[Hybrid RBRC seminar] Exploring color fluctuations in p-A and gamma-A collisions with forward neutrons at RHIC and LHC

by Mark Strikman (Penn State University)

Thursday 22 Aug 2024, 12:30 → 13:30 US/Eastern

Small Seminar Room ( https://bnl.zoomgov.com/j/16098036710?pwd=RUtaMWgzd1NWWkVPOVlmb0NadTk5QT09)

After reviewing the color fluctuation model of hadron-nucleus interactions we consider the example of pA collisions with production of dijets in the proton fragmentation region as a function of transverse energy in rapidity  range not affected by the jet fragmentation. A gross disagreement with the expectations of Glauber type models  of dijet production was reported by the LHC and RHIC experiments for $x_F > 0.3$. We demonstrate that the observed pattern can be explained quantitatively based on the expectation that the transverse spread of the proton light-cone wave function with a large-x parton shrinks with increasing x. No alternative explanation has survived since the first data were published a decade ago.

Next we consider the effects of color fluctuations in the photon in photon-nucleus collisions. We predict the distribution of the cross section over the strength of interaction and over the number of wounded nucleons   in the perturbative and nonperturbative domains and find a smooth matching between the two regimes. 

We introduce a new tool for the analysis of ultraperipheral photon-nucleus collisions (UPC) and pA  collisions sensitive to small-x dynamics: measurement of the multiplicity of forward neutrons produced in the de-excitation of the nucleus, which is correlated with the number of wounded nucleons. Several examples of the method are given: testing the dynamics of nuclear shadowing down to $x \sim 10^{-5}$, the effects of the black-disk limit in the photon fragmentation region, the enhancement of multiparton interaction signals.