Course Outline for Physics 880.05

II. D. Nucleus-Nucleus Collisions (Chs. 12,13) Part 4

We'll start by finishing our discussion started last time of the experimental evidence for nuclear stopping (see part 3 notes). Then we'll discuss the space-time picture of a heavy-ion collision and Bjorken's estimate of the initial energy density for the formation of a quark-gluon plasma.

Revisit: Total Inelastic Cross Section

Last time we defined a total inelastic cross section, \sigma^{A}_in, for the collisions of a nucleon with an A-nucleon target nucleus. We found that it was related to \sigma_in, the total inelastic nucleon-nucleon cross section by:
\sigma{A}_in = A * \sigma_in / <n'>
where <n'> is the average number of nucleon-nucleon collisions, given that there is at least one. (So <n'> is at least equal to one.) We can understand this result intuitively:

Set-up for High-Energy Heavy-Ion Collision

Space-Time Scenario

Estimate of Initial Energy Density at \tau=\tau_0

Plugging in Numbers

First we need a reasonable estimate for \tau_0. We don't have to be super precise, but we'd like an estimate for \epsilon_0 better than a factor of two, if possible.

From experiment we can get some estimates of dN/dy.

Estimate of dN/dy from Glauber model:

Put it together:

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Copyright © 1997,1998 Richard Furnstahl and James Steele.