Speaker
Description
Multiple approaches attempt to describe hard and semi-hard scattering processes in p+A-style collisions. One approach is based on leading-twist pQCD in a collinear factorization picture, where all initial and final state effects on hard processes are included within a set of nuclear parton density functions (nPDFs) universal in x and Q^2. Other approaches are based on a dynamical description of the initial state of the cold nucleus, such as from coherent multiple scattering or within a glasma calculation framework. A key topic in heavy-ion and future EIC physics is the search for the onset of gluon saturation effects, which should give rise to a variety of effects besides just the simple (x,Q^2)-dependent shadowing encoded in the nPDFs. For example, measurements of forward di-hadron or di-jet correlations are widely accepted in the community to be sensitive to the onset of non-linear QCD dynamics. However, I argue that a straightforward application of the nPDF modifications in modern nPDF sets to recent measurements by ATLAS at the LHC and STAR at RHIC can partially or fully describe the signals observed in these data in a quantitative way, purely via a (x,Q^2)-dependent reweighting of cross-sections and without including any additional dynamics. This example highlights an important question in the GHP community as to what extent these paradigms are overlapping and what range of phenomena each should be expected to describe.
