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.