Study of diphoton decays of the lightest scalar Higgs boson in the Next-to-Minimal Supersymmetric Standard Model

The CMS and ATLAS experiments at the LHC have announced the discovery of a Higgs boson with mass at approximately 125 $GeV/c^{2}$ in the search for the Standard Model Higgs boson via notably the $\gamma\gamma$ and $ZZ$ to four leptons final states. Considering the recent results on the Higgs boson searches from the LHC, we study the lightest scalar Higgs boson $h_{1}$ in the Next-to-Minimal Supersymmetric Standard Model by restricting the next-to-lightest scalar Higgs boson $h_{2}$ to be the observed 125 $GeV/c^{2}$ state. We perform a scan over the relevant NMSSM parameter space that is favoured by low fine-tuning considerations. Moreover, we also take the experimental constraints from direct searches, $B$-physics observables, relic density and anomalous magnetic moment of the muon measurements as well as the theoretical considerations into account in our specific scan. We find that the signal rate in the two-photon final state for the NMSSM Higgs boson $h_{1}$ with the mass range from approximately 80 $GeV/c^{2}$ to 122 $GeV/c^{2}$ can be enhanced by a factor up to 3.5, when the Higgs boson $h_{2}$ is required to be compatible with the excess from latest LHC results. This motivates the extension of the search at the LHC for the Higgs boson $h_{1}$ in the diphoton final state down to masses of 80 $GeV/c^{2}$ or lower, in particular with the upcoming proton-proton collision data to be taken at center-of-mass energies of 13-14 $TeV$.