4,246 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
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
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
Fragmentation Function and Nucleon Transversity Distribution in a Diquark Model
Based on a simple quark-diquark model, we propose a set of unpolarized,
longitudinally polarized and transversely polarized fragmentation functions for
the by fitting the unpolarized production data in annihilation. It is found that the helicity structure of the obtained
fragmentation functions is supported by the all available
experimental data on the longitudinal polarization. Within the same
framework of the diquark model, the nucleon transversity distributions are
presented and consistent descriptions of the available HERMES data on the
azimuthal spin asymmetries in pion electroproduction are obtained. Furthermore,
the spin transfers to the transversely polarized in the charged
lepton DIS on a transversely polarized nucleon target are predicted for future
experiments.Comment: Talk given in a seminar of U. Santa Mari
On Unique Predictions for Single Spin Azimuthal Asymmetry
Theoretically there are two approaches to predict single spin azimuthal
asymmetries. One is to take transverse momenta of partons into account by using
transverse momentum dependent parton distributions, while another is to take
asymmetries as a twist-3 effect. The nonperturbative effects in these
approaches are parameterized with different matrix elements and predictions can
be different. Recently, gauge invariant definitions of transverse momentum
dependent parton distributions were derived. With these definitions it can be
shown that there are relations between nonperturbative matrix elements in two
approaches. These relations may enable us to unify two approaches and to have
unique predictions for single spin azimuthal asymmetries.In this letter we
derive these relations by using time-reversal symmetry and show that even with
these relations the single spin azimuthal asymmetry in Drell-Yan process is
predicted differently in different approaches.Comment: Improved representatio
Single Transverse Spin Asymmetries at Parton Level
Two factorization approaches have been proposed for single transverse spin
asymmetries. One is the collinear factorization, another is the
transverse-momentum-dependent factorization. They have been previously derived
in a formal way by using diagram expansion at hadron level. If the two
factorizations hold or can be proven, they should also hold when we replace
hadrons with parton states. We examine these two factorizations at parton level
with massless partons. It is nontrivial to generate these asymmetries at parton
level with massless partons because the asymmetries require helicity-flip and
nonzero absorptive parts in scattering amplitudes. By constructing suitable
parton states with massless partons we derive the two factorizations for the
asymmetry in Drell-Yan processes. It is found from our results that the
collinear factorization derived at parton level is not the same as that derived
at hadron level. Our results with massless partons confirm those derived with
single massive parton state in our previous works.Comment: shortened version to match published versio
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 unpolarized Drell-Yan process
Taking into account the effect of final state interaction, we calculate the
non-zero (na\"{i}ve) -odd transverse momentum dependent distribution
h_1^{\perp}(x,\kp^2) of the pion in a quark-spectator-antiquark model with
effective pion-quark-antiquark coupling as a dipole form factor. Using the
model result we estimate the asymmetries in the unpolarized Drell-Yan process which can be expressed as
. We find that the resulting
h_{1\pi}^\p(x,\kp^2) has the advantage to reproduce the asymmetry that agrees
with the experimental data measured by NA10 Collaboration. We estimate the
asymmetries averaged over the kinematics of NA10 experiments for
140, 194 and 286 GeV beam and compare them with relevant experimental
data.Comment: 11 pages, 4 figures, to appear in PL
Estimate of the Collins fragmentation function in a chiral invariant approach
We predict the features of the Collins function, which describes the
fragmentation of a transversely polarized quark into an unpolarized hadron, by
modeling the fragmentation process at a low energy scale. We use the chiral
invariant approach of Manohar and Georgi, where constituent quarks and
Goldstone bosons are considered as effective degrees of freedom in the
non-perturbative regime of QCD. To test the approach we calculate the
unpolarized fragmentation function and the transverse momentum distribution of
a produced hadron, both of which are described reasonably well. In the case of
semi-inclusive deep-inelastic scattering, our estimate of the Collins function
in connection with the transversity distribution gives rise to a transverse
single spin asymmetry of the order of 10%, supporting the idea of measuring the
transversity distribution of the nucleon in this way. In the case of e+ e-
annihilation into two hadrons, our model predicts a Collins azimuthal asymmetry
of about 5%.Comment: 12 pages, 15 figures. Figs. 11-14 changed, minor changes in
discussion, few typos fixed and some references added. Final version to
appear in PR
Three-dimensional parton distribution functions and in the polarized proton-antiproton Drell-Yan process
We present predictions of the unweighted and weighted double spin asymmetries
related to the transversal helicity distribution and the longitudinal
transversity distribution , two of eight leading-twist transverse
momentum dependent parton distributions (TMDs) or three-dimensional parton
distribution functions (3dPDFs), in the polarized proton-antiproton Drell-Yan
process at typical kinematics on the Facility for Antiproton and Ion Research
(FAIR). We conclude that FAIR is ideal to access the new 3dPDFs towards a
detailed picture of the nucleon structure.Comment: 6 latex pages, 5 figures, version for publication in EPJ
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