For the first time, a search for the rare decay of the W boson to three charged pions has been performed. Proton-proton collision data recorded by the CMS experiment at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 77.3 fb(-1), have been analyzed. No significant excess is observed above the background expectation. An upper limit of 1.01 x 10(-6) is set at 95% confidence level on the branching fraction of the W boson to three charged pions. This provides a strong motivation for theoretical calculations of this branching fraction.

Search for W Boson Decays to Three Charged Pions

Azzi, P.;Bisello, D.;Boletti, A.;Bragagnolo, A.;Carlin, R.;Checchia, P.;Dall'Osso, M.;Gasparini, F.;Gozzelino, A.;Lacaprara, S.;Lujan, P.;Margoni, M.;Meneguzzo, A. T.;Pazzini, J.;Ronchese, P.;Rossin, R.;Simonetto, F.;Torassa, E.;Tosi, M.;Zanetti, M.;Zotto, P.;Zumerle, G.;Triossi, A.;Zucchetta, A.;