Search for light custodians in a clean decay channel at the LHC

TL;DR

This paper explores the potential to detect light custodial fermions predicted by warped extra dimension models at the LHC, focusing on a clean decay mode involving a Z boson and a b-quark for mass reconstruction.

Contribution

It introduces a new search strategy for light custodial fermions via the Z-b decay mode, including KK gluon contributions, enabling mass reconstruction at the LHC.

Findings

Light custodians can be identified as a peak in the bZ invariant mass.

Detection is feasible for masses around 500 GeV with current LHC capabilities.

The study highlights the importance of decay mode selection and tagging efficiencies.

Abstract

Models of warped extra dimensions with custodial symmetry usually predict the existence of a light Kaluza-Klein fermion arising as a partner of the right-handed top quark, sometimes called light custodians which we will denote $\tilde{b}_R$. The production of these particles at the LHC can give rise to multi-W events which could be observed in same-sign dilepton channels, but its mass reconstruction is challenging. In this letter we study the possibility of finding a signal for the pair production of this new particle at the LHC focusing on a rarer, but cleaner decay mode of a light custodian into a $Z$ boson and a $b$-quark. In this mode it would be possible to reconstruct the light custodian mass. In addition to the dominant standard model QCD production processes, we include the contribution of a Kaluza-Klein gluon first mode. We find that the $\tilde{b}_R$ stands out from the background as a peak in the $b Z$ invariant mass. However, when taking into account only the electronic and muonic decay modes of the $Z$ boson and $b-$tagging efficiencies, the LHC will have access only to the very light range of masses, $m_{\tilde{b}} = {\cal O} (500)$ GeV.