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 $\sqrt{s}$ = 13.6 TeV

Abstract

A search is performed for a new resonance X decaying into either a pair of Higgs bosons (HH) or into a Higgs boson and a new scalar boson Y (HY), 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 HH and HY production cross sections. For resonant HH production, the upper limit on the cross section of pp $\to$ HH production is 1 pb for a high-mass resonance. For HY production, the upper limit on the cross section of the process pp $\to$ X $\to$ bbZZ is approximately 5 fb for a high-mass resonance. This is comparable to the sensitivity achieved in other analyses, which focus on H decays to $γγ$ or $ττ$ and Y decays into a pair of bottom quarks or massive vector bosons.

Figures (6)

• Figure 1: A diagram illustrating the gluon-gluon fusion production of a resonance $\mathup{{{X}}{} _{ {}} ^{ {}}}$ , which subsequently decays into either ${ \mathup{{{H}}{} _{ {}} ^{ {}}} }\xspace{ \mathup{{{H}}{} _{ {}} ^{ {}}} }\xspace$ or ${ \mathup{{{H}}{} _{ {}} ^{ {}}} }\xspace{ \mathup{{{Y}}{} _{ {}} ^{ {}}} }\xspace$. One of the Higgs bosons or the scalar $\mathup{{{Y}}{} _{ {}} ^{ {}}}$ decays into two $\mathup{{{Z}}{} _{ {}} ^{ {}}}$ bosons. Of these, one $\mathup{{{Z}}{} _{ {}} ^{ {}}}$ boson decays either hadronically into a pair of quarks or invisibly into a pair of neutrinos, while the other $\mathup{{{Z}}{} _{ {}} ^{ {}}}$ boson decays leptonically into two charged leptons. The remaining Higgs boson decays into a pair of $\mathup{{{b}}{} _{ {}} ^{ {}}}$ quarks.
• Figure 2: Pre-fit distributions of $\Delta R({ \mathup{{{\ell}}{} _{ {}} ^{ {}}} }\xspace,{ \mathup{{{\ell}}{} _{ {}} ^{ {}}} }\xspace)$, HT, $\Delta R({{ \mathup{{{\ell}}{} _{ {}} ^{ {}}} }\xspace}_1,{{ \mathup{{{b}}{} _{ {}} ^{ {}}} }\xspace}_1)$, and $\Delta R({{ \mathup{{{\ell}}{} _{ {}} ^{ {}}} }\xspace}_1,{{ \mathup{{{b}}{} _{ {}} ^{ {}}} }\xspace}_2)$ (from upper left to lower right) in the SR qq0M, combining the electron and muon channels of ${ \mathup{{{H}}{} _{ {}} ^{ {}}} }\xspace{ \mathup{{{H}}{} _{ {}} ^{ {}}} }\xspace$ search and using all three data-taking years. Three histograms corresponding to resonance masses of 500$\,\text{Ge\spaceV}$, 1000$\,\text{Ge\spaceV}$, and 2000$\,\text{Ge\spaceV}$ are also included in the plots, with the cross section of production of resonance $\mathup{{{X}}{} _{ {}} ^{ {}}}$ set to 100$\text{\,pb}$ and its branching fraction to ${ \mathup{{{H}}{} _{ {}} ^{ {}}} }\xspace{ \mathup{{{H}}{} _{ {}} ^{ {}}} }\xspace$ set to 1. The lower panel in each plot displays the ratio of the data to the total SM prediction, with the hatched bands representing the total systematic uncertainties in the backgrounds. The last bin includes the overflow.
• Figure 3: The distributions used for the fit in the four SRs of the ${ \mathup{{{b}}{} _{ {}} ^{ {}}} }\xspace{ \mathup{{{b}}{} _{ {}} ^{ {}}} }\xspace{ \mathup{{{Z}}{} _{ {}} ^{ {}}} }\xspace({ \mathup{{{q}}{} _{ {}} ^{ {}}} }\xspace{ \mathup{{{q}}{} _{ {}} ^{ {}}} }\xspace){ \mathup{{{Z}}{} _{ {}} ^{ {}}} }\xspace({ \mathup{{{\ell}}{} _{ {}} ^{ {}}} }\xspace{ \mathup{{{\ell}}{} _{ {}} ^{ {}}} }\xspace)$ channel, combining the electron and muon channels of the ${ \mathup{{{H}}{} _{ {}} ^{ {}}} }\xspace{ \mathup{{{H}}{} _{ {}} ^{ {}}} }\xspace$ search are shown. The upper left plot displays the $s_{\text{BDT}}$ distribution in the SR qq0M. The remaining three plots show the reconstructed resonance mass $m^{\text{rec}}_{{ \mathup{{{X}}{} _{ {}} ^{ {}}} }\xspace}$ distributions in the qqZM, qqHM, and qq2M SRs, from upper right to lower right. Three histograms corresponding to resonance masses of 500$\,\text{Ge\spaceV}$, 1000$\,\text{Ge\spaceV}$, and 2000$\,\text{Ge\spaceV}$ are also included in the plots, with the cross section of production of resonance $\mathup{{{X}}{} _{ {}} ^{ {}}}$ set to 100$\text{\,pb}$ and its branching fraction to ${ \mathup{{{H}}{} _{ {}} ^{ {}}} }\xspace{ \mathup{{{H}}{} _{ {}} ^{ {}}} }\xspace$ set to 1. These histograms account for the branching fractions of the ${ \mathup{{{H}}{} _{ {}} ^{ {}}} }\xspace{ \mathup{{{H}}{} _{ {}} ^{ {}}} }\xspace\to { \mathup{{{b}}{} _{ {}} ^{ {}}} }\xspace{ \mathup{{{b}}{} _{ {}} ^{ {}}} }\xspace{ \mathup{{{Z}}{} _{ {}} ^{ {}}} }\xspace{ \mathup{{{Z}}{} _{ {}} ^{ {}}} }\xspace$ and ${ \mathup{{{Z}}{} _{ {}} ^{ {}}} }\xspace{ \mathup{{{Z}}{} _{ {}} ^{ {}}} }\xspace\to { \mathup{{{q}}{} _{ {}} ^{ {}}} }\xspace{ \mathup{{{q}}{} _{ {}} ^{ {}}} }\xspace{ \mathup{{{\ell}}{} _{ {}} ^{ {}}} }\xspace{ \mathup{{{\ell}}{} _{ {}} ^{ {}}} }\xspace$ decays. The lower panel in each plot displays the ratio of the data to the total SM prediction, with the hatched bands representing the overall uncertainty in the combined background expectations. The histograms of backgrounds are the post-fit ones, while the histograms of BSM signals are the pre-fit ones.
• Figure 4: The distributions used for the fit in the two SRs of the ${ \mathup{{{b}}{} _{ {}} ^{ {}}} }\xspace{ \mathup{{{b}}{} _{ {}} ^{ {}}} }\xspace{ \mathup{{{Z}}{} _{ {}} ^{ {}}} }\xspace({ \mathup{{{\upnu}}{} _{ {}} ^{ {}}} }\xspace{ \mathup{{{\upnu}}{} _{ {}} ^{ {}}} }\xspace){ \mathup{{{Z}}{} _{ {}} ^{ {}}} }\xspace({ \mathup{{{\ell}}{} _{ {}} ^{ {}}} }\xspace{ \mathup{{{\ell}}{} _{ {}} ^{ {}}} }\xspace)$ channel, combining the electron and muon channels of the ${ \mathup{{{H}}{} _{ {}} ^{ {}}} }\xspace{ \mathup{{{H}}{} _{ {}} ^{ {}}} }\xspace$ search are shown. The upper plot displays the $s_{\text{BDT}}$ distribution in the SR ${ \mathup{{{\upnu}}{} _{ {}} ^{ {}}} }\xspace{ \mathup{{{\upnu}}{} _{ {}} ^{ {}}} }\xspace$0M, the lower plot displays the reconstructed resonance mass ${m}^{\text{rec}}_{{ \mathup{{{X}}{} _{ {}} ^{ {}}} }\xspace^{\prime}}$ distributions in the SR ${ \mathup{{{\upnu}}{} _{ {}} ^{ {}}} }\xspace{ \mathup{{{\upnu}}{} _{ {}} ^{ {}}} }\xspace$1M. Three histograms corresponding to resonance masses of 500$\,\text{Ge\spaceV}$, 1000$\,\text{Ge\spaceV}$, and 2000$\,\text{Ge\spaceV}$ are also included in the plots, with the cross section of production of resonance $\mathup{{{X}}{} _{ {}} ^{ {}}}$ set to 100$\text{\,pb}$ and its branching fraction to ${ \mathup{{{H}}{} _{ {}} ^{ {}}} }\xspace{ \mathup{{{H}}{} _{ {}} ^{ {}}} }\xspace$ set to 1. These histograms account for the branching fractions of the ${ \mathup{{{H}}{} _{ {}} ^{ {}}} }\xspace{ \mathup{{{H}}{} _{ {}} ^{ {}}} }\xspace\to { \mathup{{{b}}{} _{ {}} ^{ {}}} }\xspace{ \mathup{{{b}}{} _{ {}} ^{ {}}} }\xspace{ \mathup{{{Z}}{} _{ {}} ^{ {}}} }\xspace{ \mathup{{{Z}}{} _{ {}} ^{ {}}} }\xspace$ and ${ \mathup{{{Z}}{} _{ {}} ^{ {}}} }\xspace{ \mathup{{{Z}}{} _{ {}} ^{ {}}} }\xspace\to { \mathup{{{\ell}}{} _{ {}} ^{ {}}} }\xspace{ \mathup{{{\ell}}{} _{ {}} ^{ {}}} }\xspace{ \mathup{{{\upnu}}{} _{ {}} ^{ {}}} }\xspace{ \mathup{{{\upnu}}{} _{ {}} ^{ {}}} }\xspace$ decays. The lower panel in each plot displays the ratio of the data to the total SM prediction, with the hatched bands representing the overall uncertainty in the combined background expectations. The histograms of backgrounds are the post-fit ones, while the histograms of BSM signals are the pre-fit ones.
• Figure 5: Upper limits on the production cross section of ${ \mathup{{{p}}{} _{ {}} ^{ {}}} }\xspace{ \mathup{{{p}}{} _{ {}} ^{ {}}} }\xspace\to { \mathup{{{X}}{} _{ {}} ^{ {}}} }\xspace\to { \mathup{{{H}}{} _{ {}} ^{ {}}} }\xspace{ \mathup{{{H}}{} _{ {}} ^{ {}}} }\xspace\xspace$ with respect to the resonance mass $m_{{ \mathup{{{X}}{} _{ {}} ^{ {}}} }\xspace}$, combining all the SRs as well as the electron and muon channels, and taking into account the theoretical prediction of the branching fraction of the resonance to ${ \mathup{{{H}}{} _{ {}} ^{ {}}} }\xspace{ \mathup{{{H}}{} _{ {}} ^{ {}}} }\xspace$. The inner (green) band and the outer (yellow) band indicate the regions containing 68% and 95%, respectively, of the distribution of limits expected under the background-only hypothesis. The theoretical values (red dashed line) are also provided on the plot.