1,837 research outputs found
Erratum to "Azimuthal asymmetry in electro-production of neutral pions in semi-inclusive DIS" published in Phys. Lett. B522 (2001) 37
We correct our analysis of the HERMES experiment for the azimuthal
sin(phi)-spin asymmetry in semi-inclusive hadroproduction in DIS on
longitudinally (with respect to the lepton momentum) polarized target because
of discovered misprint in sign in the paper P.J.Mulders and R.D.Tangerman,
Nucl. Phys. B 461 (1996) 197.Comment: 3 pages, 4 figures. Sign of sin(2phi)-asymmetry correcte
The chirally-odd twist-3 distribution e(x)
Properties of the nucleon twist-3 distribution function e(x) are reviewed. It
is emphasized that the QCD equations of motion imply the existence of a
delta-function at x=0 in e(x), which gives rise to the pion-nucleon sigma-term.
According to the resulting ``practical'' DIS sum rules the first and the second
moment of e(x) vanish, a situation analogue to that of the pure twist-3
distribution function .Comment: 19 pages, 3 figures, new references and figures adde
Non-Universality and Evolution of the Sivers Function
We examine the large-x QCD evolution of the twist-three gluonic-pole strength
defining an effective T-odd Sivers function, where evolution of the T-even
transverse-spin DIS structure function g2 is multiplicative. The result
corresponds to a colour-factor modified spin-averaged twist-two evolution.Comment: Presented at the ECT* Workshop on Recent Advances in Perturbative QCD
and Hadronic Physics (20-25 July 2009} - final version (minor modifications
Sivers vs. Collins effect in azimuthal single spin asymmetries in pion production in SIDIS
Recently it has been argued that the transverse momentum dependent twist-2
Sivers distribution function does not vanish in QCD. Therefore both, the
Collins and Sivers effects, should be considered in order to explain the
azimuthal single spin asymmetries A(UL) in pion production in semi-inclusive
deeply inelastic lepton scattering of a longitudinally polarized target. On the
basis of presently available phenomenological information on the Sivers
function we estimate that for those asymmetries A(UL) in the kinematic region
of the HERMES experiments the Sivers effect can be neglected with respect to
the Collins effect. It is argued that the same feature holds also for the
COMPASS and CLAS experiments. This justifies theoretical approaches to
understand the HERMES data on the basis of the Collins effect only.Comment: 8 pages, 4 figures. References added, small changes in text, Appendix
adde
Azimuthal asymmetry in electro-production of neutral pions in SIDIS
Recently HERMES has observed an azimuthal asymmetry in electro-production of
neutral pions in semi-inclusive deep-inelastic scattering of unpolarized
positrons off longitudinally polarized protons. This asymmetry (like those
observed in the production of charged pions) is well reproduced theoretically
by using the non-perturbative calculation of the proton transversity
distribution in the effective chiral quark-soliton model combined with
experimental DELPHI-data on the new T-odd Collins fragmentation function. There
are no free, adjustable parameters in the analysis. Using the -dependence of
the HERMES azimuthal asymmetry and the calculated transversity distributions
the z-dependence of the Collins fragmentation function is obtained. The value
obtained from HERMES data is consistent with the DELPHI result, even though
these results refer to different scales.Comment: 12 pages, 10 figures. Fig.3c, Fig.4a updated, conclusions adde
Transversity in Drell-Yan process of polarized protons and antiprotons in PAX experiment
Estimates are given for the double spin asymmetry in lepton-pair production
from collisions of transversely polarized protons and antiprotons for the
kinematics of the recently proposed PAX experiment at GSI on the basis of
predictions for the transversity distribution from the chiral quark soliton
model.Comment: 4 pages, 2 eps-figures, style files. To be published in Proceedings
of 16th Intern. spin physics symposium, October 10-16, Trieste, Ital
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