Investigating the Cronin
Hampshire College; Thomas Hemmick, Ralf Averbeck, Axel Drees, Felix Matathias,
Department of Physics and Astronomy, Stony Brook University.
Cronin Effect occurs when a deuteron collides with a large nucleus (such as Au
at RHIC). The transverse momentum
(PT) spectra of the particles that are produced in the most central
collisions are different than the spectra produced in the most peripheral ones.
There are more particles with higher PT and less at low PT.
In addition, the degree to which this difference is observed seems to be
correlated with the mass of the particles that are produced.
In deuteron-gold collisions,
the most peripheral events (60 – 90 % centrality) are generally thought of as
simple nucleon-nucleon interactions while the most central events (0 – 20 %
centrality) are thought to consist of a cascade of deflecting collisions within
the nucleus. A typical “cartoon”
of the collision process envisions the deuteron getting knocked around many
times as it bounces it’s way through the nucleus, colliding at different
angles with the Au nucleons along the way.
The goal of this project
was to determine if this widely accepted “cartoon” explanation of the Cronin
Effect is able to account for the particle species dependence of this
phenomenon. We modeled the high
centrality collisions identically to the peripheral ones except for one major
difference: we treated the high centrality interactions as taking place at an
angle rather than head-on. Applying
the necessary relativistic transformations we were able to treat these as
identical interactions taking place in different frames.
We found that when using
identical primordial spectra for all species, our intuition is indeed confirmed;
the purely naïve Cronin cartoon produces a species dependent effect similar to
that found in the data. However, we
additionally found that the strength of the effect is highly sensitive to the
primordial spectrum. Several more
realistic initial state distributions were tried, all of which exhibited reduced
species dependence of the Cronin enhancement and did not adequately describe the
data. We thus conclude that this
“cartoon” description of the Cronin Effect is not able to solely account for
the particle species dependence.
Work was supported by a grant from the National Science Foundation (Phy –