Gluon Fusion Research Articles

Measuring the CP property of Higgs coupling to tau leptons in the VBF channel at the LHC

We study the prospects of measuring the CP property of the Higgs (h) coupling to tau leptons using the vector boson fusion (VBF) production mode at the high-luminosity LHC. Utilizing the previously proposed angle between the planes spanned by the momentum vectors of the (π+π0) and (π−π0) pairs originating in τ± decays as the CP-odd observable, we perform a detailed Monte Carlo analysis, taking into account the relevant standard model backgrounds, as well as detector resolution effects. We find that excluding a pure C mathcal{O}left(400 {mathrm{fb}}^{-1}right) luminosity at the 14 TeV LHC, and values of the CP-mixing angle larger than about 25° can be excluded at 95% confidence level using 3 ab−1 data. It is observed that the uncertainty in the angular resolution of the neutral pion momenta does not constitute a significant hurdle. Achieving a signal to background ratio (S/B) close to one, while keeping a high enough signal yield required to study the angular distributions selects out VBF as a promising mode to probe the CP nature of the hτ τ coupling, with gluon fusion suffering from a low S/B, and the W±h/Zh mode (with leptonically decaying W±/Z) having a much smaller signal rate.

Multi-step production of a diphoton resonance

Among the questions that would be raised by the observation of a new resonance at the LHC, particularly pressing are those concerning the production mechanism: What is the initial state? Is the resonance produced independently or in association with other particles? Here we present two weakly-coupled renormalizable models for production of a diphoton resonance that differ in both their initial and final states. In one model, a scalar particle produced through gluon fusion decays into a diphoton particle and a light, long-lived pseudoscalar. In another model, a boson produced from the annihilation of a strange-antistrange quark pair undergoes a cascade decay that leads to a diphoton particle and two sterile neutrinos. Various kinematic distributions may differentiate these models from the canonical model where a diphoton particle is directly produced in gluon fusion.

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.

Associated production of a dilepton and a ϒ(J/ψ) at the LHC as a probe of gluon transverse momentum dependent distributions

We discuss the impact on the study of gluon transverse momentum dependent distributions (TMDs) of the associated production of a lepton pair and a ϒ (or a J/ψ) in unpolarised proton–proton collisions, pp→Qℓℓ¯X, at LHC energies, where one can assume that such final states are dominantly induced by gluon fusion. If the transverse momentum of the quarkonium–dilepton system – namely, the transverse momentum imbalance of the quarkonium state and the lepton pair – is small, the corresponding cross sections can be calculated within the framework of TMD factorisation. Using the helicity formalism, we show in detail how these cross sections are connected to the moments of two independent TMDs: the distribution of unpolarised gluons, f1g, and the distribution of linearly polarised gluons, h1⊥g. We complete our exhaustive derivation of these general relations with a phenomenological analysis of the feasibility of the TMD extraction, as well as some outlooks.

Majorana Higgses at colliders

Collider signals of heavy Majorana neutrino mass origin are studied in the minimal Left-Right symmetric model, where their mass is generated spontaneously together with the breaking of lepton number. The right-handed triplet Higgs boson Δ, responsible for such breaking, can be copiously produced at the LHC through the Higgs portal in the gluon fusion and less so in gauge mediated channels. At Δ masses below the opening of the V V decay channel, the two observable modes are pair-production of heavy neutrinos via the triplet gluon fusion gg → Δ → NN and pair production of triplets from the Higgs h → ΔΔ → 4N decay. The latter features tri- and quad same-sign lepton final states that break lepton number by four units and have no significant background. In both cases up to four displaced vertices may be present and their displacement may serve as a discriminating variable. The backgrounds at the LHC, including the jet fake rate, are estimated and the resulting sensitivity to the Left-Right breaking scale extends well beyond 10 TeV. In addition, sub-dominant radiative modes are surveyed: the γγ, Zγ and lepton flavour violating ones. Finally, prospects for Δ signals at future e+e− colliders are presented.

Novel SM-like Higgs decay into displaced heavy neutrino pairs in U(1)\u2032 models

We examine the observability of heavy neutrino (νh) signatures of a U(1)′ enlarged Standard Model (SM) encompassing three heavy Majorana neutrinos alongside the known light neutrino states at the the Large Hadron Collider (LHC). We show that heavy neutrinos can be rather long-lived particles producing distinctive displaced vertices that can be accessed in the CERN LHC detectors. We concentrate here on the gluon fusion production mechanism gg → H1,2 → νhνh, where H1 is the discovered SM-like Higgs and H2 is a heavier state, yielding displaced leptons following νh decays into weak gauge bosons. Using data collected by the end of the LHC Run 2, these signatures would prove to be accessible with negligibly small background.

Combined threshold and transverse momentum resummation for inclusive observables

We present a combined resummation for the transverse momentum distribution of a colorless final state in perturbative QCD, expressed as a function of transverse momentum pT and the scaling variable x. Its expression satisfies three requirements: it reduces to standard transverse momentum resummation to any desired logarithmic order in the limit pT → 0 for fixed x, up to power suppressed corrections in pT; it reduces to threshold resummation to any desired logarithmic order in the limit x → 1 for fixed pT, up to power suppressed correction in 1 − x; upon integration over transverse momentum it reproduces the resummation of the total cross cross at any given logarithmic order in the threshold x → 1 limit, up to power suppressed correction in 1 − x. Its main ingredient, and our main new result, is a modified form of transverse momentum resummation, which leads to threshold resummation upon integration over pT , and for which we provide a simple closed-form analytic expression in Fourier-Mellin (b, N ) space. We give explicit coefficients up to NNLL order for the specific case of Higgs production in gluon fusion in the effective field theory limit. Our result allows for a systematic improvement of the transverse momentum distribution through threshold resummation which holds for all pT, and elucidates the relation between transverse momentum resummation and threshold resummation at the inclusive level, specifically by providing within perturbative QCD a simple derivation of the main consequence of the so-called collinear anomaly of SCET.

Modeling BSM effects on the Higgs transverse-momentum spectrum in an EFT approach

We consider the transverse-momentum distribution of a Higgs boson produced through gluon fusion in hadron collisions. At small transverse momenta, the large logarithmic terms are resummed up to next-to-leading-logarithmic (NLL) accuracy. The resummed computation is consistently matched to the next-to-leading-order (NLO) result valid at large transverse momenta. The ensuing Standard Model prediction is supplemented by possible new-physics effects parametrised through three dimension-six operators related to the modification of the top and bottom Yukawa couplings, and to the inclusion of a point-like Higgs-gluon coupling, respectively. We present resummed transverse-momentum spectra including the effect of these operators at NLL+NLO accuracy and study their impact on the shape of the distribution. We find that such modifications, while affecting the total rate within the current uncertainties, can lead to significant distortions of the spectrum. The proper parametrization of such effects becomes increasingly important for experimental analyses in Run II of the LHC.

ZZ production in gluon fusion at NLO matched to parton shower

We present a calculation of the next-to-leading order (NLO) QCD corrections to the hadroproduction process $gg\to ZZ \to e^+e^- \mu^+ \mu^-$, matched to the parton shower in the POWHEG framework. We take advantage of the POWHEG BOX tool for the implementation and rely on PYTHIA 8 for the showering and hadronization stages. We fully include $\gamma^*/Z$ interference effects, while also covering the single-resonant region. For this phenomenological study we focus on four lepton production as a signal process, neglecting all quark mass effects as well as the Higgs-mediated contributions, which are known to be subdominant in this case. We provide predictions from our simulations for the 13 TeV LHC Run II setup, including realistic experimental cuts.

One-loop corrections to the Higgs self-couplings in the singlet extension

We investigate predictions on the triple Higgs boson couplings with radiative corrections in the model with an additional real singlet scalar field. In this model, the second physical scalar state (H) appears in addition to the Higgs boson (h) with the mass 125 GeV. The hhh vertex is calculated at the one-loop level, and its possible deviation from the predictions in the standard model is evaluated under various theoretical constraints. The decay rate of H→hh is also computed at the one-loop level. We also take into account the bound from the precise measurement of the W boson mass, which gives the upper limit on the mixing angle α between two physical Higgs bosons for a given value of the mass of H (mH). We find that the deviation in the hhh coupling from the prediction in the standard model can maximally be about 250%, 150% and 75% for mH=300, 500 and 1000 GeV, respectively, under the requirement that the cutoff scale of the model is higher than 3 TeV. We also discuss deviations from the standard model prediction in double Higgs boson production from the gluon fusion at the LHC using the one-loop corrected Higgs boson vertices.

Two-loop corrections to the triple Higgs boson production cross section

In this paper we compute the QCD corrections for the triple Higgs boson production cross section via gluon fusion, within the heavy-top approximation. We present, for the first time, analytical results for the next-to-leading order corrections, and also compute the soft and virtual contributions of the next-to-next-to-leading order cross section. We provide predictions for the total cross section and the triple Higgs invariant mass distribution. We find that the QCD corrections are large at both perturbative orders, and that the scale uncertainty is substantially reduced when the second order perturbative corrections are included.

Transverse-momentum resummation for Higgs boson pair production at the LHC with top-quark mass effects

We consider Higgs boson pair production via gluon fusion in hadronic collisions. We report the calculation of the transverse-momentum (qT ) distribution of the Higgs boson pair with top-quark mass (Mt) effects fully taken into account. At small values of qT we resum the logarithmically-enhanced perturbative QCD contributions up to next-to-leading logarithmic (NLL) accuracy. At intermediate and large values of qT we consistently combine resummation with the mathcal{O}left({alpha}_S^3right) fixed-order results. After integration over qT , we recover the next-to-leading order (NLO) result for the inclusive cross section with full dependence on Mt. We present illustrative numerical results at LHC energies, together with an estimate of the corresponding perturbative uncertainties, and we study the impact of the top-quark mass effects.

Searches for invisible decays of the Higgs boson in pp collisions at sqrt{s} = 7, 8, and 13 TeV

Searches for invisible decays of the Higgs boson are presented. The data collected with the CMS detector at the LHC correspond to integrated luminosities of 5.1, 19.7, and 2.3 fb−1 at centre-of-mass energies of 7, 8, and 13 TeV, respectively. The search channels target Higgs boson production via gluon fusion, vector boson fusion, and in association with a vector boson. Upper limits are placed on the branching fraction of the Higgs boson decay to invisible particles, as a function of the assumed production cross sections. The combination of all channels, assuming standard model production, yields an observed (expected) upper limit on the invisible branching fraction of 0.24 (0.23) at the 95% confidence level. The results are also interpreted in the context of Higgs-portal dark matter models.

Two-loop electroweak corrections to Higgs–gluon couplings to higher orders in the dimensional regularization parameter

We compute the two-loop electroweak correction to the production of the Higgs boson in gluon fusion to higher orders in the dimensional-regularization parameter ε=(d−4)/2. We employ the method of differential equations augmented by the choice of a canonical basis to compute the relevant integrals and express them in terms of Goncharov polylogarithms. Our calculation provides useful results for the computation of the NLO mixed QCD-electroweak corrections to gg→H and establishes the necessary framework towards the calculation of the missing three-loop virtual corrections.

Pair Production of Beyond the Standard Model Higgs Bosons

Higgs pair production is not only sensitive to the trilinear Higgs self-coupling, but it can give access to other anomolous couplings, as e.g. a novel $hht\bar{t}$ coupling. In Composite Higgs Models, this coupling usually leads to a large increase of the cross section. In such a framework an interesting question is, whether it might be possible to observe new physics for the first time in Higgs pair production. This question will be addressed by taking into account projected sensitivities for Higgs coupling measurements and for direct searches of new vector-like quarks. Higher order corrections to Higgs pair production via gluon fusion are sizeable. It is hence not only important to compute them in the Standard Model (SM) but also in its extensions. Here, the computation of the QCD corrections in the SM with dimension 6 operators as well as the SUSY-QCD corrections to Higgs pair production via gluon fusion in the MSSM are presented.

Thermal photons from gluon fusion with magnetic fields

We compute the production of thermal photons in relativistic heavy-ion collisions by gluon fusion in the presence of an intense magnetic field, and during the early stages of the reaction. This photon yield is an excess over calculations that do not consider magnetic field effects. We add this excess to recent hydrodynamic calculations that are close to describing the experimental transverse momentum distribution in RHIC and LHC. We then show that with reasonable values for the temperature, magnetic field strength, and strong coupling constant, our results provide a very good description of such excess. These results support the idea that the origin of at least some of the photon excess observed in heavy-ion experiments may arise from magnetic field induced processes.

Jet azimuthal angle correlations in the production of a Higgs boson pair plus two jets at hadron colliders

Azimuthal angle correlations of two jets in the process pprightarrow HHjj are studied. The loop induced mathcal {O}(alpha _mathrm{s}^4 alpha _{}^2) gluon fusion (GF) sub-process and the mathcal {O}(alpha _{}^4) weak boson fusion (WBF) sub-process are considered. The GF sub-process exhibits strong correlations in the azimuthal angles phi _{1,2}^{} of the two jets measured from the production plane of the Higgs boson pair and the difference between these two angles phi _1^{}-phi _2^{}, and a very small correlation in their sum phi _1^{}+phi _2^{}. Using a finite value for the mass of the loop running top quark in the amplitude is crucial for the correlations. The impact of a non-standard value for the triple Higgs self-coupling on the correlations is found small. The peak shifts of the azimuthal angle distributions reflect the magnitude of parity violation in the ggrightarrow HH amplitude and the dependence of the distributions on parity violating phases is analytically clarified. The normalised distributions and the peak positions of the correlations are stable against the variation of factorisation and renormalisation scales. The WBF sub-process also produces correlated distributions and it is found that they are not induced by the quantum effect of the intermediate weak bosons but mainly by a kinematic effect. This kinematic effect is a characteristic feature of the WBF sub-process and is not observed in the GF sub-process. It is found that the correlations are different in the GF and in the WBF sub-processes. As part of the process dependent information, they will be helpful in the analyses of the process pprightarrow HHjj at the LHC.

The minimal scalar-vectorlike top interpretation of the diphoton excess

A resonance near 750GeV has been observed at both ATLAS and CMS experiments in the diphoton channel. We propose an interpretation based on a simplified model, in which a 750GeV scalar singlet and compressed vectorlike tops are introduced. At the LHC, the new scalar is produced through gluon fusion, and subsequently decays to the diphoton final state, with the new vectorlike quarks running in the loop diagram. We find that the compressed tops with their masses around 400-500GeV and couplings around 0.5-1.5 could explain the diphoton excess, while keeping signals of other channels under the current LHC search limits. We also comment on other potential signatures of this vectorlike top model.

Gluon fusion andbb¯corrections to HW + W − / HZZ production in the POWHEG-BOX

The study of the Higgs boson properties is one of the most important tasks to be accomplished in the next years, at the Large Hadron Collider (LHC) and at future colliders such as the Future Circular Collider in hadron-hadron mode (FCC-hh), the potential 100 TeV follow-up of the LHC machine. In this view the precise study of the Higgs couplings to weak gauge bosons is crucial and requires as much information as possible. After the recent calculation of the next-to-leading order QCD corrections to the production cross sections and differential distributions of a Standard Model Higgs boson in association with a pair of weak bosons, matched with parton shower in the POWHEG-BOX framework, we present the gluon fusion correction $g g\to H W^+_{} W^-_{} ( H Z Z)$ to the process $p p \to H W^+_{} W^-_{} (H Z Z)$. This correction can be sizeable and amounts to $+3\,\%$ ($+10\,\%$) in the $H W^+_{} W^-_{}$ process and $+5\,\%$ ($+18\,\%$) in the $H Z Z$ process at the LHC (FCC-hh). We also present the first study of the impact of the bottom--quark initiated channels $b\bar{b}\to H W^+_{} W^-_{} / H Z Z$ and find that they induce a significant $+18\,\%$ correction in the $H W^+_{} W^-_{}$ channel at the FCC-hh. We present results on total cross sections and distributions at the LHC and at the FCC-hh.

NNLO QCD corrections to the Drell\u2013Yan cross section in models of TeV-scale gravity

The first results on the complete next-to-next-to-leading order (NNLO) Quantum Chromodynamic (QCD) corrections to the production of di-leptons at hadron colliders in large extra dimension models with spin-2 particles are reported in this article. In particular, we have computed these corrections to the invariant mass distribution of the di-leptons taking into account all the partonic sub-processes that contribute at NNLO. In these models, spin-2 particles couple through the energy-momentum tensor of the Standard Model with the universal coupling strength. The tensorial nature of the interaction and the presence of both quark annihilation and gluon fusion channels at the Born level make it challenging computationally and interesting phenomenologically. We have demonstrated numerically the importance of our results at Large Hadron Collider energies. The two-loop corrections contribute an additional 10% to the total cross section. We find that the QCD corrections are not only large but also important to make the predictions stable under renormalisation and factorisation scale variations, providing an opportunity to stringently constrain the parameters of the models with a spin-2 particle.