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# Recent Results from RHIC & Some Lessons for Cosmic-Ray Physicists

Spencer R. Klein

Submitted on 28 November 2006

## Abstract

The Relativistic Heavy Ion Collider (RHIC) studies nuclear matter under a variety of conditions. Cold nuclear matter is probed with deuteron-gold collisions, while hot nuclear matter(possibly a quark-gluon plasma (QGP)) is created in heavy-ion collisions. The distribution of spin in polarized nucleons is measured with polarized proton collisions, and photoproduction is studied using the photons that accompany heavy nuclei. The deuteron-gold data shows less forward particle production than would be expected from a superposition of $pp$ collisions, as expected due to saturation/shadowing. Particle production in $AA$ collisions is well described by a model of an expanding fireball in thermal equilibrium. Strong hydrodynamic flow and jet quenching shows that the the produced matter interacts very strongly. These phenomena are consistent with new non-perturbative interactions near the transition temperature to the QGP. This writeup will discuss these results, and their implications for cosmic-ray physicists.

## Preprint

Comment: 8 pgs; invited talk presented at the XIVth International Symposium on Very High Energy Cosmic Ray Interactions (ISVHECRI 2006)

Subjects: Nuclear Experiment; Astrophysics