Higgs Production Research Articles

Introducing tools to test Higgs boson interactions via WW scattering. II. The coupled-channel formalism and scalar resonances

In this work we explore in detail the presence of scalar resonances in $WW$ fusion process in the context of the LHC experiments working in the theoretical framework provided by Higgs Effective Field Theories (HEFT). While the phenomenology of vector resonances is reasonably understood in the framework of Weinberg sum-rules and unitarization studies, scalar resonances are a lot less constrained and, more importantly do depend on HEFT low-energy effective couplings different from the ones of vector resoances that are difficult to constrain experimentally. More specifically, unitarization techniques combined with the requirement of causality allows us to set non-trivial bounds on Higgs self-interactions. This is due to the need of considering coupled channels in the scalar case along the unitarization process. As a byproduct, we can gain some relevant information on the Higgs sector from $WW\to WW$ elastic processes without needing to consider two Higgs production.

Search for Higgs boson decays to a Z boson and a photon in proton-proton collisions at sqrt{s} = 13 TeV

Results are presented from a search for the Higgs boson decay H → Zγ, where Z → ℓ+ℓ− with ℓ = e or μ. The search is performed using a sample of proton-proton (pp) collision data at a center-of-mass energy of 13 TeV, recorded by the CMS experiment at the LHC, corresponding to an integrated luminosity of 138 fb−1. Events are assigned to mutually exclusive categories, which exploit differences in both event topology and kinematics of distinct Higgs production mechanisms to enhance signal sensitivity. The signal strength μ, defined as the product of the cross section and the branching fraction left[sigma left(textrm{pp}to textrm{H}right)mathcal{B}left(textrm{H}to textrm{Z}upgamma right)right] relative to the standard model prediction, is extracted from a simultaneous fit to the ℓ+ℓ−γ invariant mass distributions in all categories and is measured to be μ = 2.4 ± 0.9 for a Higgs boson mass of 125.38 GeV. The statistical significance of the observed excess of events is 2.7 standard deviations. This measurement corresponds to left[sigma left(textrm{pp}to textrm{H}right)mathcal{B}left(textrm{H}to textrm{Z}upgamma right)right]=0.21pm 0.08 pb. The observed (expected) upper limit at 95% confidence level on μ is 4.1 (1.8), where the expected limit is calculated under the background-only hypothesis. The ratio of branching fractions mathcal{B}left(textrm{H}to textrm{Z}upgamma right)/mathcal{B}left(textrm{H}to upgamma upgamma right) is measured to be {1.5}_{-0.6}^{+0.7} , which agrees with the standard model prediction of 0.69 ± 0.04 at the 1.5 standard deviation level.

First look at the evaluation of three-loop non-planar Feynman diagrams for Higgs plus jet production

We present new computations for Feynman integrals relevant to Higgs plus jet production at three loops, including first results for a non-planar class of integrals. The results are expressed in terms of generalised polylogarithms up to transcendental weight six. We also provide the full canonical differential equations, which allows us to make structural observations on the answer. In particular, we find a counterexample to previously conjectured adjacency relations, for a planar integral of the tennis-court type. Additionally, for a non-planar triple ladder diagram, we find two novel alphabet letters. This information may be useful for future bootstrap approaches.

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.

Effects of one-loop on-shell and off-shell decay H* → VV at future lepton colliders

One-loop on-shell and off-shell decays H → VV with VV = γγ, Zγ, ZZ are presented in this paper. The effects of one-loop on-shell and off-shell Higgs decays via Higgs productions at future lepton colliders are also then examined. We find that the impacts of one-loop Higgs decays are significant and they are should be taken into account at future lepton colliders.

Threshold enhanced cross sections for colorless productions

We study the threshold effect for neutral and charged Drell-Yan productions, associated production of Higgs boson with a massive vector boson and Higgs production in bottom quark annihilation at LHC to the third order in QCD. Using the third order soft-virtual results for these processes and exploiting the universality of the threshold logarithms, we extract the process-dependent coefficients for these processes and resum large threshold logarithms to next-to-next-to-next-to leading logarithmic (N$^3$LL) accuracy. By matching our results to the recently available N$^3$LO results, we provide the most precise theoretical predictions for these processes. We present numerical results for invariant mass distribution and total production cross-sections. We find the conventional scale uncertainties of about $0.4\%$ at N$^3$LO level in the fixed order results get reduced to as small as less than $0.1\%$ at N$^3$LO+N$^3$LL level in the high invariant mass region.

Amplitude evaluation with pySecDec: A Higgs + three gluons example

We present an application of the major new features of pySecDec, a program designed to numerically calculate multi-loop integrals. One important new feature is the ability to integrate weighted sums of integrals in a way which is optimised to reach a given accuracy goal on the sums rather than on the individual integrals. Another feature is the option to perform asymptotic expansions. These new assets of the program represent an important step towards the efficient evaluation of multi-loop amplitudes in a largely automated way. We will illustrate them in a pedagogical example, through the calculation of the one-loop amplitude for Higgs plus jet production in the gluon channel, mediated by a top quark loop. Numerical results in the heavy top limit, compared to their analytic counterparts, are shown as well.

Signal to background discrimination for the production of double Higgs boson events via vector boson fusion mechanism in the decay channel with four charged leptons and two b-jets in the final state at the LHC experiment

At the CERN Large Hadron Collider experiment, the non-resonant double Higgs production via vector-boson fusion represents a unique mean to probe the VVHH (V=Z, W±) Higgs self-coupling at the current center of mass energies. Such a rare signal cannot be separated efficiently from huge backgrounds by applying a few-observables cut-based selection. Indeed, in this work, a Deep Learning algorithm is used to decide whether an event is more signal- or background-like. In particular, we report on two main aspects: results on a hyper-parameters parallel scanning strategy to distribute the training process across multiple nodes on the ReCaS-Bari data center computing resources and on the discriminating performance of a Deep Neural Network architecture.

Single charged Higgs boson production at the LHC

A search for charged Higgs may yield clear and direct signs of new physics outside the realm of the Standard Model (SM). In the Two-Higgs Doublet Model (2HDM), we investigate two of the main single charged Higgs production channels at the Large Hadron Collider (LHC), assuming that either h or H replicates the detected resonance at ∼125GeV. We consider the possibility of the charged Higgs boson production through the pp→H±W∓ and pp→H±bj production processes that may present additional significance at the LHC experiments. Considering the H±→W±hi/A decay channels and mainly concentrating on the bb¯, ττ and γγ decays of hi and A, we examine the possible signatures arising from the aforementioned charged Higgs production and decay in both type-I and type-X realizations of 2HDM. Our study shows that these signatures can have sizable rates at low tan⁡β as long as the condition MH±<mt−mb is satisfied. As a result, we propose the bb, ττ and γγ final states associated with WW or Wbj as an encouraging experimental avenue that would complement the LHC search for a charged Higgs boson.

Disentangling the high- and low-cutoff scales via the trilinear Higgs couplings in the type-I two-Higgs-doublet model

The type-I two-Higgs-doublet model in the inverted Higgs scenario can retain the theoretical stability all the way up to the Planck scale. The Planck-cutoff scale, $\Lambda_{\rm cut}^{\rm Planck}$, directly impacts the mass spectra such that all the extra Higgs boson masses should be light below about 160 GeV. However, the observation of the light masses of new Higgs bosons does not indicate the high cutoff scale because a low cutoff scale can also accommodate the light masses. Over the viable parameter points that satisfy the theoretical requirements and the experimental constraints, we show that the trilinear Higgs couplings for low $\Lambda_{\rm cut}$ are entirely different from those for the Planck-cutoff scale. The most sensitive coupling to the cutoff scale is from the $h$-$h$-$h$ vertex, where $h$ is the lighter CP-even Higgs boson at a mass below 125 GeV. Among the multi-Higgs productions mediated by Higgs bosons, the gluon fusion processes of $gg \to h h $ and $gg \to AA$ are insensitive to the cutoff scale, yielding a small variation of $\mathcal{O}(1)\,{\rm fb}$ according to $\Lambda_{\rm cut}$. The smoking-gun signature is from the triple Higgs production of $q\bar{q}' \to W^* \to H^\pm hh$, which solely depends on the $h$-$h$-$h$ vertex. The cross section for $\Lambda_{\rm cut}=1\,{\rm TeV}$ is about $10^3$ times larger than that for the Planck-cutoff scale. Since the decay modes of $H^\pm \to W^* h/W^* A$ and $h/A \to bb$ are dominant, the process yields the $6b+\ell\nu$ final state, which enjoys an almost background-free environment. Consequently, the precision measurement of $pp \to H^\pm hh$ can probe the cutoff scale of the model.

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.

Double Higgs boson production at TeV e+e− colliders with effective field theories: Sensitivity to BSM Higgs couplings

In this work we study the production of two Higgs bosons at the two planned electron positron colliders with energies at the TeV domain, CLIC and ILC, within the context of Effective Field Theories (EFTs) to describe beyond the Standard Model Higgs Physics. We focus first on the case of the Higgs Effective Field Theory (HEFT) and next we compare with the case of the Standard Model Effective Field Theory (SMEFT). The predictions for double Higgs production in both EFTs are first presented for the most relevant subprocess participating in the total process of our interest, $e^+e^- \to HH \nu \bar \nu$, which is the scattering of two gauge bosons, $WW \to HH$, also called $WW$ fusion. The predictions for the cross section $ \sigma(W_X W_Y\to HH)$ as a function of the subprocess energy are analyzed in full detail for the two EFTs, for all the polarization channels with longitudinal and transverse modes $XY=LL, TT,LT,TL$, and for the most relevant effective operators in both cases. We will demonstrate that in the HEFT case, the total cross section can be fully understood in terms of the $LL$ contribution and this in turn is dominated at these TeV energies mainly by two HEFT coefficients. By doing the matching between the two EFTs at the level of the scattering amplitude for the subprocess, we will be able to find the correspondence of the leading coefficients in the HEFT and the SMEFT. In the final part of this work we will then explore the sensitivity to these two most relevant HEFT coefficients, at CLIC (3 TeV, 5 ab$^{-1}$) and ILC (1 TeV, 8 ab$^{-1}$). We will then conclude on the accessible region of these two parameters by studying the predicted rates at these two $e^+e^-$ colliders for the final state $b \bar b b \bar b \nu \bar \nu$ leading to characteristic signals with 4 bottom jets and missing energy.

Electroweak corrections to Higgs boson production via W W fusion at the future LHeC

Precision measurement of quark Yukawa couplings is a crucial aspect of the Higgs property study. Proposed as a future upgrade of the Large Hadron Collider (LHC), the Large Hadron electron Collider (LHeC) provides opportunities to probe quark Yukawa couplings with a high precision because of relatively low QCD background as compared with that of the Higgs processes at the LHC. For this purpose, it is important to have a precision prediction of the Higgs production rate at the LHeC. The leading production channel of the Higgs boson at the LHeC is via weak boson fusion (WBF) which has the unique kinematic feature of forward tagging jets. As QCD corrections are suppressed by the simple color structure of the process, electroweak (EW) radiative corrections become particularly important. In this paper, we focus on the EW radiative corrections at next-to-leading order for the Higgs-boson production via charge current WBF processes at the LHeC. In the two renormalization schemes we use, the EW corrections are respectively at the level of 9% and 18% relative to the leading order result, for a center-of-mass energy at 1.98 TeV, and the next-to-leading order results in both schemes agree up to a truncation error expected from the perturbative method. The size of the EW corrections exceeds that from QCD radiations and is shown to be important for the study of Higgs phenomenology.

The charged Higgs from the Bottom-Up: probing flavor at the LHC

We systematically study model-independent constraints on the three generic charged Higgs couplings to b-quarks and up-type quarks. While existing LHC searches have focussed on the tb coupling, we emphasize that the LHC plays a crucial role in probing also ub and cb couplings, since constraints from flavor physics are weak. In particular we propose various new searches that can significantly extend the present reach on the parameter space by: i) looking for light charged Higgses that decay into ub-quarks, ii) probing charged Higgs couplings to light and top quarks using multi-b-jet signatures, iii) looking for single b-quarks in low-mass dijet searches, iv) searching for charge asymmetries induced by charged Higgs production via ub couplings.

Measurement of the Higgs quartic coupling c 2 v from di-Higgs Vector Boson Fusion in the channel

The Brout Englert Higgs (BEH) mechanism of electroweak symmetry breaking and mass generation was experimentally confirmed after the discovery of the Higgs boson at the Large Hadron Collider in 2012. The BEH mechanism not only predicts the existence of a massive scalar particle, but also requires this scalar particle to couple to itself. Double Higgs production provides a unique handle, since it allows the extraction of the trilinear Higgs self-coupling. VBF di-Higgs production also probes the quartic Higgs bosons to vector bosons coupling (c 2 v). In this topic the effort on setting constraints on c 2 v will be discussed. Event selection and reconstruction will be illustrated as well as a Neural Network designed to identify VBF events.

Probing non-standard HVV (V = W, Z) couplings in single Higgs production at future electron-proton collider

The couplings of the Higgs boson (H) with massive gauge bosons of weak interaction (V = W, Z), can be probed in single Higgs boson production at the proposed future Large Hadron-Electron Collider (LHeC). In the collision of an electron with a pro- ton, single Higgs production takes place via so-called charged-current (e−p → νeHj) and neutral-current (e−p → e−Hj) processes. We explore the potential of the azimuthal angle correlation between the forward jet and scattered neutrino or electron in probing the non-standard HVV couplings at the collider center-of-mass energy of sqrt{s} ≈ 1.3 TeV. We choose the most general modifications (of CP-even and CP-odd nature) to these couplings due to new physics effects beyond the standard model. We derive exclusion limits on new physics parameters of HV V couplings as a function of integrated luminosity at 95% C.L. using the azimuthal angular correlations in charged- and neutral-current processes. We find that using 1000 fb−1 data, the standard model-like new physics parameters in HWW and HZZ couplings can be constrained with accuracies of 4% and 15%, respectively. The least constrained CP-even parameters of HWW coupling can be as large as 0.04, while those of HZZ coupling can have values around 0.31. Allowed values of CP-odd parameters in HWW and HZZ couplings are found to be around 0.14 and 0.34, respectively. We also study changes in the allowed values of non-trivial new physics parameters in the presence of other parameters.

NNLO study of top-quark mass renormalization scheme uncertainties in Higgs boson production

The ambiguity in the choice of a renormalization scheme and scale for the top-quark mass leads to an additional source of theoretical uncertainty in the calculation of the Higgs boson production cross section via gluon fusion. These uncertainties were found to be dominant in the case of off-shell Higgs production at next-to-leading order in QCD for large values of the Higgs virtuality {m}_H^{ast } . In this work, we study the uncertainties related to the top-quark mass definition up to next-to-next-to-leading order (NNLO) in QCD. We include the full top-quark mass dependence up to three loops in the virtual corrections, and evaluate the real contributions in the soft limit, therefore obtaining the so-called soft-virtual (SV) approximation. We construct NNLOSV predictions for off-shell Higgs boson production renormalizing the top-quark mass within both the on-shell (OS) and the overline{mathrm{MS}} schemes, and study in detail the differences between them. While the differences between the two schemes are sizeable, we find that the predictions are always compatible within scale uncertainties. We also observe that the difference between renormalization schemes is largely reduced when increasing the order of the perturbative expansion. We analyze the quality of the convergence of the perturbative series in both schemes, and find that at large invariant masses the overline{mathrm{MS}} results present much larger corrections than their OS counterparts. We also comment on the more complicated case of Higgs boson pair production.

Benchmarking di-Higgs production in various extended Higgs sector models

We present a comprehensive study on Higgs pair production in various archetypical extended Higgs sectors such as the real and the complex 2-Higgs-Doublet Model, the 2-Higgs-Doublet Model augmented by a real singlet field and the Next-to-Minimal Supersymmetric extension of the Standard Model. We take into account all relevant theoretical and experimental constraints, in particular the experimental limits on non-resonant and resonant Higgs pair production. We present the allowed cross sections for Standard Model (SM)-like Higgs pair production and the ranges of the SM-like Yukawa and trilinear Higgs self-coupling that are still compatible with the applied constraints. Furthermore, we give results for the pair production of a SM-like with a non-SM-like Higgs boson and for the production of a pair of non-SM-like Higgs bosons. We find that di-Higgs production in the models under investigation can exceed the SM rate substantially, not only in the non-resonance region but also due to resonant enhancement. We give several benchmarks with interesting features such as large cross sections, the possibility to test CP violation, Higgs-to-Higgs cascade decays or di-Higgs production beating single Higgs production. In all of our benchmark points, the next-to-leading order QCD corrections are included in the large top-mass limit. For these points, we found that, depending on the model and the Higgs pair final state, the corrections increase the leading order cross section by a factor of 1.79 to 2.24. We also discuss the relation between the description of Higgs pair production in an effective field theory approach and in the specific models investigated here.

High precision higgs from high energy muon colliders

Muon colliders are an exciting possibility for reaching the highest energies possible on the shortest timescale. They potentially combine the greatest strengths of e+e− and pp colliders by bridging the energy versus precision dichotomy. In this paper we study the sensitivity of Higgs properties that can be achieved with a future 3 or 10 TeV muon collider from single Higgs production. The results presented here represent the first comprehensive picture for the precision achievable including backgrounds and using fast detector simulation with Delphes. Additionally, we compare the results of fast detector simulation with available full simulation studies that include the muon collider specific Beam Induced Background, and show the results are largely unchanged. We comment on some of the strengths and weaknesses of a high energy muon collider for Higgs physics alone, and demonstrate the complementarity of such a collider with the LHC and e+e− Higgs factories. Furthermore, we discuss some of the exciting avenues for improving future results from both theoretical and detector R&D that could be undertaken.

NLO multijet merging for Higgs production beyond the VBF approximation

We present results of the simulation of electroweak Higgs boson production at the Large Hadron Collider using both the NLO multijet merging and NLO matching frameworks provided by the general purpose event generator Herwig 7. For the simulation of the hard scattering processes, we use the HJets library for the full calculation and VBFNLO for the approximate calculation to compute the 2rightarrow h+n amplitudes at tree-level with n=2,3,4 and at one-loop with n=2,3.