MMC Studies in Relation to Beyond-the-Standard-Model Physics*

The Missing Mass Calculator is an algorithm used by the ATLAS Experiment at the Large Hadron Collider to calculate the invariant mass of resonances decaying to two tau particles. Because tau particles always have decays that include neutrinos, which escape detection in the ATLAS detector, the direct calculation of the di-tau invariant mass is impossible. The Missing Mass Calculator (MMC) solves the system of kinematic equations involving the tau visible decay products, using the tau mass as a constraint, by minimizing a likelihood function. The MMC has seen success in several analyses involving ττ resonances, such as Z/γ∗ → ττ and H → ττ, providing accurate reconstructions of invariant masses for both the Z and the Higgs boson. In light of this success, we utilize the MMC in scenarios involving Beyond-the-Standard-Model (BSM) physics. The Two-real- scalar-singlet extension to the Standard Model (TRSM) provides a phenomenological model where the Standard Model scalar sector is extended by two scalar singlets, whose fields are labeled as X and S. We conduct an analysis of this model by assuming the X scalar decays asymmetrically into an S scalar and a Standard Model Higgs, selecting events with two b-candidates from H → bb decays and two hadronically decaying τ- leptons from S → ττ decays. This talk presents studies of the performance of the MMC in this BSM scenario. We observed that the calculated masses of the S scalar from the MMC increasingly deviate from the true value at higher X and S masses, warranting further studies and the possible need to re-calibrate this algorithm to fit these higher masses.