W bosons are produced at LHC from a forward-backward symmetric initial
state. Their decay to a charged lepton and a neutrino has a strong spin
analysing power. The combination of these effects results in characteristic
distributions of the pseudorapidity of the leptons decaying from W+ and
W− of different helicity. This observation may open the possibility to
measure precisely the W+ and W− rapidity distributions for the two
transverse polarisation states of W bosons produced at small transverse
momentum.Comment: 8 pages, 5 figure