NLO Leptoquark Production and Decay: The Narrow-Width Approximation and Beyond

TL;DR

This paper performs next-to-leading order calculations for scalar and vector leptoquark production and decay, assessing the validity of the narrow-width approximation and highlighting significant NLO effects and off-resonance contributions.

Contribution

It provides the first detailed NLO analysis of leptoquark production and decay, evaluating the accuracy of the narrow-width approximation at NLO for different leptoquark types.

Findings

NLO contributions are large, especially for vector leptoquarks.

NWA is effective for scalar leptoquarks but less so for vector leptoquarks.

Off-resonance contributions significantly affect total cross-sections.

Abstract

We study the leptoquark model of Buchm\"uller, R\"uckl and Wyler, focusing on a particular type of scalar ($R_2$) and vector ($U_1$) leptoquark. The primary aim is to perform the calculations for leptoquark production and decay at next-to-leading order (NLO) to establish the importance of the NLO contributions and, in particular, to determine how effective the narrow-width-approximation (NWA) is at NLO. For both the scalar and vector leptoquarks it is found that the NLO contributions are large, with the larger corrections occurring for the case vector leptoquarks. For the scalar leptoquark it is found that the NWA provides a good approximation for determining the resonant peak, however the NWA is not as effective for the vector leptoquark. For both the scalar and vector leptoquarks there are large contributions away from the resonant peak, which are missing from the NWA results, and these make a significant difference to the total cross-section.