6 research outputs found
New results on SIDIS SSA from Jefferson Lab
We present studies of single-spin and double-spin asymmetries in
semi-inclusive electroproduction of pions using the CEBAF 6 GeV polarized
electron beam. Kinematic dependences of single and double spin asymmetries have
been measured in a wide kinematic range at CLAS with a polarized NH target.
Significant target-spin and asymmetries have been
observed. The hypothesis of factorization has been tested with -dependence
of the double spin asymmetry.Comment: 4 pages, 6 figure
Effective role of unpolarized nonvalence partons in Drell-Yan single spin asymmetries
We perform numerical simulations of the Sivers effect from single spin
asymmetries in Drell-Yan processes on transversely polarized protons. We
consider colliding antiprotons and pions at different kinematic conditions of
interest for the future planned experiments. We conventionally name "framework
I" the results obtained when properly accounting for the various flavor
dependent polarized valence contributions in the numerator of the asymmetry,
and for the unpolarized nonvalence contribution in its denominator. We name
"framework II" the results obtained when taking a suitable flavor average of
the valence contributions and neglecting the nonvalence ones. We compare the
two methods, also with respect to the input parametrization of the Sivers
function which is extracted from data with approximations sometimes
intermediate between frameworks I and II. Deviations between the two approaches
are found to be small except for dilepton masses below 3 GeV. The Sivers effect
is used as a test case; the arguments can be generalized to other interesting
azimuthal asymmetries in Drell-Yan processes, such as the Boer-Mulders effect.Comment: 13 pages, 9 figures in eps forma
Beam-target double-spin asymmetry in quasielastic electron scattering off the deuteron with CLAS
Background: The deuteron plays a pivotal role in nuclear and hadronic physics, as both the simplest bound multinucleon system and as an effective neutron target. Quasielastic electron scattering on the deuteron is a benchmark reaction to test our understanding of deuteron structure and the properties and interactions of the two nucleons bound in the deuteron.
Purpose: The experimental data presented here can be used to test state-of-the-art models of the deuteron and the two-nucleon interaction in the final state after two-body breakup of the deuteron. Focusing on polarization degrees of freedom, we gain information on spin-momentum correlations in the deuteron ground state (due to the
D
-state admixture) and on the limits of the impulse approximation (IA) picture as it applies to measurements of spin-dependent observables like spin structure functions for bound nucleons. Information on this reaction can also be used to reduce systematic uncertainties on the determination of neutron form factors or deuteron polarization through quasielastic polarized electron scattering.
Method: We measured the beam-target double-spin asymmetry (
A
|
|
) for quasielastic electron scattering off the deuteron at several beam energies (
1.6
â
1.7
, 2.5, 4.2, and
5.6
â
5.8
GeV
), using the CEBAF Large Acceptance Spectrometer (CLAS) at the Thomas Jefferson National Accelerator Facility. The deuterons were polarized along (or opposite to) the beam direction. The double-spin asymmetries were measured as a function of photon virtuality
Q
2
(
0.13
â
3.17
(
GeV
/
c
)
2
)
, missing momentum
(
p
m
=
0.0
â
0.5
GeV
/
c
)
, and the angle between the (inferred) spectator neutron and the momentum transfer direction
(
Ξ
n
q
)
.
Results: The results are compared with a recent model that includes final-state interactions (FSI) using a complete parametrization of nucleon-nucleon scattering, as well as a simplified model using the plane wave impulse approximation (PWIA). We find overall good agreement with both the PWIA and FSI expectations at low to medium missing momenta
(
p
m
â€
0.25
GeV
/
c
)
, including the change of the asymmetry due to the contribution of the deuteron
D
state at higher momenta. At the highest missing momenta, our data clearly agree better with the calculations including FSI.
Conclusions: Final-state interactions seem to play a lesser role for polarization observables in deuteron two-body electrodisintegration than for absolute cross sections. Our data, while limited in statistical power, indicate that PWIA models work reasonably well to understand the asymmetries at lower missing momenta. In turn, this information can be used to extract the product of beam and target polarization
(
P
b
P
t
)
from quasielastic electron-deuteron scattering, which is useful for measurements of spin observables in electron-neutron inelastic scattering. However, at the highest missing (neutron) momenta, FSI effects become important and must be accounted for
Target and beam-target spin asymmetries in exclusive pion electroproduction for Q2>1 GeV2. II. epâeÏ0p
Beam-target double-spin asymmetries and target single-spin asymmetries were
measured for the exclusive electroproduction reaction , expanding an analysis of the reaction from the
same experiment. The results were obtained from scattering of 6 GeV
longitudinally polarized electrons off longitudinally polarized protons using
the CEBAF Large Acceptance Spectrometer at Jefferson Lab. The kinematic range
covered is GeV and GeV. Results were obtained for about
5700 bins in , , \cthcm, and . The beam-target asymmetries were
found to generally be greater than zero, with relatively modest \phicmsp
dependence. The target asymmetries exhibit very strong \phicmsp dependence,
with a change in sign occurring between results at low and high , in
contrast to electroproduction. Reasonable agreement is found with
phenomenological fits to previous data for GeV, but significant
differences are seen at higher . When combined with cross section
measurements, as well as observables, the present results will provide
powerful constraints on nucleon resonance amplitudes at moderate and large
values of , for resonances with masses as high as 2.4 GeV.Comment: 28 pages, 12 figures, submitted to Phys. Rev.
Measurement of Single and Double Spin Asymmetries in Deep Inelastic Pion Electroproduction with a Longitudinally Polarized Target
We report the first measurement of the transverse momentum dependence of double spin asymmetries in semi-inclusive production of pions in deep inelastic scattering off the longitudinally polarized proton. Data have been obtained using a polarized electron beam of 5.7 GeV with the CLAS detector at the Thomas Jefferson National Accelerator Facility (JLab). A significant non-zero single spin asymmetry was also observed for the first time indicating strong spin-orbit correlations for transversely polarized quarks in the longitudinally polarized proton. The azimuthal modulations of single spin asymmetries have been measured over a wide kinematic range
Quark-hadron duality in spin structure functions g(1)(p) and g(1)(d)
New measurements of the spin structure functions of the proton and deuteron g1p(x,Q2) and g1d(x,Q2) in the nucleon resonance region are compared with extrapolations of target-mass-corrected next-to-leading-order (NLO) QCD fits to higher energy data. Averaged over the entire resonance region (W\u3c2 \u3eGeV), the data and QCD fits are in good agreement in both magnitude and Q2 dependence for Q2\u3e1.7 GeV2/c2. This âglobalâ duality appears to result from cancellations among the prominent âlocalâ resonance regions: in particular strong Ï3/2 contributions in the Î(1232) region appear to be compensated by strong Ï1/2 contributions in the resonance region centered on 1.5 GeV. These results are encouraging for the extension of NLO QCD fits to lower W and Q2 than have been used previously