1. Prof. Brian A. Cole Columbia University
Experimental Confirmation of the Formation of Dense, Hot Matter in Nuclear RHIC
Prof. 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 the
Hungarian National Science Fund

2. The Relativistic Heavy Ion Collider
STAR

4. RHIC

5. PHENIX Proton-Proton Particle Spectra
Energy
Theory
Energy q
Number of Particles @ 90º
We have a good theoretical understanding of high energy, large-angle scattering.

6. Au-Au Particle Spectra From PHENIX
Expected*
Observed
Number of Particles @ 90º
Energy
* — includes only trivial increase in number of particles due to the “size” of the nuclei
Theories without energy loss
Ratio of Observed/Expected*
Energy
Theories with energy loss
We observe only 20% of the expected particles.
Consistent with theories including energy loss.

7. PHENIX: Au-Au Final Results from 2002
Submitted to Phys. Rev. Letters
Ratio of Observed to Expected* q
Energy
The suppression of high energy particles goes away when we create less matter.

8. PHENIX d-Au Measurement
Energy
d-Au 2 independent measurements
Au-Au
Ratio of Observed to Expected*
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.

9. STAR Experiment: “Jet” Observations
proton-proton jet event
Analyze by measuring angles between pairs of particles.
Number of pairs
Angle between high energy particles 0º
180º
In Au-Au collisions we see only one “jet” at a time !
How can this happen ?
Possibly due to energy loss q

10. Angle between high energy particles
STAR: Jets in d-Au
Angle between high energy particles
Number of pairs 0º
180º q
Disappearance of jet pairs in Au-Au collisions is apparently caused by the created matter.

11. Experimental 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 !

12. 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.