Search for $W$ boson decays to three charged pions
Phys.Rev.Lett. 122 (2019) 151802
The collaboration

Abstract (data abstract)
CERN-LHC. The analysis searches for the rare decay of the W boson to 3 charged pions, using 13 TeV data collected in proton-proton collisions in 2016 and 2017 with the CMS detector. The tables give the upper limit at 95\% CL on the branching fraction of the W boson to 3 charged pions.