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

Ezequiel Álvarez,Rosa María Sandá Seoane,Aurelio Juste

doi:10.1007/jhep12(2019)080

Abstract

We study the four-top (t overline{t} t overline{t} ) 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 whose masses are below the top-quark-pair production threshold. We consider simple NP models containing a new particle with either spin 0, spin 1, or spin 2, and find benchmark points compatible with current experimental results. We find that interference effects between NP and QED amplitudes can be large, pointing out the necessity of NLO contributions to be explicitly computed and taken into account when NP is present. We examine kinematic differences between these models and the Standard Model (SM) at the parton level and the reconstructed level. In the latter case, we focus on events selected requiring two same-sign leptons and multiple jets. We investigate how the different Lorentz structure of the light NP affects the kinematic hardness, the polarization, the spin correlations, and the angular distributions of the parton-level and/or final-state particles. We find that spin-2 light NP would 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 and spin-2 NP cases would also yield a signal in t overline{t} γγ with the invariant mass of the photons in- dicating the mass of the new particle. The spin-1 NP would be identified through an excess in four-top signal and slight or not modification in other observables, as for instance the lack of signal in t overline{t} γγ due to the Landau-Yang theorem. We comment on the opportunities that would open from the kinematic reconstruction of some of the top quarks in the t overline{t} t overline{t} state. Our results provide new handles to probe for light top-philic NP as part of the ongoing experimental program of searches for four-top production at the LHC Run 2 and beyond.

Highlights

Latter process, tttt, can be used to probe the top-quark Yukawa coupling, the Higgsboson width [12, 13], and anomalous off-shell Higgs behavior [14]
We study the four-top 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 whose masses are below the top-quark-pair production threshold
We study existing constraints in these NP models arising from searches for di-photon resonances and for four-top production, and we define suitable benchmark points in the model parameter space compatible with experimental results

Summary

Introduction

Latter process, tttt, can be used to probe the top-quark Yukawa coupling, the Higgsboson width [12, 13], and anomalous off-shell Higgs behavior [14]. We focus on models whose effects are expected to be more important in four-top production rather than in other processes To this end, we consider new particles whose couplings are predominantly to the top quark and whose mass M is below the ttthreshold (M < 2mt) to avoid resonance effects in ttproduction. We restrict ourselves to new particles which are color neutral to avoid interactions with gluons that would yield a large QCD-mediated production cross-section For this purpose we study the following simple models that are described below: i) Scalar, ii) Pseudo-scalar, iii) vector Z , and iv) Graviton

Objectives

Findings

Discussion

Conclusion