[JLab-seminars] Joint Physics -Theory Division Seminar: Mark Strikman; Exploring color fluctuations in p-A and gamma-A collisions with forward neutrons at LHC

[Stephanie Tysor]

Joint Physics -Theory Division Seminar
Mark Strikman
 Jefferson Lab
Exploring color fluctuations in p-A and gamma-A collisions with forward neutrons at LHC
Abstract:
After reviewing the color fluctuation model of hadron-nucleus interactions we consider the example of proton-nucleus collisions with production of dijets in the proton fragmentation region x_F >= 0.3. A strong dependence of the dijet rate on the centrality was reported by the LHC experiments, well beyond the thickness effect. 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 in the ten years since the first data were published.

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 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) 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 ~ 10^{-5}, the effects of the black-disk limit in the photon fragmentation region, the enhancement of multiparton interaction signals.

In the final part of the talk we argue that it would be interesting if JLab experiments could measure the production of soft neutrons in reactions such as eA -> e’pX and eA -> e'hX. Such measurements would sharpen models of neutron evaporation and improve the precision of the centrality determination in the collider experiments with the zero-degree calorimeter. They would also provide unique tools for the investigation of low energy final-state interactions in nuclear breakup processes.

Monday, August 5, 2024
1:00 pm
Auditorium
https://jlab-org.zoomgov.com/j/1603110571?pwd=PcmJpBpIpwMmbFxIgwZiHB31gW0vNs.1

Stephanie Tysor
Division Administrator
Physics Division
Jefferson Lab
757-269-6005


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