Study of corrections for anomalous coupling limits due to the possible background BSM contributions

TL;DR

This paper investigates how background beyond the Standard Model contributions affect limits on anomalous couplings, providing corrected limits that are more accurate and often tighter than classical estimates.

Contribution

It introduces a method to incorporate background BSM contributions into the limits on Wilson coefficients, improving the accuracy of anomalous coupling constraints.

Findings

Corrected limits are up to 9.1% tighter for individual processes.

Combined corrected limits are up to 3.0% tighter.

Two-dimensional limits show up to 17.2% improvement.

Abstract

The search of the anomalous couplings is one of the possible ways to find any deviation from the Standard Model. The effective field theory is used to parameterize the anomalous couplings in the Lagrangian with the operators of higher dimensions, constructed from the SM fields. In the classical way, the limits on the Wilson coefficients of these operators are set based on beyond the Standard Model contributions induced for signal process, whereas the ones induced for background processes are assumed to be negligible. This article provides a study of the corrections to the limits on Wilson coefficients by accounting beyond the Standard Model contributions induced for background processes. The studies of $Z(\nu\bar{\nu})\gamma jj$ and $W(\ell\nu)\gamma jj$ productions in $pp$ collisions with $\sqrt{s}=13$ TeV and conditions of the ATLAS experiment at the LHC are used as example. Cases of collected during Run II and expected from Run III integrated luminosities of 139 fb$^{-1}$ and 300 fb$^{-1}$ are considered. The expected 95% CL limits on coefficients $f_\text{T0}/\Lambda^4$, $f_\text{T5}/\Lambda^4$, $f_\text{M0}/\Lambda^4$ and $f_\text{M2}/\Lambda^4$ are obtained both in classical way and in the way, where the corrections from background anomalous contributions are applied. Corrected one-dimensional limits from $Z(\nu\bar{\nu})\gamma jj$ and $W(\ell\nu)\gamma jj$ productions are up to 9.1% and 4.4% (depending on operator) tighter than the classical ones respectively. Corrected combined limits are up to 3.0% (depending on operator) tighter than the classical ones. Corrections to two-dimensional limits are also obtained, corrected contours are more stringent, than the classical ones, and the maximal improvement is of 17.2%.