Single spin asymmetries from a gluonic background in the Drell-Yan process

We discuss the effects of so-called gluonic poles in twist-three hadronic matrix elements, as first considered by Qiu and Sterman, in the Drell-Yan process. These effects cannot be distinguished from those of time-reversal odd distribution functions, although time-reversal invariance is not broken by the presence of gluonic poles. Both gluonic poles and time-reversal odd distribution functions can lead to the same single spin asymmetries. We explicitly show the connection between gluonic poles and large distance gluon fields, identify the possible single spin asymmetries in the Drell-Yan process and discuss the role of intrinsic transverse momentum of the partons

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.

Positivity bounds on spin-one distribution and fragmentation functions

We establish a connection between the distribution functions of quarks in spin-one hadrons and the helicity matrix for forward scattering of antiquarks off spin-one hadrons. From positivity of this matrix we obtain inequality relations among the distribution functions. Analogous relations hold also for fragmentation functions. The bounds we obtained can be used to constrain estimates of unknown functions, occurring in particular in semi-inclusive deep inelastic scattering or e+ e- annihilation with vector mesons in the final state.Comment: 7 page

Angular dependences in electroweak semi-inclusive leptoproduction

We present the leading order unpolarized and polarized cross sections in electroweak semi-inclusive deep inelastic leptoproduction. The azimuthal dependences in the cross section differential in the transverse momentum of the vector boson arise due to intrinsic transverse momenta of the quarks. However, the presented asymmetries are not suppressed by inverse powers of the hard scale. We discuss the different opportunities to measure specific asymmetries as offered by neutral compared to charged current processes and point out the optimal kinematical regions. The present and (proposed) future HERA collider experiments would be most suitable for measuring some of the asymmetries discussed here, especially in case of Lambda production.Comment: 10 pages, Revtex, 5 Postscript figures, uses aps.sty, epsfig.st

Color gauge invariance in the Drell-Yan process

We consider the color gauge invariance of a factorized description of the Drell-Yan process cross section. In particular, we focus on the next-to-leading twist contributions for polarized scattering and on the cross section differential in the transverse momentum of the lepton pair in the region where the transverse momentum is small compared to the hard scale. The hadron tensor is expressed in terms of manifestly color gauge invariant, nonlocal operator matrix elements and a color gauge invariant treatment of soft gluon poles is given. Also, we clarify the discrepancy between two published results for a single spin asymmetry in the Drell-Yan cross section. This asymmetry arises if such a soft gluon pole is present in a specific twist-three hadronic matrix element.Comment: 16 pages, Revtex, 2 Postscript figures, uses aps.sty, epsf.sty; error in revision remove

Probing transverse quark polarization in deep-inelastic leptoproduction

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 $\sin (\phi + \phi_S)$ asymmetry for transversely polarized hadrons, known as the Collins effect, we find $\sin 2\phi$ asymmetries for both transversely and longitudinally polarized hadrons.Comment: 7 pages RevTe

New observables in longitudinal single-spin asymmetries in semi-inclusive DIS

We analyze longitudinal beam and target single-spin asymmetries in semi-inclusive deep inelastic scattering and in jet deep inelastic scattering, including all possible twist-3 contributions as well as quark mass corrections. We take into account the path-ordered exponential in the soft correlators and show that it leads to the introduction of a new distribution and a new fragmentation function contributing to the asymmetries.Comment: 8 page

Prospects for spin physics in semi-inclusive processes

I discuss inclusive and semi-inclusive lepton-hadron scattering emphasizing the importance of polarization in order to study various single or double spin asymmetries and the importance of particle identification and angular resolution in the dectection of final state particles to study azimuthal asymmetries. The observables obtained in this way enable a detailed study of quark and gluon correlations in hadrons.Comment: 15 pages LaTex, 20 figures using epsf.sty, revised layout, talk presented at the second ELFE Workshop, 23-27 September 1996, St. Malo, Franc

Transverse momentum dependence in gluon distribution and fragmentation functions

We investigate the twist two gluon distribution functions for spin 1/2 hadrons, emphasizing intrinsic transverse momentum of the gluons. These functions are relevant in leading order in the inverse hard scale in scattering processes such as inclusive leptoproduction or Drell-Yan scattering, or more general in hard processes in which at least two hadrons are involved. They show up in azimuthal asymmetries. For future estimates of such observables, we discuss specific bounds on these functions.Comment: 14 pages, revtex, 7 Postscript figure