424 research outputs found
Proposals for measuring transversity distributions in deep inelastic electron scattering and a model for E-704 asymmetries
We present the principles of the measurement of the quark transversity
distributions in semi-inclusive deep inelastic electron scattering, which form
the basis of HELP and one of the ELFE proposals. A string model for
Collins-type asymmetry in polarized quark fragmentation function is proposed. A
possible role of the Collins effect in the single spin asymmetries observed by
experiment E 704 at Fermilab is suggested.Comment: (Contribution to the V International Workshop on High Energy
Spin Physics, SPIN-93, September 20-24, 1993, Protvino, Russia), 4 LateX
pages + 1 page for figures, report # LYCEN/935
Recursive fragmentation model with quark spin. Application to quark polarimetry
An elementary recursive model accounting for the quark spin in the
fragmentation of a quark into mesons is presented. The quark spin degree of
freedom is represented by a two-components spinor. Spin one meson can be
included. The model produces Collins effect and jet handedness. The influence
of the initial quark polarisation decays exponentially with the rank of the
meson, at dierent rates for longitudinal and transverse polarisationsComment: XIII Workshop on High Energy Spin Physics, DSPIN 2009, Dubna, Russia,
September 1-5, 200
Impact parameter profile of synchrotron radiation
The horizontal impact parameter profile of synchrotron radiation, for fixed
vertical angle of the photon, is calculated. This profile is observed through
an astigmatic optical system, horizontally focused on the electron trajectory
and vertically focused at infinity. It is the product of the usual angular
distribution of synchrotron radiation, which depends on the vertical angle
, and the profile function of a caustic staying at distance \bcl =
(\gamma^{-2} + \psi^2) \RB/2 from the orbit circle, \RB being the bending
radius and the Lorentz factor. The {\it classical impact parameter}
\bcl is connected to the Schott term of radiation damping theory. The caustic
profile function is an Airy function squared. Its fast oscillations allow a
precise determination of the horizontal beam width
Analogy between free electron laser and channeling by crystal planes
The trapping of electrons in the ponderomotive potential wells, which governs
a free electron laser or inverse free electron laser at high gain, is analogous
to the channeling of charged particles by atomic planes of a crystal. A bent
crystal is analogous to a period-tapered free electron laser. This analogy is
different from the well-known one between channeling and undulator radiations
Photon production by charged particles in narrow optical fibers
A charged particle passing through or by an optical fiber induces emission of
light guided by the fiber. The formula giving the spontaneous emission
amplitude are given in the general case when the particle trajectory is not
parallel to the fiber axis. At small angle, the photon yield grows like the
inverse power of the angle and in the parallel limiting case the fiber
Cherenkov effect studied by Bogdankevich and Bolotovskii is recovered. Possible
application to beam diagnostics are discussed, as well as resonance effects
when the particle trajectory or the fiber is bent periodically.Comment: Presented at International Conference on Charged and Neutral
Particles Channeling Phenomena, Frascati, Italy, July 3-7, 200
Electron acceleration in a helical waveguide
Travelling wave in a helical wave guide is considered for electron
acceleration. A first determination of the travelling wave modes using a
partial wave expansion (PWE) and a point matching method is presented. It gives
a rapid solution for moderate deformation of the guide relative to a straight
cylinder. Strong deformations will give higher accelerating gradient but the
PWE diverges. Two methods overcoming this difficulties are suggested.Comment: VIII International Symposium Radiation from Relativistic Electrons in
Periodic Structure (RREPS-09) Zvenigorod, Russia, September 7-11, 200
The relativistic hydrogen atom: a theoretical laboratory for structure functions
Thanks to the Dirac equation, the hydrogen-like atom at high offers a
precise model of relativistic bound state, allowing to test properties of
unpolarized and polarized structure functions analogous to the hadronic ones,
in particular: Sivers effect, sum rules for the vector, axial, tensor charges
and for the magnetic moment, positivity constraints, sea contributions and
fracture function
Single spin asymmetry in inclusive pion production, Collins effect and the string model
We calculate the single spin asymmetry in the inclusive pion production in
proton-proton collisions. We generate the asymmetry at the level of
fragmentation function (Collins effect) by the Lund coloured string mechanism.
We compare our results with the Fermilab E704 data from polarized proton-proton
collisions at 200 GeV. We show that the transversely polarized quark densities
at high Bjorken x strongly differ from these predicted by the SU(6) proton wave
function.Comment: (11 pages in TeX; 7 figures in PS files available upon request)
LYCEN/9423, TPJU 12/9
Positivity Constraints on Spin Observables in Exclusive Pseudoscalar Meson Photoproduction
Positivity constraints have proved to be important for spin observables of
exclusive reactions involving polarized initial and final particles. Attention
is focused in this note on the photoproduction of pseudoscalar mesons from spin
1/2 baryons, more specifically gamma+ N -> K+ Lambda, gamma+ N -> K Sigma, for
which new experimental data are becoming available.Comment: 3 pages,RevTex, 1 figure, more details on the derivation, refs.
added, to appear in Phys. Rev.
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