Higgs Decay Modes Research Articles

Vector boson fusion versus gluon-gluon fusion Higgs boson production with full-event deep learning: Toward a decay-agnostic tagger

We study the benefits of jet- and event-level deep learning methods in distinguishing vector boson fusion (VBF) from gluon-gluon fusion (GGF) Higgs production at the LHC. We show that a variety of classifiers (CNNs, attention-based networks) trained on the complete low-level inputs of the full event achieve significant performance gains over shallow machine learning methods (BDTs) trained on jet kinematics and jet shapes, and we elucidate the reasons for these performance gains. Finally, we take initial steps toward the possibility of a VBF vs GGF tagger that is agnostic to the Higgs decay mode, by demonstrating that the performance of our event-level CNN does not change when the Higgs decay products are removed. These results highlight the potentially powerful benefits of event-level deep learning at the LHC.

Fiducial cross sections for the lepton-pair-plus-photon decay mode in Higgs production up to NNLO QCD

The rare three-body decay of a Higgs boson to a lepton-antilepton pair and a photon is starting to become experimentally accessible at the LHC. We investigate how higher-order QCD corrections to the dominant gluon-fusion production process impact on the fiducial cross sections in this specific Higgs decay mode for electrons and muons. Corrections up to NNLO QCD are found to be sizeable. They are generally uniform in kinematical variables related to the Higgs boson, but display several distinctive features in the kinematics of its individual decay products.

The Higgs potential in 2HDM extended with a real triplet scalar: A roadmap

We perform a comprehensive study of the Higgs potential of the two Higgs doublet model extended by a real triplet scalar field [Formula: see text]. This model, dubbed [Formula: see text], has a rich Higgs spectrum consisting of three CP-even Higgs [Formula: see text], one CP-odd [Formula: see text] and two pairs of charged Higgs [Formula: see text]. First, we determine the perturbative unitarity constraints and a set of nontrivial conditions for the boundedness from below (BFB). Then we derive the Veltman conditions by considering the quadratic divergencies of Higgs boson self-energies in [Formula: see text]. We find that the parameter space is severely delimited by these theoretical constraints, as well as experimental exclusion limits and Higgs signal rate measurements at LEP and LHC. Using HiggsBounds-5.3.2beta and HiggSignals-2.2.3beta public codes, an exclusion test at [Formula: see text] is then performed on the physical scalars of [Formula: see text]. Our analysis provides a clear insight on the nonstandard scalar masses, showing that the allowed ranges are strongly sensitive to the sign of mixing angle [Formula: see text], essentially when naturalness is involved. For [Formula: see text] scenario, our results place higher limits on the bounds of all scalar masses, and show that the pairs [Formula: see text] and [Formula: see text] are nearly mass degenerate varying within the intervals [Formula: see text] GeV and [Formula: see text] GeV, respectively. When [Formula: see text] turns positive, we show that consistency with theoretical constraints and current LHC data, essentially on the diphoton decay channel, favors Higgs masses varying within wide allowed ranges: [Formula: see text] GeV for [Formula: see text]; [Formula: see text] GeV for ([Formula: see text], [Formula: see text]) and [Formula: see text] GeV for ([Formula: see text], [Formula: see text]). Finally, we find that the [Formula: see text] and [Formula: see text] Higgs decay modes are generally correlated if [Formula: see text] lies within the reduced intervals [Formula: see text] and [Formula: see text] parameter is frozen around [Formula: see text] ([Formula: see text]) for [Formula: see text] ([Formula: see text]).

Searching for the Higgsino-Bino sector at the LHC

We study the search for electroweakinos at the 13 TeV LHC in the case of heavy scalar superpartners. We consider both the direct production mode and the one associated with the decay of heavy Higgs bosons, and concentrate on the case of light Higgsinos and Binos. In this case, the direct production searches becomes more challenging than in the light Wino scenario. In the direct production mode, we use the current experimental searches to set the reach for these particles at larger luminosities, and we emphasize the relevance of considering both the neutral gauge boson and the neutral Higgs decay modes of the second and third lightest neutralino. We show the complementarity of these searches with the ones induced by the decay of the heavy Higgs bosons, which are dominated by the associated production of the lightest neutralino with the second and third lightest ones, with the latter decaying into gauge bosons. We show that, depending on the value of tan β, the Higgs boson decay channel remains competitive with the direct production channel up to heavy Higgs boson masses of about 1 TeV. Moreover, this search is not limited by the same kinematic considerations as the ones in the direct production mode and can cover masses up to the kinematic threshold for the decay of the heavier electroweakinos into the lightest neutralino. This decay mode provides also an alternative way of looking for heavy Higgs bosons in this range of masses and hence should be a high priority for future LHC analyses.

A model for lepton flavor violating non-standard neutrino interactions

We present a model for Lepton Flavor Violating (LFV) neutral current non-standard interactions of neutrinos with matter fields parameterized by ϵαβf with α≠β. Here, unlike the previous models, the ratios of the off-diagonal LFV elements of the effective NSI coupling to the diagonal lepton flavor conserving ones (i.e.,(ϵαβf)2/(ϵααfϵββf)) are arbitrary. The model enjoys rich phenomenology, predicting invisible Higgs decay and new meson decay modes observable in upcoming experiments. The model for ϵμef also predict a μ− to e− conversion rate on nuclei accessible in the planned experiments.

R -parity violating supersymmetry and the 125 GeV Higgs boson signals

We study the impact of R-parity violating Supersymmetry (RPV SUSY) on the 125 GeV Higgs production and decay modes at the LHC. We assume a heavy SUSY spectrum with multi-TeV squarks and SU(2) scalar singlets as well as the decoupling limit in the SUSY Higgs sector. In this case the lightest CP-even Higgs is SM-like when R-parity is conserved. In contrast, we show that when R-parity violating interactions are added to the SUSY framework, significant deviations may occur in some production and decay channels of the 125 GeV Higgs-like state. Indeed, we assume a single-flavor (mostly third generation) Bilinear RPV (BRPV) interactions, which generate Higgs-sneutrino mixing, lepton-chargino mixing and neutrino-neutralino mixing, and find that notable deviations of ${\cal O}(20-30\%)$ may be expected in the Higgs signal strength observables in some channels, e.g., in $p p \to h \to \mu^+ \mu^-, \tau^+ \tau^-$. Moreover, we find that new and detectable signals associated with BRPV Higgs decays to gauginos, $h\rightarrow\nu_{\tau}\tilde{\chi}_{2}^{0}$ and $h\rightarrow\tau^{\pm}\chi_{2}^{\mp}$, may also arise in this scenario. These decays yield a typical signature of $h \to \tau^\pm \ell^\mp + {{\not\!\! E_T}}$ ($\ell =e,\mu,\tau$) that can be much larger than in the SM, and may also be accompanied by an ${\cal O}(20-30\%)$ enhancement in the di-photon signal $pp \to h \to \gamma \gamma$. We also examine potential interesting signals of Trilinear R-parity violation (TRPV) interactions in the production and decays of the Higgs-sneutrino BRPV mixed state (assuming it is the 125 GeV scalar) and show that, in this case also, large deviations up to ${\cal O}(100\%)$ are expected in e.g., $p p \to h \to \mu^+ \mu^-, \tau^+ \tau^-$, which are sensitive to the BRPV$\times$TRPV coupling product.

Freeze-in dark matter from a sub-Higgs mass clockwork sector via the Higgs portal

The clockwork mechanism allows extremely weak interactions and small mass scales to be understood in terms of the structure of a theory. A natural application of the clockwork mechanism is to the freeze-in mechanism for dark matter production. Here we consider a Higgs portal freeze-in dark matter model based on a scalar clockwork sector with a mass scale which is less than the Higgs boson mass. The dark matter scalar is the lightest scalar of the clockwork sector. Freeze-in dark matter is produced by the decay of thermal Higgs bosons to the clockwork dark matter scalars. We show that the mass of the dark matter scalar is typically in the 1-10 keV range and may be warm enough to have an observable effect on perturbation growth and Lyman-$\alpha$ observations. Clockwork Higgs portal freeze-in models have a potentially observable collider phenomenology, with the Higgs boson decaying to missing energy in the form of pairs of long-lived clockwork sector scalars, plus a distribution of different numbers of quark and lepton particle-antiparticle pairs. The branching ratio to different numbers of quark and lepton pairs is determined by the clockwork sector parameters (the number of clockwork scalars $N$ and the clockwork charge $q$), which could therefore be determined experimentally if such Higgs decay modes are observed. In the case of a minimal Standard Model observable sector, the combination of nucleosynthesis and Lyman-$\alpha$ constraints is likely to exclude on-shell Higgs decays to clockwork scalars, although off-shell Higgs decays would still be possible. On-shell Higgs decays to clockwork scalars can be consistent with cosmological constraints in simple extensions of the Standard Model with light singlet scalars.

Probing the Higgs sector of Y=0 Higgs triplet model at LHC

In this paper, we investigate the Higgs Triplet Model with hypercharge Y_{varDelta }=0 (HTM0), an extension of the Standard model, caracterized by a more involved scalar spectrum consisting of two CP even Higgs h^0, H^0 and two charged Higgs bosons H^pm . We first show that the parameter space of HTM0, usually delimited by combined constraints originating from unitarity and BFB as well as experimental limits from LEP and LHC, is severely reduced when the modified Veltman conditions at one loop are also imposed. Then, we perform an rigorous analysis of Higgs decays either when h^0 is the SM-like or when the heaviest neutral Higgs H^0 is identified to the observed 125 GeV Higgs boson at LHC. In these scenarios, we perform an extensive parameter scan, in the lower part of the scalar mass spectrum, with a particular focus on the Higgs to Higgs decay modes H^0 rightarrow h^0h^0, H^pm ,H^mp leading predominantly to invisible Higgs decays. Finally, we also study the scenario where h^0, H^0 are mass degenerate. We thus find that consistency with LHC signal strengths favours a light charged Higgs with a mass about 176–178 GeV. Our analysis shows that the diphoton Higgs decay mode and H rightarrow Z gamma are not always positively correlated as claimed in a previous study. Anti-correlation is rather seen in the scenario where h is SM like, while correlation is sensitive to the sign of the potential parameter lambda when H is identified to 125 GeV observed Higgs.

125 GeV Higgs boson mass from 5D gauge-Higgs unification

In the context of a simple gauge-Higgs unification (GHU) scenario based on the gauge group SU(3)$\times$U(1)$^\prime$ in a 5-dimensional flat space-time, we investigate a possibility to reproduce the observed Higgs boson mass of around 125 GeV. We introduce bulk fermion multiplets with a bulk mass and a (half) periodic boundary condition. In our analysis, we adopt a low energy effective theoretical approach of the GHU scenario, where the running Higgs quartic coupling is required to vanish at the compactification scale. Under this "gauge-Higgs condition," we investigate the renormalization group evolution of the Higgs quartic coupling and find a relation between the bulk mass and the compactification scale so as to reproduce the 125 GeV Higgs boson mass. Through quantum corrections at the one-loop level, the bulk fermions contribute to the Higgs boson production and decay processes and deviate the Higgs boson signal strengths at the Large Hadron Collider (LHC) experiments from the Standard Model (SM) predictions. Employing the current experimental data which show the the Higgs boson signal strengths for a variety of Higgs decay modes are consistent with the SM predictions, we obtain lower mass bounds on the lightest mode of the bulk fermions.

Tt̄H Coupling Measurement with the ATLAS Detector at the LHC

The Higgs boson was discovered on the 4th of July 2012 with a mass around 125 GeV by ATLAS and CMS experiments at LHC. Determining the Higgs properties (production and decay modes, couplings,...) is an important part of the high-energy physics programme in this decade. A search for the Higgs boson production in association with a top quark pair (tt̄H) at ATLAS [1] is summarized in this paper at an unexplored center-of-mass energy of 13 TeV, which could allow a first direct measurement of the top quark Yukawa coupling and could reveal new physics. The tt̄H analysis in ATLAS is divided into 3 channels according to the Higgs decay modes: H → Hadrons, H → Leptons and H → Photons. The best-fit value of the ratio of observed and Standard Model cross sections of tt̄H production process, using 2015-2016 data and combining all tt̄H final states, is 1:8±0:7, corresponds to 2:8σ (1:8σ) observed (expected) significance.

Entangling Higgs production associated with a single top and a top-quark pair in the presence of anomalous top-Yukawa coupling

The ATLAS and CMS collaborations observed a mild excess in the associated Higgs production with a top-quark pair left(toverline{t}hright) and reported the signal strengths of μtthATLAS = 1.81 ± 0.80 and μtthCMS = 2.75 ± 0.99 based on the data collected at sqrt{s}=7 and 8 TeV. Although, at the current stage, there is no obvious indication whether the excess is real or due to statistical fluctuations, here we perform a case study of this mild excess by exploiting the strong entanglement between the associated Higgs production with a single top quark (thX) and toverline{t}h production in the presence of anomalous top-Yukawa coupling. As well known, toverline{t}h production only depends on the absolute value of the top-Yukawa coupling. Meanwhile, in thX production, this degeneracy is lifted through the strong interference between the two main contributions which are proportional to the top-Yukawa and the gauge-Higgs couplings, respectively. Especially, when the relative sign of the top-Yukawa coupling with respect to the gauge-Higgs coupling is reversed, the thX cross section can be enhanced by more than one order of magnitude. We perform a detailed study of the influence of thX production on toverline{t}h production in the presence of the anomalous top-Yukawa coupling and point out that it is crucial to include thX production in the analysis of the toverline{t}h data to pin down the sign and the size of the top-Yukawa coupling in future. While assuming the Standard Model (SM) value for the gauge-Higgs coupling, we vary the top-Yukawa coupling within the range allowed by the current LHC Higgs data. We consider the Higgs decay modes into multileptons, boverline{b} and γγ putting a particular emphasis on the same sign dilepton events. We also discuss the prospects for the LHC Run-2 on how to disentangle thX production from toverline{t}h one and how to probe the anomalous top-Yukawa coupling.

Invisible decays in Higgs boson pair production

Observation of Higgs pair production is an important long term objective of the LHC physics program as it will shed light on the scalar potential of the Higgs field and the nature of electroweak symmetry breaking. While numerous studies have examined the impact of new physics on di-Higgs production, little attention has been given to the well-motivated possibility of exotic Higgs decays in this channel. Here we investigate the consequences of exotic invisible Higgs decays in di-Higgs production. We outline a search sensitive to such invisible decays in the $b\bar b+{\not \!\! E}_T$ channel. We demonstrate that probing invisible branching ratios of order 10$\%$ during the LHC's high-luminosity run will be challenging, but in resonance enhanced di-Higgs production, this final state can become crucial to establish the existence of physics beyond the Standard Model at collider energies. We also briefly discuss the outlook for other exotic Higgs decay modes and the potential to observe such exotic decays in the di-Higgs channel.

Measurement of the Higgs boson mass and e+e−→ZH cross section using Z→μ+μ− and Z→e+e− at the ILC

This paper presents a full simulation study of the measurement of the production cross section (${\ensuremath{\sigma}}_{ZH}$) of the Higgsstrahlung process ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}ZH$ and the Higgs boson mass (${M}_{\mathrm{H}}$) at the International Linear Collider (ILC), using events in which a Higgs boson recoils against a $Z$ boson decaying into a pair of muons or electrons. The analysis is carried out for three center-of-mass energies $\sqrt{s}=250$, 350, and 500 GeV, and two beam polarizations ${e}_{\mathrm{L}}^{\ensuremath{-}}{e}_{\mathrm{R}}^{+}$ and ${e}_{\mathrm{R}}^{\ensuremath{-}}{e}_{\mathrm{L}}^{+}$, for which the polarizations of ${e}^{\ensuremath{-}}$ and ${e}^{+}$ are $(P{e}^{\ensuremath{-}},P{e}^{+})=\phantom{\rule{0ex}{0ex}}(\ensuremath{-}80%,+30%)$ and ($+80%$, $\ensuremath{-}30%$), respectively. Assuming an integrated luminosity of $250\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ for each beam polarization at $\sqrt{s}=250\text{ }\text{ }\mathrm{GeV}$, where the best lepton momentum resolution is obtainable, ${\ensuremath{\sigma}}_{ZH}$ and ${M}_{\mathrm{H}}$ can be determined with a precision of 2.5% and 37 MeV for ${e}_{\mathrm{L}}^{\ensuremath{-}}{e}_{\mathrm{R}}^{+}$ and 2.9% and 41 MeV for ${e}_{\mathrm{R}}^{\ensuremath{-}}{e}_{\mathrm{L}}^{+}$, respectively. Regarding a 20 year ILC physics program, the expected precisions for the HZZ coupling and ${M}_{\mathrm{H}}$ are estimated to be 0.4% and 14 MeV, respectively. The event selection is designed to optimize the precisions of ${\ensuremath{\sigma}}_{ZH}$ and ${M}_{\mathrm{H}}$ while minimizing the bias on the measured ${\ensuremath{\sigma}}_{ZH}$ due to discrepancy in signal efficiencies among Higgs decay modes. For the first time, model independence has been demonstrated to a sub-percent level for the ${\ensuremath{\sigma}}_{ZH}$ measurement at each of the three center-of-mass energies. The results presented show the impact of center-of-mass energy and beam polarization on the evaluated precisions and serve as a benchmark for the planning of the ILC run scenario.

Probing the Higgs self coupling via single Higgs production at the LHC

We propose a method to determine the trilinear Higgs self coupling that is alternative to the direct measurement of Higgs pair production total cross sections and differential distributions. The method relies on the effects that electroweak loops featuring an anomalous trilinear coupling would imprint on single Higgs production at the LHC. We first calculate these contributions to all the phenomenologically relevant Higgs production ($gg{\rm F}$, VBF, $WH$, $ZH$, $t\bar tH$) and decay ($\gamma \gamma$, $WW^{*}/ZZ^{*}\to 4f$, $b\bar b$, $\tau \tau$) modes at the LHC and then estimate the sensitivity to the trilinear coupling via a one-parameter fit to the single Higgs measurements at the LHC 8 TeV. We find that the bounds on the self coupling are already competitive with those from Higgs pair production and will be further improved in the current and next LHC runs.

Higgs Physics at CLIC

The Compact Linear Collider (CLIC) is an attractive option for a future multi-TeV linear electron-positron collider, offering the potential for a rich precision physics programme, combined with sensitivity to a wide range of new phenomena. The physics reach of CLIC has been studied in the context of three distinct centre-of-mass energies, s=350 GeV, 1.4 TeV and 3.0 TeV. This staged scenario provides an excellent environment for precise studies of the properties of the 126 GeV Higgs boson. Operation at s=350 GeV allows, on the one hand, for a determination of the couplings and width of the Higgs boson in a model-independent manner through the study of the Higgsstrahlung process, and on the other hand, for a study of Higgs bosons produced in W+W− fusion for the most common Higgs decay modes. Operation at higher centre-of-mass energies, s1.4 TeV and 3 TeV, provides high statistics W+W− fusion samples allowing for high precision measurements of many Higgs couplings and a study of rare Higgs decay modes, Higgs boson samples produced in ZZ fusion, and the potential to study the top Yukawa coupling as well as the Higgs boson self-coupling. We explore the potential of the CLIC Higgs physics programme based on full simulation studies of a wide range of final states. The evolution of the physics sensitivity as a function of the centre-of-mass energy is presented in terms of combined fits to all measurements and their respective statistical uncertainty.

SM-like Higgs decay into two muons at 1.4 TeV CLIC

The potential for measuring the Standard Model (SM) Higgs boson decay into two muons at a 1.4 TeV CLIC e+e- collider, presented at ICHEP2014, is addressed in this paper. The study is performed in the full Geant4 detector simulations of CLIC_ILD, taking into consideration all the relevant physics and the beam-induced background processes, as well as the instrumentation of the very forward region to tag forward electrons. In this analysis we show that the branching ratio BR(H→μ+μ−) times the Higgs production cross-section can be measured with 38% statistical accuracy at s=1.4 TeV using an integrated luminosity of 1.5 ab-1. This study is part of an ongoing comprehensive Higgs physics benchmark study covering various Higgs production processes and decay modes, currently being carried out to estimate the full Higgs physics potential of CLIC.

Higgs [formula omitted] in Abelian and non-Abelian flavor symmetry models

We study lepton flavor violating Higgs decays in two models, with the recently found hint for Higgs→μτ at CMS as a benchmark value for the branching ratio. The first model uses the discrete flavor symmetry group A4, broken at the electroweak scale, while the second is renormalizable and based on the Abelian gauge group Lμ−Lτ. Within the models we find characteristic predictions for other non-standard Higgs decay modes, charged lepton flavor violating decays and correlations of the branching ratios with neutrino oscillation parameters.

Probing the Standard Model with Higgs signal rates from the Tevatron, the LHC and a future ILC

We explore the room for possible deviations from the Standard Model (SM) Higgs boson coupling structure in a systematic study of Higgs coupling scale factor benchmark scenarios using the latest signal rate measurements from the Tevatron and LHC experiments. We employ chi-squared fits performed with HiggsSignals, which takes into account detailed information on signal efficiencies and major correlations of theoretical and experimental uncertainties. All considered scenarios allow for additional non-standard Higgs boson decay modes, and various assumptions for constraining the total decay width are discussed. No significant deviations from the SM Higgs boson coupling structure are found in any of the investigated benchmark scenarios. We derive upper limits on an additional (undetectable) Higgs decay mode under the assumption that the Higgs couplings to weak gauge bosons do not exceed the SM prediction. We furthermore discuss the capabilities of future facilities for probing deviations from the SM Higgs couplings, comparing the high luminosity upgrade of the LHC with a future International Linear Collider (ILC), where for the latter various energy and luminosity scenarios are considered. At the ILC model-independent measurements of the coupling structure can be performed, and we provide estimates of the precision that can be achieved.

Higgs sector in NMSSM with right-handed neutrinos and spontaneous R-parity violation

R-parity violation modifies the phenomenology of supersymmetric models considerably. We study a version of NMSSM, which contains right-handed neutrinos and in which spontaneous R-parity violation is possible. We study the ensuing effects of spontaneous breaking to the Higgs decay modes, taking into account the measured mass of the Higgs boson and experimental constraints, including rare decays. We find that a possible light scalar, dominantly a sneutrino, helps to increase the Standard Model (SM) Higgs-like scalar mass to the measured value. At the same time, a lighter stop than in the MSSM is allowed. The Higgs decay rates in the studied model can somewhat differ from the SM expectations, although the most prominent difference is a universal suppression in the couplings due to the mixing of doublet scalars with singlets. The charged, pseudoscalar, and other than the two lightest scalar Higgses are typically heavier than 1 TeV in the parameter region where R-parity is spontaneously broken.

Degenerate Higgs bosons decays toγγandZγin the type II seesaw model

Using the most recent results of CMS and ATLAS, we study the Higgs decays to $\ensuremath{\gamma}\ensuremath{\gamma}$ and $Z\ensuremath{\gamma}$ in the scenario where the two $CP$-even Higgs predicted by the type II seesaw model (Higgs triplet models) are close to mass degenerate with a mass near 125 GeV. We analyze the effects of the Higgs potential parameters constrained by the full set of perturbative unitarity, boundedness from below as well as from precision electroweak measurements on these decay modes. Our analysis demonstrates that the observed excess in the diphoton Higgs decay channel can be interpreted in our scenario within a delineated region controlled by ${\ensuremath{\lambda}}_{1}$ and ${\ensuremath{\lambda}}_{4}$ coupling. We also find a deviation in the Higgs decay to $Z\ensuremath{\gamma}$ with respect to the Standard Model prediction and the largest enhancement is found for a ratio ${R}_{Z\ensuremath{\gamma}}$ of the order 1.6. Furthermore we show that consistency with current ATLAS data on the diphoton decay channel favors a light doubly charged Higgs with mass in the range 92--180 GeV. Finally, we find that the $\ensuremath{\gamma}\ensuremath{\gamma}$ and $Z\ensuremath{\gamma}$ Higgs decay modes are generally correlated and the magnitude of correlation is sensitive to the sign of the ${\ensuremath{\lambda}}_{1}$ parameter.