8,690 research outputs found
On the cos 2 phi asymmetry in unpolarized leptoproduction
We investigate the origin of the cos 2 phi azimuthal asymmetry in unpolarized
semiinclusive DIS. The contributions to this asymmetry arising from the
intrinsic transverse motion of quarks are explicitly evaluated, and predictions
for the HERMES and COMPASS kinematic regimes are presented. We show that the
effect of the leading-twist Boer-Mulders function h_1^perp(x, k_T^2), which
describes a correlation between the transverse momentum and the transverse spin
of quarks, is quite significant and may also account for a part of the cos 2
phi asymmetry measured by ZEUS in the perturbative domain.Comment: 11 pages, 7 figure
Connection between Distribution and Fragmentation Functions
We show that the quark fragmentation function and the quark
distribution function are connected in the limit by the
approximate relation , where both quantities are in
their physical regions. Predictions for proton production in inelastic annihilation, based on the new relation and standard parametrizations of
quark distribution functions, are found to be compatible with the data.Comment: 10 latex pages, 2 figures, published as Rapid Communication in PR
Single spin asymmetry in Drell-Yan process
We study the single spin asymmetries for the process. We consider the asymmetries
contributed by the coupling of the Boer-Mulders function with the transversity
distribution and the pretzelosity distribution, characterized by the
and azimuthal angular dependence,
respectively. We estimate the magnitude of these asymmetries at COMPASS by
using proper weighting functions. We find that the
asymmetry is of the size of a few percent and can be measured through the
experiment. The asymmetry is smaller than the
asymmetry. After a cut on , we succeed in enhancing
the asymmetry.Comment: 11 pages, 2 figures, final version to appear in PL
Transversity from two pion interference fragmentation
We present calculation on the azimuthal spin asymmetries for pion pair
production in semi-inclusive deep inelastic scattering (SIDIS) process at both
HERMES and COMPASS kinematics, with transversely polarized proton, deuteron and
neutron targets. We calculate the asymmetry by adopting a set of
parametrization of the interference fragmentation functions and two different
models for the transversity. We find that the result for the proton target is
insensitive to the approaches of the transversity but more helpful to
understand the interference fragmentation functions. However, for the neutron
target, which can be obtained through using deuteron and {He} targets, we
find different predictions for different approaches to the transversity. Thus
probing the two pion interference fragmentation from the neutron can provide us
more interesting information on the transversity.Comment: 15 latex pages, 6 figures, to appear in PR
Ratio of in Semi-inclusive Electroproduction
It is shown that the cross section ratio in
semi-inclusive electroproduction of and hyperons in
deep inelastic scattering of charged lepton on a nucleon target, can provide
useful information on the quark to fragmentation functions. This
ratio is calculated explicitly in a quark-diquark model, a pQCD based analysis,
and an SU(3) symmetry model, with three different options for the contribution
from the unfavored fragmentation functions. The -dependence of this ratio is
sensitive to the ratio of unfavored fragmentation functions over favored
fragmentation functions, , whereas
the -dependence is sensitive to the flavor structure of the fragmentation
functions, i.e., the ratio . Future
measurements by the HERMES Collaboration at DESY can discriminate between
various cases.Comment: 11 latex files, 6 figure
The Quark-Antiquark Asymmetry of the Nucleon Sea from and Fragmentation
We present a general analysis of the spin transfer for and
production in deep-inelastic scattering of polarized charged
leptons on the nucleon, and find that the pattern of different behaviors of
and production observed by the E665 Collaboration
suggests the possibility of quark-antiquark asymmetries either in the quark to
fragmentation functions and/or in the quark and antiquark
distributions of the target proton. We also point out that the
strange-antistrange asymmetry of the nucleon sea may produce an observable
contribution to the different behaviors of and
production. We find that a softer than as predicted by the
light-cone baryon-meson fluctuation model of intrinsic quark-antiquark pairs of
the nucleon sea might lead to a reasonable picture. However, the magnitude is
still too small to explain the E665 data and the conclusion has also strong
model-dependence. This may suggest the importance of quark-antiquark asymmetry
in the quark to fragmentation functions, provided that the E665 data
are confirmed.Comment: 15 latex pages, 2 figure
Scale Dependence of Twist-3 Quark-Gluon Operators for Single Spin Asymmetries
We derive the scale dependence of twist-3 quark-gluon operators, or ETQS
matrix elements, at one-loop. These operators are used to factorize transverse
single spin asymmetries, which are studied intensively both in experiment and
theory. The scale dependence of two special cases are particularly interesting.
One is of soft-gluon-pole matrix elements, another is of soft-quark-pole matrix
elements. From our results the evolutions in the two cases can be obtained. A
comparison with existing results of soft-gluon-pole matrix elements is made.Comment: typo in Eq.(10) corrected, references adde
Particle-Antiparticle Asymmetries of Production in Hadron-Nucleon Collisions
The particle-antiparticle asymmetries of production in 250 GeV/c
, , and --nucleon collisions are studied with two model
parametrizations of quark to fragmentation functions. It is shown
that the available data can be qualitatively explained by the calculated
results in both the quark-diquark model and a pQCD based analysis of
fragmentation functions. The differences in the two model predictions are
significant for beams, and high precision measurements of the
asymmetries with detailed and information can discriminate between
different predictions.Comment: 14 LaTex pages, 4 figures, to appear in Phys. Lett.
A systematic phenomenological study of the asymmetry in unpolarized semi--inclusive DIS
We study the azimuthal asymmetry in unpolarized semi-inclusive
DIS, taking into account both the perturbative contribution (gluon emission and
splitting) and the non perturbative effects arising from intrinsic transverse
motion and transverse spin of quarks. In particular we explore the possibility
to extract from some information about the Boer--Mulders
function $h_1^{\perp}$, which represents a transverse--polarization asymmetry
of quarks inside an unpolarized hadron. Predictions are presented for the
HERMES, COMPASS and JLab kinematics, where is dominated by the
kinematical higher--twist contribution, and turns to be of order of few
percent. We show that a larger asymmetry in production, compared to
production, would represent a signature of the Boer--Mulders effect.Comment: 14 pages, 12 figure
Up and Down Quark Contributions to Spin Content of Lambda from Fragmentation
We check the and quark contributions to the spin content of the
by means of the fragmentation and find that the and
quarks of the are likely positively polarized. The parton
distributions in the are given by a successful statistical model
which can reproduce and correlate a vast body of polarized and unpolarized
structure function and parton distribution data of the nucleon. With the
Gribov-Lipatov relation between the quark distributions and fragmentation
functions, the longitudinal spin transfer for the production in the
polarized charged lepton deep inelastic scattering (DIS) process and the
-polarization in the neutrino (antineutrino) DIS process are
predicted. The available experimental data suggests that the and quark
contributions to the spin of the are positive. In addition, our
results provide a collateral evidence for the SU(3) symmetry breaking in
hyperon semileptonic decays of the octet baryons, which is very important for a
deeper understanding of the proton 'spin crisis'.Comment: 14 pages, 3 figures, 1 tabl
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