66 research outputs found
Helicity amplitudes and crossing relations for antiproton proton reactions
Antiproton proton annihilation reactions allow unique access to the moduli
and phases of nucleon electromagnetic form factors in the time like region. We
present the helicity amplitudes for the unequal mass single photon reaction in the s channel including the lepton mass. The relative
signs of these amplitudes are determined using simple invariance properties.
Helicity amplitudes for the annihilation reaction are
also given, where is any spinor particle with structure. Crossing relations
between the scattering and the
annihilation channels are discussed and the crossing matrix for the helicity
amplitudes is given. This matrix may be used to verify known expressions for
the space like helicity amplitudes due to one photon exchange.Comment: 15 pages, 5 figures, submitted to EPJ
Spin Observables for Polarizing Antiprotons
The PAX project at GSI Darmstadt plans to polarize an antiproton beam by
repeated interaction with a hydrogen target in a storage ring. Many of the beam
particles are required to remain within the ring after interaction with the
target, so small scattering angles are important. Hence we concentrate on low
momentum transfer (small t), a region where electromagnetic effects dominate
the hadronic effects. A colliding beam of polarized electrons with energy
sufficient to provide scattering of antiprotons beyond ring acceptance may
polarize an antiproton beam by spin filtering. Expressions for spin observables
are provided and are used to estimate the rate of buildup of polarization of an
antiproton beam.Comment: 4 pages, 2 figures, to be published in the Proceedings of the 17th
International Spin Physics Symposium (SPIN 2006), Kyoto, Japan; October 2-7,
200
Dynamics of polarization buildup by spin filtering
There has been much recent research into polarizing an antiproton beam,
instigated by the recent proposal from the PAX (Polarized Antiproton
eXperiment) project at GSI Darmstadt. It plans to polarize an antiproton beam
by repeated interaction with a polarized internal target in a storage ring. The
method of polarization by spin filtering requires many of the beam particles to
remain within the ring after scattering off the polarized internal target via
electromagnetic and hadronic interactions. We present and solve sets of
differential equations which describe the buildup of polarization by spin
filtering in many different scenarios of interest to projects planning to
produce high intensity polarized beams. These scenarios are: 1) spin filtering
of a fully stored beam, 2) spin filtering while the beam is being accumulated,
i.e. unpolarized particles are continuously being fed into the beam, 3) the
particle input rate is equal to the rate at which particles are being lost due
to scattering beyond ring acceptance angle, the beam intensity remaining
constant, 4) increasing the initial polarization of a stored beam by spin
filtering, 5) the input of particles into the beam is stopped after a certain
amount of time, but spin filtering continues. The rate of depolarization of a
stored polarized beam on passing through an electron cooler is also shown to be
negligible.Comment: 15 pages, references added, introduction elaborated on, some
variables defined in more detail. Submitted to Eur. Phys. J.
An absolute polarimeter for high energy protons
A study of the spin asymmetries for polarized elastic proton proton
collisions in the electromagnetic hadronic interference (CNI) region of
momentum transfer provides a method of self calibration of proton polarization.
The method can be extended to non-identical spin half scattering so that, in
principle, the polarization of a proton may be obtained through an analysis of
its elastic collision with a different polarized particle, helium 3 for
instance. Sufficiently large CNI spin asymmetries provide enough information to
facilitate the evaluation of nearly all the helicity amplitudes at small t as
well as the polarization of both initial spin half fermions. Thus it can serve
equally well as a polarimeter for helium 3
Energy Dependence of the Pomeron Spin-Flip
There is no theoretical reason to think that the spin-flip component of the
Pomeron is zero. One can measure the spin-flip part using Coulomb-nuclear
interference (CNI). Perturbative QCD calculations show that the spin-flip
component is sensitive to the smallest quark separation in the proton, while
the non-flip part probes the largest separation. According to HERA results on
the proton structure function at very low x the energy dependence of the
cross-section correlates with the size of the color dipole. Analysing the data
from HERA we predict that the ratio of the spin-flip to non-flip amplitude
grows with energy as , violating Regge
factorisation of the Pomeron.Comment: A few comments and references are added. Based on invited talks at
the International Workshop on Diffraction Physics, Rio de Janeiro, February
16-20, 1998, and at DIS'98, Brussels, April 4-8, 199
Form of analyzing power and the determination of the basic parameters of hadron scattering amplitude
The determination of magnitudes of basic parameters of the high energy
elastic scattering amplitude are examined at small momentum transfers with
taking account of the Coulomb-hadron interference effects.Comment: 6 pages, LaTeX, 4 figures (files.ps), Talk at the International
Workshop "Spin and Symmetry" (Prague, Chech., 13-19 July 2000
Polarisation observables in lepton antilepton to proton antiproton reactions including lepton mass
General expressions, including the lepton mass, for the spin averaged
differential cross section for the annihilation reaction lepton antilepton to
proton antiproton are given, as well as general formulae for the single and
double spin asymmetries in the centre of mass frame. In particular we discuss
the single spin asymmetry, normal to the scattering plane, which measures the
relative phase difference between nucleon electromagnetic form factors
and . Recent experimental investigations of these form factors in the
space and time like region are reviewed. It is thought that measurements of the
phase of these form factors will provide fundamental information on the
internal nucleon structure. The phases between and are accessible
through polarisation observables measured in the antiproton proton to lepton
antilepton reaction, or in its time reversed process.Comment: 14 pages, to be submitted to EPJ
Impact of saturation on spin effects in proton-proton scattering
For pomerons described by a sum of two simple-pole terms, a soft and a hard
pomeron, the unitarity bounds from saturation in impact-parameter space are
examined. We consider the effect of these bounds on observables linked with
polarisation, such as the analyzing power in elastic proton-proton scattering,
for LHC energies. We obtain the s and t dependence of the Coulomb-nuclear
interference at small momentum transfer, and show that the effect of the hard
pomeron may be observed at the LHC.Comment: 8 pages, 2 figures, presented by O.V.S. at the Advanced Studies
Institute "Symetries and Spin" (SPIN-Praha-2004), Prague, July 5 - July 10,
200
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