Pseudoscalar Higgs Boson Research Articles

Search for heavy Higgs bosons decaying to a top quark pair in proton-proton collisions at sqrt{s} = 13 TeV

A search is presented for additional scalar (H) or pseudoscalar (A) Higgs bosons decaying to a top quark pair in proton-proton collisions at a center-of-mass energy of 13 TeV. The data set analyzed corresponds to an integrated luminosity of 35.9 fb−1 collected by the CMS experiment at the LHC. Final states with one or two charged leptons are considered. The invariant mass of the reconstructed top quark pair system and variables that are sensitive to the spin of the particles decaying into the top quark pair are used to search for signatures of the H or A bosons. The interference with the standard model top quark pair background is taken into account. A moderate signal-like deviation compatible with an A boson with a mass of 400 GeV is observed with a global significance of 1.9 standard deviations. New stringent constraints are reported on the strength of the coupling of the hypothetical bosons to the top quark, with the mass of the bosons ranging from 400 to 750 GeV and their total relative width from 0.5 to 25%. The results of the search are also interpreted in a minimal supersymmetric standard model scenario. Values of mA from 400 to 700 GeV are probed, and a region with values of tan β below 1.0 to 1.5, depending on mA, is excluded at 95% confidence level.

Search for a heavy pseudoscalar Higgs boson decaying into a 125 GeV Higgs boson and a Z boson in final states with two tau and two light leptons at sqrt{s} = 13 TeV

A search is performed for a pseudoscalar Higgs boson, A, decaying into a 125 GeV Higgs boson h and a Z boson. The h boson is specifically targeted in its decay into a pair of tau leptons, while the Z boson decays into a pair of electrons or muons. A data sample of proton-proton collisions collected by the CMS experiment at the LHC at sqrt{s} = 13 TeV is used, corresponding to an integrated luminosity of 35.9 fb−1. No excess above the standard model background expectations is observed in data. A model-independent upper limit is set on the product of the gluon fusion production cross section for the A boson and the branching fraction to Zh → ℓℓττ. The observed upper limit at 95% confidence level ranges from 27 to 5 fb for A boson masses from 220 to 400 GeV, respectively. The results are used to constrain the extended Higgs sector parameters for two benchmark scenarios of the minimal supersymmetric standard model.

Two loop QCD amplitudes for di-pseudo scalar production in gluon fusion

We compute the radiative corrections to the four-point amplitude g+g → A+A in massless Quantum Chromodynamics (QCD) up to order {alpha}_s^4 in perturbation theory. We used the effective field theory that describes the coupling of pseudo-scalars to gluons and quarks directly, in the large top quark mass limit. Due to the CP odd nature of the pseudo-scalar Higgs boson, the computation involves careful treatment of chiral quantities in dimensional regularisation. The ultraviolet finite results are shown to be consistent with the universal infrared structure of QCD amplitudes. The infrared finite part of these amplitudes constitutes the important component of any next to next to leading order corrections to observables involving pair of pseudo-scalars at the Large Hadron Collider.

Phenomenology of Higgs bosons in inverse seesaw model with Type-X two Higgs doublet at the LHC

Type-X two Higgs doublet model is known to explain the muon g − 2 anomaly with a relatively light charged Higgs boson at large tan β. The light charged Higgs boson has been searched in the main τ ν mode at the colliders. Invoking a scenario of inverse seesaw as the origin of neutrino masses and mixing, the charged Higgs boson can decay additionally to right-handed neutrinos which leads to interesting phenomenology. Considering generic lepton flavour violating signatures at the final states, a 5σ discovery can be achieved with the early data of LHC, at 14 TeV, for relatively large inverse seesaw Yukawa coupling YN. The very light pseudoscalar and charged Higgs boson mass reconstruction are performed using the new modes and the results look promising. The inverse seesaw Yukawa coupling is shown to be probed down to YN ∼ 0.2 at HL LHC with 3000 fb−1.

Search for neutral Higgs bosons within type-I 2HDM at future linear colliders

In this study, we investigate observability of the neutral scalar (H) and pseudoscalar (A) Higgs bosons in the framework of the type-I 2HDM at SM-like scenario at a linear collider operating at sqrt{s}= 500 and 1000 GeV. The signal process is e^- e^+ rightarrow A H rightarrow ZHHrightarrow jj b{bar{b}}b{bar{b}} where jj is a di-jet resulting from the Z boson decay and b{bar{b}} is a b-jet pair from scalar Higgs boson decay. Several benchmark scenarios with different mass hypotheses are studied. The assumed signal process is mainly motivated by the large decay rate of Arightarrow ZH (at high tan beta and enough Higgs boson mass splitting) and Hrightarrow b{bar{b}} in the type-I. After event generation the detector response is simulated based on the SiD detector at the ILC. The ISR and beamstrahlung effects are also included for each center of mass energy assuming unpolarized beams. The simulated events are analyzed to obtain candidate mass distributions of the Higgs bosons. Among standard model backgrounds, the top quark pair production process is the main background but is under control. Results indicate that, in all considered scenarios, both Higgs bosons H and A are observable with signals exceeding 5sigma with possibility of mass measurement. Final results are shown as 5sigma contours in (m_H,m_A) or (m_A,tan beta ) space.

Pseudoscalar Higgs boson pair production at a photon-photon collision in the two Higgs doublet model

In this study, the direct pair production of the pseudoscalar Higgs boson at a photon-photon collision is analyzed in the context of two Higgs doublet model, taking account the complete one-loop contributions. In order to illustrate the effect of the new physics, four benchmark points scenarios, which are consistent with theoretical and current experimental constraints, are chosen in the type-I of THDM with an exact alignment limit. In these benchmark points, the CP even lightest Higgs boson ($h^0$) have the Standard Model like couplings to the gauge bosons. The effect of individual contributions from each type of one-loop diagrams on the total cross section are examined in detail. The dependence of total cross section on the center-of-mass energy is also presented at the various polarization configurations of the incoming photons. Moreover, the regions $m_{12}^2-\tan\beta$ and $m_A-\tan\beta$ in the parameter space of the THDM are scanned for some fixed values of other parameters. The box-type diagrams make a much larger contribution to the total cross section than the others at high energies. Total cross section can be enhanced by a two factor thanks to opposite polarized photons as well as threshold effects.

Resummed transverse momentum distribution of pseudo-scalar Higgs boson at NNLOA+NNLL

In this article we have studied the transverse momentum distribution of the pseudo-scalar Higgs boson at the Large Hadron Collider (LHC). The small pT region which provides the bulk of the cross section is not accessible to fixed order perturbation theory due to the presence of large logarithms in the series. Using the universal infrared behaviour of the QCD we resum these large logarithms up to next-to-next-to-leading logarithmic (NNLL) accuracy. We observe a significant reduction in theoretical uncertainties due to the unphysical scales at NNLL level compared to the previous order. We present the pT distribution matched to NNLOA+NNLL, valid for the whole pT region and provide a detailed phenomenological study in the context of both 14 TeV and 13 TeV LHC using different choices of masses, scales and parton distribution functions which will be useful for the search of such particle at the LHC in near future.

Search for a lighter Higgs boson in the Next-to-Minimal Supersymmetric Standard Model**Supported by National Natural Science Foundation of China (11505208, 11661141007, 11705016, 11875275), China Ministry of Science and Technology (2018YFA0403901) and partially by the France China Particle Physics Laboratory (FCPPL) and CAS Center for Excellence in Particle Physics (CCEPP)

Following the discovery of the Higgs boson with a mass of approximately 125 GeV at the LHC, many studies have been performed from both the theoretical and experimental viewpoints to search for a new Higgs Boson that is lighter than 125 GeV. We explore the possibility of constraining a lighter neutral scalar Higgs boson h1 and a lighter pseudo-scalar Higgs boson a1 in the Next-to-Minimal Supersymmetric Standard Model by restricting the next-to-lightest scalar Higgs boson h2 to be the one observed at the LHC after applying the phenomenological constraints and those from experimental measurements. Such lighter particles are not yet completely excluded by the latest results of the search for a lighter Higgs boson in the diphoton decay channel from LHC data. Our results show that some new constraints on the Next-to-Minimal Supersymmetric Standard Model could be obtained for a lighter scalar Higgs boson at the LHC if such a search is performed by experimental collaborations and more data. The potentials of discovery for other interesting decay channels of such a lighter neutral scalar or pseudo-scalar particle are also discussed.

CP tests of Higgs couplings in tt¯h semileptonic events at the LHC

The CP nature of the Higgs coupling to top quarks is addressed in this paper, in single charged lepton final states of $t\bar{t}h$ events produced in proton-proton collisions at the LHC. Pure scalar ($h=H$) and pseudo-scalar ($h=A$) Higgs boson signal events, generated with MadGraph5_aMC@NLO, are fully reconstructed using a kinematic fit. Angular distributions of the decay products, as well as CP-sensitive asymmetries, are exploited to separate and gain sensitivity to possible pseudo-scalar components of the Higgs boson and reduce the contribution from the dominant irreducible background $t\bar{t}b\bar{b}$. Significant differences are found between the pure CP-even and -odd signal hypotheses as well as with respect to the Standard Model background, in particular the $t\bar{t} b\bar{b}$ contribution. Such differences survive the event reconstruction, allowing to define optimal observables to extract the Higgs couplings parameters from a global fit. A dedicated analysis is applied to efficiently identify signal events and reject as much as possible the expected Standard Model background. The results obtained are compared with a similar analysis in the dilepton channel. We show that the single lepton channel is more promising overall and can be used in combination to study the CP nature of the Higgs coupling to top quarks.

Search for Heavy Higgs Bosons A/H Decaying to a Top Quark Pair in pp Collisions at sqrt[s]=8 TeV with the ATLAS Detector.

A search for heavy pseudoscalar (A) and scalar (H) Higgs bosons decaying into a top quark pair (tt[over ¯]) has been performed with 20.3 fb^{-1} of proton-proton collision data collected by the ATLAS experiment at the Large Hadron Collider at a center-of-mass energy sqrt[s]=8 TeV. Interference effects between the signal process and standard model tt[over ¯] production, which are expected to distort the signal shape from a single peak to a peak-dip structure, are taken into account. No significant deviation from the standard model prediction is observed in the tt[over ¯] invariant mass spectrum in final states with an electron or muon, large missing transverse momentum, and at least four jets. The results are interpreted within the context of a type-II two-Higgs-doublet model. Exclusion limits on the signal strength are derived as a function of the mass m_{A/H} and the ratio of the vacuum expectation values of the two Higgs fields, tanβ, for m_{A/H}>500 GeV.

Search for a light pseudoscalar Higgs boson produced in association with bottom quarks in pp collisions at sqrt{s}=8 TeV

A search for a light pseudoscalar Higgs boson (A) produced in association with bottom quarks and decaying into a muon pair is reported. The search uses 19.7 fb−1 of proton-proton collisions at a center-of-mass energy of 8 TeV, collected by the CMS experiment. No signal is observed in the dimuon mass range from 25 to 60 GeV. Upper limits on the cross section times branching fraction, sigma left(mathrm{pp}to mathrm{b}overline{mathrm{b}}mathrm{A}right)mathrm{mathcal{B}}left(mathrm{A}to mu mu right) , are set.

Two loop QCD corrections for the process pseudo-scalar Higgs \u2192 3 partons

We present virtual contributions up to two loop level in perturbative Quantum Chromodynamic (QCD) to the decay of pseudo-scalar Higgs boson (A) to three gluons (g) and also to quark (q), anti-quark ( overline{q} ) and a gluon. With appropriate crossing, they are well suited for predicting the differential distribution of A in association with a jet in hadron colliders up to next-to-next-to-leading order (NNLO) in strong coupling constant and also for the subsequent decay of A to hadrons. We use effective field theory approach to integrate out the top quarks in the heavy top limit. The resulting theory involves two pseudo-scalar composite operators describing the interaction of A with gluons as well as with quark and anti-quark. We perform our computation in dimensional regularisation and use minimal subtraction ( overline{MS} ) scheme to renormalise strong coupling constant as well as the composite operators. The ultraviolet (UV) finite amplitudes contain infrared (IR) divergences that are found to be in agreement with the predictions by Catani. For both the amplitudes namely A → ggg and Ato qoverline{q}g , the leading transcendental terms at one and two loops are found to be identical to those in a three point form factor (FF) of the half-BPS operator in mathcal{N}=4 Supersymmetric Yang Mills (SYM) theory when the QCD color factors are adjusted in a specific way. We present our results in terms of harmonic polylogs well suited for further numerical study.

Detection prospects of light pseudoscalar Higgs boson at the LHC

The discovery potential of light pseudo scalar Higgs boson for the mass range 10-60 GeV is explored. In the context of the next-to-minimal supersymmetric standard (NMSSM) model, the branching fraction of light pseudo scalar Higgs boson decaying to a pair of photon can be quite large. A pair of light pseudo scalar Higgs boson produced indirectly through the standard model Higgs boson decay yields multiple photons in the final state and the corresponding production rate is restricted by ATLAS data. Discussing the impact of this constraint in the NMSSM, the detection prospects of light pseudoscalar Higgs boson in the channel consisting of at least three photons, a lepton and missing transverse energy are reported. It is observed that the possibilities of finding the pseu-doscalar Higgs boson for the above mass range are promising for an integrated luminosity mathrm{mathcal{L}} = 100fb−1 with moderate significances, which can reach to more than 5σ for higher luminosity options.

Two Higgs bosons near 125 GeV in the NMSSM: beyond the narrow width approximation

In the next-to-minimal supersymmetric (NMS) Standard Model (SM), it is possible for either one of the additional singlet-like scalar and pseudoscalar Higgs bosons to be almost degenerate in mass with the sim 125 GeV SM-like Higgs state. In the real NMSSM (rNMSSM), when the mass difference between two scalar states is comparable to their individual total decay widths, the quantum mechanical interference, due to the relevant diagonal as well as off-diagonal terms in the propagator matrix, between them can become sizeable. This possibility invalidates usage of the narrow width approximation (NWA) to compute the cross section for the production of a di-photon pair with a given invariant mass via resonant Higgs boson(s) in the gluon fusion process at the Large Hadron Collider (LHC). When, motivated by the baryon asymmetry of the universe, CP-violating (CPV) phases are explicitly invoked in the Higgs sector of the NMSSM, all the interaction eigenstates mix to give five CP-indefinite physical Higgs bosons. In this scenario, the interference effects due to the off-diagonal terms in the Higgs mass matrix that mix the pseudoscalar-like state with the SM-like one can also become significant, when these two are sufficiently mass-degenerate. We perform a detailed analysis, in both the real and complex NMSSM, of these interference effects, when the full propagator matrix is taken into account, in the production of a photon pair with an invariant mass near 125 GeV through gluon fusion. We find that these effects can account for up to sim 40% of the total cross section for certain model parameter configurations. We also investigate how such mutually interfering states contributing to the sim 125 GeV signal observed at the LHC can be distinguished from a single resonance.

Probing the CP nature of the Higgs coupling in tt¯h events at the LHC

The determination of the CP nature of the Higgs coupling to top quarks is addressed in this paper, using $t{\bar t} h$ events produced in $\sqrt{s} = 13$ TeV proton-proton collisions at the LHC. Dileptonic final states are employed, with two oppositely charged leptons and four jets, corresponding to the decays $t\rightarrow bW^+ \rightarrow b \ell^+\nu_\ell$, $\bar{t}\rightarrow \bar{b}W^- \rightarrow \bar{b} \ell^-\bar{\nu}_\ell$ and $h\rightarrow b\bar{b}$. Pure scalar ($h=H$), pure pseudo-scalar ($h=A$) and CP-violating Higgs boson signal events, generated with MadGraph5_aMC@NLO, are fully reconstructed through a kinematic fit. We furthermore generate samples that have both a CP-even and a CP-odd component in the $t \bar t h$ coupling in order to probe the ratio of the two components. New angular distributions of the decay products, as well as CP angular asymmetries, are explored in order to separate the scalar from the pseudo-scalar components of the Higgs boson and reduce the contribution from the dominant irreducible background, $t{\bar t}b{\bar b}$. Significant differences between the angular distributions and asymmetries are observed, even after the full kinematic fit reconstruction of the events, allowing to define the best observables for a global fit of the Higgs couplings parameters.

Leptophilic neutral Higgs bosons in two Higgs doublet model at a linear collider

This paper addresses the question of the observability of neutral Higgs bosons through the leptonic decay in a two Higgs doublet model (2HDM). Both scalar and pseudo-scalar Higgs bosons (H, A) are considered. The model is set to type IV to enhance the leptonic decay. In such a scenario, a signal production process like e^+e^- rightarrow A^0H^0 rightarrow tau tau mu mu or mu mu tau tau would provide a clear signal on top of the background in a di-muon invariant mass distribution far from the Z boson pole mass. The analysis is based on a tau -id algorithm which preselects events if they have two tau jets by requiring a hadronic tau decay. Several benchmark points are defined for the search, requiring a linear collider operating at sqrt{s} = 0.5 and 1 TeV. It is shown that the signal can be observed on top of the background in all benchmark points at an integrated luminosity of 1000 mathrm{fb}^{-1}.

Diphoton signal of a light pseudoscalar in the NMSSM at the LHC

We explore the detection possibility of light pseudoscalar Higgs boson in the next-to-minimal supersymmetric Standard Model(NMSSM) at the LHC with the center of mass energy, $\sqrt{S}=13$ TeV. We focus on the parameter space which provides one of the Higgs boson as the SM-like with a mass of 125 GeV and some of the non-SM-like Higgs bosons can be light having suppressed couplings with fermions and gauge bosons due to their singlet nature. It is observed that for certain region of model parameter space, the singlet like light pseudoscalar can decay to di-photon($\gamma\gamma$) channel with a substantial branching ratio. In this study, we consider this di-photon signal of light pseudoscalar Higgs boson producing it through the chargino-neutralino production and the subsequent decay of neutralino. We consider signal consisting of two photons plus missing energy along with a lepton from the chargino decay. Performing a detailed simulation of the signal and backgrounds including detector effects, we present results for a few benchmark points corresponding to the pseudoscalar Higgs boson mass in the range 60 -100 GeV. Our studies indicate that some of the benchmark points in the parameter space can be probed with a reasonable significance for 100 fb$^{-1}$ integrated luminosity. We also conclude that exploiting this channel it is possible to distinguish the NMSSM from the other supersymmetric models.

Alignment without decoupling: The portal to light dark matter in the MSSM

We study light, thermal neutralino dark matter in the sub-GeV to $\ensuremath{\sim}65\text{ }\text{ }\mathrm{GeV}$ mass range in the minimal supersymmetric extension of the Standard Model. We consider realizations of the limit of alignment without decoupling in the Higgs sector where the heavier $CP$-even Higgs impersonates the observed Higgs state at 125 GeV, while the lighter $CP$-even Higgs is the mediator of dark matter annihilation. We single out three distinct and novel possibilities for light dark matter: (i) a neutralino with mass around half the light Higgs mass, in the sub-GeV to $\ensuremath{\sim}30\text{ }\text{ }\mathrm{GeV}$ mass range; (ii) a neutralino with a mass around half the pseudoscalar Higgs boson mass, in our examples around $(60--65)\text{ }\text{ }\mathrm{GeV}$; (iii) a very light neutralino with mass around the light Higgs mass, pair annihilating to Higgs pairs. We discuss the implications of all these possibilities for indirect and direct dark matter detection experiments, and we demonstrate that all scenarios will be tested by next generation direct detection experiments. We also emphasize that the unique Higgs phenomenology of this setup warrants a dedicated search program at the LHC.

Search for dark matter in association with a Higgs boson decaying to b-quarks in pp collisions at s=13 TeV with the ATLAS detector

A search for dark matter pair production in association with a Higgs boson decaying to a pair of bottom quarks is presented, using 3.2 $fb^{-1}$ of $pp$ collisions at a centre-of-mass energy of 13 TeV collected by the ATLAS detector at the LHC. The decay of the Higgs boson is reconstructed as a high-momentum $b\bar{b}$ system with either a pair of small-radius jets, or a single large-radius jet with substructure. The observed data are found to be consistent with the expected backgrounds. Results are interpreted using a simplified model with a $Z'$ gauge boson mediating the interaction between dark matter and the Standard Model as well as a two-Higgs-doublet model containing an additional $Z'$ boson which decays to a Standard Model Higgs boson and a new pseudoscalar Higgs boson, the latter decaying into a pair of dark matter particles.

Where to look for natural supersymmetry

Why is natural supersymmetry neither detected nor ruled-out to date? To answer this question we use the Bayesian approach where the emphasis on finding prior-independent features within broader and minimally biased frames is taken as the guiding principle. The 20-parameter minimal supersymmetric standard model (MSSM) fits to subjective naturalness indicate the existence of a prior-independent upper bound on the pseudoscalar Higgs boson mass $m_A$ as a function of $\tan \beta$, the ratio of the vacuum expectation values of the MSSM Higgs doublets. For a 30-parameter MSSM this implies that $m_A \lesssim 3$ TeV and $\tan \beta \lesssim 25$ at 95\% Bayesian confidence. Removing the contradictory subjectiveness within the electroweak fine-tuning measure leads to finding the naturalness line, $m_A \sim \frac{1}{\sqrt{2}} \, m_Z \, \tan \beta,$ that reduces by one the number of MSSM Higgs sector free parameters.