Nucleon Compton Scattering with Two Space--Like Photons

We calculated two--photon exchange effects for elastic electron--proton scattering at high momentum transfers. The corresponding nucleon Compton amplitude is defined by two space--like virtual photons that appear to have significant virtualities. We make predictions for a) a single--spin beam asymmetry, and b) a single--spin target asymmetry or recoil proton polarization caused by an unpolarized electron beam.Comment: 9 pages, 4 figures, requires ws-procs9x6 (enclosed), Talk presented at the Workshop on Exclusive Processes at High Momentum Transfer, Jefferson Lab, Newport News, VA, May 15-18, 200

Bhabha scattering at LEP1. Calorimeter event selection

Analitical calculations have been used to describe the calorimeter event selection in small-angle electron-positron scattering at LEP1. The first-order QED correction to the Born cross-section has been derived with leading log and the next-to-leading log approximations. The second- and the third-order corrections were computed with leading accuracy. The present analytical results are illustated by Tabeles and compared with the corresponding results obtained with the Monte Carlo generator BHLUMI.Comment: 26p., submitted to Journ. of Physics

Pair Production in Small-Angle Bhabha Scattering

Radiative corrections due to the production of virtual as well as real soft and hard pairs in small-angle Bhabha scattering are calculated analytically. Both the collinear and the semi-collinear kinematical regions of hard pair production are considered. The calculation, within the leading and next-to-leading logarithmic approximation, provides an accuracy of O(0.1%). Numerical results show that the effects of pair production have to be taken into account for a luminosity determination accurate to O(0.1%) at LEP.Comment: Latex. 20 page

Hadronic Cross Sections in Electron-Positron Annihilation with Tagged Photon

Events with tagged photons in the process of electron-positron annihilation into hadrons are considered. The initial state radiation is suggested to scan the hadronic cross section with the energy. QED radiative corrections are taken into account. The results for the total and exclusive cross sections are given in an analytic form. Some numerical estimates are presented.Comment: 12 pages, 2PS figures, the final journal versio