16 research outputs found
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
Beam-size effect and particle losses at Super factory (Italy)
In the colliders, the macroscopically large impact parameters give a
substantial contribution to the standard cross section of the process. These impact parameters may be much larger than the
transverse sizes of the colliding bunches. It means that the standard cross
section of this process has to be substantially modified. In the present paper
such a beam-size effect is calculated for bremsstrahlung at Super factory
developed in Italy. We find out that this effect reduces beam losses due to
bremsstrahlung by about 40%.Comment: 11 pages, 4 figure
Deviation from standard QED at large distances: influence of transverse dimensions of colliding beams on bremsstrahlung
The radiation at collision of high-energy particles is formed over a rather
long distances and therefore is sensitive to an environment. In particular the
smallness of the transverse dimensions of the colliding beams leads to
suppression of bremsstrahlung cross section for soft photons. This beam-size
effect was discovered and investigated at INP, Novosibirsk around 1980. At that
time an incomplete expression for the bremsstrahlung spectrum was calculated
and used because a subtraction associated with the extraction of pure
fluctuation process was not performed. Here this procedure is done. The
complete expression for the spectral-angular distribution of incoherent
bremsstrahlung probability is obtained. The case of Gaussian colliding beams is
investigated in details. In the case of flat beams the expressions for the
bremsstrahlung spectrum are simplified essentially. Comparison of theory with
VEPP4 and HERA data is performed. Possible application of the effect to linear
collider tuning is discussed.Comment: 23 pagers,5 figure
Observation of the beam-size effect at HERA
A precise measurement of the spectrum of the photons from bremsstrahlung
with the ZEUS luminosity monitor at HERA is reported. The measurement shows a
reduced rate compared to the Bethe-Heitler spectrum for photon energies below
5~GeV. This suppression, called the beam-size effect, is explained by the
finite transverse size of the beam overlap relative to the typical impact
parameter in the process of bremsstrahlung at HERA energies.Comment: 12 pages, late
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
New type of beam size effect and the -boson production at colliders
The cross section for the reactions of the type
can not be calculated by the standard methods due to the --channel
singularity in the physical region. In this letter we show that accounting for
the finite sizes of the colliding beams results in the regularization of this
singularity. The finite cross section, which is obtained in this way, turns out
to be linear proportional to the transverse sizes of the colliding beams. As an
application of the above result, we calculate the cross section of the
boson production at colliders in the reaction .Comment: Latex, 8 pages, 2 figure
Physical mechanism of the linear beam-size effect at colliders
We present qualitative but precise description of the linear beam-size effect
predicted for the processes in which unstable but long--living particles
collide with each other. We derive physically pronounced equation for the
events rate which proves that the linear beam-size effect corresponds to the
scattering of one beam of particles on the decay products of the other. We
compare this linear beam-size effect with the known logarithmic beam-size
effect measured in the experiments on a single bremsstrahlung at VEPP-4 and
HERA.Comment: 12 pages, LaTeX, 1 figur
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
Influence of the transverse beam sizes on the epsilonrho->epsilonrho cross section at HERA
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