Radiative muon pair production in high-energy electron-positron annihilation process

The lowest order radiative correction to the differential cross section of process of muon pair production with the emission of a hard photon at high energy electron-positron annihilation are calculated. Taking into account the emission of additional soft and hard photon, the cross section can be put in the form of the Drell-Yan process in leading logarithmical approximation. Applying the crossing transformation, we obtain the cross section of the radiative electron-muon high-energy scattering process. Virtual and soft photon emission contributions of the nonleading form are tabulated for several typical kinematical points. The limit of the small invariant mass of a muon pair is in agreement with our previous analysis.     

Nonresonant photocreation of electron-positron pair on a nucleus in the field of a pulsed light wave

The nonresonant Coulomb photocreation of electron-positron pair on a nucleus in the field of a pulsed light wave is theoretically investigated. The approximation is examined when pulsewidth is considerably greater than the characteristic time of wave oscillations. The interaction of an electron and a positron with a Coulomb potential of a nucleus is considered in the first order of perturbation theory (the Born approximation). An analytic expression for the nonresonant differential cross section was obtained for the range of moderately strong fields in the case relativistic and nonrelativistic energies. It is shown, that the nonresonant cross section of Coulomb photocreation of nonrelativistic pair in the field of a pulsed light wave is two times larger than the cross section of Coulomb photocreation in the absence of an external field.     

Electroweak corrections to muon pair production in electron-positron annihilation at high energy

The lowest-order radiative corrections to the reaction e⁺ + e⁻ → μ⁺ + μ⁻ are analyzed in the standard SU(2) × U(1) electroweak theory. The virtual corrections are calculated in the on-shell renormalization scheme. The masses of the recently discovered Z-boson and W-boson are used to fix the weak coupling constants. The decay width of the Z-boson is also taken into account. By including the cross section of hard photon emission, various kinds of distribution are obtained both analytically and numerically. The magnitude of the effective axial vector coupling is confirmed to be quite different from that previously taken in the calculations within QED. This difference, which is due to the genuine electroweak corrections, reaches about 10% in angular distribution at the energy around the Z-boson mass, even if the reasonable effect of a hard photon is included.     

One-photon annihilation of an electron-positron pair in the field of pulsed circularly polarized light wave

The one-photon annihilation of an electron-positron pair in the pulsed light field is investigated theoretically. The pulsed laser field is described by the plane circularly polarized electromagnetic wave with the envelope function. The analytical expressions for an amplitude and probability of the studied process are derived. The conditions for an observation of the one-photon annihilation the pulsed light field are ascertained. It is demonstrated, that the region of numerical values of the initial particles parameters within which the one-photon annihilation in the pulsed light field may be possibly realized is significantly broader in comparison with the monochromatic wave case. Within the observation domain the probability of one-photon annihilation process in the pulsed light field essentially exceeds the correspondent one the external field absence, except the points with the strong suppression of the probability which is the result of an interference of the amplitude’s parts; the last ones correspond to the contributions of the front and posterior segments of the pulse.     

Gluino pair production in electron-positron annihilation

We summarize the effects of some unknown supersymmetry breaking mechanism by the addition to the super-QCD lagrangian of explicit, and different, mass terms for the scalar superpartners of quarks and antiquarks. Allowing also a possible Majorana mass for the gluino, we then calculate cross sections for e⁺e^? → two gluinos, a process which may be observable if the gluino is sufficiently long-lived.     

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.     

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     

Radiative corrections to muon pair and quark pair production in electron-positron collisions in the Z0 region

A calculation of first-order radiative corrections to the process e⁺e^?→μ⁺μ^? is presented, which is in particular applicable to the Z₀ region. The emphasis is on a detailed treatment of hard photon effects, which affect the size of the corrections in the Z₀ region considerably. The technique used is that of a Monte Carlo simulation of μ⁺μ^? and μ⁺μ^?γ events. In an appendix the generalization to quark pair production is presented.     

Single weak boson production in electron-positron annihilation

The cross sections for the process,e ⁺ e ^?→W ^±+hadrons are estimated extensively at the lowest order in the minimal gauge theory ofSU(2) _L ×U(1). It is pointed out that our result on the angular distribution is not compatible with the result reported by Neufeld.     

Resonant electron-positron pair photoproduction on a nucleus in a pulsed light field

The resonant photoproduction of an electron-positron pair on a nucleus in the field of a pulsed light wave is studied theoretically. The approximation where the electromagnetic pulse duration is much longer than the characteristic time of wave oscillations is considered. The interaction of the electron and positron with the Coulomb potential of the nucleus is considered in the Born approximation. An analytical expression for the resonant differential cross section is derived for the range of moderately strong external fields. This cross section contains a resonant peak whose height and width are determined by the external pulsed wave characteristics. The resonant cross section for pair photoproduction on a nucleus in a pulsed laser field can exceed the corresponding cross section for pair photoproduction on a nucleus in the absence of an external field by an order of magnitude.     

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.     

Photon damping caused by electron-positron pair production in a strong magnetic field

Damping of an electromagnetic wave in a strong magnetic field is analyzed in the kinematic region near the threshold of electron-positron pair production. Damping of the electromagnetic field is shown to be noticeably nonexponential in this region. The resulting width of the photon γ→e ⁺ e ^? decay is considerably smaller than previously known results.     

Narrow muon bundles from muon pair production in rock

We revise the process of muon pair production by high-energy muons in rock using the recently published cross-section. The three-dimensional Monte Carlo code MUSIC has been used to obtain the characteristics of the muon bundles initiated via this process. We have compared them with those of conventional muon bundles initiated in the atmosphere and shown that large underground detectors, capable of collecting hundreds of thousands of multiple muon events, can discriminate statistically muon induced bundles from conventional ones. However, we find that the enhancement of the measured muon decoherence function over that predicted at small distances, recently reported by the MACRO experiment, cannot be explained by the effect of muon pair production alone, unless its cross-section is underestimated by a factor of 3.     

Laser field absorption in self-generated electron-positron pair plasma

Recently, much attention has been attracted to the problem of limitations on the attainable intensity of high power lasers [A.?M. Fedotov et al., Phys. Rev. Lett. 105, 080402 (2010)]. The laser energy can be absorbed by electron-positron pair plasma produced from a seed by a strong laser field via the development of the electromagnetic cascades. The numerical model for a self-consistent study of electron-positron pair plasma dynamics is developed. Strong absorption of the laser energy in self-generated overdense electron-positron pair plasma is demonstrated. It is shown that the absorption becomes important for a not extremely high laser intensity I ～ 10(24) W/cm(2) achievable in the near future.