Four tops for LHC

Lamagna

Szewc

2020

J. High Energ. Phys.

Self Cite

We study the implementation of a Topic Model algorithm in four-top searches at the LHC as a test-probe of a not ideal system for applying this technique. We study the Topic Model behavior as its different hypotheses such as mutual reducibility and equal distribution in all samples shift from true. The four-top final state at the LHC is not only relevant because it does not fulfill these conditions, but also because it is a difficult and inefficient system to reconstruct and current Monte Carlo modeling of signal and backgrounds suffers from non-negligible uncertainties. We implement the Topic Model algorithm in the Same-Sign lepton channel where S/B is of order one and all backgrounds cannot have more than two b-jets at parton level. We define different mixtures according to the number of b-jets and we use the total number of jets to demix. Since only the background has an anchor bin, we find that we can reconstruct the background in the signal region independently of Monte Carlo. We propose to use this information to tune the Monte Carlo in the signal region and then compare signal prediction with data. We also explore Machine Learning techniques applied to the Topic Model algorithm and find slight improvements as well as potential roads to investigate. Although our findings indicate that still with the full LHC run 3 data the implementation would be challenging, we pursue through this work to find ways to reduce the impact of Monte Carlo simulations in four-top searches at the LHC.

Section: Discussionmentioning

confidence: 65%

Topic model for four-top at the LHC

Lamagna

Szewc

2020

J. High Energ. Phys.

Self Cite

“…As pointed out in Ref. [15], having the Z coupled to an unconserved current such ast R γ µ t R yields a factor (m t /M ) 2 , due to the longitudinal polarization of the vector propagator. For small M this translates into an enhancement in the cross-section, as discussed below.…”

Section: Pseudo-scalar Np: Amentioning

confidence: 89%

“…Vertices of this kind are found in Ref. [15], and Ref. [38] discusses a UV complete model with additional scalars that presents this kind of phenomenology.…”

Section: Np Modelsmentioning

confidence: 99%

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

Juste

Seoane

2019

J. High Energ. Phys.

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.

“…For instance, a light (M < 2m t ) NP that couples exclusively to top quark would be visible in a tttt final state and t-channel diagrams would affect the total cross-section with no other special features, as studied in Ref. [19]. Also, for large coupling to b-quarks and M 2m t , the t-channel bb → Y Y diagram is important, and some times more important than gg-fusion.…”

Section: General Featuresmentioning

confidence: 94%

“…However, this final state has the difficulty of being hidden in QCD background as well as being hard to tag the bottoms. The four-top final state is many times analyzed as possible signatures of heavy resonances decaying to tt [16], and also lately in looking for the SM four-top process [17,18], which may also hide non-resonant NP [19]. Notice, however, that four-top is a very heavy final state and usually its cross-section has important suppressions.…”

Section: Introductionmentioning

confidence: 99%

tt¯bb¯ as a probe of new physics at the LHC

Estévez

2017

Phys. Rev. D

We study the ttbb final state at the LHC as a probe of New Physics that couples mainly to third generation of quarks. We analyze New Physics simplified models with resonances of spin 0, 1 and 2. The sensitivity of the final states ttbb, tttt, bbbb and tt on each of these models is used to identify an important region in parameter space that is still not excluded and where ttbb is the most sensitive final state. We indicate possible experimental hints and discuss potential issues of observables that rely mainly in Montecarlo predictions. A new observable is proposed that, at the price of requiring more statistics, reduces the impact of Montecarlo predictions. We use preliminary 13 TeV results to give a raw estimate on the discovery reach and propose simple improvements on the observables.