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Search for W Boson Decays to Three Charged Pions.

Physical review letters (2019-05-06)
A M Sirunyan, A Tumasyan, W Adam, F Ambrogi, E Asilar, T Bergauer, J Brandstetter, M Dragicevic, J Erö, A Escalante Del Valle, M Flechl, R Frühwirth, V M Ghete, J Hrubec, M Jeitler, N Krammer, I Krätschmer, D Liko, T Madlener, I Mikulec, N Rad, H Rohringer, J Schieck, R Schöfbeck, M Spanring, D Spitzbart, W Waltenberger, J Wittmann, C-E Wulz, M Zarucki, V Chekhovsky, V Mossolov, J Suarez Gonzalez, E A De Wolf, D Di Croce, X Janssen, J Lauwers, A Lelek, M Pieters, H Van Haevermaet, P Van Mechelen, N Van Remortel, F Blekman, J D'Hondt, J De Clercq, K Deroover, G Flouris, D Lontkovskyi, S Lowette, I Marchesini, S Moortgat, L Moreels, Q Python, K Skovpen, S Tavernier, W Van Doninck, P Van Mulders, I Van Parijs, D Beghin, B Bilin, H Brun, B Clerbaux, G De Lentdecker, H Delannoy, B Dorney, G Fasanella, L Favart, A Grebenyuk, A K Kalsi, J Luetic, A Popov, N Postiau, E Starling, L Thomas, C Vander Velde, P Vanlaer, D Vannerom, Q Wang, T Cornelis, D Dobur, A Fagot, M Gul, I Khvastunov, C Roskas, D Trocino, M Tytgat, W Verbeke, B Vermassen, M Vit, N Zaganidis, O Bondu, G Bruno, C Caputo, P David, C Delaere, M Delcourt, A Giammanco, G Krintiras, V Lemaitre, A Magitteri
ABSTRACT

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 1.01×10^{-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.