First measurement of the forward rapidity dependence of $W$ boson transverse helicity fractions

LHCb collaboration, R. Aaij, M. Abdelfatah +1160

The transverse helicity fractions of $W$ bosons are measured as a function of the $W$ boson rapidity, $y_W$, in the range $0\le y_W\le 5$ using $W\to \mu {\nu }_{\mu }$ decays in $pp$ co…