Prospect for precision measurements of MW+ -MW- & MW at the LHC: Shortcuts revisited

The claim that the W boson mass might be measured at the LHC with a precision of O(10 MeV) is critically reviewed. It is argued that such a precision cannot be achieved, unless a dedicated measurement program, specific to the LHC is pursued. We propose such a program. Its main target is to significantly improve the experimental control of the relative polarisation of the W+, W- and Z bosons. We propose to achieve this goal either by running dedicated isoscalar beams at the LHC or by running, in parallel to the standard p-p collision program, a dedicated muon scattering "LHC-support-experiment" at the CERN SPS. One of these auxiliary measurements is necessary for the "precision measurement program" at the LHC, but not sufficient. It must be followed by dedicated measurement strategies which are robust with respect to both the systematic measurement uncertainties and to the perturbative and non-perturbative QCD effects. We propose such strategies and evaluate their precision. At the LHC, contrary to the Tevatron case, both the masses of the W+ and of the W- bosons must be measured with high precision. In this context, we propose and evaluate LHC dedicated strategies to measure the difference of the masses of the W+ and W- bosons and of the absolute mass of the W boson assuming both masses are equal. We show how one can overcome the obstacles in measuring the masses of W+ and W- to a precision of 10 MeV. We present a detailed evaluation of the precision of the proposed methods based on the studies of a large, O(10^11), sample of simulated W and Z production events.