Production of singleW bosons ine + e − ande − p collisions

The production ofW bosons in electronpositron colliding beams below theW ⁺ W ^? threshold is discussed. The corresponding reactions \(e^ + e^ - \to l^ \pm W^ \mp \mathop {\nu _l }\limits^{( - )} \) yield total cross-sections of the order of 10^?37 cm² (forl=e) and 10^?38 cm² (forl=μ). The total cross-sections as well as the angular and energy distributions of theW boson in \(e^ + e^ - \to e^ \pm W^ \mp \mathop {\nu _e }\limits^{( - )} \) are sensitive to the magnetic moment of theW. So, with this reaction, not onlyW bosons can be produced but also the gauge nature of the interaction can be tested. The decay \(Z^0 \to l^ \pm W^ \mp \mathop {\nu _l }\limits^{( - )} \) is discussed in view of its observation ine ⁺ e ^? experiments. Finally the crosssections ofe ^- p→ν _e W ^- X ⁺ are computed. They are of the order of 10^?38 cm² for \(\sqrt s \simeq 200\) GeV.     

Search for charged Higgs bosons in e+e− collisions at s=189 GeV

A search for pair-produced charged Higgs bosons is performed with the L3 detector at LEP using data collected at a centre-of-mass energy of 188.6 GeV, corresponding to an integrated luminosity of 176.4 pb⁻¹. Higgs decays into a charm and a strange quark or into a tau lepton and its associated neutrino are considered. The observed events are consistent with the expectations from Standard Model background processes. A lower limit of 65.5 GeV on the charged Higgs mass is derived at 95% confidence level, independent of the decay branching ratio Br(H^±→τν).     

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.     

Charged Higgs boson production ine + e −-annihilation

A detailed analysis of the processe ⁺ e ^?→H ^± tb including total as well as differential cross sections is presented and possible signatures for charged Higgs boson searches relevant for LEP energies are discussed and compared with standard model background stemming fromt \(\bar t\) production.     

Spontaneous e+e− pair creation in heavy ion collisions

We demonstrate that vibrational perturbations of supercritical “quasimolecules” which may occur in collisions of heavy ions can, within the context of first-order perturbation,theory, result in the production of coincident narrow e⁺e⁻ peaks, in place of and with a larger yield than that predicted for spontaneous positron emission from static supercritical systems. Certain features of this phenomenon coincide with those of the e⁺e⁻ peaks observed by the EPOS collaboration although some important aspects of the observations cannot be reproduced within our approximation. A detailed attempt to reconcile this theoretical model with the EPOS experiment must go beyond perturbation theory.     

Limits on the τ neutrino electromagnetic properties from single photon searches ate + e − colliders

We set limits on the magnetic moment and charge radius of the τ neutrino by examining the contributions to the processe ⁺ e ^?→v \(\bar \nu \) γ due to such interactions. We find thatK(ν_τ)<4×10^?6 (i.e.μ(ν_τ)<4×10^?6μ _B , μ _B =e/2m _e ) and 〈r ²〉<2×10^?31 cm² using the combined data of the MAC, ASP, CELLO, and Mark J collaborations for this process. We briefly discuss whether these bounds can be improved in any futuree ⁺ e ^? experiments.     

Production and decay of neutralinos in e+e− annihilation

We study in detail production and decay of neutralinos in e⁺e⁻ annihilation. Formulae for the cross section, the single lepton, lepton pair, and missing energy spectra are given. Particular attention is paid to the mixing of gauginos and higgsinos. In order to illustrate its importance numerical results for four different mixing scenarios are presented.     

Inclusive Production Λc in the e+e− - Annihilation

In the framework of the quark-diquark model of baryons, Λ_c can be considered as constituent c quark and ud diquark. In hadronizasion process baryon Λ_c can be produced from ud scalar diquark and c quark fragmentation. So in this work, in the lowest order of perturbative QCD, fragmentation functions c → Λ_c and ud → Λ_c are calculated and finally in the electron-positron annihilation in LEP, the inclusive cross section production of Λ_c is calculated about pole of z⁰.     

Higgs decay to τ+τ−A possible signature of intermediate mass Higgs bosons at high energy hadron colliders

This paper considers the decay of a standard model Higgs boson into a tau pair, as a possible signature at the SSC or LHC for a Higgs boson of mass between 110 and 160 GeV. The production of the Higgs in association with a large transverse momentum jet is considered, since this may aid in reconstructing the Higgs mass. The background from the production of tau pairs via virtual photons and Z's is studied. We comment on the possible use of this process to search for a light Higgs at the Tevatron collider.     

Production of supersymmetric particles ine + e − andep collisions

A review is given of the theoretical predictions for chargino, neutralino and selectron pair production ine ⁺ e ^– annihilation and for slepton and squark production inep collisions. The energy range considered is that of LEP, SLC and HERA. The expectations for the production of SUSY particles at ane ⁺ ev ^– collider in the TeV energy range are also discussed.Invited talk at the International Symposium Hadron Interactions — Theory and Phenomenology, Bechyn, Czechoslovakia, June 26–July 1, 1988.I want to thank H. Baer, H. Fraas, D. Karatas, W. Majerotto and X. Tata for discussions and correspondence. Financial supports of the Czechoslovak Academy of Sciences and the Austrian Academy of Sciences are gratefully acknowledged.     

Delayed unitary cancellation and heavy particle effects in e+e−→W+W−

We examine one-loop radiative corrections to e⁺e⁻→W⁺W⁻ in the standard model with one Higgs doublet, concentrating on the effects of very heavy fermions. These disturb the delicate unitarity cancellation between s- and t-channel diagrams, raising the cross section even well below the fermion threshold and giving a clear experimental signature for the heavy sector.     

Charged Higgs boson discovery potential at a 500 GeV e+e− linear collider

The discovery potential for charged Higgs bosons has been studied with full-statistics background simulations for $\sqrt s$ =500 GeV and ?=10fb^?1. For the hadronic decay channels $H^ + H^ - \to \operatorname{c} \bar s\bar cs$ , a microvertex detector is crucial for establishing a signal over the $e^ + e^ - \to t\bar t$ background. A combination with a search in the channels $H^ + H^ - \to c\bar s\tau ^ - \nu ,\tau ^ + \nu \tau ^ - \bar \nu$ allows detection sensitivity for charged Higgs bosons up to a mass of about 210GeV, independent of the charged Higgs decay modes. Sensitivity regions in them _A-tanβ parameter space of the Minimal Supersymmetric extention of the Standard Model (MSSM) are given.