We measured the ratios of electroproduction cross-sections from a proton target for three exclusive meson-baryon final states: $Lambda K^+$, $ppi^0$, and $npi^+$, with the CLAS detector at Jefferson Lab. Using a simple model of quark hadronization we
extract q-qbar creation probabilities for the first time in exclusive two-body production, in which only a single q-qbar pair is created. We observe a sizable suppression of strange quark-antiquark pairs compared to non-strange pairs, similar to that seen in high-energy production.
The exclusive electroproduction of $pi^+$ above the resonance region was studied using the $rm{CEBAF}$ Large Acceptance Spectrometer ($rm{CLAS}$) at Jefferson Laboratory by scattering a 6 GeV continuous electron beam off a hydrogen target. The large
acceptance and good resolution of $rm{CLAS}$, together with the high luminosity, allowed us to measure the cross section for the $gamma^* p to n pi^+$ process in 140 ($Q^2$, $x_B$, $t$) bins: $0.16<x_B<0.58$, 1.6 GeV$^2<$$Q^2$$<4.5$ GeV$^2$ and 0.1 GeV$^2<$$-t$$<5.3$ GeV$^2$. For most bins, the statistical accuracy is on the order of a few percent. Differential cross sections are compared to two theoretical models, based either on hadronic (Regge phenomenology) or on partonic (handbag diagram) degrees of freedom. Both can describe the gross features of the data reasonably well, but differ strongly in their ingredients. If the handbag approach can be validated in this kinematical region, our data contain the interesting potential to experimentally access transversity Generalized Parton Distributions.
We report the first extraction of the pion-nucleon multipoles near the production threshold for the $npi^+$ channel at relatively high momentum transfer ($Q^2$ up to 4.2 $rm{GeV^2}$). The dominance of the s-wave transverse multipole ($E_{0+}$), expec
ted in this region, allowed us to access the generalized form factor $G_1$ within the light-cone sum rule (LCSR) framework as well as the axial form factor $G_A$. The data analyzed in this work were collected by the nearly $4pi$ CEBAF Large Acceptance Spectrometer (CLAS) using a 5.754 $rm{GeV}$ electron beam on a proton target. The differential cross section and the $pi-N$-multipole $E_{0+}/G_D$ were measured using two different methods, the LCSR and a direct multipole fit. The results from the two methods are found to be consistent and almost $Q^2$ independent.
The exclusive electroproduction process $vec{e}p to e^prime n pi^+$ was measured in the range of the photon virtuality $Q^2 = 1.7 - 4.5 rm{GeV^2}$, and the invariant mass range for the $npi^+$ system of $W = 1.15 - 1.7 rm{GeV}$ using the CEBAF Large
Acceptance Spectrometer. For the first time, these kinematics are probed in exclusive $pi^+$ production from protons with nearly full coverage in the azimuthal and polar angles of the $npi^+$ center-of-mass system. The $npi^+$ channel has particular sensitivity to the isospin 1/2 excited nucleon states, and together with the $ppi^0$ final state will serve to determine the transition form factors of a large number of resonances. The largest discrepancy between these results and present modes was seen in the $sigma_{LT}$ structure function. In this experiment, 31,295 cross section and 4,184 asymmetry data points were measured. Because of the large volume of data, only a reduced set of structure functions and Legendre polynomial moments can be presented that are obtained in model-independent fits to the differential cross sections.
