= Solution
Use leptonic decays: an isolated high <transverse momentum> positive <electron> or <muon>, together with substantial <missing transverse momentum> from the <neutrino>, provides a clean $W^+$ signature. The <lepton> <transverse momentum> has a <W-decay Jacobian peak>[Jacobian] scale near $m_W/2$, and the <lepton>–missing-momentum <transverse mass> has an edge near $m_W$, broadened by <decay width>[width], recoil and resolution. <Lepton> identification, isolation and a prompt primary-vertex origin suppress <Jets> faking <leptons> and heavy-flavour decays. Missing-momentum quality requirements suppress mismeasured multijet events; a veto on a second oppositely <charged lepton> suppresses $Z\to\ell^+\ell^-$ when both are reconstructed. Hadronic $W$ decays have a much larger ordinary-QCD background.
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