Yu. M. Bystritskiy

QED radiative corrections to the decay π0→e+e-

We reconsider QED radiative corrections (RC) to the π0→e+e- decay width. One kind of RC investigated earlier has a renormalization group origin and can be associated with the final state interaction of electron and positron. It determines the distribution of lepton pair invariant masses in the whole kinematic region. The other type of RC has a double-logarithmic character and is related to almost on-mass-shell behavior of the lepton form factors. The total effect of RC for π0→e+e- decay is estimated to be 3.2%, and for η→e+e- decay it is 4.3%.

Compilation and analysis of charge asymmetry measurements from electron and positron scattering on nucleon and nuclei

World data on the lepton-charge asymmetry in the elastic and inelastic lepton scattering off the proton and nuclei are compiled and discussed. After reviewing the published results, we compare the elastic data to a model calculation of the two-photon-exchange mechanism. We show that the existing data do not provide any evidence for enhancement of the two-photon contribution. At confidence level 95% the data allow to exclude the two-photon exchange as an explanation for the difference between Rosenbluth and polarization transfer measurements of proton electromagnetic form factors.

The Decay phi ---> f(0)(980) gamma and the process e+ e- ---> phi f(0)(980)

The decay \phi -> f_0(980) \gamma and process e^+e^- -> \phi f_0(980) are considered within the local Nambu-Jona-Lasinio model. In the amplitudes of these processes contributions of s-quark and kaon loops are taken into account. The kaon loop gives a dominant contribution. Our estimation for the decay width of \phi -> f_0 \gamma is in satisfactory agreement with recent experimental data. This allows us to make some predictions for cross sections of the process e^+e^- -> \gamma^* -> \phi f_0 which can be tested in the C-\tau factory. The total and differential cross sections of this process are calculated and presented in the figures.

Structure function approach in QED for high energy processes

In this review we consider the structure function method, based on the renormalization group approach: when combined with exact calculation at the lowest order of perturbation theory it allows one to calculate the differential cross sections in leading and next to leading order approximations, again providing the thousands accuracy.

Peripherical processes in QED at high energies

In this review we consider the high energy processes in QED frames in peripherical kinematics. The key feature of this kinematics is that processes have a large cross section which do not decrease with the increasing of the initial center of mass energy. Two purposes to study peripheral processes are: the background processes with large total cross sections and the structure of jets in the fragmentation region.

Target normal spin asymmetry and charge asymmetry for e μ elastic scattering and the crossed processes

Two kinds of asymmetry arise from the interference of the Born amplitude and the box-type amplitude corresponding to two virtual photon exchange, namely, charge-odd and single-spin asymmetries. In the case of unpolarized particles the charge-odd correlation is calculated. It can be measured in a combination of electron-muon and positron-muon experiments. The forward-backward asymmetry is the corresponding quantity which can be measured for the crossed processes. In the case of a polarized muon the single-spin asymmetry for annihilation and scattering channels has been calculated. The additional structure function arising from the interference is shown to suffer from infrared divergencies. The background due to electroweak interaction is discussed.

A MODEL OF A TRANSITION NEUTRAL PION FORM FACTOR MEASURED IN ANNIHILATION AND SCATTERING CHANNELS AT HIGH MOMENTUM TRANSFER

We consider an alternative explanation of newly found growth of neutral pion transition form factor with high virtuality of one of photons. It is based on Sudakov suppression of quark-photon vertex. Some applications to scattering and annihilation channels are considered including the relevant experiments with lepton-proton scattering.

2γ decays of scalar mesons (σ(600), f0(980), and a0(980)) in the Nambu-Jona-Lasinio model

The two-photon decay widths of scalar mesons σ(600), f0(980), and a0(980) are calculated in the framework of the local Nambu-Jona-Lasinio model. The contributions of the quark loops (Hartree-Fock approximation) and the meson loops (next 1/Nc approximation, where Nc is the number of colors) are taken into account. These contributions, as we show, are the values of the same order of magnitude. For the f0 decay the K-loop contribution turns out to play the dominant role. The results are in satisfactory agreement with modern experimental data.

Annihilation of + \bar p + p → e+ + e− + π0 and + \bar p + p → γ + π0 through an ω-Meson intermediate state

AbstractThe s-channel annihilation of a proton and an antiproton into a neutral pion and a real or virtual photon followed by lepton pair emission is studied. Such a mechanism is expected to play a role at moderate values of the total energy