Measurement of jet modification at rhic
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Measurement of Jet Modification at RHIC. Fuqiang Wang Purdue University. – THE PLAN – Physics motivation Results on high p T inclusive yield Results on high p T angular correlation Results on high p T + low p T angular correlation Summary and open question.

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Measurement of Jet Modification at RHIC

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Measurement of jet modification at rhic

Measurement of Jet Modification at RHIC

Fuqiang Wang

Purdue University

– THE PLAN –

Physics motivation

Results on high pT inclusive yield

Results on high pT angular correlation

Results on high pT + low pT angular correlation

Summary and open question

thanks tothe Collaboration


Physics motivation

Lattice QCD prediction at mB = 0:

T

Quark-GluonPlasma

F. Karsch, Nucl. Phys. A698, 199c (2002).

~200

MeV

r/r0

5-10

TC ~ 170 15 MeV

eC ~ 0.5 GeV/fm3

Physics motivation

QuantumChromodynamicspredicts phase transition between hadrons and Quark-Gluon Plasma (a state of thermalized partons) at high energy density.

Fuqiang Wang – Moriond QCD 2004


Physics motivation cont d

Physics motivation – cont’d

What medium are we creating in heavy ion collisions: QGP or hadron gas?

Want to probe the density of the medium.

self-generated, penetrating probe: large pT hadrons, jets

  • they are generated early (by initial hard-scatterings);

  • they need some time to escape from the collision zone – the size of nuclei;

  • during this time frame, a QGP (or whatever medium) is expected to form;

  • they interact with the medium, giving us information about the medium.

Fuqiang Wang – Moriond QCD 2004


Inclusive high p t yield suppressed

Large pT hadrons are mainly from jets produced by initial hard-scattering.

Small cross-sections, scale with number of binary collisions.

If no nuclear effect, AA = binary-scaled pp; AA binary-scaled pp  nuclear effect.

Inclusive high pT yield – suppressed

Fuqiang Wang – Moriond QCD 2004


Jet like angular correlation disappeared

Jet-like angular correlation – disappeared

Peripheral Au + Au

near-side well-described

peripheral collision:

similar to p+p

away side hadrons are suppressed!

Central Au + Au

central collision:

strong absorption in medium

Fuqiang Wang – Moriond QCD 2004


D au control experiment

Phys. Rev. Lett. 91, No. 7, August 15, 2003

d+Au control experiment

Yes, there is nuclear effect. Energy loss  suppression of high pT hadron yield.

But, were jets initially there?

Maybe the initial hard scatterings in AA were different from pp: e.g. modified PDF’s.

Fuqiang Wang – Moriond QCD 2004


Reconstructing those jets

High pT:

High pT particle

STAR Preliminary: Quark M 2004

High pT particle

p+p

Jet-like structures

Au+Au

p+p

(1/Ntrig) dN/d(Df)

Low pT:

Signal

Au+Au top 5%

1/Ntrigger dN/d(Df)

background

Df

D f (radians)

Reconstructing those jets…

Fuqiang Wang – Moriond QCD 2004


Jet charge multiplicity and energy

p+p

Jet charge multiplicity and “energy”

STAR Preliminary: QM 2004

With the same final leading particle,

we are selecting a larger energy jet

in central AA than in pp.

Estimate of energy loss scale.

Fuqiang Wang – Moriond QCD 2004


Associated particles p t distributions

Near side:

Overall

enhancement

from pp to AA

larger initial

parton energy

(and modest

energy loss)

Away side:

energy from the

initial parton has

been converted to

lower pT particles

energy loss in

medium!

syst. error

Away

Associated particles pT distributions

STAR Preliminary: Quark Matter 2004

Near

softening in spectra: equilibration with medium

Fuqiang Wang – Moriond QCD 2004


Summary

syst. error

away side

energy from theinitial parton hasbeen converted tolower pT particlesby final stateinteractions

dense mediumin AuAu collisions

approachingthermalization

1/Ntrigger dN/d(Df)

pT (GeV/c)

D f (radians)

Summary

Large pT hadrons are suppressed in AuAu relative to pp.

Large pT angular correlation disappeared at away side.

Low pT angular correlation is there and stronger than pp.

Fuqiang Wang – Moriond QCD 2004


Conclusion open question

Conclusion / Open question

  • Have we created a new form of matter?

Definitely!

It’s dense, strongly interacting, dissipative.

  • Is it a QGP (i.e. a state of deconfined, thermalized quarks and gluons)?

Fuqiang Wang – Moriond QCD 2004


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