5-2 fm/cIn 2005 (arXiv:hep-ph/0506095, JETP Lett.85,104 ) I use
formation time 2.3 fm/c in peripheral zone
of the collision and describe RAA AND v2
My the only statement is that the
energy loss mechanism is still not
fully understood
Formation time dependence vs. distance from the center
for Au+Au 5% central collisions. Depends on distance
between hard scattering vertexes
At LHC RAA and v2 about two times smaller,
“Last call for predictions”
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Again, My personal “back on the envelop” slide:
Transforming Atlas/CMS parameter “Aj” to
RHIC “style”: GeV and IAA
0
0.002
0.004
0.006
0.008
0.01
0.012
0.014
0.016
0.018
0 20 40 60 80 100 120 140 160
Away jet, GeV
dN
/dE
, G
ev
^-1
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
0 50 100 150
Away Jet, GeV
Iaa
E_T1>100 GeV
I use <E_T1>=150 GeV
http://arxiv.org/PS_cache/arxiv/pdf/1011/1011.6182v2.pdf
PS. Errors ~10% are not shown
pp
PbPb
ratio
0.5!
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g – hadron correlations.
Very hard to measure!
Phys. Rev. C 80, 024908 (2009)
The first PHENIX attempt:
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With better statistics, Run7:
No surprise that g – hadron IAA = RAA for hadrons,
But g-h have advantage – energy is roughly known,
see Aneta talk
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p0 – h correlations. Away
side vs. reaction plane,
yet another “knob”
arXiv:1010.1521
Better control of geometry
and thickness of the reaction
zone
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Mid-central 20-60% centrality
Near – side trigger jet fragments
are consistent with no energy
loss and no dependence on
orientation wrt. reaction plane.
Surface bias, fluctuations?
Away – side jet demonstrates
significantly larger suppression
for out-of-plane trigger particle,
where energy loss is bigger for
the larger system size
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Most central collisions
Near and away – side jet have
no dependence on the
orientation of trigger particle.
Interaction zone is almost
symmetric.
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Ratio out-of-plane to in-plane
In mid-central collisions, where in-plane and out-of-
plane system sizes are very different we see factor
4-5 larger suppression for out-of-plane
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Heavy flavor e-hadron correlation.
Near side Away side
Recoil jet from heavy (c, b) quark demonstrates the
same suppression as a light quark/hadron trigger
PHENIX already demonstrate that c- and b- quarks suppression is almost the same as for light quarks
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Summary At RHIC formation of new type of matter was discovered
PHENIX, as well as other RHIC experiments developed set of “tools” to investigate properties of the new matter
LHC opens new, more precise, more sensitive capabilities and methods: full jet reconstruction, direct photons…
Some fundamental questions should be posted and solved at LHC
We still well far away from the answer to the question on
the origin of color confinement (but this was one of our “banner”
20 years ago ). Any hope from parton fragmentation?