Higgs-boson production together with neutrino pair at e+e− colliders

The cross section for production of supersymmetric neutral Higgs boson in association with a neutrino-antineutrino muon pair in e⁺e^? annihilation are calculated, i.e. $e^ + e^ - \to \nu _\mu \bar \nu _\mu H_i^0 $ via different propagators.     

Possible deviations in W pair production at e+e− colliders due to a strong electroweak sector

Standard model predictions for W pair production at e⁺e⁻ colliders are compared to those of an effective lagrangian where the electroweak symmetry breaking occurs via a strong dynamics implying new spin-1 states. Both the differential cross section and the longitudinal asymmetry are evaluated at LEP II (√s=190 GeV) and at SLC (√s=600 GeV) energies. These quantities appear to be sensitive to specific ranges of the parameter space, with distinctive experimental signatures.     

Zinos and scalar muon production at e+e− colliders

Single scalar muon production is examined in detail which results in a final state particularly favourable for detection: two strongly acollinear muons plus large missing energy. Cross sections, missing energy and angular distributions are given. A strong dependence on the zino total width, common to all single production channel, is found.     

Radiative corrections for associatedZH production at futuree + e − colliders

The \(ZHf\bar f\) four-point function is calculated in the one-loop approximation of the Standard Model and full analytic results are presented. The loop contributions due to both light and new heavy fermions are inspected in detail. The dominant mechanisms of Higgs-boson production from fermions are compared. The effect of radiative corrections on the cross section of \(f\bar f \to ZH\) including bremsstrahlung is studied. The spectrum of hard bremsstrahlung is integrated analytically. The implications for Higgs-boson searches at futuree ⁺ e ^? colliders in the energy range 200 \(200GeV \le \sqrt s \le 1.5TeV\) , which includes both LEP 2 and the Next Linear Collider, are analyzed. ForM _H <2m _t weak corrections in the modified on-mass-shell scheme are generally negative and feebly vary withM _H , while forM _H >2m _t , they strongly increase withM _H and may take large positive values. Electromagnetic corrections dramatically reduce the cross section close to theZH-production threshold, while they may considerably enhance it far above this threshold.     

Light charged Higgs scalars at high-energy e+e− colliders

We study the prospects for detecting light charged Higgs scalars (H^±) at future e⁺e⁻ colliders. Various two-Higgs-doublet models (2HDM) and a general multi-Higgs-doublet model (MHDM) are considered, all of which may contain a H^± in the discovery range of LEP2. The potentially troublesome cases of M_H^± ∼ M_W and M_H^± ∼ M_Z are discussed, as well as ways of distinguishing the different models.     

The production ofW + W − pairs in proton-antiproton colliders

We present the predictions of the Glashow-Weinberg-Salam [1] (GWS) model for the total cross-section and the angular and invariantmass differential cross sections for the reaction \(p\bar p \to W^ + W^ - X\) . We contrast these GWS predictions with those obtained by varying the anomalous magnetic moment of theW(κ), the analogue for theZWW coupling (κ _z ) and the relative strength of the γWW andZWW couplings (ω) from their GWS values. We find that changes in these parameters produce significant changes in both the total cross section and the angular and invariant mass differential cross sections. We also present the angular distribution of the decay leptons (W ⁺→/+v _l) and find in all cases it closely mirrors theW ⁺ angular distribution. We have given the intermediate results for the dominant quark subprocesses \((u\bar u \to W^ + W^ - ,d\bar d \to W^ + W^ - )\) .     

Aspects of two-photon physics at lineare + e − colliders

We discuss various reactions at futuree ⁺ e ^– and colliders involving real (beamstrahlung or backscattered laser) or quasi-real (bremsstrahlung) photons in the initial state and hadrons in the final state. The production of two central jets with large transverse momentump _T is described in some detail; we give distributions for the rapidity andp _T of the jets as well as the di-jet invariant mass, and discuss the relative importance of various initial state configurations and the uncertainties that arise from the at present rather poor knowledge of the parton content of the photon. We also present results for mono-jet production where one jet goes down a beam pipe, for the production of charm, bottom and top quarks, and for single production ofW andZ bosons. Where appropriate, the two-photon processes are compared with annihilation reactions leading to similar final states. We also argue that the behaviour of the total inelastic cross section at high energies will probably have little impact on the severity of background problems caused by soft and semi-hard (minijet) two-photon reactions. We find very large differences in cross sections for all two-photon processes between existing desings for futuree ⁺ e ^– colliders, due to the different beamstrahlung spectra; in particular, both designs with 1 and 1 events per bunch crossing exist. The number of hadronic two-photon events is expected to rise quickly with the beam energy. Hadronic backgrounds will be even worse if thee ⁺ e ^– collider is converted into a collider.     

W+W−γ production in e+e− annihilation in the TeV region

The reaction e⁺e⁻→γW⁺W⁻ has been studied at TeV energies as a possible background to Higgs production. Our results differ significantly from previous estimates and show that the ratio signal/background can be kept reasonably large.     

SUSY-QCD corrections to scalar quark pair production in e+e− annihilation

We calculate the supersymmetric O(α_s) QCD corrections to the cross section e⁺e⁻ → q̃_iq̃_j (i, j = 1,2) within the Minimal Supersymmetric Standard Model. We pay particular attention to the case of the left-right squark mixing and to the renormalization of the mixing angle. The corrections due to gluino exchange turn out to be smaller than those due to gluon exchange, but they can be significant at higher energies, even for a gluino mass of a few hundred GeV.     

e+ e− production from pp reactions at BEVALAC energies

We have performed a detailed study of dilepton production from pp collisions including the subthreshold ϱ production via baryonic resonances (N(1520), N(1700)) in addition to the conventional dilepton sources as π⁰, η, ω and Δ Dalitz decays and direct decays of vector mesons (ϱ, ω). The role of baryonic resonances in ϱ production from nucleon-nucleon collisions is studied in comparison to the DLS data which are well described.     

Higgss-channel production ine + e − collisions below theW + W − threshold

The cross section for direct neutral Higgs production in the reaction is calculated in theE _CM energy range of 40 to 160 GeV and compared to the corresponding Electro-Weak (EW) process . Neglecting radiation effects, a signal of the order of 10^–4 to 10^–3 over the EW can be expected outside theZ ⁰ region for the Minimal Standard Model Higgs in its decay to a state. For \sqrt s - M_Z $$ " align="middle" border="0"> , thes-channel Higgs formation can surpass the Bjorken Bremsstrahlung process and thus may afford at LEP 2 a realistic search method for high mass, say 100 GeV Higgs, given enough luminosity. For a non-Standard Model Higgs, in some cases, significantly higher signals are expected. The effects of initial state radiation and-machine energy resolution are evaluated and the gain in using longitudinal polarized electron beams is discussed.Supported in part by the Israel Ministry for Science and Technology     

Vector boson pair production in e−e− collisions with polarized beams

The W-boson pair production in e⁻e⁻ collisions with polarized beams is investigated. The helicity amplitudes are derived for general couplings and the conditions for a good high-energy behaviour of the cross-section are given. The results are applied to the heavy vector boson production in the context of the left-right symmetric model. The Ward identities and the equivalence theorem are also discussed.     

Inclusive one- and two-jet cross sections in γγ reactions at e+e− colliders

We have calculated inclusive one- and two jet production in photon-photon collisions superimposing direct, single-resolved and double-resolved cross sections for center of mass energies of the LEP1, LEP2 and NLC range. The direct and single-resolved cross sections are calculated up to next-to-leading order. The double-resolved two-jet cross section is calculated only in LO with a k factor estimated from the NLO one jet cross section. Various differential cross sections as functions of transverse momenta and rapidities of the jets are evaluated.     

Alternative vector-boson self-couplings and e+e− → W+W−

Employing global SU(2)_WI symmetry and γW³ mixing we derive a lagrangian for vector-boson self-interactions whose strength may considerably differ from the ones required by the standard model; the neutral-current structure and the mass relationship of the standard model remain intact, however. Numerical results for the cross section for e⁺e⁻ → W⁺W⁻ are presented.     

Towards slow μ− production via muon catalyzed fusion

Slow ^– production via dd-CF using a two-layer arrangement is investigated. To determine its feasibility, experimental measurements are now in progress using the muonic X-ray detection method. The following experimental steps are being considered: (1) measurement of the number of ^– stopped inside a solid H₂/D₂ layer by detecting p K X-rays, (2) hot d emission detection by placing a secondary target at a distance of 10–30 mm from the layer and by detecting specific delayed X-rays, (3) measurement of the disappearance of d emission as the added D₂ layer is increased, (4) dd-CF measurement by detecting fusion protons, and (5) slow ^– emission detection. Results of the initial test experiment are presented.     

Z–Z' mixing effects in W boson pair production processes at hadron and lepton high-energy colliders

Potential possibilities to detect the effects of Z–Z' mixing in the W-pair production process in proton-proton and electron–positron collisions at the Large Hadron Collider (LHC) and International Linear Collider (ILC) have been studied. It has been established that the processes of W boson pair production are very sensitive to the angle of Z–Z' mixing and their measurements in current and future experiments will make it possible to improve modern restrictions on the angle of Z–Z' mixing in the models with extended gauge sector. At a nominal energy of 14 TeV and an integral luminosity of 100 fb^–1, the LHC collider can offer much more precise information on the parameter of Z–Z' mixing and the mass M ₂ than can be obtained using the ILC leptonic collider (0.5 TeV).