W-Jet Tagging: Optimizing the Identification of Boosted Hadronically-Decaying W Bosons

Abstract

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 (\sim 2) improvement in (S/\sqrt{B}) for jet (p_T \ge 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 (\sim 5) improvement in (S/\sqrt{B}). 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-je)t tagging algorithm is publicly available at http://jets.physics.harvard.edu/wtag.