76 research outputs found
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 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
conversion for future 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 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 -quanta traversing a bunch of polarized laser photons
The elastic light-light scattering below the threshold of the pair
production leads to a variation in polarization of hard -quanta
traversing without loss a region where the laser light is focused. Equations
are obtained which determine the variation of Stokes parameters of
-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
colliders.Comment: 8 pages, LaTeX, 2 PS figure
Production of pairs to all orders in for collisions of high-energy muons with heavy nuclei
The pair production in collisions of muon with atoms is considered
to all orders in the parameter . We obtain energy distribution of
and 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 - 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 ps.Comment: 7 pages, 1 figure, submitted to Physical Review Letter
- âŠ