The measurement of the W mass at the LHC: shortcuts revisited

The claim that the W mass will be measured at the LHC with a precision of $cal{O}$(10)~MeV is critically reviewed. It is argued that in order to achieve such precision, a considerably better knowledge of the $u_{m v}$, $d_{m v}$, $s$, $c$, and $b$ structure functions of the proton than available today is needed. This will permit to assess with adequate precision the production characteristics of the W and Z bosons in the proton--proton collisions at the LHC, and their effect on the $p_{m T}$ spectra of charged leptons from W and Z decays. An experimental programme is suggested that will deliver the missing information. The core of this programme is a dedicated muon scattering experiment at the CERN SPS, with simultaneous measurements on hydrogen and deuterium targets.