Four-top as probe of light top-philic New Physics

ÁLVAREZ, EZEQUIEL; JUSTE, AURELIO; SEOANE, ROSA MARÍA SANDÁ

JOURNAL OF HIGH ENERGY PHYSICS - (Online)

APS

Año: 2019 vol. 2019

1029-8479

We study the four-top (tt̄tt̄) final state at the LHC as a probe for New Physics(NP) effects due to new particles that couple predominantly to the top quark and whosemasses are below the top-quark-pair production threshold. We consider simple NP modelscontaining a new particle with either spin 0, spin 1, or spin 2, and find benchmark pointscompatible with current experimental results. We find that interference effects betweenNP and QED amplitudes can be large, pointing out the necessity of NLO contributions tobe explicitly computed and taken into account when NP is present. We examine kinematicdifferences between these models and the Standard Model (SM) at the parton level and thereconstructed level. In the latter case, we focus on events selected requiring two same-signleptons and multiple jets. We investigate how the different Lorentz structure of the lightNP affects the kinematic hardness, the polarization, the spin correlations, and the angulardistributions of the parton-level and/or final-state particles. We find that spin-2 light NPwould be identified by harder kinematics than the SM. We also show that the angular sepa-ration between the same-sign leptons is a sensitive observable for spin-0 NP. The spin-0 andspin-2 NP cases would also yield a signal in tt̄γγ with the invariant mass of the photons in-dicating the mass of the new particle. The spin-1 NP would be identified through an excessin four-top signal and slight or not modification in other observables, as for instance the lackof signal in tt̄γγ due to the Landau-Yang theorem. We comment on the opportunities thatwould open from the kinematic reconstruction of some of the top quarks in the tt̄tt̄ state.Our results provide new handles to probe for light top-philic NP as part of the ongoingexperimental program of searches for four-top production at the LHC Run 2 and beyond.