Search for standard model production of four top quarks with same-sign and multilepton final states in proton–proton collisions at 
                $$\sqrt{s} = 13\,\text {TeV} $$
                        s
                      =
                      13
                      TeV

We study, from theoretical and phenomenological angles, the Higgs boson oblique parameterĤ, as the hallmark of off-shell Higgs physics.Ĥ is defined as the Wilson coefficient of the sole dimension-6 operator that modifies the Higgs boson propagator, within a Universal EFT. Theoretically, we describe self-consistency conditions on Wilson coefficients, derived from the Källén-Lehmann representation. Phenomenologically, we demonstrate that the process gg → h * → V V is insensitive to propagator corrections fromĤ, and instead advertise four-top production as an effective high-energy probe of off-shell Higgs behaviour, crucial to break flat directions in the EFT.

Section: Four-top Productionmentioning

confidence: 99%

The Ĥ-parameter: an oblique Higgs view

Englert

Giudice

Greljo

et al. 2019

“…For this reason, partners of the top quark are ubiquitous in models of new physics at the weak scale, and their production often results in multi-top signatures at the LHC, leading to many interesting phenomena. The four top final state has been previously investigated [8][9][10][11][12] and is starting to be visible in experimental analysis [13,14]. However, even more tops in the final state naturally occur under simple assumptions and provides a spectacular collider signature and a complementary method to search for new physics.…”

Section: Introductionmentioning

confidence: 99%

Six top messages of new physics at the LHC

Han

Huang

et al. 2019

Six top signatures provide a novel probe of new physics. We discuss production of six top quarks as the decay products of a pair of top partners in the setting of a composite Higgs model, and argue that the six top signal may generically provide one of the first final states to show a discrepancy. We construct an analysis based on quantities such as H T and the numbers of jets which are tagged as boosted tops, W s, or containing b-tags, and show that the LHC with 3 ab −1 can discover top partners with masses up to around 2.5 TeV in the six top signature.

“…The simulated events are then preselected using requirements based in Ref. [30], which can be summarized as: exactly two same-sign leptons, H jet T > 300 GeV, E miss T > 50 GeV, and either ≥ 5 jets of which at least three are b-tagged, or ≥ 6 jets of which at least two are b-tagged.…”

Section: Phenomenology Of Non-resonant Light Np In Four-top Productionmentioning

confidence: 99%

“…Most of these articles consider heavy NP, above the tt production threshold. Searches for SM four-top production have been performed by the ATLAS and CMS collaborations at center-of-mass energies of 8 TeV [9,10,26,27] and 13 TeV [11,[28][29][30][31][32][33]. These searches have focused on either the single-lepton (1L) and oppositesign dilepton (2LOS) channels, or the same-sign dileptons (2LSS) and multilepton (ML) channels.…”

Section: Introductionmentioning

confidence: 99%

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

Álvarez

Juste

Seoane

2019

We study the four-top (tttt) 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 separation 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 ttγγ with the invariant mass of the photons indicating 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 ttγγ 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 tttt 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. and predicted cross-sections is µ tttt = σ meas tttt /σ SM tttt = 1.05 +0.52 −0.48 . Therefore, an enhancement in the four-top production cross-section due to NP contributions of up to a factor of 1.5 (2.0) is still compatible with the measurements at about 1 s.d. (2 s.d.) level.This article is organized as follows. In Sect. 2 we describe a set of simple NP models containing new particles with either spin 0, spin 1, or spin 2, which couple predominantly to the top quark and whose masses are below the tt production threshold. We study existing constraints in these NP models arising from searches for di-photon (γγ) resonances and for four-top production, and we define suitable benchmark points in the model parameter space compatible with experimental results. In Sect. 3 we study the phenomenology of four-top production for some of these benchmark points. In Sect. 4 we present a discussion on the obtained results, and Sect. 5 contains the conclusions. We include three appendices to show more results on the full set of benchmark points, to describe the one-loop features of the NP models, and to summarize the numerical simulation details.