Heavy SUSY Higgs bosons at e + e − linear colliders

The production mechanisms and decay modes of the heavy neutral and charged Higgs bosons in the Minimal Supersymmetric Standard Model are investigated at future e ⁺ e ^? colliders in the TeV energy regime. We generate supersymmetric particle spectra by requiring the MSSM Higgs potential to produce correct radiative electroweak symmetry breaking, and we assume a common scalar mass m₀, gaugino mass m_1/2 and trilinear coupling A, as well as gauge and Yukawa coupling unification at the Grand Unification scale. Particular emphasis is put on the low tan β solution in this scenario where decays of the Higgs bosons to Standard Model particles compete with decays to supersymmetric charginos/neutralinos as well as sfermions. In the high tan β case, the supersymmetric spectrum is either too heavy or the supersymmetric decay modes are suppressed, since the Higgs bosons decay almost exclusively into b and τ pairs. The main production mechanisms for the heavy Higgs particles are the associated AH production and H ⁺H^? pair production with cross sections of the order of a few fb.     

Two-and three-body decay modes of SUSY Higgs particles

We summarize the dominant decay modes of the neutral and charged Higgs bosons in the Minimal Supersymmetric extension of the Standard Model. While two-body decays are in general dominating, the branching ratios for three-body decays of the heavy scalar, pseudoscalar and charged Higgs bosons can be large below the thresholds if top quarks, W/Z bosons or heavy scalar bosons are involved. Analytical expressions have been derived for the partial decay widths and the physical implications of these decay modes are discussed.     

Final results from DELPHI on the searches for SM and MSSM neutral Higgs bosons

These final results from DELPHI searches for the Standard Model (SM) Higgs boson, together with benchmark scans of the Minimal Supersymmetric Standard Model (MSSM) neutral Higgs bosons, used data taken at centre-of-mass energies between 200 and 209 GeV with a total integrated luminosity of 224 pb^-1. The data from 192 to 202 GeV are reanalysed with improved b-tagging for MSSM final states decaying to four b-quarks. The 95% confidence level lower mass bound on the Standard Model Higgs boson is 114.1 GeV/c ². Limits are also given on the lightest scalar and pseudo-scalar Higgs bosons of the MSSM.Received: 7 March 2003, Revised: 30 September 2003, Published online: 3 December 2003     

Higgs radiation off top quarks in high-energye + e − colliders

Higgs particles can be radiated off heavy top quarks which will be produced copiously in high energye ⁺ e ^? colliders. This process can be used to measure the Higgs-top quark coupling. We present the cross section for the production of Higgs bosons in the Standard Model. In addition we have studied the production of neutral and charged Higgs particles in association with heavy fermions in the Minimal Supersymmetric Standard Model.     

Search for neutral Higgs bosons in Z0 decays using the OPAL detector at LEP

A search for neutral Higgs bosons has been performed using the full sample of Z⁰ decays collected by the OPAL detector at LEP up to 1995. The data were taken at centre-of-mass energies between 88 GeV and 95 GeV and correspond to an integrated luminosity of approximately 160 pb^?1. The present search addresses the processes Z⁰→H⁰Z* and h⁰Z*, where H⁰ is the Higgs boson predicted by the Standard Model and h⁰ the lightest neutral scalar Higgs boson predicted in the framework of the Minimal Supersymmetric Standard Model. For the virtual Z⁰ boson, Z*, the following decay channels are considered: Z*→vv?, e⁺e^? and μ⁺μ^?. Two candidate events have been found in the vv?H⁰ channel and one in the μ⁺μ^?H⁰ channel. Combined with earlier searches, the present search excludes the SM Higgs boson, at the 95% confidence level (CL), from the mass range below 59.6 GeV. In the framework of the Minimal Supersymmetric Standard Model, allowing a wide range of variation for most relevant model parameters, a 95% CL lower limit of 44.3 GeV is obtained for the mass of the h⁰ boson. Combined with earlier direct searches for the Higgs boson pair production process Z⁰→h⁰A⁰ and with measurements of the Z⁰ line shape, a 95% CL lower limit of 23.5 GeV is obtained for the mass of the pseudoscalar Higgs boson A⁰, assuming tan β≥ 1.     

Heavy scalar tau decays in the complex MSSM: a full one-loop analysis

We evaluate all two-body decay modes of the heavy scalar tau in the Minimal Supersymmetric Standard Model with complex parameters (cMSSM) and no generation mixing. The evaluation is based on a full one-loop calculation of all decay channels, also including hard and soft QED radiation. The renormalization of the relevant sectors is briefly reviewed. The dependence of the heavy scalar tau decay on the relevant cMSSM parameters is analyzed numerically, including also the decay to Higgs bosons and another scalar lepton or to a tau and the lightest neutralino. We find sizable contributions to many partial decay widths and branching ratios. They are mostly of $\mathcal{O}(5\mbox{--}10~\%)$ of the tree-level results, but can go up to 20 %. These contributions are potentially important for the correct interpretation of scalar tau decays at the LHC and, if kinematically allowed, at the ILC or CLIC. The evaluation of the branching ratios of the heavy scalar tau will be implemented into the Fortran code FeynHiggs.     

The Higgs sector of the minimal <Emphasis Type="Italic">B</Emphasis>−<Emphasis Type="Italic">L</Emphasis> model at future Linear Colliders

We investigate the phenomenology of the Higgs sector of the minimal B−L extension of the Standard Model at a future e ⁺ e ⁻ Linear Collider. We consider the discovery potential of both a sub-TeV and a multi-TeV machine. We show that, within such a theoretical scenario, several novel production and decay channels involving the two physical Higgs states, precluded at the LHC, could experimentally be accessed at such machines. Amongst these, several Higgs signatures have very distinctive features with respect to those of other models with enlarged Higgs sector, as they involve interactions of Higgs bosons between themselves, with Z′ bosons as well as with heavy neutrinos. In particular, we present the scope of the Z′ strahlung process for single and double Higgs production, the only suitable mechanism enabling one to access an almost decoupled heavy scalar state (therefore outside the LHC range).     

K +→π + vv andK L 0 →μ + μ − decays within the Minimal Supersymmetric Standard Model

We present a detailed calculation of the contributions of charginos, scalar quarks, and charged Higgs boson to theK ⁺→π ⁺ vv andK _L ⁰ →μ ⁺ μ ⁻ decays. We include mixings: that of charginos and that of the scalar partners of the left and right handed top quark. We find that the box contribution to the amplitudes is much smaller than the penguin contribution, which can be ∼10% of the Standard Model contribution, even for relatively large SUSY masses. The charged Higgs contribution can be as large as 25% of the SM contribution in the first decay and as much as 40% of the SM contribution in the second decay.     

Electroweak corrections to the fermionic decay width of the standard Higgs boson

The partial decay width of the standard model Higgs particle into a general species of fermions is given at the electroweak 1-loop level. The analytic formulae are applicable to light and heavy fermions. Numerical results are presented for Higgs decays intob andt quarks and into charged leptons. For not too heavy Higgs bosons the radiative corrections are of the order of a few per cent. In particular for Higgs bosons below theW ⁺ W ^– threshold the correction to the partial width intob quarks is very small and insensitive to the top mass. For every heavy Higgs bosons the 1-loop corrections increase the fermionic decay widths for all channels up to 15%.     

Higgs bosons in supersymmetric models (III). Decays into neutralinos and charginos

We give explicit formulae for the decays of the Higgs bosons of the minimal supersymmetric model to neutralinos and charginos. The important features of these decays are illustrated and their phenomenological implications discussed. Particular attention is given to the decays of heavy Higgs bosons (with masses larger than m_Z) which can only be observed at a future supercollider. When phase-space allowed, Higgs decays into neutralinos and charginos are at least as important as, and often dominate, other types of Higgs decay modes, such as WW, ZZ, and heavy quark (or lepton) pairs.     

S earch for anomalous production of di-l epton ev ents with missing transv ers e mom entum in e + e- collisions at $\sqrt{s} = {}$183-209 G eV

In total 1317 di-lepton events with significant missing transverse momentum were identified in a total data sample of 680 pb^-1 collected at e ⁺ e^- centre-of-mass energies ranging from 183 GeV to 209 GeV. The number of di-lepton events, the dependence on centre-of-mass energy, and the event properties are consistent with expectations from Standard Model processes, predominantly W ⁺ W^- production with both W bosons decaying leptonically. This topology is also an experimental signature for the pair production of new particles that decay to a charged lepton accompanied by one or more invisible particles. No evidence for new phenomena is apparent. Upper limits are presented on the production cross-section multiplied by the relevant branching ratio squared for sleptons, leptonically decaying charginos and charged Higgs bosons. Mass limits are also given.Received: 14 July 2003, Published online: 9 January 2004     

Gluino decays in the complex MSSM: a full one-loop analysis

We evaluate all two-body decay modes of the gluino, in the Minimal Supersymmetric Standard Model with complex parameters (cMSSM). This constitutes an important step in the cascade decays of SUSY particles at the LHC. The evaluation is based on a full one-loop calculation of all two-body decay channels, also including hard QED and QCD radiation. The dependence of the gluino decay to a scalar quark and a quark on the relevant cMSSM parameters is analyzed numerically. We find sizable contributions to the decay widths and branching ratios. They are, roughly of O(±5%)\mathcal{O}({\pm 5\%)}, but can go up to ±10% or higher, where the pure SUSY QCD contributions alone can give an insufficient approximation to the full one-loop result. Therefore the full corrections are important for the correct interpretation of gluino decays at the LHC. The results will be implemented into the Fortran code FeynHiggs.     

Decays of Higgs Bosons Into a Fermion-Antifermion Pair

Russian Physics Journal - Within the framework of the Minimal Supersymmetric Standard Model, decay channels of Higgs bosons (h, A), H± into arbitrarily polarized fermion-antifermion pairs $$...     

Decays of H(h; A) Higgs Bosons into Two Photons (Gluons)

Russian Physics Journal - Within the framework of the Minimal Supersymmetric Standard Model, we have investigated decay channels of Higgs bosons into circularly polarized photons (gluons): H(h; A)...     

Precise predictions for the Higgs-boson masses in the NMSSM

The particle discovered in the Higgs-boson searches at the LHC with a mass of about \(125 \, \mathrm{GeV}\) can be identified with one of the neutral Higgs bosons of the Next-to-Minimal Supersymmetric Standard Model (NMSSM). We calculate predictions for the Higgs-boson masses in the NMSSM using the Feynman-diagrammatic approach. The predictions are based on the full NMSSM one-loop corrections supplemented with the dominant and sub-dominant two-loop corrections within the Minimal Supersymmetric Standard Model (MSSM). These include contributions at \(\mathcal {O}{(\alpha _t \alpha _s, \alpha _b \alpha _s, \alpha _t^2,\alpha _t\alpha _b)}\), as well as a resummation of leading and subleading logarithms from the top/scalar top sector. Taking these corrections into account in the prediction for the mass of the Higgs boson in the NMSSM that is identified with the observed signal is crucial in order to reach a precision at a similar level as in the MSSM. The quality of the approximation made at the two-loop level is analysed on the basis of the full one-loop result, with a particular focus on the prediction for the Standard Model-like Higgs boson that is associated with the observed signal. The obtained results will be used as a basis for the extension of the code FeynHiggs to the NMSSM.     

Bound states of scalar bosons in extensions of the Standard Model

We explore systematically, in a general two Higgs doublet model, the possibility that bound systems of scalar bosons do exist. We find a wide region of parameter space in the scalar potential for which S-wave bound states of Higgs bosons do indeed exist. On the contrary we show that the Minimal Supersymmetric Standard Model does not admit such bound systems.     

Searches for invisibly decaying Higgs bosonswith the DELPHI detector at LEP

Searches for H Z production with the Higgs boson decaying into an invisible final state were performed using the data collected by the DELPHI experiment at centre-of-mass energies between 188 GeV and 209 GeV. Both hadronic and leptonic final states of the Z boson were analysed. In addition to the search for a heavy Higgs boson, a dedicated search for a light Higgs boson down to 40 GeV/c² was performed. No signal was found. Assuming the Standard Model HZ production cross-section, the mass limit for invisibly decaying Higgs bosons is 112.1 GeV/c² at 95% confidence level. An interpretation in the Minimal Supersymmetric extension of the Standard Model (MSSM) and in a Majoron model is also given.Received: 2 September 2003, Revised: 10 November 2003, Published online: 15 January 2004     

Neutral Higgs sector of the MSSM with explicit CP violation and non-holomorphic soft breaking

Using the effective potential method, we computed one-loop corrections to the mass matrix of neutral Higgs bosons of the Non-Holomorphic Supersymmetric Standard Model (NHSSM) with explicit CP violation, where the radiative corrections due to the quarks and squarks of the third generation were taken into account. We observed that the non-holomorphic trilinear couplings can compete with the holomorphic ones in CP violating issues for the mass and mixing of the neutral Higgs bosons.     

Higgs boson searches via dileptonic bottomonium decays

We explore the pseudoscalar ηb${\eta }_b$ and the scalar χ_b0${\chi }_{b0}$ decays into ?⁺?⁻${?}^{+}{?}^{-}$ to probe whether it is possible to probe the Higgs sectors beyond that of the Standard Model. We, in particular, focus on the Minimal Supersymmetric Standard Model, and determine the effects of its Higgs bosons on the aforementioned bottomonium decays into lepton pairs. We find that the dileptonic branchings of the bottomonia can be sizeable for a relatively light Higgs sector.     

Enhanced di-photon Higgs signal in the Next-to-Minimal Supersymmetric Standard Model

In the Next-to-Minimal Supersymmetric Standard Model, CP-even Higgs bosons can have masses in the range of 80–110 GeV in agreement with constraints from LEP due to their sizeable singlet component. Nevertheless their branching ratio into two photons can be more than 10 times larger than the one of a Standard Model Higgs boson of similar mass due to a reduced coupling to b quarks. This can lead to a spectacular enhancement of the Higgs signal rate in the di-photon channel at hadron colliders by a factor 6. Corresponding scenarios can occur in the Next-to-Minimal Supersymmetric Standard Model for a relatively low Susy breaking scale.