A search for a new charged particle X with mass between 0.3 and 2.0 TeV decaying to a W boson and a photon is presented, using proton-proton collision data at a center-of-mass energy of 13 TeV, collected by the CMS experiment and corresponding to an integrated luminosity of 138 fb$^{-1}$. Particle X has electric charge $\pm$ 1 and is assumed to have spin 0. The search is performed using the electron and muon decays of the W boson. No significant excess above the predicted background is observed. The upper limit at 95% confidence level on the product of the production cross section of the X and its branching fraction to a W boson and a photon is found to be 94 (137) fb for a 0.3 TeV resonance and 0.75 (0.81) fb for a 2.0 TeV resonance, for an X width-to-mass ratio of 0.01% (5%). This search presents the most stringent constraints to date on the existence of such resonances across the probed mass range. A statistical combination with an earlier study based on the hadronic decay mode of the W boson is also performed, and the upper limit at 95% confidence level for a 2.0 TeV resonance is reduced to 0.50 (0.63) fb for an X width-to-mass ratio of 0.01% (5%).
The red, blue, and orange curves are the product of detector acceptance and analysis selections efficiency for different particle mass assumptions---300, 1000, and 2000 GeV, respectively---to pass sequential requirements, for the electron channel.
The red, blue, and orange curves are the product of detector acceptance and analysis selections efficiency for different particle mass assumptions---300, 1000, and 2000 GeV, respectively---to pass sequential requirements, for the muon channel.
The product of detector acceptance and analysis selection efficiency in the electron channel as functions of the particle X mass. Three analysis requirements are applied consecutively: event reconstruction, HLT, and final signal selection. The product of detector acceptance and analysis selection efficiencies are shown at each stage in red, blue, and orange, respectively.
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