$Z\gamma$ production at NNLO including anomalous couplings

TL;DR

This paper presents a precise NNLO QCD calculation for Zγ production processes, including anomalous couplings, with high numerical accuracy, and assesses its impact on experimental limits and background estimations.

Contribution

The authors implement NNLO QCD corrections for Zγ production including anomalous couplings in MCFM, using the jettiness slicing method, and analyze the effects on phenomenology and limits.

Findings

NNLO cross sections computed with ~0.1% numerical uncertainty.

NNLO corrections have a small but significant impact on coupling limits.

Method shows broad agreement with previous SM calculations.

Abstract

In this paper we present a next-to-next-to-leading order (NNLO) QCD calculation of the processes $pp\rightarrow l^+l^-\gamma$ and $pp\rightarrow \nu\bar\nu\gamma$ that we have implemented in MCFM. Our calculation includes QCD corrections at NNLO both for the Standard Model (SM) and additionally in the presence of $Z\gamma\gamma$ and $ZZ\gamma$ anomalous couplings. We compare our implementation, obtained using the jettiness slicing approach, with a previous SM calculation and find broad agreement. Focusing on the sensitivity of our results to the slicing parameter, we show that using our setup we are able to compute NNLO cross sections with numerical uncertainties of about $0.1\%$, which is small compared to residual scale uncertainties of a few percent. We study potential improvements using two different jettiness definitions and the inclusion of power corrections. At $\sqrt{s}=13$ TeV we present phenomenological results and consider $Z\gamma$ as a background to $H\to Z\gamma$ production. We find that, with typical cuts, the inclusion of NNLO corrections represents a small effect and loosens the extraction of limits on anomalous couplings by about $10\%$.