Search for Narrow $H\gamma$ Resonances in Proton-Proton Collisions at $\sqrt{s}=13\mathrm{TeV}$

A search for heavy, narrow resonances decaying to a Higgs boson and a photon ($H\gamma$) has been performed in proton-proton collision data at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of $35.9{\mathrm{fb}}^{-1}$ collected with the CMS detector at the LHC in 2016. Events containing a photon and a Lorentz-boosted hadronically decaying Higgs boson reconstructed as a single, large-radius jet are considered, and the $\gamma +\text{jet}$ invariant mass spectrum is analyzed for the presence of narrow resonances. To increase the sensitivity of the search, events are categorized depending on whether or not the large-radius jet can be identified as a result of the merging of two jets originating from $b$ quarks. Results in both categories are found to agree with the predictions of the standard model. Upper limits on the production rate of $H\gamma$ resonances are set as a function of their mass in the range of 720–3250 GeV, representing the most stringent constraints to date.

Figure 1

Signal acceptance times efficiency ($A\epsilon$) after the final selection, shown for the $b$-tagged and untagged categories.

Figure 2

The observed $J\gamma$ invariant mass spectra in the signal region, shown along with the background fit and a few selected signals, for the $b$-tagged (left) and untagged (right) categories. Signal samples are plotted with arbitrary normalizations and are shown for illustration purposes. The green and yellow bands correspond to the 1 and 2 standard deviation uncertainties in the background-only fit. For bins with a low number of data entries, the error bars correspond to the Garwood confidence intervals [65]. Shown in the lower panels are the differences between the number of events in data and the nominal background prediction from the fit, divided by the combined statistical uncertainty in the data and the background fit. The error bars correspond to the statistical uncertainty in the data alone.

Figure 3

Upper limits at 95% C.L. on the product of the signal cross section and the branching fraction to $H\gamma$ for the $b$-tagged and untagged categories, as well as the statistical combination of the two categories.