Comparative study of Z′ searches in e+e− and e−e− scattering

We consider indirect searches for additional neutral vector bosons in e⁺e⁻ and e⁻e⁻ collisions, and compare these two linear collider modes with similar analysis procedures and assumptions. Discovery limits and resolving power are discussed in a model-independent way.     

Jet masses in e+e− annihilation

We calculate heavy (M _H ² /s) and light (M _L ² /s) jet masses up toO(α _s ² ) in perturbative Quantum Chromodynamics (QCD). The sensitivity of these quantities to radiative corrections, quark masses, fragmentation effects as well as their infrared stability properties, are investigated and compared to those exhibited by other jet measures. A comparison with recent Mark II data is also presented.     

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.     

e + e − multiplicity distribution from branching process

We present a multiplicity distribution which is a solution to the stochastic branching equation proposed by Giovannini. This solution is more commonly known as generalized multiplicities distribution (GMD) and has already been successfully applied to bothpp andp collisions. It assumes that shapes and energy dependence of distributions are basically determined by hard parton scattering and subsequent branching. We apply GMD to the recente ⁺ e ^– data by Tasso Collaboration.     

Duality ine + e − annihilation

With the help of a relativistic generalization of the formula for the leptonic width of quarkonium in the semiclassical approximation it is shown that for any confinement potential nonsingular at the origin the sum of total cross sections for the production of the heavy quarkonium states \((Q\bar Q)_n\) with masses \(M_n \leqq \sqrt s\) ine ⁺ e ^?-annihilation is equal to the cross section at givens for the production of the free quark-antiquark pair \(Q\bar Q\) . We obtain also a family of dual sum rules for quarkonium which are in agreement with the available experimental data on charmonium and beautionium within experimental errors.     

Thrust ine + e −-annihilation

The thrust distribution ine ⁺ e ^–-annihilation is analysed in perturbative QCD. Proper account is taken of multiple emission of gluons. Scaling holds for this quantity in the sense that its energy dependence comes only through the change in the QCD effective coupling. It thus provides an ideal means to determine the value of the QCD mass scale experimentally. From the data atW=91 GeV by the ALEPH collaboration at LEP, we obtain .     

Tests for planar events in e+e− annihilation

We present a new class of observables which distinguish events containing two or three hadron jets from those containing a larger number. These observables, which essentially measure the coplanary of events, are calculable in QCD perturbation theory. Their use should allow the mechanism of

decay to be determined.     

Double P-wave charmonium production in e + e − annihilation

On the basis of perturbative QCD and relativistic quark model we calculate relativistic and bound state corrections in the production processes of a pair of \(\mathcal{P}\) -wave charmonium states. Relativistic factors in the production amplitude are taken into account connected with the relative motion of heavy quarks and the transformation law of the bound-state wave function to the reference frame of the moving \(\mathcal{P}\) -wave mesons. Relativistic corrections to the quark bound-state wave functions in the rest frame are considered by means of the Breit-like potential. It turns out that the examined effects change essentially nonrelativistic results of the cross section for the reaction e ⁺ + e ^? → h _c + χ _c J at the center-of-mass energy √s = 10.6 GeV.     

Study of the K − → e − νπ 0 decay

The decay K ^? → e ^? νπ ⁰ has been studied using in-flight decays detected with the ISTRA₊ setup working at the 25-GeV negative secondary beam of the U-70 PS. About 130K events were used for the analysis. The λ ₊ parameter of the vector form factor has been measured: λ ₊=0.0293±0.0015(stat.)±0.002(syst.). The limits on the possible tensor and scalar couplings have been derived: f _T/f ₊(0)=?0.045±0.060(stat.) and f _S/f ₊(0)=?0.019 _?0.016 ^+0.025 (stat.).     

Rapidity distribution ine + e − annihilation

A method to systematically calculate the rapidity distribution of hadrons in a high-energy jet is formulated in terms of an integral equation for the multiplicity. The distribution has the following properties at high energies: (i) a translational invariance; (ii) an increasingly steep distribution with a width proportional to \(\sqrt {\ln s} \) , but without a widening “central plateau”; (iii) if the rapidity is scaled by \(\sqrt {\ln s} \) , it approaches to a universal exponential curve. In the large rapidity region, however, the translational invariance is broken because of the recoil of the quark by the emission of soft gluons. It is also discussed that a gluon jet has a wider angular distribution.     

Search for the e + e − → K ± K S π ∓ process on the VEPP-2M e + e − collider

We report on the results of the search for the e ⁺ e ^? → K ^± K _S π ^? process. Data with an integrated luminosity of 1.36 pb^?1 collected in experiment with a spherical neutral detector (SND) on the VEPP-2M e ⁺ e ^? collider in the energy range from 1.36 to 1.38 GeV have been analyzed. The upper limits of the σ < 150 pb cross sections of the sought process have been established for an energy of 1.37 GeV at a confidence level of 90%.     

Characterising WIMPs at a future e + e − linear collider

We investigate the prospects for detecting and measuring the parameters of WIMP dark matter in a model-independent way at the International Linear Collider. The signal under study is direct WIMP pair production with associated initial state radiation e ⁺ e ^?→χχγ. The analysis accounts for the beam energy spectrum of the ILC and the dominant machine induced backgrounds. The influence of the detector parameters are incorporated by full simulation and event reconstruction within the framework of the ILD detector concept. We show that by using polarised beams, the detection potential is significantly increased by reduction of the dominant SM background of radiative neutrino production $e^{+}e^{-} \rightarrow \nu \bar {\nu }\gamma The light-by-light contribution from the lightest neutral pseudoscalar and scalar mesons to the anomalous magnetic moment of muon is calculated in the framework of the nonlocal SU(3)×SU(3) quark model. The model is based on chirally symmetric four-quark interaction of the Nambu?CJona-Lasinio type and Kobayashi?CMaskawa?C??t?Hooft U _A (1) breaking six-quark interaction. Full kinematic dependence of vertices with off-shell mesons and photons in intermediate states in the light-by-light scattering amplitude is taken into account. The small positive contributions from the scalar mesons stabilize the total result with respect to change of model parameters and reduces to $a_{\mu}^{\mathrm{LbL},\mathrm{PS}+\mathrm{S}}=(6.25\pm0.83)\cdot10^{-10}$ .     

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.     

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.     

Annihilation mechanisms of e+e− and μ+μ− production in relativistic nuclear collisions

We revise the μ⁺μ^? and $q\bar q$ annihilation mechanisms of dilepton production during relativistic nuclear collisions. We focus on the modifications caused by the specific features of in-medium pion and quark states rather than by medium modification of the ρ-meson spectral density. The main ingreditent emerging in our approach is a form-factor of the multi-pion (multi-quark) system. Replacing the usual delta-function the form-factor plays the role of distribution which, in some sense, “connects” the total 4-momenta of the annihilating and outgoing particles. The difference between the c.m.s. velocities attributed to annihilating and outgoing particles is a particular consequence of this replacement and results in the appearance of a new factor in the formula for the lepton pair production rate. We obtained that the form-factor of the multi-pion (multi-quark) system causes broadening of the rate which is most pronounced for small invariant masses, in particular, we obtain a growth of the rate for the invariant masses below two masses of the annihilating particles.     

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.     

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.     

Radiative production of the lightest neutralino in e + e − annihilation

The production of the lightest stable neutralino in the process including general mixing of gauginos and Higgsinos is studied. General formulas for the differential cross section are presented. The dependence of the differential cross section on the photon energy spectrum and also the dependence of the total cross section on the beam energies for three different mixing scenarios are illustrated. The text was submitted by the author in English.     

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.     

Physics opportunities with polarized e − and e + beams at TESLA

Beam polarization at e⁺-e^– linear colliders will be a powerful tool for high precision analyses. Often it is assumed that the full information from polarization effects is provided by polarization of the electron beam and no further information can be obtained by the simultaneous polarization of the positrons. In this paper we point out the advantages of polarizing both beams, and summarize the polarization-related results of the Higgs, Electroweak, QCD, SUSY and Alternative Theories working groups of the ECFA/DESY workshop for a planned linear collider operating in the energy range s = 500-800 GeV.