Diphoton signals for the Georgi-Machacek scenario at the Large Hadron Collider

TL;DR

This paper investigates the potential of the diphoton channel at the LHC to detect the custodial SU(2) singlet scalar in the Georgi-Machacek model, showing promising sensitivity with advanced analysis techniques.

Contribution

It provides a detailed simulation and analysis of the diphoton signal for the GM scenario, highlighting the detectability of the custodial singlet scalar at the LHC.

Findings

Significant regions of GM parameter space are accessible at the LHC.

Neural network analysis improves signal significance over cut-based methods.

The custodial singlet scalar has a notable branching ratio into two photons.

Abstract

The diphoton channel for exploring the Georgi-Machacek (GM) scenario containing scalar triplets at the Large Hadron Collider (LHC) has been identified as germane, and subjected to a detailed study. The scalar spectrum of the model, which imposes a custodial SU(2) on the potential, gets classified into a 5-plet, a 3-plet and two singlets under the custodial symmetry. While most attempts to probe or constrain the scenario at the LHC depend largely on signals of charged scalars, we point out that the custodial SU(2) singlet state H can have a substantial branching ratio (amounting to a few percent) into two photons. We carry out a detailed simulation of the resulting signal and the standard model backgrounds, obtaining the signal significance in different regions of the parameter space using the profile likelihood ratio method. Substantial regions of the GM parameter space is thus shown to be accessible to LHC studies, both at the high-luminosity run with $\int {\cal L} dt = 3000 fb^{-1}$, and also in Run-3 with $\int {\cal L} dt = 300 fb^{-1}$, even after folding in systematic errors. We have also demonstrated that a rather subtantial improvement in the signal significance is achieved by switching over from a cut-based analysis to one based on neural network.