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Register a new userAutomated Predictions from Polarized Matrix Elements
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The anticipated experimental resolution and data cache of the High Luminosity Large Hadron Collider will enable precision investigations of polarization in multiboson processes. This includes, for the first time, vector boson scattering. To facilitate such studies, we report the automation of polarized matrix element computations in the publicly available Monte Carlo tool suite, MadGraph5_aMC@NLO. This enables scattering and decay simulations involving helicity-polarized asymptotic or intermediate states, preserving both spin-correlation and off-shell effects. As demonstrations of the method, we investigate the leading order production and decay of polarized weak gauge bosons in the process $pp to j j W^+_lambda W^-_{lambda}$, with helicity eigenstates $(lambda,lambda)$ defined in various reference frames. We consider the Standard Model at both $mathcal{O}(alpha^4)$ and $mathcal{O}(alpha^2 alpha_s^2)$ as well as a benchmark composite Higgs scenario. We report good agreement with polarization studies based on the On-Shell Projection (OSP) technique. Future capabilities are discussed.
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The prevalence of null results in searches for new physics at the LHC motivates the effort to make these searches as model-independent as possible. We describe procedures for adapting the Matrix Element Method for situations where the signal hypothesis is not known a priori. We also present general and intuitive approaches for performing analyses and presenting results, which involve the flattening of background distributions using likelihood information. The first flattening method involves ranking events by background matrix element, the second involves quantile binning with respect to likelihood (and other) variables, and the third method involves reweighting histograms by the inverse of the background distribution.
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The heavy quark effects in deep--inelastic scattering in the asymptotic regime $Q^2 gg m^2$ can be described by heavy flavor operator matrix elements. Complete analytic expressions for these objects are currently known to ${sf NLO}$. We present first results for fixed moments at ${sf NNLO}$. This involves a recalculation of fixed moments of the corresponding ${sf NNLO}$ anomalous dimensions, which we thereby confirm.
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