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Title: General partonic structure for hadronic spin asymmetries

Abstract

The high energy and large p{sub T} inclusive polarized process, (A,S{sub A})+(B,S{sub B}){yields}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{sub perpendicular} 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 Appendixes. The formal expressions for single and double spin asymmetries are derived. The transverse single spin asymmetry A{sub N}, for p{sup {up_arrow}}p{yields}{pi}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.

Authors:
;  [1]; ; ;  [2];  [3]
  1. Dipartimento di Fisica Teorica, Universita di Torino and INFN, Sezione di Torino, Via P. Giuria 1, I-10125 Turin (Italy)
  2. INFN, Sezione di Cagliari and Dipartimento di Fisica, Universita di Cagliari, C.P. 170, I-09042 Monserrato (Canada) (Italy)
  3. Imperial College London, Prince Consort Road, London SW7 2BW (United Kingdom)
Publication Date:
OSTI Identifier:
20774605
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review. D, Particles Fields; Journal Volume: 73; Journal Issue: 1; Other Information: DOI: 10.1103/PhysRevD.73.014020; (c) 2006 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; AMPLITUDES; ASYMMETRY; CROSS SECTIONS; FACTORIZATION; GLUONS; HADRONS; HELICITY; INCLUSIVE INTERACTIONS; POLARIZATION; QUANTUM CHROMODYNAMICS; QUARKS; SPIN; TRANSVERSE MOMENTUM

Citation Formats

Anselmino, M., Boglione, M., D'Alesio, U., Melis, S., Murgia, F., and Leader, E.. General partonic structure for hadronic spin asymmetries. United States: N. p., 2006. Web. doi:10.1103/PhysRevD.73.014020.
Anselmino, M., Boglione, M., D'Alesio, U., Melis, S., Murgia, F., & Leader, E.. General partonic structure for hadronic spin asymmetries. United States. doi:10.1103/PhysRevD.73.014020.
Anselmino, M., Boglione, M., D'Alesio, U., Melis, S., Murgia, F., and Leader, E.. Sun . "General partonic structure for hadronic spin asymmetries". United States. doi:10.1103/PhysRevD.73.014020.
@article{osti_20774605,
title = {General partonic structure for hadronic spin asymmetries},
author = {Anselmino, M. and Boglione, M. and D'Alesio, U. and Melis, S. and Murgia, F. and Leader, E.},
abstractNote = {The high energy and large p{sub T} inclusive polarized process, (A,S{sub A})+(B,S{sub B}){yields}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{sub perpendicular} 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 Appendixes. The formal expressions for single and double spin asymmetries are derived. The transverse single spin asymmetry A{sub N}, for p{sup {up_arrow}}p{yields}{pi}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.},
doi = {10.1103/PhysRevD.73.014020},
journal = {Physical Review. D, Particles Fields},
number = 1,
volume = 73,
place = {United States},
year = {Sun Jan 01 00:00:00 EST 2006},
month = {Sun Jan 01 00:00:00 EST 2006}
}
  • A simple model of a composite nucleon is developed in which a fermion and a boson, representing quark and diquark constituents of the nucleon, form a bound state owing to a contact interaction. Photon and pion couplings to the quark provide vertex functions for the photon and pion interactions with the composite nucleon. By a suitable choice of cutoff parameters of the model, realistic electromagnetic form factors are obtained. When a pseudoscalar pion-quark coupling is used, the pion-nucleon coupling is predominantly pseudovector. A virtual photopion amplitude is considered in which there are two types of contributions: hadronic contributions where themore » photon and pion interactions have an intervening propagator of the nucleon or its excited states, and contact-like contributions where the photon and pion interactions occur within a single vertex. At large Q, the contact-like contributions are dominant. The model nucleon exhibits scaling behavior in deep-inelastic scattering and the normalization of the parton distribution provides a rough normalization of the contact-like contributions. Calculations for the virtual photopion amplitude are performed using kinematics appropriate to its occurrence as a meson-exchange current in electron-deuteron scattering. The results show that the contact-like terms can dominate the meson-exchange current for Q > 1 GeV/c. There is a direct connection of the contact-like terms to the off-forward parton distributions of the model nucleon.« less
  • A simple model of a composite nucleon is developed in which a fermion and a boson, representing quark and diquark constituents of the nucleon, form a bound state owing to a contact interaction. Photon and pion couplings to the quark provide vertex functions for the photon and pion interactions with the composite nucleon. By a suitable choice of cutoff parameters of the model, realistic electromagnetic form factors are obtained for the proton. When a pseudoscalar pion-quark coupling is used, the pion-nucleon coupling is predominantly pseudovector. A virtual photopion amplitude is considered in which there are two types of contributions: hadronicmore » contributions where the photon and pion interactions have an intervening propagator of the nucleon or its excited states, and contactlike contributions where the photon and pion interactions occur within a single vertex. At large Q, the contactlike contributions are dominant. The model nucleon exhibits scaling behavior in deep-inelastic scattering and the normalization of the parton distribution provides a rough normalization of the contactlike contributions. Calculations for the virtual photopion amplitude are performed using kinematics appropriate to its occurrence as a meson-exchange current in electron-deuteron scattering. The results suggest that the contactlike terms can dominate the meson-exchange current for Q>1GeV/c. There is a direct connection of the contactlike terms to the off-forward parton distributions of the model nucleon.« less
  • The investigation of the partonic degrees of freedom beyond collinear approximation (3D description) has been gained increasing interest in the last decade. At the HERMES experiment, azimuthal single-spin asymmetries of pions and charged kaons produced in semi-inclusive deep-inelastic scattering of electrons and positrons off a transversely (polarized) hydrogen and deuterium target have been measured. Such asymmetries provide new insights on crucial aspects of the parton dynamics. By measuring various hadron types in the initial and final states, flavor sensitivity is achieved. Evidence is reported of the poorly known transversity function and of naive-T-odd transverse-momentum-dependent parton distribution functions related to spin-orbitmore » effects. Evidence of spin-orbit effects in quark fragmentation is also observed, which are opposite in sign for favored and disfavored processes.« less
  • Using helicity-amplitude techniques, we derive the partonic level transverse spin-spin asymmetries {ital {cflx a}}{sub {ital N}{ital N}} for the processes relevant to the hadronic production of three-jet events: namely, {ital qq}{prime}{r arrow}{ital qq}{prime}{ital g} and {ital qq}{r arrow}{ital qqg}. Just as in the case of two-jet production, we find that the partonic level asymmetries ({ital {cflx a}}{sub {ital N}{ital N}}) are roughly 10 times smaller than the corresponding longitudinal asymmetries ({ital {cflx a}}{sub {ital L}{ital L}}).