1,149 research outputs found

    Proposals for measuring transversity distributions in deep inelastic electron scattering and a model for E-704 asymmetries

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    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 Vth^{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

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    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

    The Transverse Spin

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    Contents : 1. Pre-history 2. Transversity versus helicity 3. The massless limit. "Cardan" and "see-saw" transformations 4. Transversity distribution delta q(x). The diquark spectator model 5. Soffer inequality 6. Tensor charge sum rule 7. t-channel analysis 8. Selection rules for delta q(x) measurements 9. Evolution with Q squared 10. Quark polarimetry. The sheared-jet (Collins) effect 11. Single-spin asymmetries in inclusive experiments 12. Quark distribution dependent on both spin and transverse momentum 13. First evidence of quark transversityComment: 20 pages, 7 figures. Lecture given at Xeme Seminaire Rhodanien de Physique "Le Spin en Physique", 3-8 March, Torino, Italy. To appear in the proceeding

    Impact parameter profile of synchrotron radiation

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    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 ψ\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 Îł\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

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    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

    Probing transverse quark polarization in deep-inelastic leptoproduction

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    The azimuthal dependence of hadrons produced in lepton scattering off a polarized hadron probes the quark transverse-spin distributions. In the calculation of the asymmetries, transverse momenta of quarks in the distribution and fragmentation functions must be incorporated. In addition to the sin⁥(ϕ+ϕS)\sin (\phi + \phi_S) asymmetry for transversely polarized hadrons, known as the Collins effect, we find sin⁥2ϕ\sin 2\phi asymmetries for both transversely and longitudinally polarized hadrons.Comment: 7 pages RevTe

    Measuring transverse spin correlations by 4-particle correlations in e+e−→2 jetse^+ e^-\to 2 \ {\rm jets}

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    The azimuthal distribution of pairs of particles in a jet is sensitive to the transverse polarization of the quark initiating the jet, but with a sensitivity that involves a nonperturbative analyzing power. We show in detail how to measure the analyzing power from 4-hadron correlations in e+e−→2 jetse^+ e^- \to 2 \ {\rm jets}. We explain the combinations of particle flavor that are likely to give the biggest effect.Comment: 19 pages in RevTeX 3.0 and epsf, with 3 figure files (tarred, compressed uuencoded encapsulated postcript). Postscript version of paper available at ftp://ftp.phys.psu.edu/pub/preprint/psuth158/psuth158.ps Revised version has extra references, and correction of misprint in Eq. (7

    Transverse Spin Structure of the Nucleon from COMPASS

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    The measurement of transverse spin effects in semi-inclusive deep-inelastic scattering is an important part of the COMPASS physics program. In the years 2002-2004 data were taken by scattering a 160 GeV muon beam on a transversely polarized deuteron target. In 2007, additional data were collected on a transversely polarized proton target. New results for the Collins and Sivers asymmetries from the analysis of the proton data are presented.Comment: Proceedings of QCD08, Montpellier, July 200

    Positivity Constraints on Spin Observables in Exclusive Pseudoscalar Meson Photoproduction

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    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.

    Photon production by charged particles in narrow optical fibers

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    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
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