Search for a new resonance decaying to a Higgs boson and a scalar boson in events with two b jets and two Z bosons in proton-proton collisions at $\sqrt{s}$ = 13 TeV

Abstract

A search is performed for a new resonance X decaying into a Higgs boson and a new scalar boson Y (HY) including the case where Y is assumed to be a second Higgs boson (HH), using proton-proton collision data collected at $\sqrt{s}$ = 13 TeV, corresponding to an integrated luminosity of 138 fb$^{-1}$. This study performs a comprehensive exploitation of the bbZZ events, encompassing the following decay topologies. One H candidate is identified through its decay into a bottom quark-antiquark pair, while the other H or the Y candidate is selected through its decay into a pair of Z bosons. One Z boson is required to decay leptonically and the other, to decay into a pair of quarks or neutrinos. Events of interest are categorized based on the Lorentz boosts of the hadronically decaying H and Z bosons. Machine-learning-based discriminants, together with the reconstructed resonance mass, are employed across the different categories to separate signal from backgrounds, and their corresponding distributions are included in a simultaneous fit. No significant deviations from the standard model predictions are observed. Upper limits at the 95% confidence level are set on the HY and HH production cross sections. For HY production, the upper limit on the cross section pp $\to$ X $\to$ HY $\to$ bbZZ ranges from 500 to 5 fb, with the most stringent constraints achieved for high-mass X resonances and Y masses near the threshold for decay into a pair of massive vector bosons. This is comparable to the sensitivity achieved in other analyses, which focus on H decays to $\gamma\gamma$ or $\tau\tau$ and Y decays into a pair of bottom quarks or massive vector bosons. For resonant HH production, the upper limit on the cross section of pp $\to$ X $\to$ HH production is 1 pb for a high-mass resonance.