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Register a new userExclusive $eta$ electroproduction at $W>2$ GeV with CLAS and transversity generalized parton distributions
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The cross section of the exclusive $eta$ electroproduction reaction $epto e^prime p^prime eta$ was measured at Jefferson Lab with a 5.75-GeV electron beam and the CLAS detector. Differential cross sections $d^4sigma/dtdQ^2dx_Bdphi_eta$ and structure functions $sigma_U = sigma_T+epsilonsigma_L, sigma_{TT}$ and $sigma_{LT}$, as functions of $t$ were obtained over a wide range of $Q^2$ and $x_B$. The $eta$ structure functions are compared with those previously measured for $pi^0$ at the same kinematics. At low $t$, both $pi^0$ and $eta$ are described reasonably well by generalized parton distributions (GPDs) in which chiral-odd transversity GPDs are dominant. The $pi^0$ and $eta$ data, when taken together, can facilitate the flavor decomposition of the transversity GPDs.
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Exclusive neutral-pion electroproduction ($epto e^prime p^prime pi^0$) was measured at Jefferson Lab with a 5.75-GeV electron beam and the CLAS detector. Differential cross sections $d^4sigma/dtdQ^2dx_Bdphi_pi$ and structure functions $sigma_T+epsilonsigma_L, sigma_{TT}$ and $sigma_{LT}$ as functions of $t$ were obtained over a wide range of $Q^2$ and $x_B$. The data are compared with Regge and handbag theoretical calculations. Analyses in both frameworks find that a large dominance of transverse processes is necessary to explain the experimental results. For the Regge analysis it is found that the inclusion of vector meson rescattering processes is necessary to bring the magnitude of the calculated and measured structure functions into rough agreement. In the handbag framework, there are two independent calculations, both of which appear to roughly explain the magnitude of the structure functions in terms of transversity generalized parton distributions.
We report on the first measurement of cross sections for exclusive deeply virtual pion electroproduction off the proton, $e p to e^prime n pi^+$, above the resonance region at backward pion center-of-mass angles. The $varphi^*_{pi}$-dependent cross sections were measured, from which we extracted three combinations of structure functions of the proton. Our results are compatible with calculations based on nucleon-to-pion transition distribution amplitudes (TDAs) and shed new light on nucleon structure.
We discuss the recent data of exclusive $pi^0$ (and $pi^+$) electroproduction on the proton obtained by the CLAS collaboration at Jefferson Lab. It is observed that the cross sections, which have been decomposed in $sigma_T +epsilonsigma_L$, $sigma_{TT}$ and $sigma_{LT}$ structure functions, are dominated by transverse amplitude contributions. The data can be interpreted in the Generalized Parton Distribution formalism provided that one includes helicity-flip transversity GPDs.
We report measurements of the exclusive electroproduction of $K^+Lambda$ and $K^+Sigma^0$ final states from an unpolarized proton target using the CLAS detector at the Thomas Jefferson National Accelerator Facility. The separated structure functions $sigma_U$, $sigma_{LT}$, $sigma_{TT}$, and $sigma_{LT}$ were extracted from the $Phi$-dependent differential cross sections acquired with a longitudinally polarized 5.499 GeV electron beam. The data span a broad range of momentum transfers $Q^2$ from 1.4 to 3.9 GeV$^2$, invariant energy $W$ from threshold to 2.6 GeV, and nearly the full center-of-mass angular range of the kaon. The separated structure functions provide an unprecedented data sample, which in conjunction with other meson photo- and electroproduction data, will help to constrain the higher-level analyses being performed to search for missing baryon resonances.
This paper reports on the most comprehensive data set obtained on differential and fully integrated cross sections for the process $e p to e p pi^{+} pi^{-} $. The data were collected with the CLAS detector at Jefferson Laboratory. Measurements were carried out in the so-far unexplored kinematic region of photon virtuality 0.2 $<$ $Q^{2}$ $<$ 0.6 GeV$^{2}$ and invariant mass of the final hadron system $W$ from 1.3 to 1.57 GeV. For the first time, nine independent 1-fold differential cross sections were determined in each bin of $W$ and $Q^{2}$ covered by the measurements. A phenomenological analysis of the data allowed us to establish the most significant mechanisms contributing to the reaction. The non-resonant mechanisms account for a major part of cross-sections. However, we find sensitivity to s-channel excitations of low-mass nucleon resonances, especially to the $N(1440)P_{11}$ and $N(1520)D_{13}$ states in kinematical dependencies of the 1-fold differential cross-sections.
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