Event Selection For Beyond Standard Model X → S(γγ)H(Bb) Signal With Atlas In Run–3

The Standard Model of particle physics fails to explain key phenomena such as the matter-antimatter asymmetry observed in the universe. Theories beyond the Standard Model propose mechanisms often involving additional scalar bosons to address this imbal- ance. This study investigates the theoretically possible X → S(γγ)H(b ̄b) decay channel using Monte Carlo simulations of proton-proton collisions at the ATLAS detector. A tai- lored set of selection criteria for this channel is developed using the Asimov significance and the Punzi figure of merit metrics to maximize the sensitivity of this signal while min- imizing background contamination from γγ + jets events. Similarly, the potential of 32 additional observables, including angular separations, transverse momentum ratios and Lorentz-invariant masses, some both in detector and center-of-mass frame, are explored to further improve the signal-to-background ratio.