Search for a new heavy scalar particle decaying into a Higgs boson and a new scalar singlet in final states with one or two light leptons and a pair of tau-leptons with the ATLAS detector
Abstract
A search for a new heavy scalar particle X decaying into a Standard Model (SM)
Higgs boson and a new singlet scalar particle S is presented. The search uses a protonproton
(pp) collision data sample with an integrated luminosity of 140 fb-1 recorded at a centre-of-mass energy of SQUARE ROOT s = 13TeV with the ATLAS detector at the Large Hadron
Collider. The most sensitive mass parameter space is explored in X mass ranging from 500 to 1500 GeV, with the corresponding S mass in the range 200-500 GeV. The search selects events with two hadronically decaying τ -lepton candidates from H RIGHTWARDS ARROW τ+τ- decays and one or two light leptons (ℓ = e, μ) from S RIGHTWARDS ARROW V V (V = W, Z) decays while the remaining
V boson decays hadronically or to neutrinos. A multivariate discriminant based on event kinematics is used to separate the signal from the background. No excess is observed beyond the expected SM background and 95% confidence level upper limits between 72 fb and 542 fb are derived on the cross-section σ(pp RIGHTWARDS ARROW X RIGHTWARDS ARROW SH) assuming the same SM-Higgs boson-like decay branching ratios for the S RIGHTWARDS ARROW V V decay. Upper limits on the visible cross-sections
σ(pp RIGHTWARDS ARROW X RIGHTWARDS ARROW SH RIGHTWARDS ARROW WWτ τ ) and σ(pp RIGHTWARDS ARROW X RIGHTWARDS ARROW SH RIGHTWARDS ARROW ZZτ τ ) are also set in the ranges 3-26 fb and 6-33 fb, respectively.