Revisiting mono-$\tau$ tails at the LHC

TL;DR

This paper reevaluates constraints on semileptonic operators from mono-$ au$ events at the LHC, highlighting the impact of systematics and the importance of considering particle propagation effects on bounds.

Contribution

It provides updated limits on New Physics couplings from recent LHC data, accounting for systematic uncertainties and the effects of particle propagation beyond EFT assumptions.

Findings

CMS data yields stronger limits than ATLAS despite similar luminosity

Neglected systematics on $ au$ reconstruction affect constraint strength

Including particle propagation effects can weaken bounds significantly

Abstract

We revisit the constraints on semileptonic operators derived from the mono-$\tau$ high-$p_T$ events in $pp$ collisions at LHC. Like in previous studies, we obtain limits on the New Physics couplings from the CMS data much stronger than from the ATLAS data, despite a nearly equal integrated luminosity. We find that a neglected systematics on the $\tau$ lepton reconstruction efficiency can partly explain that difference. We then provide new limits on the New Physics couplings relevant to decays based on $b\to c\tau\bar{\nu}$ by using the recent ATLAS data with 139 ${\rm fb}^{-1}$. We also show that the inclusion of propagation of the New Physics particle can significantly worsen the bounds obtained by relying on Effective Field Theoretical treatment of New Physics.