Search for the rare decay of the W boson into a pion and a photon in proton-proton collisions at $\sqrt{s}$=13TeV

Albert M. Sirunyan, Armen Tumasyan, Wolfgang Adam, Thomas Bergauer, Marko Dragicevic, Janos Erö, Alberto Escalante Del Valle, Rudolf Fruehwirth, Manfred Jeitler, Natascha Krammer, Lukas Lechner, Dietrich Liko (+2339 others)
2020
A search is performed for the rare decay W ± → π ± γ in proton-proton collisions at √ s = 13 TeV. Data corresponding to an integrated luminosity of 137 fb −1 were collected during 2016 to 2018 with the CMS detector. This analysis exploits a novel search strategy based on W boson production in top quark pair events. An inclusive search for the W ± → π ± γ decay is not optimal at the LHC because of the high trigger thresholds. Instead, a trigger selection is exploited in which the W boson
more » ... ing from one of the top quarks is used to tag the event in a leptonic decay. The W boson emerging from the other top quark is used to search for the W ± → π ± γ signature. Such decays are characterized by an isolated track pointing to a large energy deposit, and by an isolated photon of large transverse momentum. The presence of b quark jets reduces the background from the hadronization of light-flavor quarks and gluons. The W ± → π ± γ decay is not observed. An upper exclusion limit is set to this branching fraction, corresponding to 1.50 × 10 −5 at 95% confidence level, whereas the expected upper exclusion limit is 0.85 +0.52 −0.29 × 10 −5 . Events are reconstructed using the particle-flow (PF) algorithm [23], which combines information from the subdetectors to reconstruct and identify individual particles. The candidate A The CMS Collaboration
doi:10.18154/rwth-2021-08384 fatcat:bxunfb2ytvfcpbqhodocjpxwn4