Back-to-back azimuthal correlations in mathrm {Z} +jet events at high transverse momentum in the TMD parton branching method at next-to-leading order

Abstract

Azimuthal correlations in mathrm {Z} +jet production at large transverse momenta are computed by matching Parton-Branching (PB) TMD parton distributions and showers with NLO calculations via MCatNLO. The predictions are compared with those for dijet production in the same kinematic range. The azimuthal correlations Delta phi between the Z boson and the leading jet are steeper compared to those in dijet production at transverse momenta mathcal{O}(100) GeV , while they become similar for very high transverse momenta {{mathcal {O}}}(1000) GeV . The different patterns of mathrm {Z} +jet and dijet azimuthal correlations can be used to search for potential factorization-breaking effects in the back-to-back region, which depend on the different color and spin structure of the final states and their interferences with the initial states. In order to investigate these effects experimentally, we propose to measure the ratio of the distributions in Delta phi for mathrm {Z} +jet- and multijet production at low and at high transverse momenta, and compare the results to predictions obtained assuming factorization. We examine the role of theoretical uncertainties by performing variations of the factorization scale, renormalization scale and matching scale. In particular, we present a comparative study of matching scale uncertainties in the cases of PB-TMD and collinear parton showers.