Hadronic cross-section fluctuations

The physics of color transparency and color opacity is usefully incorporated into the dynamics of relativistic nuclear collisions through the concept of hadronic cross-section fluctuations. We show how such fluctuations can be consistently related to inelastic shadowing and diffractive dissociation. For the nucleon-nucleon system we find a rather large dispersion of the cross section around its mean value; for the $\pi$-nucleon system, experiment shows even larger fluctuations, as predicted in constituent quark models, due to the smaller number of degrees of freedom. We show how the third moment of the distribution is probed in proton-deuteron diffractive dissociation. We estimate the form of the cross-section distribution from available information; data up to $p_{\mathrm{lab}}=300\mathrm{}$ GeV indicate that the width of the distribution grows logarithmically with energy. The triple-Pomeron limit indicates that the fluctuations could grow by a factor of 2 from energies reached at CERN to energies reached at the BNL Relativistic Heavy Ion Collider, but more data are needed for a firmer prediction.