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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One of the major RHIC discovery – jet quenching

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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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RAA for identified particles

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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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Experimental data on jet suppression, RAA

constrains model parameters

PQM – Arnold, Moore, Yaffe

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Very different models with different

parameters CAN explain RAA !

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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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Results with different detectors are

consistent within few %Resolution

good

worse

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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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pQCD models doing well with RAA but can’t

explain large v2

radiative AdS/CF

T

to=1.5-2

fm/c

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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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Correlations at high pT

p0 – hadron

g – hadron

Correlations vs. reaction plane

e – hadron

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At low pT of secondary particle there is definite response from the medium

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0.5

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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?