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$^{th}$ 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 $\psi$, 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 $\gamma$ 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 $Z$ 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.