Experimental Confirmation of Experimental Confirmation of the Formation of Dense, Hot the Formation of Dense, Hot Matter in Nuclear Collisions Matter in Nuclear Collisions

@ RHIC@ RHICProf. Brian A. Cole

Columbia University

On Sabbatical leave at KFKI, RMKI

Supported by a Fulbright grant from the US State Dept. and the Hungarian-American Commission for Educational Exchange, a NATO

Fellowship, and theHungarian National Science Fund

                       

The Relativistic Heavy Ion The Relativistic Heavy Ion Collider Collider

STAR

                       

Experiment @ RHICExperiment @ RHIC

                       

Energy

Theory

Energy

PHENIX Proton-Proton Particle PHENIX Proton-Proton Particle SpectraSpectra

We have a good theoretical understanding of high energy, large-angle scattering.

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Observed

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Au-Au Particle Spectra From Au-Au Particle Spectra From PHENIXPHENIX

Theories without energy loss

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Energy

Theories with energy loss

* — includes only trivial increase in number of particles due to the “size” of the nuclei

We observe only 20% of the expected particles.

Consistent with theories including energy loss.

                       

PHENIX: Au-Au Final Results from PHENIX: Au-Au Final Results from 20022002

The suppression of high energy particles goes away when we create less matter.

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Energy

Submitted to Phys. Rev. Letters

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Energy

d-Au 2 independent measurements

Au-Au

PHENIX d-Au Measurement PHENIX d-Au Measurement

Control measurement shows no suppression If anything we see a modest excess

Understood theoretically (was predicted!)

Suppression of high energy particles in Au-Au is apparently caused by the created matter.

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STAR Experiment: “Jet” STAR Experiment: “Jet” Observations Observations

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Angle between high energy particles0º 180º

proton-proton jet event

In Au-Au collisions we see only one “jet” at a time !

How can this happen ? Possibly due to energy loss

Analyze by measuring angles between pairs of particles.

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STAR: Jets in d-AuSTAR: Jets in d-Au

Disappearance of jet pairs in Au-Au collisions is apparently caused by the created matter.

Angle between high energy particles

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Experimental SummaryExperimental Summary We have shown two striking experimental observations: Consistent observations have been

obtained by all 4 experiments at RHIC (where applicable)

In both Au-Au and deuteron-gold collisions currently can only be explained as resulting

from the “quenching” of high energy particles in the hot dense medium created in Au-Au collisions.

deuteron-gold control measurements were essential to rule out alternative explanations for the observations.

Triumph of the scientific method !

My profound thanks to

Hungarian Fulbright Commission,

Dr. Bruckner and his staff

RMKI, Dept. of Theoretical Physics,

and NATO

for their outstanding support on behalf of myself

and my family.