Higgs Production Processes Research Articles

Constraints on the trilinear and quartic Higgs couplings from triple Higgs production at the LHC and beyond

AbstractExperimental information on the trilinear Higgs boson self-coupling $$\kappa _3$$ κ 3 and the quartic self-coupling $$\kappa _4$$ κ 4 will be crucial for gaining insight into the shape of the Higgs potential and the nature of the electroweak phase transition. While Higgs pair production processes provide access to $$\kappa _3$$ κ 3 , triple Higgs production processes, despite their small cross sections, will provide valuable complementary information on $$\kappa _3$$ κ 3 and first experimental constraints on $$\kappa _4$$ κ 4 . We investigate triple Higgs boson production at the HL-LHC, employing efficient Graph Neural Network methodologies to maximise the statistical yield. We show that it will be possible to establish bounds on the variation of both couplings from the HL-LHC analyses that significantly go beyond the constraints from perturbative unitarity. We also discuss the prospects for the analysis of triple Higgs production at future high-energy lepton colliders operating at the TeV scale.

Higgs production at next generation e+e− colliders

In this study, Higgs production processes, Higgsstrahlung and vector boson ([Formula: see text] and [Formula: see text]) fusion processes, are investigated for four different future lepton colliders (CEPC, ILC, CLIC, and FCC-ee). The cross-sections for each production process and corresponding backgrounds are calculated considering the Initial State Radiation (ISR) and Beamstrahlung (BS) effects. Various cuts and the b-tagging method are used to reduce the background. Finally, the number of events for each collider is determined, and significance calculations are performed. In our calculations, high event numbers are obtained for all four colliders for the Higgsstrahlung, [Formula: see text], and [Formula: see text] fusion process. This shows that electron–positron colliders will play an important role in future Higgs physics research.

Constraining lepton flavor violating Higgs couplings at the HL-LHC in the vector boson fusion channel

We explore the parameter space of lepton flavor violating (LFV) neutral Higgs Yukawa couplings with the muon and tau leptons that can be probed at the high-luminosity Large Hadron Collider (HL-LHC) via the vector boson fusion (VBF) Higgs production process. Our projected sensitivities for the Standard Model Higgs ($h$) LFV branching ratio $\text{Br}(h\ensuremath{\rightarrow}\ensuremath{\mu}\ensuremath{\tau})$ in the $pp\ensuremath{\rightarrow}hjj\ensuremath{\rightarrow}(h\ensuremath{\rightarrow}\ensuremath{\mu}\ensuremath{\tau})jj$ channel at the HL-LHC are contrasted with the current and future low-energy constraints from the anomalous magnetic moment and electric dipole moment of the muon, as well as with other LFV observables, such as $\ensuremath{\tau}\ensuremath{\rightarrow}3\ensuremath{\mu}$ and $\ensuremath{\tau}\ensuremath{\rightarrow}\ensuremath{\mu}\ensuremath{\gamma}$. We also study the LFV prospects of a generic beyond the Standard Model neutral Higgs boson ($H$) with a mass in the range of ${m}_{H}\ensuremath{\in}[20,800]\text{ }\text{ }\mathrm{GeV}$ and give the projected model-independent upper limits on the VBF production cross section of $Hjj$ times the branching ratio of $H\ensuremath{\rightarrow}\ensuremath{\mu}\ensuremath{\tau}$ at the HL-LHC. We interpret these results in the context of a two-Higgs doublet model as a case study.

Anomalous Higgs boson couplings in weak boson fusion production at NNLO in QCD

The production of Higgs bosons in weak boson fusion has the second largest cross section among Higgs-production processes at the LHC. As such, this process plays an important role in detailed studies of Higgs interactions with vector bosons. In this paper we extend the available description of Higgs boson production in weak boson fusion by considering anomalous $HVV$ interactions and NNLO QCD radiative corrections at the same time. We find that, while leading order QCD predictions are too uncertain to allow for detailed studies of the anomalous couplings, NLO QCD results are sufficiently precise, most of the time. The NNLO QCD corrections alter the NLO QCD predictions only marginally, but their availability enhances the credibility of conclusions based on NLO QCD computations.

Collider search of light dark matter model with dark sector decay * *W. Liao is Supported by National Natural Science Foundation of China (11875130). Q.S.Yan is Supported by the National Natural Science Foundation of China (11475180, 11875260)

We explore the possibility that the dark matter relic density is not produced by a thermal mechanism directly, but by the decay of other heavier dark-sector particles which themselves can be produced by the thermal freeze-out mechanism. Using a concrete model with light dark matter from dark sector decay, we study the collider signature of the dark sector particles associated with Higgs production processes. We find that future lepton colliders could be a better place to probe the signature of this kind of light dark matter model than hadron colliders such as LHC. Also, we find that a Higgs factory with center-of-mass energy 250 GeV has a better potential to resolve the signature of this kind of light dark matter model than a Higgs factory with center-of-mass energy 350 GeV.

VH + jet production in hadron-hadron collisions up to order {alpha}_{mathrm{s}}^3 in perturbative QCD

We present precise predictions for the hadronic production of an on-shell Higgs boson in association with a leptonically decaying gauge boson and a jet up to order {alpha}_{mathrm{s}}^3 . We include the complete set of NNLO QCD corrections to both charged- and neutral-current Drell-Yan type contributions, as well as the previously known leading heavy quark loop induced contributions which involve a direct Higgs-quark coupling. As an application, we study a range of differential observables in proton-proton collisions at sqrt{s} = 13 TeV for both the charged- and neutral-current production modes. For each Higgs production process, we assess the improvement in the theoretical uncertainty for both the exclusive (njet = 1) and inclusive (njet ≥ 1) jet categories. We find that the inclusion of the NNLO corrections to the Drell-Yan type contributions is essential in stabilising the predictions and in reducing the theoretical uncertainty for both inclusive and exclusive jet production for all three modes. This is particularly true in the kinematical regimes associated with low to medium values of the transverse momentum of the produced vector boson and where the differential cross sections are the largest. For the neutral-current process, we find that the heavy quark loop induced contributions have their largest phenomenological impact (an increase in the size of the NNLO corrections, a distortion of the distribution shape and an enlargement of the left over remaining uncertainties) in kinematical regions associated to large values of pT,Z (typically above 150 GeV) where the cross sections are smaller.

Mixed QCD-EW corrections for Higgs leptonic decay via HW+W\u2212 vertex

We consider the two-loop corrections to the HW+W− vertex at order ααs. We construct a canonical basis for the two-loop integrals using the Baikov representation and the intersection theory. By solving the ϵ-form differential equations, we obtain fully analytic expressions for the master integrals in terms of multiple polylogarithms, which allow fast and accurate numeric evaluation for arbitrary configurations of external momenta. We apply our analytic results to the decay process H → νeeW, and study both the integrated and differential decay rates. Our results can also be applied to the Higgs production process via W boson fusion.

Two paths towards precision at a very high energy lepton collider

We illustrate the potential of a very high energy lepton collider (from 10 to 30 TeV center of mass energy) to explore new physics indirectly in the vector boson fusion double Higgs production process and in direct diboson production at high energy. Double Higgs production is found to be sensitive to the anomalous Higgs trilinear coupling at the percent level, and to the Higgs compositeness ξ parameter at the per mille or sub-per mille level thanks to the measurement of the cross-section in the di-Higgs high invariant mass tail. High energy diboson (and tri-boson) production is sensitive to Higgs-lepton contact interaction operators at a scale of several tens or hundred TeV, corresponding to a reach on the Higgs compositeness scale well above the one of any other future collider project currently under discussion. This result follows from the unique capability of the very high energy lepton collider to measure Electroweak cross-sections at 10 TeV energy or more, where the effect of new physics at even higher energy is amplified. The general lesson is that the standard path towards precision physics, based on measurements of high-statistics processes such as single and double Higgs production, is accompanied at the very high energy lepton collider by a second strategy based on measurements at the highest available energy.

A comparative study of the anomalous tHq couplings via the diphoton channel at the LHC

We present a comparative study about the flavor changing neutral Higgs (FCNH) interactions of top quark, i.e., tqh (q=u,c), from two processes with the h→γγ decay channel: top quark pair production pp→tt¯ with one top decaying to hq, and the anomalous single top plus Higgs production process pp→th. We perform a full simulation for the signals and the relevant SM backgrounds based on two separate cut selections at the future 14 TeV High Luminosity LHC (HL-LHC). The results show that the SM background can be greatly reduced for both selection methods. The branching ratios of t→uh and t→ch can be, respectively, probed to 1.4×10−4 and 1.5×10−4 at the 95% Confidence Level (CL), which is consistent with the dedicated study performed by the ATLAS collaboration. The advantage of the pp→th process is that the origin of the signal from tuh or tch couplings could be clarified by studying the diphoton pseudo-rapidity and the charges of the charged lepton from the top decay. If we only consider the signal coming from this process, the upper limit on the branching ratio of about Br(t→uh)=2.4×10−4 at the 95% CL is obtained. Altogether, these limits are one order of magnitude better than the current 13 TeV LHC experimental results.

NNLOPS description of the H\u2192 boverline{b} decay with MiNLO

We present an event generator that describes the Higgs boson decay into b-quarks at next-to-next-to-leading-order (NNLO) in QCD and allows for a consistent matching to parton shower. For this purpose, we work within the POWHEG framework and employ the MiNLO method to produce an NNLO-accurate H → boverline{b} event sample which can further be interfaced with a generic Higgs boson production mode. The resulting events, that combine Higgs production and decay, can be matched to parton shower by means of a vetoed shower. As an example, we present a short phenomenological study for associated Higgs production (HZ) and vector boson fusion (VBF) processes. We release the source code that was used to obtain these results as an h_bbg user process in POWHEG-BOX-V2. We also provide tools that enable interfacing the decay events with events for an arbitrary Higgs production mode and subsequent matching of the combined Les Houches (LH) events with a parton shower.

Direct measurement of the Higgs self-coupling in e+e− → ZH

A new method to measure the trilinear Higgs self-coupling λ3 in a single Higgs production process is proposed. Time-reversal-odd (T-odd) asymmetries in the process e+e−→ZH, Z→ff¯ are computed from the absorptive part of the electroweak one-loop amplitude. Since the T-odd asymmetries measure the tree-level t-channel ZH→ZH scattering, they can be direct probes of λ3. The proposed method is quite challenging; a relatively large statistics and polarized e+e− beams are demanded. However, this is probably the only approach to directly measure λ3 in e+e− collisions, when a beam energy above the ZHH production threshold is not available.

One-loop effects of Minimal Supersymmetric Standard Model particles in $e^-e^+\to Zh$ and $e^-e^+\to \nu\bar\nu h$ at the International Linear Collider

The 1-loop effects of the MSSM at the ILC are investigated through numerical analysis. We studied the higgs production processes $e^-e^+\rightarrow Zh$ and $e^-e^+\rightarrow \nu\bar{\nu}h$ at the ILC. It is found that the magnitude of the MSSM contribution through the 1-loop effects is sizable enough to be detected. In the study, three sets of the MSSM parameters are proposed, which are consistent with the observed higgs mass, the muon $g$-$2$, the dark matter abundance and the decay branching ratios of $B$ mesons. In the $e^-e^+\rightarrow Zh$ process, the 1-loop effects of the MSSM are visible and the distinction of the parameter sets is partially possible. For the study of $e^-e^+\rightarrow \nu\bar{\nu}h$, we used the equivalent $\it W$-boson approximation in the evaluation of the 1-loop cross section. While the 1-loop effect of the MSSM is visible, the distinction of the parameter sets might not be possible in this process under the value of realistic luminosity at the ILC.

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.

Electroweak precision tests in high-energy diboson processes

A promising avenue to perform precision tests of the SM at the LHC is to measure differential cross-sections at high invariant mass, exploiting in this way the growth with the energy of the corrections induced by heavy new physics. We classify the leading growing-with-energy effects in longitudinal diboson and in associated Higgs production processes, showing that they can be encapsulated in four real “high-energy primary” parameters. We assess the reach on these parameters at the LHC and at future hadronic colliders, focusing in particular on the fully leptonic W Z channel that appears particularly promising. The reach is found to be superior to existing constraints by one order of magnitude, providing a test of the SM electroweak sector at the per-mille level, in competition with LEP bounds. Unlike LHC run-1 bounds, which only apply to new physics effects that are much larger than the SM in the high-energy tail of the distributions, the probe we study applies to a wider class of new physics scenarios where such large departures are not expected.

Optimizing Higgs factories by modifying the recoil mass**JG is Supported by an International Postdoctoral Exchange Fellowship Program between the Office of the National Administrative Committee of Postdoctoral Researchers of China (ONACPR) and DESY. YYL is Supported by Hong Kong PhD Fellowship (HKPFS) and the Collaborative Research Fund (CRF) (HUKST4/CRF/13G)

It is difficult to measure the WW-fusion Higgs production process at a lepton collider with a center of mass energy of 240-250 GeV due to its small rate and the large background from the Higgsstrahlung process with an invisible Z . We construct a modified recoil mass variable, , defined using only the 3-momentum of the reconstructed Higgs particle, and show that it can separate the WW-fusion and Higgsstrahlung events better than the original recoil mass variable mrecoil. Consequently, the variable can be used to improve the overall precisions of the extracted Higgs couplings, in both the conventional framework and the effective-field-theory framework. We also explore the application of the variable in the inclusive cross section measurements of the Higgsstrahlung process, while a quantitive analysis is left for future studies.

Electroweak Higgs production with HiggsPO at NLO QCD

We present the HiggsPO UFO model for Monte Carlo event generation of electroweak VH and VBF Higgs production processes at NLO in QCD in the formalism of Higgs pseudo-observables (PO). We illustrate the use of this tool by studying the QCD corrections, matched to a parton shower, for several benchmark points in the Higgs PO parameter space. We find that, while being sizable and thus important to be considered in realistic experimental analyses, the QCD higher-order corrections largely factorize. As an additional finding, based on the NLO results, we advocate to consider 2D distributions of the two-jet azimuthal-angle difference and the leading jet p_T for new physics searches in VBF Higgs production. The HiggsPO UFO model is publicly available.

Next-to-leading-order QCD corrections to e+e− → H + γ

The associated production of Higgs boson with a hard photon at lepton collider, i.e., e+e−→Hγ, is known to bear a rather small cross section in Standard Model, and can serve as a sensitive probe for the potential new physics signals. Similar to the loop-induced Higgs decay channels H→γγ,Zγ, the e+e−→Hγ process also starts at one-loop order provided that the tiny electron mass is neglected. In this work, we calculate the next-to-leading-order (NLO) QCD corrections to this associated H+γ production process, which mainly stem from the gluonic dressing to the top quark loop. The QCD corrections are found to be rather modest at lower center-of-mass energy range (s<300 GeV), thus of negligible impact on Higgs factory such as CEPC. Nevertheless, when the energy is boosted to the ILC energy range (s≈400 GeV), QCD corrections may enhance the leading-order cross section by 20%. In any event, the e+e−→Hγ process has a maximal production rate σmax≈0.08 fb around s=250 GeV, thus CEPC turns out to be the best place to look for this rare Higgs production process. In the high energy limit, the effect of NLO QCD corrections become completely negligible, which can be simply attributed to the different asymptotic scaling behaviors of the LO and NLO cross sections, where the former exhibits a milder decrement ∝1/s , but the latter undergoes a much faster decrease ∝1/s2.

NLO electroweak corrections in general scalar singlet models

If no new physics signals are found, in the coming years, at the Large Hadron Collider Run-2, an increase in precision of the Higgs couplings measurements will shift the discussion to the effects of higher order corrections. In Beyond the Standard Model (BSM) theories this may become the only tool to probe new physics. Extensions of the Standard Model (SM) with several scalar singlets may address several of its problems, namely to explain dark matter, the matter-antimatter asymmetry, or to improve the stability of the SM up to the Planck scale. In this work we propose a general framework to calculate one loop-corrections to the propagators and to the scalar field vacuum expectation values of BSM models with an arbitrary number of scalar singlets. We then apply our method to a real and to a complex scalar singlet models. We assess the importance of the one-loop radiative corrections first by computing them for a tree level mixing sum constraint, and then for the main Higgs production process gg → H. We conclude that, for the currently allowed parameter space of these models, the corrections can be at most a few percent. Notably, a non-zero correction can survive when dark matter is present, in the SM-like limit of the Higgs couplings to other SM particles.

Implications of CP -violating top-Higgs couplings at the LHC and Higgs factories

We utilise the LHC Run-1 and -2 Higgs data to constrain the CP-violating top-Higgs couplings. In order to satisfy the current full Higgs data sets at $2\sigma$ level, the CP-odd component $C^p_t$ and the CP-even component $C^s_t$ have to be within the ranges $|C^p_t|< 0.37$ and $0.85 <C^s_t< 1.20$, respectively, which is stronger than the LHC Run-1 bound $|C^p_t|< 0.54$ and $0.68 <C^s_t< 1.20$. With the new bound, we explore the impact on the CP-violating top-Higgs couplings in the Higgs production processes $pp \to t\bar{t}h, thj, hh$ at 13 TeV LHC, and $e^+e^- \to hZ, h\gamma$ at future 240 GeV Higgs factories. We find that the cross sections of $pp \to t\bar{t}h$, $pp \to thj$, $pp \to hh$, $e^+e^- \to hZ$ and $e^+e^- \to h\gamma$ can be enhanced up to 1.41, 1.18, 2.20, 1.001 and 1.09 times as large as the SM predictions, respectively. The future precision measurement of the process $e^+e^- \to h\gamma$ with an accuracy of 5\% will be able to constrain $|C^p_t|<0.19$ at most at a 240 GeV $e^+e^-$ Higgs factory.

Effective fermion–Higgs interactions at an e+e− collider with polarized beams

We consider the possibility of new physics giving rise to effective interactions of the form e+e−Hff¯, where f represents a charged lepton ℓ or a (light) quark q, and H the recently discovered Higgs boson. Such vertices would give contributions beyond the standard model to the Higgs production processes e+e−→Hℓ+ℓ− and e+e−→Hqq¯ at a future e+e− collider. We write the most general form for these vertices allowed by Lorentz symmetry. Assuming that such interactions contribute in addition to the standard model production processes, where the final-state fermion pair comes from the decay of the Z boson, we obtain the differential cross section for the processes e+e−→Hℓ+ℓ− and e+e−→Hqq¯ to linear order in the effective interactions. We propose several observables with differing CP and T properties which, if measured, can be used to constrain the couplings occurring in interaction vertices. We derive possible limits on these couplings that may be obtained at a collider with centre-of-mass energy of 500 GeV and an integrated luminosity of 500 fb−1. We also carry out the analysis assuming that both the electron and positron beams can be longitudinally polarized, and find that the sensitivity to the couplings can be improved by a factor of 2–4 by a specific choice of the signs of the polarizations of both the electron and positron beams for the same integrated luminosity.