Gluon Fusion Research Articles

Approaching robust EFT limits for CP violation in the Higgs sector

Constraining CP-violating interactions in effective field theory (EFT) of dimension six faces two challenges. Firstly, degeneracies in the multi-dimensional space of Wilson coefficients have to be lifted. Secondly, quadratic contributions of CP-odd dimension six operators are difficult to disentangle from squared contributions of CP-even dimension six operators and from linear contributions of dimension eight operators. Both of these problems are present when new sources of CP-violation are present in the interactions between the Higgs boson and heavy strongly-interacting fermions. We show that degeneracies in the Wilson coefficients can be removed by combining measurements of Higgs-plus-two-jet production via gluon fusion with measurements of top-pair associated Higgs production. In addition, we demonstrate that the sensitivity of the analysis can be improved by exploiting the top-quark threshold in the gluon fusion process. Finally, we substantiate a perturbative argument about the validity of EFT by comparing the quadratic and linear contributions from CP-odd dimension six operators and use this to show explicitly that high statistics measurements at future colliders enable the extraction of perturbatively robust constraints on the associated Wilson coefficients.

One-loop QCD contributions to differential cross-sections for Higgs production at N3LO

We present one-loop contributions to the fully differential Higgs boson gluon-fusion cross-section for Higgs production via gluon fusion. Our results constitute a necessary ingredient of a complete N3LO determination of the cross-section. We perform our computation using a subtraction method for the treatment of soft and collinear singularities. We identify the infrared divergent parts in terms of universal splitting and eikonal functions, and demonstrate how phase-space integrations yield poles (up to 1/ε6) in the dimensional regulator ε = (4 − d)/2. We compute the coefficients of the ε expansion, including the finite part numerically. As a demonstration of our numerical implementation, we present the corrections at N3LO due to one-loop amplitudes in the rapidity and transverse momentum of the Higgs boson.

Combined measurements of Higgs boson couplings in proton\u2013proton collisions at sqrt{s}=13,text {Te}text {V}

Combined measurements of the production and decay rates of the Higgs boson, as well as its couplings to vector bosons and fermions, are presented. The analysis uses the LHC proton–proton collision data set recorded with the CMS detector in 2016 at sqrt{s}=13,text {Te}text {V} , corresponding to an integrated luminosity of 35.9{,text {fb}^{-1}} . The combination is based on analyses targeting the five main Higgs boson production mechanisms (gluon fusion, vector boson fusion, and associated production with a mathrm {W} or mathrm {Z} boson, or a top quark-antiquark pair) and the following decay modes: mathrm {H} rightarrow gamma gamma , mathrm {Z}mathrm {Z}, mathrm {W}mathrm {W}, mathrm {tau }mathrm {tau }, mathrm {b} mathrm {b} , and mathrm {mu }mathrm {mu }. Searches for invisible Higgs boson decays are also considered. The best-fit ratio of the signal yield to the standard model expectation is measured to be mu =1.17pm 0.10, assuming a Higgs boson mass of 125.09,text {Ge}text {V} . Additional results are given for various assumptions on the scaling behavior of the production and decay modes, including generic parametrizations based on ratios of cross sections and branching fractions or couplings. The results are compatible with the standard model predictions in all parametrizations considered. In addition, constraints are placed on various two Higgs doublet models.

Finite quark-mass effects in Higgs boson production with dijets at large energies

The production of a Higgs boson in association with at least two jets receives contributions both from the fusion of weak vector bosons (VBF) and from QCD processes, especially gluon fusion (GF). The former process is important for measuring the coupling of the Higgs boson to weak bosons, whereas the latter process plays an important role in determining any CP-admixtures in the Higgs sector. In this paper we go beyond the current state-of-the-art for fixed order calculations of the GF process (i.e. one loop H + 2j including full quark mass effects) by including the all-order effects in leading log(ŝ/pt2), together with full quark mass and loop-propagator kinematic effects. We calculate the mass-dependent components and implement the resummation within the framework of High Energy Jets.The high-energy effects suppress the prediction compared to fixed order at large Δy12 and mjj (and therefore within the usual VBF cuts of widely separated jets), just as found in the limit of mt → ∞. The mass dependence is more significant than at fixed order, because the systematic inclusion of the leading logarithms in ŝ/pt2 results in a hardening of the transverse momentum of the Higgs boson, which in turn probes in more detail the loop-structure of the coupling. In particular, the full mass dependence reduces the cross section within VBF cuts by 11% compared to a calculation based just on the infinite top mass limit, but the impact of the bottom quark remains small. This all implies that the gluon-fusion contribution within VBF-cuts is less severe than current estimates suggest.

Probing the scalar potential via double Higgs boson production at hadron colliders

We present a sensitivity study on the cubic and quartic self couplings in double Higgs production via gluon fusion at hadron colliders. Considering the relevant operators in the Standard Model Effective Field Theory up to dimension eight, we calculate the dominant contributions up to two-loop level, where the first dependence on the quartic interaction appears. Our approach allows to study the independent variations of the two self couplings and to clearly identify the terms necessary to satisfy gauge invariance and to obtain UV-finite results order by order in perturbation theory. We focus on the boverline{b}gamma gamma signature for simplicity and provide the expected bounds for the cubic and quartic self couplings at the 14 TeV LHC with 3000 fb−1 (HL-LHC) and for a future 100 TeV collider (FCC-100) with 30 ab−1. We find that while the HL-LHC will provide very limited sensitivity on the quartic self coupling, precision measurements of double Higgs production at a FCC-100 will offer the opportunity to set competitive bounds. We show that combining information from double and triple Higgs production leads to significantly improved prospects for the determination of the quartic self coupling.

Mixed QCD-electroweak corrections to Higgs production via gluon fusion in the small mass approximation

We compute the mixed QCD-electroweak corrections to the cross section for the production of a Higgs boson via gluon fusion, in the limit of a small mass of the electroweak gauge bosons. This limit is regular and we calculate it by setting the W, Z masses to zero in the Feynman rules for their propagators. Our analytic results provide an independent check, in a non-trivial limit, of a recent exact computation for the three-loop mixed QCD and electroweak virtual corrections [1] and the corresponding contribution to the cross section in the soft-virtual approximation [2]. From our calculation in the small mass approximation, we can infer the second term in the expansion of the cross section around the threshold limit with its exact dependence on the masses of the W, Z bosons. Furthermore we find that in the small mass approximation the non-factorizable contributions from the real radiation, so far unknown for full gauge boson mass dependence, are modest in comparison to the known factorizable and virtual contributions to the full mathcal{O}left({alpha}_s^3{alpha}^2right) mixed QCD and electroweak cross-section. This furnishes a new phenomenological test of estimates [3] for the mixed QCD and electroweak corrections, which were based on the hypothesis of factorization of QCD and electroweak corrections.

Measurement of the triple Higgs coupling at a HE-LHC

The currently unmeasured triple Higgs coupling is one of the strong motivations for future physics programs at the LHC and beyond. A sufficiently precise measurement can lead to qualitative changes in our understanding of electroweak symmetry breaking and the cosmological history of the Higgs potential. As such, the quantitative measurement of this coupling is now one of the benchmark measurements for any proposed collider. We study the capability of a potential 27 TeV HE-LHC upgrade in measuring the Higgs trilinear coupling via the di-Higgs production process in the boverline{b}upgamma upgamma channel. We emphasize that a key background from single Higgs production via gluon fusion has been underestimated and underappreciated in prior studies. We perform a detailed study taking into account two different potential detector scenarios, and validate against HL-LHC projections from ATLAS. We find that the di-Higgs production process can be observed at ≥ 4.5σ, corresponding to a ∼ 40% measurement of the Higgs self-coupling, with 15 ab−1 of data at the HE-LHC.

Interference effects in toverline{t} production at the LHC as a window on new physics

Many extensions of the Standard Model (SM) contain (pseudo)scalar bosons with masses in the TeV range. At hadron colliders, such particles would predominantly be produced in gluon fusion and would decay into top quark pair final sates, a signal that interferes with the large QCD background ggto toverline{t} . This phenomenon is of interest for searches for by the LHC experiments. Here, we consider the signal and background interference in this process and study it in various benchmark scenarios, including models with extra singlet (pseudo)scalar resonances, two-Higgs doublet models (2HDM), and the minimal supersymmetric extension of the SM with parameters chosen to obtain the measured light Higgs mass (the hMSSM). We allow for the possible exchanges of beyond the SM vector-like particles as well as scalar quarks. We calculate the possible interference effects including realistic estimates of the attainable detection efficiency and mass resolution. Studies of our benchmark scenarios indicate that searches with an LHC detector could permit the observation of the toverline{t} final states or constrain significantly large regions of the parameter spaces of the benchmark scenarios.

ZZ production at the LHC: NLO QCD corrections to the loop-induced gluon fusion channel

We consider QCD radiative corrections to the production of four charged leptons in hadron collisions. We present the computation of the next-to-leading order QCD corrections to the loop-induced gluon fusion contribution. Our predictions include, for the first time, also the quark-gluon partonic channels. The computed corrections, which are formally of mathcal{O}left({alpha}_{mathrm{S}}^3right) , turn out to increase the loop-induced Born-level result by an amount ranging from 75% to 71% as sqrt{s} ranges from 8 to 13 TeV. We combine our result with state-of-the-art NNLO corrections to the quark annihilation channel, and present updated predictions for fiducial cross sections and distributions for this process.

Precision predictions at N3LO for the Higgs boson rapidity distribution at the LHC

We present precise predictions for the Higgs boson rapidity distribution at the LHC in the gluon fusion production mode. Our approach relies on the fully analytic computation of six terms in a systematic expansion of the partonic differential cross section around the production threshold of the Higgs boson at next-to-next-to-next-to leading order (N$^3$LO) in QCD perturbation theory. We observe a mild correction compared to the previous perturbative order and a significant reduction of the dependence of the cross section on the perturbative scale throughout the entire rapidity range.

Higgs boson production at the LHC using the qT subtraction formalism at N3LO QCD

We consider higher-order QCD corrections to Higgs boson production through gluon-gluon fusion in the large top quark mass limit in hadron collisions. We extend the transverse-momentum (qT ) subtraction method to next-to-next-to-next-to-leading order (N3LO) and combine it with the NNLO Higgs-plus-jet calculation to numerically compute differential infrared-safe observables at N3LO for Higgs boson production in gluon fusion. To cancel the infrared divergences, we exploit the universal behaviour of the associated qT distributions in the small-qT region. We document all the necessary ingredients of the transverse-momentum subtraction method up to N3LO. The missing third-order collinear functions, which contribute only at qT = 0, are approximated using a prescription which uses the known result for the total Higgs boson cross section at this order. As a first application of the third-order qT subtraction method, we present the N3LO rapidity distribution of the Higgs boson at the LHC.

Measurements of gluon–gluon fusion and vector-boson fusion Higgs boson production cross-sections in the H → WW⁎ → eνμν decay channel in pp collisions at [formula omitted] with the ATLAS detector

Higgs boson production cross-sections in proton–proton collisions are measured in the H→WW⁎→eνμν decay channel. The proton–proton collision data were produced at the Large Hadron Collider at a centre-of-mass energy of 13 TeV and recorded by the ATLAS detector in 2015 and 2016, corresponding to an integrated luminosity of 36.1fb−1. The product of the H→WW⁎ branching fraction times the gluon–gluon fusion and vector-boson fusion cross-sections are measured to be 11.4−1.1+1.2(stat.)−1.7+1.8(syst.)pb and 0.50−0.22+0.24(stat.)±0.17(syst.)pb, respectively, in agreement with Standard Model predictions.

Production of prompt photons associated with jets at LHC in kT-factorization

We use the kT–factorization approach to calculate total and differential cross sections of associated production of prompt photons and hadronic jets at the LHC energies. Our consideration relies on the pegasus Monte-Carlo generator with implemented ℴ(αα2s) off-shell gluon–gluon fusion subprocess g*g* → γqq− and several subleading quark-initiated contributions from ℴ(ααs) and ℴ(αα2s) subprocesses, taken into account in the collinear limit. Using Monte-Carlo generators CASCADE and PYTHIA, we investigate parton showering effects and compare our predictions with the data, taken by CMS and ATLAS collaborations at the LHC. We demostrate reasonabledescription of the data and the importance of parton shower effects in the kT–factorization.

Confronting the fourth generation two-Higgs-doublet model with the phenomenology of heavy Higgs bosons

A sequential fourth generation is known to be excluded because the non-decoupling contribution to $\kappa_g$, the Higgs coupling modifier with a gluon pair, is unacceptably large. Recently a new way to save the model was suggested in the Type-II two Higgs doublet model: if the Yukawa couplings of down-type fermions have wrong-sign, the contributions from $t'$ and $b'$ to $\kappa_g$ are cancelled. We study the theoretical and experimental constraints on this model, focusing on the heavy Higgs bosons. Two constraining features are pointed out. First the exact wrong-sign limit does not allow the alignment, which makes the perturbative unitarity for the scalar-scalar scattering put the upper bounds on the heavy Higgs boson masses like $M_H, M_A \lesssim 920$ GeV and $M_{H^\pm} \lesssim 620$ GeV. Secondly, the Yukawa couplings of the fourth generation fermions to the heavy Higgs bosons are generically large as being proportional to the heavy fermion mass and, for the down-type fermions, to $\tan\beta$ as well. The gluon fusion productions of $H$ and $A$ through the fourth generation quark loops become significant. We found that the current LHC data on $pp \to Z Z$ for $H$ along with the theoretical and indirect constraints exclude the model at leading order.

Extended scalar sectors, effective operators and observed data

The available data on the 125 GeV scalar h is analysed to explore the room for new physics in the electroweak symmetry breaking sector. The first part of the study is model-independent, with h couplings to standard model particles scaled by quantities that are taken to be free parameters. At the same time, the additional loop contributions to h → γγ and h → Zγ, mediated by charged scalar contributions in the extended scalar sector, are treated in terms of gauge-invariant effective operators. Having justified this approach for cases where the concerned scalar masses are a little above the Z-boson mass, we fit the existing data to obtain marginalized 1σ and 2σ regions in the space of the coefficients of such effective operators, where the limit on the h → Zγ branching ratio is used as a constraint. The correlation between, say, the gluon fusion and vector-boson fusion channels, as reflected in a non-diagonal covariance matrix, is taken into account. After thus obtaining model-independent fits, the allowed values of the coefficients are translated into permissible regions of the parameter spaces of several specific models. In this spirit we constrain four different types of two Higgs doublet models, and also models with one or two Y = 2 scalar triplets, taking into account the correlatedness of the scale factors in h-interactions and the various couplings of charged Higgs states in each extended scenario.

High-energy limit of mass-suppressed amplitudes in gauge theories

We present a detailed analysis of the factorization and all-order resummation of the double-logarithmic radiative corrections which determine the asymptotic behavior of the gauge theory amplitudes suppressed by the leading power of the fermion mass in the limit of high-energy fixed-angle scattering. The result is applied to estimate the bottom quark mediated contribution to the Higgs boson production in gluon fusion.

Analytical Method for Next-to-Leading-Order QCD Corrections to Double-Higgs Production.

We propose a new method to calculate analytically higher-order perturbative corrections and we apply it to the calculation of the two-loop virtual corrections to Higgs pair production through gluon fusion. The method is based on the expansion of the amplitudes in terms of a small Higgs transverse momentum. This approach gives a very good approximation (better than per mille) of the partonic cross section in the center-of-mass energy region sqrt[s[over ^]]≲750 GeV, where ∼95% of the total hadronic cross section is concentrated. The presented method is general and can be applied in a straightforward way to the computation of virtual higher-order corrections to other 2→2 processes, representing an improvement with respect to calculations based on heavy mass expansions.

Multi-lepton signatures of additional scalar bosons beyond the Standard Model at the LHC

Following a prediction made in von Buddenbrock et al (2015 arXiv:1506.00612), Kumar et al (2017 J. Phys.: Conf. Ser. 802 012007), von Buddenbrock et al (2016 Eur. Phys. J. C 76 580), this paper focuses on multi-lepton signatures arising from two new hypothetical scalar bosons, H and S, at the Large Hadron Collider. These two new bosons are an extension to the Standard Model and interact with the SM Higgs boson, h. We consider two production modes for H, one being gluon fusion and the other being in association with top quarks. The decay mode is considered, where leptonic final states are studied. The CP properties of S are characterised by considering effective couplings derived from dimension six operators through SWW vertices. The nature of the S boson is considered in two separate contexts. Firstly in a simplified model, it is considered to have Higgs-like couplings. Secondly, we consider a heavy neutrino model and its interactions with the Z, W and S bosons. The predictions of the models are compared both to ATLAS and CMS results at and 13 TeV, where appropriate. The data is interpreted using a simplified model where all the signal comes from , assuming S to be Higgs-like, mH = 270 GeV and mS = 150 GeV. The combined result yields gives a best fit value for the parameter βg (the strength of the Yukawa coupling of H to top quarks), . A number of regions of the phase space are suggested to the experiments for further exploration.

The production of charged-kaon pairs in proton–antiproton collisions: The role of higher-twist mechanism

The higher-twist (HT) contribution to the charged-kaon pair production in the high energy proton–antiproton collisions at large transverse momentum [Formula: see text] is investigated by using the frozen coupling constant approach for various kaon distribution amplitudes (DAs), which are predicted by light-cone formalism, the light-front quark model, the nonlocal chiral quark model and the light-front holographic AdS/CFT approach. In the numerics, the dependencies of the HT contribution on the transverse momentum [Formula: see text], the rapidity [Formula: see text], and the variable [Formula: see text] are discussed with special emphasis put on DAs. The HT contribution is also compared with the leading-twist ones. It is shown that the HT contributions are dependent on the kaon DAs and also some other phenomenological parameters such as momentum cutoff parameter [Formula: see text]. Inclusive kaon pair production presents a remarkable test case in which HT terms dominate those of LT in certain kinematic regions. The HT direct production process via gluon–gluon fusion contributes significantly to the inclusive cross-section at large [Formula: see text].

Higgs boson production at large transverse momentum within the SMEFT: analytical results

We consider Higgs boson production through gluon fusion at large transverse momentum in hadronic collisions. We present the analytic expressions of the relevant one-loop QCD amplitudes including the effects of the complete set of dimension-six operators. The latter correspond to modifications of the top and bottom Yukawa couplings, to an effective point-like Higgs coupling to gluons and to the chromomagnetic operator of the top quark. The quantitative impact of the chromomagnetic operator is also studied. Our results confirm previous findings that the effect of the chromomagnetic operator at high p_T can be large and should not be neglected.