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

TL;DR

This paper investigates azimuthal correlations in Z+jet events at high transverse momentum using the TMD parton branching method at NLO, comparing with dijet production to explore potential factorization-breaking effects.

Contribution

It introduces a method to compute azimuthal correlations in Z+jet production at NLO with TMD parton distributions and compares these with dijet correlations to identify factorization-breaking signatures.

Findings

Z+jet azimuthal correlations are steeper than dijet at ~100 GeV

Correlations become similar at ~1000 GeV transverse momentum

Proposed ratio measurement to detect factorization-breaking effects

Abstract

Azimuthal correlations in 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 ${\cal O}(100)$ GeV, while they become similar for very high transverse momenta ${\cal O}(1000)$ GeV. The different patterns of Z+jet and dijet azimuthal correlations can be used to search for potential {\it 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 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.