Hunting leptoquarks in monolepton searches

TL;DR

This paper demonstrates that analyzing the spectral shape of monolepton and dilepton events at the LHC can set the most stringent limits on certain leptoquarks, potentially probing masses up to 18 TeV with future data.

Contribution

It introduces a novel method of constraining leptoquarks using spectral shape analysis of Drell-Yan processes, surpassing previous bounds from pair production and atomic parity violation.

Findings

Most stringent limits on first-generation leptoquarks to date.

Potential to probe leptoquark masses between 8 and 18 TeV with 3000 fb$^{-1}$ of data.

Constructive, destructive, or no interference effects with the Standard Model signals.

Abstract

We show that stringent limits on leptoquarks that couple to first-generation quarks and left-handed electrons or muons can be derived from the spectral shape of the charged-current Drell-Yan process ($p p \to \ell^\pm \nu$) at Run 2 of the LHC. We identify and examine all six leptoquark species that can generate such a monolepton signal, including both scalar and vector leptoquarks, and find cases where the leptoquark exchange interferes constructively, destructively or not at all with the Standard Model signal. When combined with the corresponding leptoquark-mediated neutral-current ($p p \to \ell^+ \ell^-$) process, we find the most stringent limits obtained to date, outperforming bounds from pair production and atomic parity violation. We show that, with 3000 fb$^{-1}$ of data, combined measurements of the transverse mass in $p p \to \ell^\pm \nu$ events and invariant mass in $p p \to \ell^+ \ell^-$ events can probe masses between 8 TeV and 18 TeV, depending on the species of leptoquark, for electroweak-sized couplings. In light of such robust sensitivities, we strongly encourage the LHC experiments to interpret Drell-Yan (dilepton and monolepton) events in terms of leptoquarks, alongside usual scenarios like $Z'$ bosons and contact interactions.