13 research outputs found
Emission of polarized photons from unpolarized electrons moving in crystals
Radiation emitted by unpolarized high-energy electrons penetrating crystals
may be linearly polarized. This occurs when the particle velocity makes an
angle, with respect to some major crystal axis, being sufficiently larger than
the axial-channelling angle. For such orientation, a complete description of
spectral and polarization characteristics of the radiation is derived. At
planar channelling, a non-perturbative contribution to the probability of the
process appears caused by the plane field, and we must solve exactly a
one~-~dimensional mechanical problem. For that, the approximate form of the
actual plane potential is suggested which provides a precise fit for any
crystal plane and an analytical solution to the motion problem. In a practical
case, we must consider electron-photon showers developing in sufficiently thick
crystals. For the first time, this development is described taking into account
the polarization of photons. We discuss qualitative features of the phenomenon,
present results of numerical calculations for thin and thick crystals, and
evaluate the possibility of the use of differently oriented crystals in a
polarized hard photon source.Comment: 16 pages, 7 PostScript figure
Polarization effects in non-relativistic scattering
The cross section which addresses the spin-flip transitions of a proton
(antiproton) interacting with a polarized non-relativistic electron or positron
is calculated analytically. In the case of attraction, this cross section is
greatly enhanced for sufficiently small relative velocities as compared to the
result obtained in the Born approximation. However, it is still very small, so
that the beam polarization time turns out to be enormously large for the
parameters of beams available now. This practically rules out a use
of such beams to polarize stored antiprotons or protons.Comment: 9 pages; version accepted for publication in Nucl.Instr.Methods B
where cross sections without averaging over directions of relative velocities
are adde
Spin effects in interaction and their possible use to polarize antiproton beams
Low energy interaction is considered taking into account the
polarization of both particles. The corresponding cross sections are calculated
using the Paris nucleon-antinucleon optical potential. Then they are applied to
the analysis of the polarization buildup which is due to the interaction of
stored antiprotons with polarized protons of a hydrogen target. It is shown
that, at realistic parameters of a storage ring and a target, the filtering
mechanism provides a noticeable polarization in a time comparable with the beam
lifetime.Comment: 10 pages, 4 figure
On measurement of beam size in linear colliders using beamstrahlung and pair creation
SIGLEAvailable at INIST (FR), Document Supply Service, under shelf-number : RP 10290 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc
First results concerning a crystal radiator dedicated to positron production by photons from channeled multi-gev electrons
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Spin-Filtering Studies at COSY
We propose to use an internal polarised target in the COSY ring to determine the polarisation
buildâup in a proton beam. Spinâfiltering experiments at COSY would provide
the necessary data to test our present understanding of spinâfiltering processes in storage
rings.
Measurements of the polarisation buildâup of stored protons are crucial to progress
towards the PAX goal to eventually produce stored polarised antiproton beams. The
availability of intense stored beams of polarised antiprotons will provide access to a wealth
of singleâ and doubleâspin observables, opening a new window on QCD spin physics. It
is planned to realise this experimental programme at the new Facility for Antiproton and
Ion Research (FAIR) at GSI in Darmstadt, Germany.
A recent experiment at COSY revealed that e~p spinâflip cross sections are too small to
cause a detectable depolarisation of a stored proton beam. This measurement rules out a
proposal to use polarised electrons to polarise a proton beam by ~ep spinâflip interactions.
Thus, our approach to provide a beam of polarised protons is based on spinâfiltering using
an internal polarised gas target.
In total 22 weeks of beam time are needed to complete the experimental program at
COSY. We now ask for two weeks of beam time for commissioning of the lowâÎČ section
and measuring the machine acceptance