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Register a new userTarget and Beam-Target Spin Asymmetries in Exclusive $pi^+$ and $pi^-$ Electroproduction with 1.6 to 5.7 GeV Electrons
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Beam-target double spin asymmetries and target single-spin asymmetries in exclusive $pi^+$ and $pi^-$ electroproduction were obtained from scattering of 1.6 to 5.7 GeV longitudinally polarized electrons from longitudinally polarized protons (for $pi^+$) and deuterons (for $pi^-$) using the CEBAF Large Acceptance Spectrometer (CLAS) at Jefferson Lab. The kinematic range covered is $1.1<W<2.6$ GeV and $0.05<Q^2<5$ GeV$^2$, with good anglular coverage in the forward hemisphere. The asymmetry results were divided into approximately 40,000 kinematic bins for $pi^+$ from free protons and 15,000 bins for $pi^-$ production from bound nucleons in the deuteron. The present results are found to be in reasonable agreement with fits to previous world data for $W<1.7$ GeV and $Q^2<0.5$ GeV$^2$, with discrepancies increasing at higher values of $Q^2$, especially for $W>1.5$ GeV. Very large target-spin asymmetries are observed for $W>1.6$ GeV. When combined with cross section measurements, the present results will provide powerful constraints on nucleon resonance amplitudes at moderate and large values of $Q^2$, for resonances with masses as high as 2.3 GeV.
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Beam-target double-spin asymmetries and target single-spin asymmetries were measured for the exclusive $pi^+$ electroproduction reaction $gamma^* p to n pi^+$. 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 $1.1<W<3$ GeV and $1<Q^2<6$ GeV$^2$. Results were obtained for about 6000 bins in $W$, $Q^2$, $cos(theta^*)$, and $phi^*$. Except at forward angles, very large target-spin asymmetries are observed over the entire $W$ region. Reasonable agreement is found with phenomenological fits to previous data for $W<1.6$ GeV, but very large differences are seen at higher values of $W$. A GPD-based model is in poor agreement with the data. When combined with cross section measurements, the present results provide powerful constraints on nucleon resonance amplitudes at moderate and large values of $Q^2$, for resonances with masses as high as 2.4 GeV.
Beam-target double-spin asymmetries and target single-spin asymmetries were measured for the exclusive $pi^0$ electroproduction reaction $gamma^* p to p pi^0$, expanding an analysis of the $gamma^* p to n pi^+$ 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 $1.1<W<3$ GeV and $1<Q^2<6$ GeV$^2$. Results were obtained for about 5700 bins in $W$, $Q^2$, cthcm, and $phi^*$. 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 $W$ and high $W$, in contrast to $pi^+$ electroproduction. Reasonable agreement is found with phenomenological fits to previous data for $W<1.6$ GeV, but significant differences are seen at higher $W$. When combined with cross section measurements, as well as $pi^+$ observables, the present results will provide powerful constraints on nucleon resonance amplitudes at moderate and large values of $Q^2$, for resonances with masses as high as 2.4 GeV.
The first data on target and beam-target asymmetries for the $gamma ptopi^0eta p$ reaction at photon energies from 1050 up to 1450 MeV are presented. The measurements were performed using the Crystal Ball and TAPS detector setup at the Glasgow tagged photon facility of the Mainz Microtron MAMI. The general assumption that the reaction is dominated by the $Delta 3/2^-$ amplitude is confirmed. The data are in particular sensitive to small contributions from other partial waves.
The target and double spin asymmetries of the exclusive pseudoscalar channel $vec evec pto eppi^0$ were measured for the first time in the deep-inelastic regime using a longitudinally polarized 5.9 GeV electron beam and a longitudinally polarized proton target at Jefferson Lab with the CEBAF Large Acceptance Spectrometer (CLAS). The data were collected over a large kinematic phase space and divided into 110 four-dimensional bins of $Q^2$, $x_B$, $-t$ and $phi$. Large values of asymmetry moments clearly indicate a substantial contribution to the polarized structure functions from transverse virtual photon amplitudes. The interpretation of experimental data in terms of generalized parton distributions (GPDs) provides the first insight on the chiral-odd GPDs $tilde{H}_T$ and $E_T$, and complement previous measurements of unpolarized structure functions sensitive to the GPDs $H_T$ and $bar E_T$. These data provide necessary constraints for chiral-odd GPD parametrizations and will strongly influence existing theoretical handbag models.
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.
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