Universal Extra Dimension models with gravity mediated decays after LHC Run II data

TL;DR

This paper investigates how gravity-mediated decays in Universal Extra Dimension models influence collider signals, constraining model parameters using recent ATLAS data from 13 TeV LHC runs.

Contribution

It provides the first detailed analysis of gravity-mediated decays in UED models with fat-branes, applying LHC Run II data to constrain model parameters.

Findings

No significant excess observed in ATLAS di-photon and multi-jet searches.

Constraints placed on the fundamental Planck mass $M_{D}$ and extra dimension size $R$.

Model parameters are limited based on collider data, narrowing the viable parameter space.

Abstract

In the 'fat-brane' realization of Universal Extra Dimension (UED) models, the gravity mediated decays of Kaluza-Klein (KK) excitations of the Standard Model (SM) particles offer interesting collider signals. Colored level-1 KK-particles (quarks $q^1$ and/or gluons $g^{1}$) are pair-produced at the colliders due to conserved KK-parity. These particles, then, cascade decay into lighter level-1 KK-particle in association with one or more SM particles until producing lightest KK particle (LKP). The gravity mediation allows LKP to decay into photon or $Z$-boson plus gravity excitation, hence resulting in di-photon/$ZZ$/$Z\gamma$ plus missing transverse energy signatures at collider experiments. Alternatively, pair-produced level-1 KK quarks/gluons may directly decay into the corresponding SM quark/gluon and a gravity excitation resulting in di-jet plus missing transverse energy signal. The ATLAS Collaboration has recently communicated the results for di-photon and multi-jet plus missing transverse energy searches with $36.1$ inverse-femtobarn of integrated luminosity at $13$ TeV center-of-mass energy. No significant excess of events above the SM expectation was observed in both searches. We constrain the 'fat-brane' UED model parameters, namely the fundamental Planck mass $M_{D}$ and the size of small extra dimensions $R$, in the light of above-mentioned ATLAS searches.