Higgsstrahlung Process Research Articles

Some Phenomenological Aspects of Higgs Production in Two Leptons and bb ̅ Final State Processes

Abstract: We present a partonic-level analysis of the two leptons and bb ̅ final states processes at the ILC e^+ e^-→e^+ e^- bb ̅. This process contains Higgs production with an electron-positron pair, where the Higgs decays into a bb ̅ quark pair as a sub-process, e^+ e^-→e^+ e^- H→e^+ e^- bb ̅. We tried to isolate this sub-process with a minimum set of cuts. Particularly, cross-sections are estimated at different energies, and the main distributions of kinematic variables characterizing the process are derived using the software Calchep [16]. The results provide information on signal and background characteristics for different ILC operating stages. Keywords: Higgs physics at ILC, Higgsstrahlung process, ZZ fusion process, Calchep.

Analysis of the laser geometry effect on the Higgs-strahlung process

Analysis of the laser geometry effect on the Higgs-strahlung process

Probing dark QCD sector through the Higgs portal with machine learning at the LHC

The QCD-like dark sector with GeV-scale dark hadrons has the potential to generate new signatures at the Large Hadron Collider (LHC). In this paper, we consider a singlet scalar mediator in the tens of GeV-scale that connects the dark sector and the Standard Model (SM) sector via the Higgs portal. We focus on the Higgs-strahlung process, qoverline{q} ′ → W* → WH, to produce a highly boosted Higgs boson. Our scenario predicts two different processes that can generate dark mesons: (1) the cascade decay from the Higgs boson to two light scalar mediators and then to four dark mesons; (2) the Higgs boson decaying to two dark quarks, which then undergo a QCD-like shower and hadronization to produce dark mesons. We apply machine learning techniques, such as Convolutional Neural Network (CNN) and Energy Flow Network (EFN), to the fat-jet structure to distinguish these signal processes from large SM backgrounds. We find that the branching ratio of the Higgs boson to two light scalar mediators can be constrained to be less than about 10% at 14 TeV LHC with mathcal{L} = 3000 fb−1.

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.

Riding the Seesaw: what Higgsstrahlung may reveal about massive neutrinos

We investigate if the projected high-precision measurements of the cross section of the Higgsstrahlung process e^+ e^- rightarrow Zh at a future electron–positron collider can be utilised to indirectly probe the fermionic Seesaw models. We consider the two centre-of-mass energies sqrt{s}=240 GeV and 365 GeV, and compare the collider reaches to constraints from electroweak observables, probes of lepton flavour universality and the existing and prospective bounds from searches for lepton flavour violation. For the analysis we assume the limit of an exactly conserved lepton-number symmetry. We find that while any appreciable correction to the Higgsstrahlung cross section is already strictly constrained in the Type-I Seesaw model, effects of up to {mathcal {O}}(10%) are possible within Type-III Seesaw.

Search for a Dark Photon and an Invisible Dark Higgs Boson in μ^{+}μ^{-} and Missing Energy Final States with the Belle II Experiment.

The dark photon A^{'} and the dark Higgs boson h^{'} are hypothetical particles predicted in many dark sector models. We search for the simultaneous production of A^{'} and h^{'} in the dark Higgsstrahlung process e^{+}e^{-}→A^{'}h^{'} with A^{'}→μ^{+}μ^{-} and h^{'} invisible in electron-positron collisions at a center-of-mass energy of 10.58GeV in data collected by the Belle II experiment in 2019. With an integrated luminosity of 8.34 fb^{-1}, we observe no evidence for signal. We obtain exclusion limits at 90% Bayesian credibility in the range of 1.7-5.0fb on the cross section and in the range of 1.7×10^{-8}-200×10^{-8} on the effective coupling ϵ^{2}×α_{D} for the A^{'} mass in the range of 4.0 GeV/c^{2}<M_{A^{'}}<9.7 GeV/c^{2} and for the h^{'} mass M_{h^{'}}<M_{A^{'}}, where ϵ is the mixing strength between the standard model and the dark photon and α_{D} is the coupling of the dark photon to the dark Higgs boson. Our limits are the first in this mass range.

Next-to-next-to-leading order event generation for VH production with H → boverline{b} decay

We consider the Higgsstrahlung process in hadronic collisions and present the computation of next-to-next-to-leading order predictions matched to parton showers for both production and H → boverline{b} decay employing the MiNNLOPS method. We present predictions for ZH and W±H production including spin correlations and off-shell effects by calculating the full processes pp → ℓ+ℓ−H → ℓ+ℓ− boverline{b} , pp → {nu}_{ell }{overline{nu}}_{ell }H → {nu}_{ell }{overline{nu}}_{ell }boverline{b} and pp → ℓ±νℓH → {ell}^{pm }{overline{nu}}_{ell }boverline{b} in the narrow-width approximation for the Higgs boson. For the W±H process, NNLO+PS accuracy in production and decay is achieved for the first time. Our calculations are validated against earlier simulations in the NNLOPS approach that includes NNLO corrections via multi-differential reweighting. The new MiNNLOPS generators for these processes, which evaluate NNLO corrections on-the-fly in the event generation, will supersede those earlier calculations. Our predictions are in good agreement with recent measurements of the Higgsstrahlung cross sections.

Higgs and top physics reconstruction challenges and opportunities at FCC-ee

The Higgs bosons and the top quark decay into rich and diverse final states, containing both light and heavy quarks, gluons, photons as well as W and Z bosons. This article reviews the challenges involved in reconstructing Higgs and top events at the FCC-ee and identifies the areas where novel developments are needed. The precise identification and reconstruction of these final states at the FCC-ee rely on the capability of the detector to provide excellent flavour tagging, jet energy and angular resolution, and global kinematic event reconstruction. Excellent flavour tagging performance requires low-material vertex and tracking detectors, and advanced machine learning techniques as successfully employed in LHC experiments. In addition, the Z pole run will provide abundant samples of heavy flavour partons that can be used for calibration of the tagging algorithms. For the reconstruction of jets, leptons, and missing energy, particle-flow algorithms are crucial to explore the full potential of the highly granular tracking and calorimeter systems, and give access to excellent energy–momentum resolution and precise identification of heavy bosons in their hadronic decays. This enables, among many other key elements, the reconstruction of Higgsstrahlung processes with leptonically and hadronically decaying Z bosons, and an almost background-free identification of top quark pair events. Exploiting the full available kinematic constraints together with exclusive jet clustering algorithms will allow for the optimisation of global event reconstruction with kinematic fitting techniques.

Next-to-leading-order corrections to the Higgs strahlung process from electron\u2013positron collisions in extended Higgs models

We present the cross section for e^{+}e^{-}rightarrow hZ with arbitrary sets of electron and Z boson polarizations at the full next-to-leading order in various extended Higgs models, such as the Higgs singlet model (HSM), the inert doublet model (IDM) and the two Higgs doublet model (2HDM). We systematically perform complete one-loop calculations to the helicity amplitudes in the on-shell renormalization scheme, and present the full analytic results as well as numerical evaluations. The deviation Delta R^{hZ} in the total cross section from its standard model (SM) prediction is comprehensively analyzed, and the differences among these models are discussed in details. We find that new physics effects appearing in the renormalized hZZ vertex almost govern the behavior of Delta R^{hZ}, and it takes a negative value in most cases. The possible size of Delta R^{hZ} reaches several percent under the theoretical and experimental bounds. We also analyze the deviation Delta R^{hZ}_{XY} in the total cross section times decay branching ratios of the discovered Higgs boson by utilizing the H-COUP program. It is found that the four types of 2HDMs can be discriminated by analyzing the correlation between Delta R^{hZ}_{tau tau } and Delta R^{hZ}_{bb} and those between Delta R^{hZ}_{tau tau } and Delta R^{hZ}_{cc}. Furthermore, the HSM and the IDM can be discriminated from the 2HDMs by measuring Delta R^{hZ}_{WW}. These signatures can be tested by precision measurements at future Higgs factories such as the International Linear Collider.

Probing extended scalar sectors with precision e+e\u2212\u2192 Zh and Higgs diphoton studies

We compute the one-loop corrections to σ(e+e−→ Zh) arising from representative extended Standard Model scalar sector scenarios. According to the new scalar SU(2)L representations, we consider the inert doublet, real and complex triplet, quintuplet, and septuplet models. With the sub-percent level precision expected for prospective future e+e− collider measurements of σ(e+e−→ Zh), studies of the Higgsstrahlung process will probe extended scalar sector particle spectrum and interactions in a manner complementary to direct searches at the Large Hadron Collider and possible future pp colliders. We also compare with the sensitivity of future Higgs diphoton decay rate measurements. We find that the σ(e+e−→ Zh) and Γ(h → γγ) complementarity is particularly pronounced for the complex triplet model.

Polarized NLO EW [formula omitted] cross section calculations with ReneSANCe-v1.0.0

In this paper we present a new Monte Carlo event generator ReneSANCe for simulation of processes at electron–positron colliders. In the current release of the generator the Bhabha scattering (e+e−→e−e+) and Higgs-strahlung (e+e−→ZH) process are implemented. Based on the SANC (Support for Analytic and Numeric Calculations for experiments at colliders) modules, the new generator takes into account complete one-loop and some higher-order electroweak radiative corrections with finite particle masses and polarizations. The new generator effectively operates in the collinear region and at the ZH production threshold. It is constructed in such a way that new processes can be easily added. The paper contains a theoretical description of the SANC approach, numerical validations and manual. Program summaryProgram Title: ReneSANCe-v1.0.0Program Files doi:http://dx.doi.org/10.17632/wp36f7t3ft.1Licensing provisions: GPLv3Programming language: Fortran, C, C++Supplementary material: Looptools [1], FOAM [2]Nature of problem: Theoretical calculations at next-to-leading order in perturbation theory allow to compute higher precision amplitudes for Standard Model processes and decays, provided proper treatments of UV divergences and IR singularities are performed.Solution method: Numerical integration of the precomputed differential expressions for cross sections of certain processes implemented as SANC modules [3,4].Restrictions: The list of processes is limited to e+e−→e−e+ and e+e−→ZH.

Higgsstrahlung at NNLL′+NNLO matched to parton showers in GENEVA

We present results for the Higgsstrahlung process within the GENEVA Monte Carlo framework. We combine the fully differential NNLO calculation with the higher-order resummation in the 0-jettiness resolution variable (beam-thrust). The resulting parton-level events are further showered and hadronised by Pythia8. The beam-thrust resummation is carried out to NNLL$'$ accuracy, which consistently incorporates all singular virtual and real NNLO corrections. It thus provides a natural perturbative connection between the NNLO calculation and the parton shower regime, including a systematic assessment of perturbative uncertainties. In this way, observables which are inclusive over the additional radiation are correct to NNLO, while the description of 0-jet-like resummation variables is improved beyond the parton shower approximation. We provide predictions for the 13 TeV LHC.

Probing anomalous gauge-Higgs couplings using Z boson polarization at e+e− colliders

We study possible new physics interactions in the ZZH vertex contributing to the Higgsstrahlung process e+e−→ZH at proposed future e+e− colliders using the polarization of the Z as a probe. We calculate the spin density matrix of the Z for the process and determine the eight independent polarization parameters of the Z boson which have the potential to constrain the anomalous couplings. We study angular asymmetries using the decay leptons from the Z boson which are simply related to the polarization observables. We also estimate the limits that can be placed on the anomalous couplings using measurements of these angular asymmetries at centre of mass energies of 250 GeV and 500 GeV and various combinations of polarized e+ and e− beams.

WW fusion and Higgsstrahlung interplay in Higgs precision tests with the e−e+→νν¯h process

Higgs precision program at future lepton collider aims at (sub) percent level precision measurement of the Higgs properties, shedding light to new physics through the Higgs lamppost. Amongst many exclusive Higgs channels that can be measured precisely, the $WW$-fusion to Higgs with subsequent decays into $b\bar b$ final state are of particular importance. This channel provide leading constrains on Higgs total width in the $\kappa$-framework and greatly improves the constraints in the EFT framework as a distinct production mode other than the Higgsstrahlung process. We argue in this paper that, there are two interference effects both affects the physical information one can extract from the precision measurements. One takes place at quantum level from the interference between the two amplitudes that amounts to $-10\%$ of the $WW$-fusion signal strength, failing to take into account which will result in a $4$-$5\sigma$ discrepancy between theory and measurement. The other takes place at the classical level from the global fitting procedure where the $ZH$ process is the dominant background with its cross section around six times larger than the $WW$-fusion signal. Despite that $ZH$ process can be measured to great precision at future lepton colliders, failing take this interplay in the coupling extraction will result in a 100\% too aggressive constraints on $\kappa_W$, the Higgs coupling to $W$-boson pairs. This effect will also be important for lepton colliders running at slightly higher energies where the phase space overlap are still sizable between the two processes.

Higgs boson ZZ couplings in Higgs-strahlung at the ILC

We derive the fully differential cross section of the Higgs-strahlung process $f \bar{f} \to Z \to Z (\to f_Z \bar{f}_Z) X (\to f_X \bar{f}_X)$, where $f$, $f_Z$, and $f_X$ are arbitrary fermions and $X$ is a spin-zero particle with arbitrary couplings to $Z$ bosons and fermions. This process with $f = e$ and $X = h$ ($h$ denotes the Higgs boson) is planned to be measured at the ILC to put constraints on the couplings $g_1$, $g_2$, $g_3$ of the Higgs boson to $Z$ bosons. Using the obtained fully differential cross section, we define observables measurement of which yields the tightest constraints on the couplings. Explicit dependences of these observables on $g_i$ are derived.

B-L extension of the SM - Z′ and heavy Higgs boson analysis at future e+ e− linear colliders ILC and CLIC

We propose a U(1)B−L (baryon minus lepton) extension to the Standard Model, which adds a complex singlet to the scalar sector where an extra neutral gauge boson Z′ corresponding to the U(1)B−L gauge symmetry and an extra SM like singlet scalar H (heavy Higgs) are predicted. We consider the mixture of the Z and Z′. The model also yields Majorana masses for three right handed neutrinos. We study the phenomenology of the light h and heavy H Higgs boson production and decay at future e+ e− linear colliders with center-of-mass energies of √s = 500 − 3000 GeV and integrated luminosities of ℒ = 500 − 2000 fb−1. The study includes the Higgs-strahlung processes e+ e− → (Z Z′) → Zh, e+ e− → (Z Z′) → ZH, and we complement our previous works with the addition of the process.

Constraints from Heavy Higgs Boson Masses in the two Higgs Doublet Model

Upon the absence of signals of new physics at the LHC, a reasonable strategy is to assume that new particles are very heavy and the other model parameters are unknown yet. In the aligned two Higgs doublet model, however, heavy Higgs boson masses above 500 GeV enhance some couplings in the scalar potential, which causes a breakdown of the perturbative unitariry in general. Some tuning among model parameters is required. We find that one information on the heavy Higgs boson mass, say $M_H$, has significant theoretical implications: (i) the other heavy Higgs bosons should have similar masses to $M_H$ within $\pm \mathcal{O}(10)\%$; (ii) the inequalities from the theoretical constraints are practically reduced to an equation such that $m_{12}^2 \tan\beta$ is constant, where $m_{12}^2$ is the soft $Z_2$ breaking parameter and $\tan\beta$ is the ratio of two vacuum expectation values; (iii) the triple Higgs coupling $\lambda_{HHh}$ is constant over $\tan\beta$ while $\lambda_{HHH}$ and $\lambda_{AAH}$ are linearly proportional to $\tan\beta$. The double Higgs-strahlung process of $e^+ e^- \to ZHH$ is also studied, of which the total cross section is almost constant with the given $M_H$.

Next-to-leading order QCD and electroweak corrections to Higgs-strahlung processes at the LHC**Supported by the National Natural Science Foundation of China (11465018)

In this paper we calculate the total and fiducial cross sections as well as differential distributions for the Higgs-strahlung or VH process pp → VH → lνl/l− l+ + H, (V = W or Z, l = e, μ) including QCD and electro-weak corrections up to next-to-leading order before and after reweighting photon PDFs of NNPDF2.3qed, NNPDF3.0qed, MRST2004qed, CT14QEDinc, and LUXqed at the LHC with 13 TeV and Higgs boson mass MH = 125 GeV. The predictions from the various photon PDFs before and after reweighting against each other are in good agreement. The photon PDF uncertainties of the photon-induced cross sections decrease significantly with the reweighting PDFs.

Vh@nnlo-v2: new physics in Higgs Strahlung

Introducing version 2 of the code vh@nnlo [1], we study the effects of a number of new-physics scenarios on the Higgs-Strahlung process. In particular, the cross section is evaluated within a general 2HDM and the MSSM. While the Drell-Yan-like contributions are consistently taken into account by a simple rescaling of the SM result, the gluon-initiated contribution is supplemented by squark-loop mediated amplitudes, and by the s-channel exchange of additional scalars which may lead to conspicuous interference effects. The latter holds as well for bottom-quark initiated Higgs Strahlung, which is also included in the new version of vh@nnlo. Using an orthogonal rotation of the three Higgs CP eigenstates in the 2HDM and the MSSM, vh@nnlo incorporates a simple means of CP mixing in these models. Moreover, the effect of vector-like quarks in the SM on the gluon-initiated contribution can be studied. Beyond concrete models, vh@nnlo allows to include the effect of higher-dimensional operators on the production of CP-even Higgs bosons. Transverse momentum distributions of the final state Higgs boson and invariant mass distributions of the Vϕ final state for the gluon- and bottom-quark initiated contributions can be studied. Distributions for the Drell-Yan-like component of Higgs Strahlung can be included through a link to MCFM. vh@nnlo can also be linked to FeynHiggs and 2HDMC for the calculation of Higgs masses and mixing angles. It can also read these parameters from an SLHA-file as produced by standard spectrum generators. Throughout the manuscript, we highlight new-physics effects in various numerical examples, both at the inclusive level and for distributions.

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.