76 research outputs found
Probing transverse quark polarization via azimuthal asymmetries in leptoproduction
We consider the leading order result for polarized leptoproduction, putting
emphasis on transverse momentum dependent effects appearing in azimuthal
asymmetries. Measurements of weighted cross sections enable extraction of the
distribution of transversely polarized quarks. We focus on the distribution in
a longitudinally polarized hadron and estimate the expected asymmetries in
leptoproduction.Comment: 7 pages RevTex using epsfig.sty, including 2 figures; revised
version, accepted for publication in Phys. Lett.
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
Novel Transversity Properties in Semi-Inclusive Deep Inelastic Scattering
The -odd distribution functions contributing to transversity properties of
the nucleon and their role in fueling nontrivial contributions to azimuthal
asymmetries in semi-inclusive deep inelastic scattering are investigated. We
use a dynamical model to evaluate these quantities in terms of HERMES
kinematics.Comment: 5 pages revtex; 5 eps figures. References added. To appear as a Rapid
Communication in Physical Review
A mechanism for the T-odd pion fragmentation function
We consider a simple rescattering mechanism to calculate a leading twist
-odd pion fragmentation function, a favored candidate for filtering the
transversity properties of the nucleon. We evaluate the single spin azimuthal
asymmetry for a transversely polarized target in semi-inclusive deep inelastic
scattering (for HERMES kinematics). Additionally, we calculate the double
-odd asymmetry in this framework.Comment: 6 pages revtex, 7 eps figures, references added and updated in this
published versio
Longitudinal Polarization of Lambda and anti-Lambda Hyperons in Lepton-Nucleon Deep-Inelastic Scattering
We consider models for the spin transfers to and
hyperons produced in lepton-nucleon deep-inelastic scattering. We make
predictions for longitudinal and spin transfers for
the COMPASS experiment and for HERA, and for the spin transfer to
hyperons produced at JLAB. We demonstrate that accurate measurements of the
spin transfers to and hyperons with COMPASS
kinematics have the potential to probe the intrinsic strangeness in the
nucleon. We show that a measurement of polarisation could
provide a clean probe of the spin transfer from quarks and provides a
new possibility to measure the antistrange quark distribution function. COMPASS
data in a domain of x that has not been studied previously will provide
valuable extra information to fix models for the nucleon spin structure. The
spin transfer to hyperons, which could be measured by the
COMPASS experiment, would provide a new tool to distinguish between the SU(6)
and Burkardt-Jaffe (BJ) models for baryon spin structure. In the case of the
HERA electron-proton collider experiments with longitudinally-polarised
electrons, the separation between the target and current fragmentation
mechanisms is more clear. It provides a complementary probe of the strange
quark distribution and helps distinguish between the SU(6) and BJ models for
the and spin structure. Finally, we show that the
spin transfer to hyperons measured in a JLAB experiment would be
dominated by the spin transfer of the intrinsic polarised-strangeness in the
remnant nucleon, providing an independent way to check our model predictions.Comment: minor changes after accepted to EPJ
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
Transversity distributions in the nucleon in the large-N_c limit
We compute the quark and antiquark transversity distributions in the nucleon
at a low normalization point of 600 MeV in the large- limit, where the
nucleon can be described as a soliton of an effective chiral theory (chiral
quark-soliton model). The flavor-nonsinglet distributions, and , appear in leading order
of the -expansion, while the flavor-singlet distributions, and , are non-zero only in
next-to-leading order. The transversity quark and antiquark distributions are
found to be significantly different from the longitudinally polarized
distributions and , respectively, in contrast to the prediction of the naive
non-relativistic quark model. We show that this affects the predictions for the
spin asymmetries in Drell-Yan pair production in transversely polarized pp and
ppbar collisions.Comment: 45 pages, 16 figure
A new measurement of the Collins and Sivers asymmetries on a transversely polarised deuteron target
New high precision measurements of the Collins and Sivers asymmetries of
charged hadrons produced in deep-inelastic scattering of muons on a
transversely polarised 6LiD target are presented. The data were taken in 2003
and 2004 with the COMPASS spectrometer using the muon beam of the CERN SPS at
160 GeV/c. Both the Collins and Sivers asymmetries turn out to be compatible
with zero, within the present statistical errors, which are more than a factor
of 2 smaller than those of the published COMPASS results from the 2002 data.
The final results from the 2002, 2003 and 2004 runs are compared with naive
expectations and with existing model calculations.Comment: 40 pages, 28 figure
Gluon polarization in the nucleon from quasi-real photoproduction of high-pT hadron pairs
We present a determination of the gluon polarization Delta G/G in the
nucleon, based on the helicity asymmetry of quasi-real photoproduction events,
Q^2<1(GeV/c)^2, with a pair of large transverse-momentum hadrons in the final
state. The data were obtained by the COMPASS experiment at CERN using a 160 GeV
polarized muon beam scattered on a polarized 6-LiD target. The helicity
asymmetry for the selected events is = 0.002 +- 0.019(stat.) +-
0.003(syst.). From this value, we obtain in a leading-order QCD analysis Delta
G/G=0.024 +- 0.089(stat.) +- 0.057(syst.) at x_g = 0.095 and mu^2 =~ 3
(GeV}/c)^2.Comment: 10 pages, 3 figure
Spin asymmetry A_1^d and the spin-dependent structure function g_1^d of the deuteron at low values of x and Q^2
We present a precise measurement of the deuteron longitudinal spin asymmetry
A_1^d and of the deuteron spin-dependent structure function g_1^d at Q^2 < 1
GeV^2 and 4*10^-5 < x < 2.5*10^-2 based on the data collected by the COMPASS
experiment at CERN during the years 2002 and 2003. The statistical precision is
tenfold better than that of the previous measurement in this region. The
measured A_1^d and g_1^d are found to be consistent with zero in the whole
range of x.Comment: 17 pages, 10 figure
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