Phys. Rev. Lett. 113, 232505 (2014) We present a precise measurement of double-polarization asymmetries in the
$^3\vec{\mathrm{He}}(\vec{\mathrm{e}},\mathrm{e}'\mathrm{d})$ reaction. This
particular ...process is a uniquely sensitive probe of hadron dynamics in
$^3\mathrm{He}$ and the structure of the underlying electromagnetic currents.
The measurements have been performed in and around quasi-elastic kinematics at
$Q^2 = 0.25\,(\mathrm{GeV}/c)^2$ for missing momenta up to
$270\,\mathrm{MeV}/c$. The asymmetries are in fair agreement with the
state-of-the-art calculations in terms of their functional dependencies on
$p_\mathrm{m}$ and $\omega$, but are systematically offset. Beyond the region
of the quasi-elastic peak, the discrepancies become even more pronounced. Thus,
our measurements have been able to reveal deficiencies in the most
sophisticated calculations of the three-body nuclear system, and indicate that
further refinement in the treatment of their two- and/or three-body dynamics is
required.
Phys. Rev. C.90.055201, 2014 We report the first measurement of target single spin asymmetries of charged
kaons produced in semi-inclusive deep inelastic scattering of electrons off a
transversely ...polarized $^3{\rm{He}}$ target. Both the Collins and Sivers
moments, which are related to the nucleon transversity and Sivers
distributions, respectively, are extracted over the kinematic range of
0.1$<$$x_{bj}$$<$0.4 for $K^{+}$ and $K^{-}$ production. While the Collins and
Sivers moments for $K^{+}$ are consistent with zero within the experimental
uncertainties, both moments for $K^{-}$ favor negative values. The Sivers
moments are compared to the theoretical prediction from a phenomenological fit
to the world data. While the $K^{+}$ Sivers moments are consistent with the
prediction, the $K^{-}$ results differ from the prediction at the 2-sigma
level.
We have performed precision measurements of the double-spin virtual-photon
asymmetry $A_1$ on the neutron in the deep inelastic scattering regime, using
an open-geometry, large-acceptance ...spectrometer. Our data cover a wide
kinematic range $0.277 \leq x \leq 0.548$ at an average $Q^2$ value of
3.078~(GeV/c)$^2$, doubling the available high-precision neutron data in this
$x$ range. We have combined our results with world data on proton targets to
extract the ratio of polarized-to-unpolarized parton distribution functions for
up quarks and for down quarks in the same kinematic range. Our data are
consistent with a previous observation of an $A_1^n$ zero crossing near
$x=0.5$. We find no evidence of a transition to a positive slope in $(\Delta d
+ \Delta \bar{d})/(d + \bar{d})$ up to $x=0.548$.
Double-spin asymmetries and absolute cross sections were measured at large
Bjorken $x$ (0.25 $ \le x \le $ 0.90), in both the deep-inelastic and resonance
regions, by scattering longitudinally ...polarized electrons at beam energies of
4.7 and 5.9 GeV from a transversely and longitudinally polarized $^3$He target.
In this dedicated experiment, the spin structure function $g_2$ on $^3$He was
determined with precision at large $x$, and the neutron twist-three matrix
element $d_2^n$ was measured at $\left< Q^2\right>$ of 3.21 and 4.32
GeV$^2$/$c^2$, with an absolute precision of about $10^{-5}$. Our results are
found to be in agreement with lattice QCD calculations and resolve the
disagreement found with previous data at $\left< Q^2\right> =$ 5 GeV$^2$/$c^2$.
Combining $d_2^n$ and a newly extracted twist-four matrix element, $f_2^n$, the
average neutron color electric and magnetic forces were extracted and found to
be of opposite sign and about 30 MeV/fm in magnitude.
Phys. Rev. C 90, 055209 (2014) An experiment to measure single-spin asymmetries in semi-inclusive production
of charged pions in deep-inelastic scattering on a transversely polarized
$^3$He target ...was performed at Jefferson Lab in the kinematic region of
$0.16<x<0.35$ and $1.4<Q^2<2.7$ ${\rm GeV^2}$. The pretzelosity asymmetries on
$^3$He, which can be expressed as the convolution of the $h^\perp_{1T}$
transverse momentum dependent distribution functions and the Collins
fragmentation functions in the leading order, were measured for the first time.
Using the effective polarization approximation, we extracted the corresponding
neutron asymmetries from the measured $^3$He asymmetries and cross-section
ratios between the proton and $^3$He. Our results show that for both
$\pi^{\pm}$ on $^3$He and on the neutron the pretzelosity asymmetries are
consistent with zero within experimental uncertainties.
Phys. Rev. C 89, 042201(R), 2014 We report the first measurement of target single-spin asymmetries (A$_N$) in
the inclusive hadron production reaction,
$e~$+$~^3\text{He}^{\uparrow}\rightarrow h+X$, ...using a transversely polarized
$^3$He target. The experiment was conducted at Jefferson Lab in Hall A using a
5.9-GeV electron beam. Three types of hadrons ($\pi^{\pm}$, $\text{K}^{\pm}$
and proton) were detected in the transverse hadron momentum range 0.54 $<p_T<$
0.74 GeV/c. The range of $x_F$ for pions was -0.29 $<x_F<$ -0.23 and for kaons
-0.25 $<x_F<$-0.18. The observed asymmetry strongly depends on the type of
hadron. A positive asymmetry is observed for $\pi^+$ and $\text{K}^+$. A
negative asymmetry is observed for $\pi^{-}$. The magnitudes of the asymmetries
follow $|A^{\pi^-}| < |A^{\pi^+}| < |A^{K^+}|$. The K$^{-}$ and proton
asymmetries are consistent with zero within the experimental uncertainties. The
$\pi^{+}$ and $\pi^{-}$ asymmetries measured for the $^3$He target and
extracted for neutrons are opposite in sign with a small increase observed as a
function of $p_T$.
Phys. Rev. Lett. 113, 022502 (2014) We report the first measurement of the target-normal single-spin asymmetry in
deep-inelastic scattering from the inclusive reaction
$^3$He$^{\uparrow}\left(e,e' ...\right)X$ on a polarized $^3$He gas target.
Assuming time-reversal invariance, this asymmetry is strictly zero in the Born
approximation but can be non-zero if two-photon-exchange contributions are
included. The experiment, conducted at Jefferson Lab using a 5.89 GeV electron
beam, covers a range of $1.7 < W < 2.9$ GeV, $1.0<Q^2<4.0$ GeV$^2$ and
$0.16<x<0.65$. Neutron asymmetries were extracted using the effective nucleon
polarization and measured proton-to-$^3$He cross section ratios. The measured
neutron asymmetries are negative with an average value of $(-1.09 \pm 0.38)
\times10^{-2}$ for invariant mass $W>2$ GeV, which is non-zero at the
$2.89\sigma$ level. Our measured asymmetry agrees both in sign and magnitude
with a two-photon-exchange model prediction that uses input from the Sivers
transverse momentum distribution obtained from semi-inclusive deep-inelastic
scattering.
The discrepancy between proton electromagnetic form factors extracted using
unpolarized and polarized scattering data is believed to be a consequence of
two-photon exchange (TPE) effects. However, ...the calculations of TPE corrections
have significant model dependence, and there is limited direct experimental
evidence for such corrections. We present the results of a new experimental
technique for making direct $e^\pm p$ comparisons, which has the potential to
make precise measurements over a broad range in $Q^2$ and scattering angles. We
use the Jefferson Lab electron beam and the Hall B photon tagger to generate a
clean but untagged photon beam. The photon beam impinges on a converter foil to
generate a mixed beam of electrons, positrons, and photons. A chicane is used
to separate and recombine the electron and positron beams while the photon beam
is stopped by a photon blocker. This provides a combined electron and positron
beam, with energies from 0.5 to 3.2 GeV, which impinges on a liquid hydrogen
target. The large acceptance CLAS detector is used to identify and reconstruct
elastic scattering events, determining both the initial lepton energy and the
sign of the scattered lepton. The data were collected in two days with a
primary electron beam energy of only 3.3 GeV, limiting the data from this run
to smaller values of $Q^2$ and scattering angle. Nonetheless, this measurement
yields a data sample for $e^\pm p$ with statistics comparable to those of the
best previous measurements. We have shown that we can cleanly identify elastic
scattering events and correct for the difference in acceptance for electron and
positron scattering. The final ratio of positron to electron scattering:
$R=1.027\pm0.005\pm0.05$ for $<Q^2>=0.206$ GeV$^2$ and $0.830\leq \epsilon\leq
0.943$.
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