Higgs Pair Production Research Articles

Higgs boson pair production at future hadron colliders: From kinematics to dynamics

The measurement of the triple Higgs coupling is a key benchmark for the LHC and future colliders. It directly probes the Higgs potential and its fundamental properties in connection to new physics beyond the Standard Model. There exist two phase space regions with an enhanced sensitivity to the Higgs self-coupling, the Higgs pair production threshold and an intermediate top pair threshold. We show how the invariant mass distribution of the Higgs pair offers a systematic way to extract the Higgs self-coupling, focusing on the leading channel $pp\to hh+X\to b\bar b\ \gamma\gamma+X$. We utilize new features of the signal events at higher energies and estimate the potential of a high-energy upgrade of the LHC and a future hadron collider with realistic simulations. We find that the high-energy upgrade of the LHC to 27 TeV would reach a 5$\sigma$ observation with an integrated luminosity of 2.5 ab$^{-1}$. It would have the potential to reach 15% (30%) accuracy at the 68% (95%) confidence level to determine the SM Higgs boson self-coupling. A future 100 TeV collider could improve the self-coupling measurement to better than 5% (10%) at the 68% (95%) confidence level.

Light (and darkness) from a light hidden Higgs

We examine light diphoton signals from extended Higgs sectors possessing (approximate) fermiophobia with Standard Model (SM) fermions as well as custodial symmetry. This class of Higgs sectors can be realized in various beyond the SM scenarios and is able to evade many experimental limits, even at light masses, which are otherwise strongly constraining. Below the WW threshold, the most robust probes of the neutral component are di and multi-photon searches. Utilizing the dominant Drell-Yan Higgs pair production mechanism and combining it with updated LHC diphoton data, we derive robust upper bounds on the allowed branching ratio for masses between 45 − 160 GeV. Furthermore, masses ≲ 110 GeV are ruled out if the coupling to photons is dominated by W boson loops. We then examine two simple ways to evade these bounds via cancellations between different loop contributions or by introducing decays into an invisible sector. This also opens up the possibility of future LHC diphoton signals from a light hidden Higgs sector. As explicit realizations, we consider the Georgi-Machacek (GM) and Supersymmetric GM (SGM) models which contain custodial (degenerate) Higgs bosons with suppressed couplings to SM fermions and, in the SGM model, a (neutralino) LSP. We also breifly examine the recent ∼ 3σ CMS diphoton excess at ∼ 95 GeV.

A new insight into the phase transition in the early Universe with two Higgs doublets

We study the electroweak phase transition in the alignment limit of the CP-conserving two-Higgs-doublet model (2HDM) of Type I and Type II. The effective potential is evaluated at one-loop, where the thermal potential includes Daisy corrections and is reliably approximated by means of a sum of Bessel functions. Both 1-stage and 2-stage electroweak phase transitions are shown to be possible, depending on the pattern of the vacuum development as the Universe cools down. For the 1-stage case focused on in this paper, we analyze the properties of phase transition and discover that the field value of the electroweak symmetry breaking vacuum at the critical temperature at which the first order phase transition occurs is largely correlated with the vacuum depth of the 1-loop potential at zero temperature.We demonstrate that a strong first order electroweak phase transition (SFOEWPT) in the 2HDM is achievable and establish benchmark scenarios leading to different testable signatures at colliders. In addition, we verify that an enhanced triple Higgs coupling (including loop corrections) is a typical feature of the SFOPT driven by the additional doublet. As a result, SFOEWPT might be able to be probed at the LHC and future lepton colliders through Higgs pair production.

Fully differential Higgs boson pair production in association with a Z boson at next-to-next-to-leading order in QCD

We present a fully differential next-to-next-to-leading order calculation of the Higgs pair production in association with a $Z$ boson, which is important for probing the trilinear Higgs self-coupling. The next-to-next-to-leading-order corrections enhance the next-to-leading order total cross sections by a factor of $1.2\sim 1.5$, depending on the collider energy, and change the shape of next-to-leading order kinematic distributions. We discuss how to determine the trilinear Higgs self-coupling using our results.

Corrections to di-Higgs boson production with light stops and modified Higgs couplings

The Higgs pair production in gluon fusion is a sensitive probe of beyond-standard model (BSM) phenomena and its detection is a major goal for the LHC and higher energy hadron collider experiments. In this work we reanalyze the possible modifications of the Higgs pair production cross section within low energy supersymmetry models. We show that the supersymmetric contributions to the Higgs pair production cross section are strongly correlated with the ones of the single Higgs production in the gluon fusion channel. Motivated by the analysis of ATLAS and CMS Higgs production data, we show that the scalar superpartners' contributions may lead to significant modification of the di-Higgs production rate and invariant mass distribution with respect to the SM predictions. We also analyze the combined effects on the di-Higgs production rate of a modification of the Higgs trilinear and top-quark Yukawa couplings in the presence of light stops. In particular, we show that due to the destructive interference of the triangle and box amplitude contributions to the di-Higgs production cross section, even a small modification of the top-quark Yukawa coupling can lead to a significant increase of the di-Higgs production rate.

Hh+text {Jet} production at 100\xa0TeV

Higgs pair production is a crucial phenomenological process in deciphering the nature of the TeV scale and the mechanism underlying electroweak symmetry breaking. At the Large Hadron Collider, this process is statistically limited. Pushing the energy frontier beyond the LHC’s reach will create new opportunities to exploit the rich phenomenology at higher centre-of-mass energies and luminosities. In this work, we perform a comparative analysis of the hh+text {jet} channel at a future 100 TeV hadron collider. We focus on the hhrightarrow bbar{b} bbar{b} and hh rightarrow bbar{b} tau ^+tau ^- channels and employ a range of analysis techniques to estimate the sensitivity potential that can be gained by including this jet-associated Higgs pair production to the list of sensitive collider processes in such an environment. In particular, we observe that hh rightarrow bbar{b} tau ^+tau ^- in the boosted regime exhibits a large sensitivity to the Higgs boson self-coupling and the Higgs self-coupling could be constrained at the 8% level in this channel alone.

Model-independent determination of the triple Higgs coupling at e+e− colliders

The observation of Higgs pair production at high-energy colliders can give evidence for the presence of a triple Higgs coupling. However, the actual determination of the value of this coupling is more difficult. In the context of general models for new physics, double Higgs production processes can receive contributions from many possible beyond-Standard-Model effects. This dependence must be understood if one is to make a definite statement about the deviation of the Higgs field potential from the Standard Model. In this paper, we study the extraction of the triple Higgs coupling from the process $e^+e^-\to Zhh$. We show that, by combining the measurement of this process with other measurements available at a 500 GeV $e^+e^-$ collider, it is possible to quote model-independent limits on the Effective Field Theory parameter c6 that parametrizes modifications of the Higgs potential. We present precise error estimates based on the anticipated ILC physics program, studied with full simulation. Our analysis also gives new insight into the model-independent extraction of the Higgs boson coupling constants and total width from $e^+e^-$ data.

Reconstruction of top-quark mass effects in Higgs pair production and other gluon-fusion processes

We propose a novel method for the treatment of top-quark mass effects in the production of H(∗), HH, HZ and ZZ final states in gluon fusion. We show that it is possible to reconstruct the full top-quark mass dependence of the virtual amplitudes from the corresponding large-mt expansion and the non-analytic part of the amplitude near the top-quark threshold ŝ = 4mt2 with a Padé ansatz. The reliability of our method is clearly demonstrated by a comparison with the recent NLO result for Higgs pair production with full top-quark mass dependence.

The CP-violating 2HDM in light of a strong first order electroweak phase transition and implications for Higgs pair production

We investigate the strength of the electroweak phase transition (EWPT) within the CP-violating 2-Higgs-Doublet Model (C2HDM). The 2HDM is a simple and well-studied model, which can feature CP violation at tree level in its extended scalar sector. This makes it, in contrast to the Standard Model (SM), a promising candidate for explaining the baryon asymmetry of the universe through electroweak baryogenesis. We apply a renormalisation scheme which allows efficient scans of the C2HDM parameter space by using the loop-corrected masses and mixing matrix as input parameters. This procedure enables us to investigate the possibility of a strong first order EWPT required for baryogenesis and study its phenomenological implications for the LHC. Like in the CP-conserving (real) 2HDM (R2HDM) we find that a strong EWPT favours mass gaps between the non-SM-like Higgs bosons. These lead to prominent final states comprised of gauge+Higgs bosons or pairs of Higgs bosons. In contrast to the R2HDM, the CP-mixing of the C2HDM also favours approximately mass degenerate spectra with dominant decays into SM particles. The requirement of a strong EWPT further allows us to distinguish the C2HDM from the R2HDM using the signal strengths of the SM-like Higgs boson. We additionally find that a strong EWPT requires an enhancement of the SM-like trilinear Higgs coupling at next-to-leading order (NLO) by up to a factor of 2.4 compared to the NLO SM coupling, establishing another link between cosmology and collider phenomenology. We provide several C2HDM benchmark scenarios compatible with a strong EWPT and all experimental and theoretical constraints. We include the dominant branching ratios of the non-SM-like Higgs bosons as well as the Higgs pair production cross section of the SM-like Higgs boson for every benchmark point. The pair production cross sections can be substantially enhanced compared to the SM and could be observable at the high-luminosity LHC, allowing access to the trilinear Higgs couplings.

A global view on the Higgs self-coupling at lepton colliders

We perform a global effective-field-theory analysis to assess the precision on the determination of the Higgs trilinear self-coupling at future lepton colliders. Two main scenarios are considered, depending on whether the center-of-mass energy of the colliders is sufficient or not to access Higgs pair production processes. Low-energy machines allow for ∼ 40% precision on the extraction of the Higgs trilinear coupling through the exploitation of next-to-leading-order effects in single Higgs measurements, provided that runs at both 240/250 GeV and 350 GeV are available with luminosities in the few attobarns range. A global fit, including possible deviations in other SM couplings, is essential in this case to obtain a robust determination of the Higgs self-coupling. High-energy machines can easily achieve a ∼ 20% precision through Higgs pair production processes. In this case, the impact of additional coupling modifications is milder, although not completely negligible.

Trigger studies for the Higgs pair production in the WWbb final state at √{{s}} = 13 TeV with the ATLAS detector

Trigger studies for the Higgs pair production in the WWbb final state at √{{s}} = 13 TeV with the ATLAS detector

Higgs pair production in the CP-violating two-Higgs-doublet model

The SM-like Higgs pair production is discussed in the framework of the general CP-violating two-Higgs-doublet model, where we find that the CP-violating mixing angles can be related to the Higgs self-couplings. Therefore, the future experimental searches for Higgs boson pairs can be constrained by the improved precision of the electric dipole moment measurements. Based on a series of constraints of the SM-like Higgs boson signal fits, the perturbative unitarity and stability bounds to the Higgs potential, and the most recent LHC searches for heavy Higgs bosons, we suggest a set of benchmark models for the future high-energy collider searches for Higgs pair production. The [Formula: see text] colliders operating at [Formula: see text] are capable of measuring the Higgs cubic self-couplings of the benchmark models directly. We also estimate the cross sections of the resonance contributions to the Higgs pair productions for the benchmark models at the future LHC and SppC/FCC-hh runs.

Higgs pair production at NLO QCD for CP-violating Higgs sectors

Higgs pair production through gluon fusion is an important process at the LHC to test the dynamics underlying electroweak symmetry breaking. Higgs sectors beyond the Standard Model (SM) can substantially modify this cross section through novel couplings not present in the SM or the on-shell production of new heavy Higgs bosons that subsequently decay into Higgs pairs. CP violation in the Higgs sector is important for the explanation of the observed matter-antimatter asymmetry through electroweak baryogenesis. In this work we compute the next-to-leading order (NLO) QCD corrections in the heavy top quark limit, including the effects of CP violation in the Higgs sector. We choose the effective theory (EFT) approach, which provides a rather model-independent way to explore New Physics (NP) effects by adding dimension-6 operators, both CP-conserving and CP-violating ones, to the SM Lagrangian. Furthermore, we perform the computation within a specific UV-complete model and choose as benchmark model the general 2-Higgs-Doublet Model with CP violation, the C2HDM. Depending on the dimension-6 coefficients, the relative NLO QCD corrections are affected by several per cent through the new CP-violating operators. This is also the case for SM-like Higgs pair production in the C2HDM, while the relative QCD corrections in the production of heavier C2HDM Higgs boson pairs deviate more strongly from the SM case. The absolute cross sections both in the EFT and the C2HDM can be modified by more than an order of magnitude. In particular, in the C2HDM the resonant production of Higgs pairs can by far exceed the SM cross section.

Dimension-six operators in Higgs boson pair production via vector-boson fusion at the LHC

The effective Lagrangian formalism provides a way to study the new physics effects at the electroweak scale. We study the Higgs pair production via the vector-boson fusion (VBF) at the Large Hadron Collider within the framework of the effective field theory. The effects from the dimension-six operators involved in the VBF Higgs pair production, particularly $\mathcal{O}_{\Phi,2}$ and $\mathcal{O}_{\Phi,3}$ which are relevant to the triple Higgs self-coupling, on the integrated cross section and various kinematic distributions are investigated. We find that the distributions of Higgs pair invariant mass, Higgs transverse momentum and rapidity are significantly altered by the operators $\mathcal{O}_{\Phi,2}$ and $\mathcal{O}_{\Phi,3}$. These features are helpful in disentangling the contributions from the operators $\mathcal{O}_{\Phi,2}$ and $\mathcal{O}_{\Phi,3}$ in triple Higgs self-coupling. We also provide the 5$\sigma$ discovery and 3$\sigma$ exclusion limits for the coefficients of $\mathcal{O}_{\Phi,2}$ and $\mathcal{O}_{\Phi,3}$ by measuring the VBF Higgs pair production process including the sequential $H \rightarrow b\bar{b}$ decays at the $14~ {\rm TeV}$ LHC.

Resonant Higgs pair production as a probe of stop at the LHC

Searching for top squark (stop) is a crucial task of the LHC. When the flavor conserving two body decays of the stop are kinematically forbidden, the stops produced near the threshold will live long enough to form bound states which subsequently decay through annihilation into the Standard Model (SM) final states. In the region of stop mixing angle {theta}_{tilde{t}}to 0 or π/2, we note that the LHC-13 TeV diphoton resonance data can give a strong bound on the spin-0 stoponium ( {eta}_{tilde{t}} ) and exclude the constituent stop mass {m}_{tilde{t}} up to about 290 GeV. While in the large stop mixing region, the stoponium will dominantly decay to the Higgs pair. By analyzing the process ppto {eta}_{tilde{t}}to hleft(to boverline{b}right)hleft(to {tau}^{+}{tau}^{-}right) , we find that a large portion of the parameter space on the {m}_{{tilde{t}}_1}-{theta}_{tilde{t}} plane can be probed at 2σ- significance level at the LHC with the luminosity ℒ = 3000 fb−1.

Higgs pair production in vector-boson fusion at the LHC and beyond

The production of pairs of Higgs bosons at hadron colliders provides unique information on the Higgs sector and on the mechanism underlying electroweak symmetry breaking (EWSB). Most studies have concentrated on the gluon-fusion production mode which has the largest cross section. However, despite its small production rate, the vector-boson fusion channel can also be relevant since even small modifications of the Higgs couplings to vector bosons induce a striking increase of the cross section as a function of the invariant mass of the Higgs boson pair. In this work we exploit this unique signature to propose a strategy to extract the hhVV quartic coupling and provide model-independent constraints on theories where EWSB is driven by new strong interactions. We take advantage of the higher signal yield of the bbar{b} bbar{b} final state and make extensive use of jet-substructure techniques to reconstruct signal events with a boosted topology, characteristic of large partonic energies, where each Higgs boson decays to a single collimated jet. Our results demonstrate that the hhVV coupling can be measured with 45% (20%) precision at the LHC for mathscr {L}=300 (3000) fb^{-1}, while a 1% precision can be achieved at a 100 TeV collider.

Di-Higgs enhancement by neutral scalar as probe of new colored sector

We study a class of models in which the Higgs pair production is enhanced at hadron colliders by an extra neutral scalar. The scalar particle is produced by the gluon fusion via a loop of new colored particles, and decays into di-Higgs through its mixing with the Standard Model Higgs. Such a colored particle can be the top/bottom partner, such as in the dilaton model, or a colored scalar which can be triplet, sextet, octet, etc., called leptoquark, diquark, coloron, etc., respectively. We examine the experimental constraints from the latest Large Hadron Collider (LHC) data, and discuss the future prospects of the LHC and the Future Circular Collider up to 100 TeV. We also point out that the 2.4,sigma excess in the b bar{b} gamma gamma final state reported by the ATLAS experiment can be interpreted as the resonance of the neutral scalar at 300 GeV.

Measuring trilinear Higgs coupling in WHH and ZHH productions at the high-luminosity LHC

Determination of trilinear Higgs coupling ($\lambda_{HHH}=\kappa\lambda_{HHH}^{\rm SM}$) through Higgs pair productions is a major motivation for the LHC high luminosity phase. We perform a detailed collider simulation to explore the potential of measuring $\lambda_{HHH}$ in the $VHH$ ($V=W,Z$) production at the HL-LHC. We find that the trilinear Higgs coupling in the SM ($\lambda_{HHH}^{\rm SM}$) could be measured at the level of $1.3\sigma$. Combining with the gluon fusion, vector boson fusion and $t\bar{t}HH$ channels, $\lambda_{HHH}^{\rm SM}$ is expected to be measured at the level of $3.13\sigma$. If no evidence of Higgs pair productions were observed, the $VHH$ production, together with the gluon fusion channel, would impose a bound of $0.5\leq \kappa \leq 2.2$ at the 95\% confidence level.

Constraints on the trilinear Higgs self coupling from precision observables

We present the constraints on the trilinear Higgs self coupling that arise from loop effects in the W boson mass and the effective sine predictions. We compute the contributions to these precision observables of two-loop diagrams featuring an anomalous trilinear Higgs self coupling. We explicitly show that the same anomalous contributions are found if the analysis of mW and sin2θefflep is performed in a theory in which the scalar potential in the Standard Model Lagrangian is modified by an (in)finite tower of (Φ†Φ)n terms with Φ the Higgs doublet. We find that the bounds on the trilinear Higgs self coupling from precision observables are competitive with those coming from Higgs pair production.

Maximizing the significance in Higgs boson pair analyses

We study Higgs pair production with a subsequent decay to a pair of photons and a pair of bottoms at the LHC. We use the log-likelihood ratio to identify the kinematic regions which either allow us to separate the di-Higgs signal from backgrounds or to determine the Higgs self-coupling. We find that both regions are separate enough to ensure that details of the background modelling will not affect the determination of the self-coupling. Assuming dominant statistical uncertainties we determine the best precision with which the Higgs self- coupling can be probed in this channel. We finally comment on the same questions at a future 100 TeV collider.