Search for resonances decaying to an anomalous jet and a Higgs boson in proton-proton collisions at s = 13 Te V

Abstract

This paper presents a search for new physics through the process where a massive particle, X, decays into a Higgs boson and a second particle, Y. The Higgs boson subsequently decays into a bottom quark-antiquark pair, which is reconstructed as a single large-radius jet. The decay products of Yare also assumed to produce a single large-radius jet. The identification of the Yparticle is enhanced by computing the anomaly score of its candidate jet using an autoencoder, which measures deviations from typical quark- or gluon-induced jets. This allows a simultaneous search for multiple Ydecay scenarios within a single analysis. In the main benchmark process, Yis a scalar particle that decays into a Wboson pair. Two other scalar Ydecay processes are also considered as benchmarks: decays to a light quark-antiquark pair, and decays to a top quark-antiquark pair. A fourth benchmark process considers Yas a hadronically decaying top quark, arising from the decay of a vector-like quark into a top quark and a Higgs boson. Data recorded by the CMS experiment at a center-of-mass energy of 13 $\text{Te}\text{V}$ in 2016-2018, corresponding to an integrated luminosity of 138 ${\text{fb}}^{-1}$ , are analyzed. The search covers Xmasses between 1.4 and 3.0 $\text{Te}\text{V}$ and Ymasses between 90 and 400 $\text{Ge}\text{V}$ , with all simulated signals produced in the narrow-width approximation. No significant excess above the standard model background expectation is observed. The most stringent upper limits to date are placed on benchmark signal cross sections for various masses of X and Y particles.

Fig. 1

An illustration showing the signal targeted by this analysis. The final state consists of a large-radius jet originating from Hdecaying to $\text{b}\overline{\text{b}}$and another large-radius jet originating from the decay of a second particle, Y

Fig. 2

The $M_{\text{jj}}$ (left) and $M_{\text{j}}^{\text{Y}}$ (right) projections showing the number of observed events per $\text{Ge}\text{V}$ (black markers) compared with the backgrounds estimated in the fit to the data (filled histograms) in the CR. Pass (upper) and Fail (lower) categories are shown. The high level of agreement between the model and the data in the Fail region arises because this region is used to constrain the background estimate. The lower panels show the “Pull” defined as $(\text{observed events}-\text{expected events})/\sqrt{{\sigma }_{\text{obs}}^2+{\sigma }_{\text{bkg}}^2},$ where ${\sigma }_{\text{obs}}$ and ${\sigma }_{\text{bkg}}$ are the total uncertainties in the observation and the background estimation, respectively

Fig. 3

The $M_{\text{jj}}$ (left) and $M_{\text{j}}^{\text{Y}}$ (right) projections showing the number of observed events per $\text{Ge}\text{V}$ (black markers) compared with the backgrounds estimated in the fit to the data (filled histograms) in the MR. Pass (upper) and Fail (lower) categories are shown. The expected contribution from the signal benchmark with $M_{\text{X}}=2200\text{Ge}\text{V}$ and $M_{\text{Y}}=250\text{Ge}\text{V}$ is overlaid in the MR Pass, assuming a production cross section of 5$\text{fb}$. The high level of agreement between the model and the data in the Fail region arises because this region is used to constrain the background estimate. The lower panels show the “Pull” defined as $(\text{observed events}-\text{expected events})/\sqrt{{\sigma }_{\text{obs}}^2+{\sigma }_{\text{bkg}}^2},$ where ${\sigma }_{\text{obs}}$ and ${\sigma }_{\text{bkg}}$ are the total uncertainties in the observation and the background estimation, respectively

Fig. 4

The expected (upper) and observed (lower) 95% confidence level upper limits on $\sigma (\text{p}\to \text{X}\to \text{HY})\mathcal{B}(\text{H}\to \text{b}\overline{\text{b}})\mathcal{B}(\text{Y}\to \text{WW}\to 2\text{q}2{\overline{\text{q}}}^{\prime })$ for different values of $M_{\text{X}}$ and $M_{\text{Y}}$. The limits have been evaluated in discrete steps corresponding to the centers of the boxes. The numbers in the boxes are given in fb

Fig. 5

The median expected (dashed line) 95% confidence level upper limits on the main and three alternative signal scenarios as a function of $M_{\text{X}}$. The inner (green) and outer (yellow) bands represent the regions containing 68% and 95%, respectively, of the distribution of limits expected under the background-only hypothesis. The solid dots indicate the observed limits, which are only evaluated at the simulated mass points