W-jet tagging: Optimizing the identification of boosted hadronically-decaying W bosons

A method is proposed for distinguishing highly boosted hadronically-decaying W's (W jets) from QCD-jets using jet substructure. Previous methods, such as the filtering/mass-drop method, can give a factor of similar to 2 improvement in S/root B for jet p(T) greater than or similar to 200 GeV. In contrast, a multivariate approach including new discriminants such as R cores, which characterize the shape of the W jet, subjet planar flow, and grooming-sensitivities is shown to provide a much larger factor of similar to 5 improvement in S/root B p. For longitudinally polarized W's, such as those coming from many new physics models, the discrimination is even better. Comparing different Monte Carlo simulations, we observe a sensitivity of some variables to the underlying event; however, even with a conservative estimates, the multivariate approach is very powerful. Applications to semileptonic WW resonance searches and all-hadronic W + jet searches at the LHC are also discussed. Code implementing our W-jet tagging algorithm is publicly available at http://jets.physics.harvard.edu/wtag.