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Register a new userMeasurement of Target and Double-spin Asymmetries for the $vec evec pto epi^+ (n)$ Reaction in the Nucleon Resonance Region at Low $Q^2$
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We report measurements of target- and double-spin asymmetries for the exclusive channel $vec evec pto epi^+ (n)$ in the nucleon resonance region at Jefferson Lab using the CEBAF Large Acceptance Spectrometer (CLAS). These asymmetries were extracted from data obtained using a longitudinally polarized NH$_3$ target and a longitudinally polarized electron beam with energies 1.1, 1.3, 2.0, 2.3 and 3.0 GeV. The new results are consistent with previous CLAS publications but are extended to a low $Q^2$ range from $0.0065$ to $0.35$ (GeV$/c$)$^2$. The $Q^2$ access was made possible by a custom-built Cherenkov detector that allowed the detection of electrons for scattering angles as low as $6^circ$. These results are compared with the unitary isobar models JANR and MAID, the partial-wave analysis prediction from SAID and the dynamic model DMT. In many kinematic regions our results, in particular results on the target asymmetry, help to constrain the polarization-dependent components of these models.
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The cross section of the $p(e,epi^+)n$ reaction has been measured for five kinematic settings at an invariant mass of $W = 1094$ MeV and for a four-momentum transfer of $Q^2 = 0.078$ (GeV/$c$)$^2$. The measurement has been performed at MAMI using a new short-orbit spectrometer (SOS) of the A1 collaboration, intended for detection of low-energy pions. The transverse and longitudinal cross section terms were separated using the Rosenbluth method and the transverse-longitudinal interference term has been determined from the left-right asymmetry. The experimental cross section terms are compared with the calculations of three models: DMT2001, MAID2007 and $chi$MAID. The results show that we do not yet understand the dynamics of the fundamental pion.
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.
We report the first beam-target double-polarization asymmetries in the $gamma + n(p) rightarrow pi^- + p(p)$ reaction spanning the nucleon resonance region from invariant mass $W$= $1500$ to $2300$ MeV. Circularly polarized photons and longitudinally polarized deuterons in $H!D$ have been used with the CLAS detector at Jefferson Lab. The exclusive final state has been extracted using three very different analyses that show excellent agreement, and these have been used to deduce the {it{E}} polarization observable for an effective neutron target. These results have been incorporated into new partial wave analyses, and have led to significant revisions for several $gamma nN^*$ resonance photo-couplings.
We report on a high-statistics measurement of the most basic double pionic fusion reaction $vec{n}p to dpi^0pi^0$ over the energy region of the $d^*(2380)$ resonance by use of a polarized deuteron beam and observing the double fusion reaction in the quasifree scattering mode. The measurements were performed with the WASA detector setup at COSY. The data reveal substantial analyzing powers and confirm conclusions about the $d^*$ resonance obtained from unpolarized measurements. We also confirm the previous unpolarized data obtained under complementary kinematic conditions.
We report the first large-acceptance measurement of polarization transfer from a polarized photon beam to a recoiling nucleon, pioneering a novel polarimetry technique with wide application to future nuclear and hadronic physics experiments. The commissioning measurement of polarization transfer in the $^{1}H$($vec{gamma}$,$vec{p}$)$pi^{0}$ reaction in the range $0.4<E_{gamma}<1.4$ GeV is highly selective regarding the basic parameterizations used in partial wave analyses to extract the nucleon excitation spectrum. The new data strongly favor the recently proposed Chew-Mandelstam formalism.
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