Measuring Deeply Virtual Compton Scattering on the neutron is one of the necessary steps to understand the structure of the nucleon in terms of Generalized Parton Distributions (GPDs). Neutron ...targets play a complementary role to transversely polarized proton targets in the determination of the GPD \(E\). This poorly known and poorly constrained GPD is essential to obtain the contribution of the quarks' angular momentum to the spin of the nucleon. DVCS on the neutron was measured for the first time selecting the exclusive final state by detecting the neutron, using the Jefferson Lab longitudinally polarized electron beam, with energies up to 10.6 GeV, and the CLAS12 detector. The extracted beam-spin asymmetries, combined with DVCS observables measured on the proton, allow a clean quark-flavor separation of the imaginary parts of the GPDs \(H\) and \(E\).
The polarized cross section ratio $\sigma_{LT'}/\sigma_{0}$ from hard
exclusive $\pi^{-} \Delta^{++}$ electroproduction off an unpolarized hydrogen
target has been extracted based on beam-spin ...asymmetry measurements using a
10.2 GeV / 10.6 GeV incident electron beam and the CLAS12 spectrometer at
Jefferson Lab. The study, which provides the first observation of this channel
in the deep-inelastic regime, focuses on very forward-pion kinematics in the
valence regime, and photon virtualities ranging from 1.5 GeV$^{2}$ up to 7
GeV$^{2}$. The reaction provides a novel access to the $d$-quark content of the
nucleon and to $p \rightarrow \Delta^{++}$ transition generalized parton
distributions. A comparison to existing results for hard exclusive $\pi^{+} n$
and $\pi^{0} p$ electroproduction is provided, which shows a clear impact of
the excitation mechanism, encoded in transition generalized parton
distributions, on the asymmetry.
We report results of $\Lambda$ hyperon production in semi-inclusive
deep-inelastic scattering off deuterium, carbon, iron, and lead targets
obtained with the CLAS detector and the Continuous Electron ...Beam Accelerator
Facility 5.014~GeV electron beam. These results represent the first
measurements of the $\Lambda$ multiplicity ratio and transverse momentum
broadening as a function of the energy fraction~($z$) in the current and target
fragmentation regions. The multiplicity ratio exhibits a strong suppression at
high~$z$~and~an enhancement at~low~$z$. The measured transverse momentum
broadening is an order of magnitude greater than that seen for light mesons.
This indicates that the propagating entity interacts very strongly with the
nuclear medium, which suggests that propagation of diquark configurations in
the nuclear medium takes place at least part of the time, even at high~$z$. The
trends of these results are qualitatively described by the Giessen
Boltzmann-Uehling-Uhlenbeck transport model, particularly for the multiplicity
ratios. These observations will potentially open a new era of studies of the
structure of the nucleon as well as of strange baryons.
A multidimensional extraction of the structure function ratio
$\sigma_{LT'}/\sigma_{0}$ from the hard exclusive $\vec{e} p \to e^\prime n
\pi^+$ reaction above the resonance region has been ...performed. The study was
done based on beam-spin asymmetry measurements using a 10.6 GeV incident
electron beam on a liquid-hydrogen target and the CLAS12 spectrometer at
Jefferson Lab. The measurements focus on the very forward regime ($t/Q^{2}$
$\ll$ 1) with a wide kinematic range of $x_{B}$ in the valence regime (0.17 $<$
$x_{B}$ $<$ 0.55), and virtualities $Q^{2}$ ranging from 1.5 GeV$^{2}$ up to 6
GeV$^{2}$. The results and their comparison to theoretical models based on
Generalized Parton Distributions demonstrate the sensitivity to chiral-odd GPDs
and the directly related tensor charge of the nucleon. In addition, the data is
compared to an extension of a Regge formalism at high photon virtualities. It
was found that the Regge model provides a better description at low $Q^{2}$,
while the GPD model is more appropriate at high $Q^{2}$.
Several factors can contribute to the difficulty of aligning the sensors of tracking detectors, including a large number of modules, multiple types of detector technologies, and non-linear strip ...patterns on the sensors. All three of these factors apply to the CLAS12 CVT, which is a hybrid detector consisting of planar silicon sensors with non-parallel strips, and cylindrical micromegas sensors with longitudinal and arc-shaped strips located within a 5~T superconducting solenoid. To align this detector, we used the Kalman Alignment Algorithm, which accounts for correlations between the alignment parameters without requiring the time-consuming inversion of large matrices. This is the first time that this algorithm has been adapted for use with hybrid technologies, non-parallel strips, and curved sensors. We present the results for the first alignment of the CLAS12 CVT using straight tracks from cosmic rays and from a target with the magnetic field turned off. After running this procedure, we achieved alignment at the level of 10~\(\mu\)m, and the widths of the residual spectra were greatly reduced. These results attest to the flexibility of this algorithm and its applicability to future use in the CLAS12 CVT and other hybrid or curved trackers, such as those proposed for the future Electron-Ion Collider.
Strange matter is believed to exist in the cores of neutron stars based on
simple kinematics. If this is true, then hyperon-nucleon interactions will play
a significant part in the neutron star ...equation of state (EOS). Yet, compared
to other elastic scattering processes, there is very little data on
$\Lambda$-$N$ scattering. This experiment utilized the CLAS detector to study
the $\Lambda p \rightarrow \Lambda p$ elastic scattering cross section in the
incident $\Lambda$ momentum range 0.9-2.0 GeV/c. This is the first data on this
reaction in several decades. The new cross sections have significantly better
accuracy and precision than the existing world data, and the techniques
developed here can also be used in future experiments.
The polarized cross section ratio \(\sigma_{LT'}/\sigma_{0}\) from hard exclusive \(\pi^{-} \Delta^{++}\) electroproduction off an unpolarized hydrogen target has been extracted based on beam-spin ...asymmetry measurements using a 10.2 GeV / 10.6 GeV incident electron beam and the CLAS12 spectrometer at Jefferson Lab. The study, which provides the first observation of this channel in the deep-inelastic regime, focuses on very forward-pion kinematics in the valence regime, and photon virtualities ranging from 1.5 GeV\(^{2}\) up to 7 GeV\(^{2}\). The reaction provides a novel access to the \(d\)-quark content of the nucleon and to \(p \rightarrow \Delta^{++}\) transition generalized parton distributions. A comparison to existing results for hard exclusive \(\pi^{+} n\) and \(\pi^{0} p\) electroproduction is provided, which shows a clear impact of the excitation mechanism, encoded in transition generalized parton distributions, on the asymmetry.
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