Estudo do decaimento do h −→ Za −→ ℓℓγγ no Experimento ATLAS

Abstract

The ATLAS collaboration observed the H → Z(ℓℓ)γ decay with an upper limit 6.6 times the Standard Model (MP) prediction, with 95% C.L. for 125 GeV Higgs mass during the Run I. The CMS collaboration reported an observed upper limit of 7.4 times the SM prediction, considering the same process and period. The results published in 2020 based on data from Run II present an upper limit 3.6 times the SM expected value, further strengthening the idea of new physics contribution as predicted in the Two Higgs Doublet Model (2HDM).The excess in this channel H → Z(ℓℓ)γ may come from the exotic decay of the SM Higgs, h → Z(ℓℓ)a(γγ), where the “a” is an axion-like particle (ALP) candidate, a narrow (pseudoscalar) resonance predicted in the Two Higgs Doublet Model (2HDM) that will be studied in the present work. The searches carried out for decays h → Za → ℓℓγγ can explore a region of ALP couplings to fótons that can be detected in the ATLAS Experiment. When produced at a maximum distance of 1.5 m from the primary vertex, the identification of the photons becomes more precise but there is a low mass region in the ALP decay where the two photons are emitted beyond the region of the electromagnetic calorimeter, being seen as a jet. Thus, we need to define strategies using jet reconstruction to study the possibility of separating these particles using the annealing algorithm, as light ALPs can increase the observed ratio in channel h → Zγ.