Hydrodynamical approach to the electron-positron annihilation into hadrons

The problem is reconsidered and it stressed that viscosity must be taken into account. This makes superfluous introduction of an “initial hadronic volume” V_o ～ m_π^?1 which in the e⁺e^? case can hardly be physically motivated. The viscosity becomes the single source of dissipation. Rough estimate of multiplicity is presented. Further, black body electromagnetic radiation from the hot hadronic clump turns out to be essential. It leads to an increase of energy spent on neutral component.     

Jet-structure and the statistical model for electron-positron annihilation into hadrons

We consider a statistical model for electron-positron annihilation into hadrons, whose input single particle distribution function $\text{?(p)}$ is power behaved for large values of the momentum $\text{p, ?(p) ～ p}{}^{\mathrm{m?2}}$. Three classes can be distinguished, corresponding to m > 0, m = 0 and m < 0. The first two classes have asymptotically a spherically symmetric event structure, while for the case m < 0 we argue that energy-momentum conservation forces the events to be jet-like.     

Production of hard photons in electron-positron annihilation into hadrons

Frequency of emission of prompt, hard photons radiated by the fast-moving quarks (antiquarks) ine ^– e ⁺ annihilation into hadrons is estimated for the string model. The differential probability of emission of such photons is obtained from a sum rule which takes for the initial state of the emitter a classical trajectory. It is found that the string models are quite effective in production of hard photons (i.e., photons whose energies are substantial fractions of the energies of the initiale ^– e ⁺ pair) associated with production of hadrons. For 100 GeVe ⁺ e ^– initial energy the frequency of emission,v, of 10 GeV<><40gev photons=" is=" estimated=" to=" be=">^–4v<>^–3.Supported in part by the Polish Ministry of Education, Grant DNS-P-04/215/90-2 and KBN Grant No 2-00054-91-01     

Fragmentation production of charmed hadrons in electron-positron annihilation

Processes involving the production of D* mesons and Λ _c baryons in electron-positron annihilation at the energies of 10.58 and 91.18 GeV are considered. At the energy of 10.58 GeV, the production of pairs of B mesons that is followed by their decay to charmed particles is analyzed along with direct charm production. The violation of scaling in the respective fragmentation functions is taken into account in the next-to-leading-logarithmic approximation of perturbative QCD. The required nonperturbative fragmentation functions are extracted numerically from experimental data obtained at B factories and are approximated by simple analytic expressions. It is shown that the difference in the nonperturbative fragmentation functions for transitions to mesons and baryons can readily be explained on the basis of the quark-counting rules.     

A new quantity for finding four-jet events in electron-positron annihilation into hadrons

We introduce a new jet measure, tripodityD ₃, which offers good prospects to identify four-jet events ine ⁺ e ^? annihilation into hadrons. TheoreticalD ₃ distributions are presented for quantum chromodynamics, for an abelian model and for a phase space distribution of four jets.     

Electron-positron annihilation into hadrons at high energies

In the limit of extremely high energies with the transverse momentum of each hadron fixed, the reaction e⁺ + e⁻ → hadrons proceeds by the annihilation of this pair into two virtual photons which turn into two fireballs of hadrons with negligible final-state interaction.     

Inclusive properties of the ee annihilation into hadrons

The reaction e⁺e⁻ → hadrons is described on the basis of an hadronic structure for the photon. The structure functions of the inclusive reaction e⁺e⁻ → h + anything describe then the parton constitution of the photon in the scaling limit. Various types of couplings and models are considered (global couplings with vector mesons, fundamental photon-parton-antiparton couplings with formation of jets or fans). Precise shapes for the inclusive spectra and multiplicity distributions are deduced. Detailed comparisons with hadronic collisions A + B → h + anything are proposed in the fragmentation, the phase space boundary and the pionisation regions which could determine the nature of the partons and their interactions.     

Maybe the quark-parton model can survive electron-positron annihilation

Using a covariant parton model we show that scaling in e⁺e^? annihilation is extremely cunctative.     

Distributions for electron-positron annihilation into two and three photons

In this paper a procedure is outlined to simulate events for the reactions e⁺e^? → γγ and γγγ. Various distributions thus obtained are presented. The standard radiative corrections are also calculated in this way. Moreover, an analytical expression for the total annihilation cross section is given up to order α³.     

Final-state radiation in electron-positron annihilation into a pion pair

New, accurate measurements of the pion and kaon electromagnetic form factors are expected in the near future from experiments at electron-positron colliders, using the radiative return method. We construct a model for the timelike pion electromagnetic form factor that is valid also at momentum transfers far above the resonance. The ansatz is based on vector dominance and includes a pattern of radial excitations expected from dual resonance models. The form factor is fitted to the existing data in the timelike region, continued to the spacelike region and compared with the measurements there and with the QCD predictions. Furthermore, the model is extended to the kaon electromagnetic form factor. Using isospin and SU(3)-flavor symmetry relations we extract the isospin-one contribution and predict the kaon weak form factor accessible in semileptonic decays.Received: 7 October 2004, Published online: 17 December 2004     

Radiation zeros in high-energy e^+e^- annihilation into hadrons

The process contains radiation zeros, i.e. configurations of the four–momenta for which the scattering amplitude vanishes. We calculate the positions of these zeros for –quark and –quark production and assess the feasibility of identifying the zeros in experiments at high energies. The radiation zeros are shown to occur also for massive quarks, and we discuss how the final state may offer a particularly clean environment in which to observe them. Received: 16 December 1997 / Published online: 10 March 1998     

Senile scaling in electron-positron annihilation

An important difference is pointed out between the approach to scaling behaviour in deep inelastic scattering and annihilation. In the framework of the massive quark model a quantitative analysis of the breaking terms is carried out for the total and the one-particle inclusive cross-sections. Good agreement with available data is found.     

Spinless bosons in electron-positron annihilation

The contributions to the processes \(e^ + e^ - \to \mu ^ + \mu ^ - ,q\bar q,\gamma \gamma ,e^ + e^ - \) , mediated by scalar and/or pseudoscalar bosons are calculated. The constraints on their coupling constants and their masses are investigated as they arise from the radiative decayZ ⁰→⁺ e ^? γ and from the experimental data for the annihilation processes into lepton, photon and quark pairs. Data one ⁺ e ^?→μ⁺ μ^?, γγ ande ⁺ e ^? seriously reduce the domain of coupling constants to leptons and photons still allowed by the probable value of the width ofZ ⁰→e ⁺ e ^? γ. Experimentse ⁺ e ^?→μ⁺ μ^?, γγ,e ⁺ e ^? at 45 GeV c.m.s. energy with a sensitivity of 10% will decide about the existence of a heavy spinless boson with the presumed phenomenological couplings to leptons and photons. Assuming universality of the coupling to leptons and quarks a conservative bound on the contribution toR arising from spinless boson exchange is already in conflict with the presumed radiative width ofZ ⁰→e ⁺ e ^? γ.     

Supersymmetric three-jets in electron-positron annihilation

The bremsstrahlung of gluons and gluinos off quarks and squarks is studied in e⁺e^? annihilation for longitudinally polarized beams. The contribution of a given supersymmetric state is found to be 11–27% of the conventional gluon bremsstrahlung. With all supersymmetric channels open this adds up to 90–100% of the q$\text{q}$g contribution. Dalitz-plot and angular distributions are investigated. A pronounced forward-backward asymmetry is found for gluino bremsstrahlung. Characteristic features are also exhibited by the angular distribution of the normal to the event plane.     

Gluino production in electron-positron annihilation

We discuss the pair production of gluinos in electron-positron annihilation at LEP, in a model with soft supersymmetry breaking, allowing for mixing between the squarks. In much of the parameter space of the Minimal Supersymmetric Model (MSSM) the cross section corresponds to aZ branching ratio above 10^–5, even up to 10^–4. A non-observation of gluinos at this level restricts the allowed MSSM parameter space. In particular, it leads to lower bounds on the soft mass parameters in the squark sector.     

Three-photon annihilation of the electron-positron pairs

Three-photon annihilation of the electron-positron pairs (=(e⁻,e⁺)-pairs) is considered in the electron rest frame. The energy of the incident positron can be arbitrary. The analytical expression for the cross-section of three-photon annihilation of the (e⁻,e⁺)-pair has been derived and investigated.