Searches for the Zγ decay mode of the Higgs boson and for new high-mass resonances in pp collisions at s = 13 $$ \sqrt{s}=13 $$ TeV with the ATLAS detector

We calculate the S-matrix element for the Higgs boson decay to a Z-boson and a photon, h → Zγ, at one-loop in the Standard-Model Effective Field Theory (SMEFT) framework and in linear R ξ -gauges. Our SMEFT expansion includes all relevant operators up to dimension-6 considered in Warsaw basis without resorting to any flavour or CP-conservation assumptions. Within this approximation there are 23 dimension-6 operators affecting the amplitude, not including flavour and hermitian conjugation. The result for the on-shell h → Zγ amplitude is gauge invariant, renormalisation-scale invariant and gauge-fixing parameter independent. The calculated ratio of the SMEFT versus the SM expectation for the h → Zγ decay width is then written in a semi-numerical form which is useful for further comparisons with related processes. For example, the h → Zγ amplitude contains 16 operators in common with the h → γγ amplitude and one can draw useful results about its feasibility at current and future LHC data.

Section: The Amplitudementioning

confidence: 85%

Section: Introductionmentioning

confidence: 93%

Section: Operatorsmentioning

confidence: 99%

Section: Operatorsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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The decay h → Zγ in the Standard-Model Effective Field Theory

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Suxho

Trifyllis

2019

Signatures of vector-like top partners decaying into new neutral scalar or pseudoscalar bosons

Benbrik

Kuutmann

Franzosi

et al. 2020

Self Cite

We explore the phenomenology of models containing one Vector-Like Quark (VLQ), t , which can decay into the Standard Model (SM) top quark, t, and a new spin-0 neutral boson, S, the latter being either a scalar or pseudoscalar state. We parametrise the underlying interactions in terms of a simplified model which enables us to capture possible Beyond the SM (BSM) scenarios. We discuss in particular three such scenarios: one where the SM state is supplemented by an additional scalar, one which builds upon a 2-Higgs Doublet Model (2HDM) framework and another which realises a Composite Higgs Model (CHM) through partial compositeness. Such exotic decays of the t can be competitive with decays into SM particles, leading to new possible discovery channels at the Large Hadron Collider (LHC). Assuming t pair production via strong interactions, we design signal regions optimised for one t → S t transition (while being inclusive on the othert decay, and vice versa), followed by the decay of S into the two very clean experimental signatures S → γ γ and S → Z(→ + −)γ. We perform a dedicated signalto-background analysis in both channels, by using Monte Carlo (MC) event simulations modelling the dynamics from the proton-proton to the detector level. Under the assumption of BR(t → S t) = 100%, we are therefore able to realistically quantify the sensitivity of the LHC to both the t and S masses, assuming both current and foreseen luminosities. This approach paves the way for the LHC experiments to surpass current VLQ search strategies based solely on t decays into SM bosons (W ± , Z, h).

Sgoldstino signature in hh, W+W− and ZZ spectra at the LHC

Demidov

Gorbunov

Kriukova

2020

In a supersymmetric extension of the Standard Model of particle physics (SM) with low scale of supersymmetry breaking, sgoldstino of (sub)TeV mass can be observed at the Large Hadron Collider (LHC) as a peak in diboson mass spectra. Moreover, as a singlet with respect to the SM gauge group, scalar sgoldstino can mix with the SM-like Higgs boson and interfere in all neutral channels providing with the promising signatures of new physics if superpartners are heavy. Sgoldstino couplings to the SM particles are determined by the pattern of soft supersymmetry breaking parameters. Here we concentrate on the cases with a noticeable sgoldstino contribution to di-Higgs channel. Having found a phenomenologically viable region in the model parameter space where scalar sgoldstino, produced at the LHC in gluon fusion, decays into a pair of the lightest Higgs boson we give predictions for corresponding cross section. Using the results of the LHC searches for scalar resonances we place bounds on the supersymmetry breaking scale √ F in this region of parameter space. Remarkably, in this region sgoldstino may also be observed in W + W − and ZZ channels, yielding independent signatures, since their signal strengths are related to that of di-Higgs channel.