Probing parton saturation with forward Z⁰-boson production at small transverse momentum in p+p and p+A collisions

We calculate and compare the differential cross sections for forward Z⁰-boson production at small transverse momentum, in proton-proton and proton-nucleus collisions, using both the collinear and dilute-dense factorization frameworks. In both cases, we implement a Sudakov resummation of the large logarithms generated by soft-gluon emissions, which is essential in order to describe the transverse momentum distribution of forward Z⁰ bosons measured at the Tevatron and the LHC. We further compute the nuclear modification factor in the dilute-dense framework, hoping to single out signals of saturation effects at small values of x. Our predictions are compared with those obtained in the collinear factorization framework, using two different nuclear parton distribution functions.