A new method for calculating jet-like QED processes

We consider inelastic QED processes, the cross sections of which do not drop with increasing energy. Such reactions have the form of two-jet processes with the exchange of a virtual photon in the t-channel. We consider them in the region of small scattering angles m/E <= theta << 1, which yield the dominant contribution to their cross sections. A new effective method is presented to calculate the corresponding helicity amplitudes. Its basic idea consists in replacing spinor structures for real and weakly virtual intermediate leptons by simple transition vertices for real leptons. The obtained compact amplitudes are particularly suitable for numerical calculations in jet-like kinematics.Comment: 6 pages, 2 figures, Contribution presented by V.G. Serbo at PHOTON 2003, Frascati, Ital

Influence of the beam-size or MD-effect on particle losses at B-factories PEP-II and KEKB

For the $e^+ e^- \to e^+ e^- \gamma$ process at colliding beams, macroscopically large impact parameters give an essential contribution to the standard cross section. These impact parameters may be much larger than the transverse sizes of the colliding bunches. It means that the standard calculations have to be essentially modify. In the present paper such a beam-size or MD-effect is calculated for bremsstrahlung at B-factories PEP-II and KEKB using the list of nominal parameters from Review of Particle Physics (2002). We find out that this effect reduces beam losses due to bremsstrahlung by about 20%.Comment: 10 Latex page

Polarization of high-energy electrons traversing a laser beam

When polarized electrons traverse a region where the laser light is focused their polarization varies even if their energy and direction of motion are not changed. This effect is due to interference of the incoming electron wave and an electron wave scattered at zero angle. Equations are obtained which determine the variation of the electron density matrix, and their solutions are given. The change in the electron polarization depends not only on the Compton cross section but on the real part of the forward Compton amplitude as well. It should be taken into account, for example, in simulations of the $e \to \gamma$ conversion for future $\gamma \gamma$ colliders.Comment: 11 pages, LaTeX , 2 postscript figures include

Helicity amplitudes for the small--angle process e^-e^{\pm}\to e^-\gamma\gamma + e^{\pm} with both photons along one direction and its cross channel

We study the small--angle double bremsstrahlung in $e^-e^\pm$ scattering for a jet kinematics where both photons move along the electron direction. This region gives the main contribution to the cross section. We present analytic expressions for all 64 amplitudes with arbitrary helicity states of the initial and final leptons and the produced photons convenient for analytic and numerical studies. The accuracy of the obtained amplitudes is given omitting only terms of the order of m^2/E_j^2, \theta_j^2 and \theta_j m/E_j. The helicity amplitudes for the cross channel \gamma e^\pm \to \gamma e^+e^- + e^\pm are given. Several limits for the helicity amplitudes of hard or soft final particles are considered.Comment: 20 pp, LaTeX, 7 EPS figs, uses elsart packag

Variation in polarization of high-energy γ\gamma-quanta traversing a bunch of polarized laser photons

The elastic light-light scattering below the threshold of the $e^+e^-$ pair production leads to a variation in polarization of hard $\gamma$-quanta traversing without loss a region where the laser light is focused. Equations are obtained which determine the variation of Stokes parameters of $\gamma$-quanta in this case, and their solutions are given. It is pointed out that this effect can be observed in the experiment E-144 at SLAC. It should be taken into account (and, perhaps, it can be used) in experiments at future $\gamma \gamma$ colliders.Comment: 8 pages, LaTeX, 2 PS figure

Production of e+e−e^+e^- pairs to all orders in ZαZ\alpha for collisions of high-energy muons with heavy nuclei

The $e^+e^-$ pair production in collisions of muon with atoms is considered to all orders in the parameter $Z\alpha$. We obtain energy distribution of $e^+$ and $e^-$ as well as energy loss of muon passing through matter with heavy atoms. The found corrections to the Born contribution do not depend on the details of the target properties except of a simple factor. For the considered example of Pb target the muon energy loss corrections vary from -65 % to -10 % depending on the pair energy.Comment: 9 pages, 3 figures, LaTex; Introduction slightly enlarged, 2 references adde

Large contribution of virtual Delbrueck scattering to the emission of photons by relativistic nuclei in nucleus-nucleus and electron-nucleus collisions

Delbrueck scattering is an elastic scattering of a photon in the Coulomb field of a nucleus via a virtual electron loop. The contribution of this virtual subprocess to the emission of a photon in the collision of ultra-relativistic nuclei Z_1 Z_2 -> Z_1 Z_2 gamma is considered. We identify the incoming virtual photon as being generated by one of the relativistic nuclei involved in the binary collision and the scattered photon as being emitted in the process. The energy and angular distributions of the photons are calculated. The discussed process has no infrared divergence. The total cross section obtained is 14 barn for Au-Au collisions at the RHIC collider and 50 barn for Pb-Pb collisions at the LHC collider. These cross sections are considerably larger than those for ordinary tree-level nuclear bremsstrahlung in the considered photon energy range m_e << E_\gamma << m_e gamma, where gamma is the Lorentz factor of the nucleus. Finally, photon emission in electron-nucleus collisions e Z -> e Z gamma is discussed in the context of the eRHIC option.Comment: 10 pages; 7 figure

Measurement of the B0-anti-B0-Oscillation Frequency with Inclusive Dilepton Events

The $B^0$-$\bar B^0$ oscillation frequency has been measured with a sample of 23 million \B\bar B pairs collected with the BABAR detector at the PEP-II asymmetric B Factory at SLAC. In this sample, we select events in which both B mesons decay semileptonically and use the charge of the leptons to identify the flavor of each B meson. A simultaneous fit to the decay time difference distributions for opposite- and same-sign dilepton events gives $\Delta m_d = 0.493 \pm 0.012{(stat)}\pm 0.009{(syst)}$ ps$^{-1}$.Comment: 7 pages, 1 figure, submitted to Physical Review Letter