Parton intrinsic motion: suppression of the Collins mechanism for transverse single spin asymmetries in p(transv. polarised) p --> pion + X

We consider a general formalism to compute inclusive polarised and unpolarised cross sections within pQCD and the factorisation scheme, taking into account parton intrinsic motion in distribution and fragmentation functions, as well as in the elementary dynamics. Surprisingly, the intrinsic partonic motion, with all the correct azimuthal angular dependences, produces a strong suppression of the transverse single spin asymmetry arising from the Collins mechanism. As a consequence, and in contradiction with earlier claims, the Collins mechanism is unable to explain the large asymmetries found in p(transv. polarised) p --> pion + X at moderate to large Feynman x_F. The Sivers effect is not suppressed.Comment: LaTeX, 21+1 pages, 1 ps figur

General partonic structure for hadronic spin asymmetries

The high energy and large p_T inclusive polarized process, (A, S_A) + (B, S_B) --> C + X, is considered under the assumption of a generalized QCD factorization scheme. For the first time all transverse motions, of partons in hadrons and of hadrons in fragmenting partons, are explicitly taken into account; the elementary interactions are computed at leading order with noncollinear exact kinematics, which introduces many phases in the expressions of their helicity amplitudes. Several new spin and k_T dependent soft functions appear and contribute to the cross sections and to spin asymmetries; we put emphasis on their partonic interpretation, in terms of quark and gluon polarizations inside polarized hadrons. Connections with other notations and further information are given in some Appendices. The formal expressions for single and double spin asymmetries are derived. The transverse single spin asymmetry A_N, for p(transv. polarized) p --> pion + X processes is considered in more detail, and all contributions are evaluated numerically by saturating unknown functions with their upper positivity bounds. It is shown that the integration of the phases arising from the noncollinear kinematics strongly suppresses most contributions to the single spin asymmetry, leaving at work predominantly the Sivers effect and, to a lesser extent, the Collins mechanism.Comment: RevTeX, 46 pages, 5 ps figures. v2: some clarifying comments and appendix on kinematics added, references updated, published versio

Parton distribution functions of proton in a light-front quark-diquark model

We present the parton distribution functions (PDFs) for un- polarised, longitudinally polarized and transversely polarized quarks in a proton using the light-front quark diquark model. We also present the scale evolution of PDFs and calculate axial charge and tecsor charge for $u$ and $d$ quarks at a scale of experimental findings.Comment: XXII DAE-BRNS High Energy Physics Symposium, December 12-16, 2016, University of Delhi, India; 4 pages, 1 figur

Azimuthal Spin Asymmetries in Semi-Inclusive Production from Positron-Proton Scattering

The recent measurements of azimuthal single spin asymmetries by the HERMES collaboration at DESY may shed some light on presently unknown fragmentation and distribution functions. We present a study of such functions and give some estimates of weighted integrals directly related to those measurements.Comment: 10 pages, 5 figures, comments added, figures changed, revised version to be published on Phys. Lett.

Tau polarization in charge current neutrino-nucleon Deep Inelastic Scattering

Numerical results for the degree of polarization of \tau^- produced in (CC) neutrino - nucleon Deep Inelastic Scattering (DIS) are presented. Calculations are done in the threshold region, where the \tau^- scattered by the small angles and can be partially polarized. The cross sections and polarization are calculated by using the GRV98 parton distributions functions (PDF's) and the GRV98 with modifications of A. Bodek at.al.Comment: 4 pages, 2 figures, Poster Session of the NuInt04 Conference, Gran Sasso 200

Permutations Containing Many Patterns

It is shown that the maximum number of patterns that can occur in a permutation of length $n$ is asymptotically $2^n$. This significantly improves a previous result of Coleman

On the controversy concerning the definition of quark and gluon angular momentum

A major controversy has arisen in QCD as to how to split the total angular momentum into separate quark and gluon contributions, and as to whether the gluon angular momentum can itself be split, in a gauge invariant way, into a spin and orbital part. Several authors have proposed various answers to these questions and offered a variety of different expressions for the relevant operators. I argue that none of these is acceptable and suggest that the canonical expression for the momentum and angular momentum operators is the correct and physically meaningful one. It is then an inescapable fact that the gluon angular momentum operator cannot, in general, be split in a gauge invariant way into a spin and orbital part. However, the projection of the gluon spin onto its direction of motion i.e. its helicity is gauge invariant and is measured in deep inelastic scattering on nucleons. The Ji sum rule, relating the quark angular momentum to generalized parton distributions, though not based on the canonical operators, is shown to be correct, if interpreted with due care. I also draw attention to several interesting aspects of QED and QCD, which, to the best of my knowledge, are not commented upon in the standard textbooks on Field Theory.Comment: 41 pages; Some incorrect statements have been rectified and a detailed discussion has been added concerning the momentum carried by quarks and the Ji sum rule for the angular momentu

A social psychological study of ethnonyms: Cognitive representation of the ingroup and intergroup hostility

Ethnonyms (M. G. Levin & L. P. Potapov, 1964; from the Greek roots meaning "a national group" and "name") are the names an in-group uses to distinguish itself from out-groups. There has been no social psychological research to date exploring the effects of ethnonyms. The authors report the results of 3 studies examining the potential effects of various features of ethnonyms on intergroup behavior. Analyses of archival data indicate that among indigenous African cultures (Study 1), indigenous Native American cultures (Study 2), and African Americans (Study 3), intergroup hostility was greater among in-groups characterized by less complex ethnonyms. Discussion considers the implications of these results and suggests new directions for research in the social psychological study of ethnonyms