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.     

Measuring the Higgs branching fraction into two photons at future linear {\mathrm e}^+{\mathrm e}^- colliders

We examine the prospects for a measurement of the branching fraction of the decay mode of a Standard Model-like Higgs boson with a mass of 120 GeV at the future TESLA linear collider, assuming an integrated luminosity of 1 ab and centre-of-mass energies of 350 GeV and 500 GeV. A relative uncertainty on BF(\hgg) of 16% can be achieved in unpolarised collisions at = 500 GeV, while for = 350 GeV the expected precision is slightly poorer. With appropriate initial state polarisations the uncertainty can be improved to 10%. If this measurement is combined with a measurement of the total Higgs width, a precision of 10% on the Higgs boson partial width for the decay mode appears feasible. Received: 6 December 2000 / Revised version: 19 February 2001 / Published online: 23 March 2001     

Search for Yukawa Production of a light neutral Higgs Boson at LEP

Within a Two-Higgs-Doublet Model (2HDM) a search for a light Higgs boson in the mass range of 4–12 GeV has been performed in the Yukawa process , using the data collected by the OPAL detector at LEP between 1992 and 1995 in collisions at about 91 GeV centre-of-mass energy. A likelihood selection is applied to separate background and signal. The number of observed events is in good agreement with the expected background. Within a CP-conserving 2HDM type II model the cross-section for Yukawa production depends on and for the production of the CP-odd A and the CP-even h, respectively, where is the ratio of the vacuum expectation values of the Higgs doublets and is the mixing angle between the neutral CP-even Higgs bosons. From our data 95% C.L. upper limits are derived for within the range of 8.5 to 13.6 and for between 8.2 to 13.7, depending on the mass of the Higgs boson, assuming a branching fraction into of 100%. An interpretation of the limits within a 2HDM type II model with Standard Model particle content is given. These results impose constraints on several models that have been proposed to explain the recent BNL measurement of the muon anomalous magnetic moment. Received: 1 November 2001 / Published online: 22 February 2002     

CP-violating top quark couplings at future linear $$e^+e^-$$ colliders

We study the potential of future lepton colliders to probe violation of the CP symmetry in the top quark sector. In certain extensions of the Standard Model, such as the two-Higgs-doublet model (2HDM), sizeable anomalous top quark dipole moments can arise, which may be revealed by a precise measurement of top quark pair production. We present results from detailed Monte Carlo studies for the ILC at \(500 \hbox { GeV}\) and CLIC at \(380 \hbox { GeV}\) and use parton-level simulations to explore the potential of high-energy operation. We find that precise measurements in \(e^+e^- \rightarrow t\bar{t}\) production with subsequent decay to lepton plus jets final states can provide sufficient sensitivity to detect Higgs-boson-induced CP violation in a viable two-Higgs-doublet model. The potential of a linear \(e^+e^-\) collider to detect CP-violating electric and weak dipole form factors of the top quark exceeds the prospects of the HL-LHC by over an order of magnitude.     

Exploring the SUSY Higgs sector ate +e− linear colliders: a synopsis

We discuss the Higgs scenario in the minimal supersymmetric extension of the Standard Model ate ⁺e^? linear colliders operating in the c.m. energy range between 300 and 500 GeV. Besides decays of the Higgs particles into ordinary fermions and cascade decays, we analyze also decays into gaugino/Higgsinos and in particular, neutral Higgs decays into the lightest supersymmetric particles which are invisible ifR-parity is conserved. The cross sections for the various production channels of SUSY Higgs particles ine ⁺e^? collisions are discussed in detail. The lightest Higgs boson cannot escape detection, and in major parts of the MSSM parameter space all five Higgs particles can be observed.     

Double Higgs production at the linear colliders and the probing of the Higgs self-coupling

We study double Higgs production in the e⁺e^? and γγ modes of the linear collider. It is also shown how one can probe the scalar potential in these reactions. We discuss the effective longitudinal W approximation in γγ processes and the W _LW_L luminosities in the two modes of a high-energy linear collider. A generalised non-linear gauge-fixing condition, which is particularly useful for tree-level calculations of electroweak processes for the laser induced collider, is presented. Its connection with the background-field approach to gauge fixing is given.     

Future e(+)e(-) colliders' sensitivity to Hbb coupling and CP violation

We perform a complete simulation of the process e(+)e(-)-->bbvv, where nu can be an electron, muon, or tau neutrino, in the context of a general Higgs coupling to b quarks. We parametrize the Hbb; coupling as (m(b)/v)(a+igamma(5)b). Taking into account interference effects between pure Higgs and Standard Model contributions, we find that sensitivities of the order of 2% and 20% can be obtained at a future e(+)e(-) collider for deviations of the a and b parameters, respectively, from their Standard Model values. Combining our analysis with an independent measurement of Gamma(H-->bb) can provide evidence about the CP nature of the Higgs sector.     

Determining resonance parameters of heavy Higgs bosonsat a future linear collider

This study investigates the potential of an Electron-Positron Linear Collider for measuring resonance parameters of Higgs bosons beyond the mass range studied so far. The analysis is based on the reconstruction of events from the Higgs-strahlung process . It is shown that the total width , the mass m_H and the event rate N can be measured from the mass spectrum in a model independent way. Also, the branching ratios BR ^H_WW and BR ^H_ZZ can be measured, assuming these are the only relevant Higgs decay modes. The simulation includes realistic detector effects and all relevant Standard Model background processes. Results are given for m_H = 200-320 GeV assuming fb^-1 integrated luminosity at a collision energy GeV.Received: 13 February 2004, Revised: 14 April 2004, Published online: 18 May 2004     

Single top production at the next generation lineare + e − colliders

Zeitschrift für Physik C Particles and Fields - Stochastic differential equations are investigated which reduce in the deterministic limit to the canonical equations of motion of a Hamiltonian...     

Measuring Higgs CP properties through top quark production at a photon collider

We study resonant effects of heavy Higgs bosons on the top-pair production process at a photon linear collider. Observables which can be obtained by circular polarization of colliding photons and polarization measurement through the angular distribution of the top quark decays are useful not only for measuring the Higgs CP parity but also for resolving degeneracy of Higgs bosons.