Search

The differential cross-sections σ0 = σT + εσL , σLT , and σTT of π0 electroproduction from the proton were measured from threshold up to an additional center-of-mass energy of 40MeV, at a value of the photon four-momentum transfer of Q 2 = 0.05 GeV2/c2 and a center-of-mass angle of θ = 90° . By an additional out-of-plane measurement with polarized electrons σLT' was determined. This showed for the first time the presence of an imaginary part of the s -wave above the π+ threshold, which is usually interpreted as a unitary cusp. The predictions of the Heavy Baryon Chiral Perturbation Theory (HBChPT) are in disagreement with these data. On the other hand, the data are somewhat better predicted by the MAID phenomenological model and are in good agreement with the dynamical model DMT. [ABSTRACT FROM AUTHOR]

The reaction p( e, e'p)π0 has been studied at Q 2 = 0.2 (GeV/ c)2 in the region of W = 1232MeV. From measurements left and right of $ \vec{q}\,$ , cross-section asymmetries ρLT have been obtained in forward kinematics ρLT( $ \theta_{{\pi^0}}^{{cm}}$ = 20°) = (- 11.68±2.36stat±2.36sys) and backward kinematics ρLT( $ \theta_{{\pi^0}}^{{cm}}$ = 160°) = (12.18±0.27stat±0.82sys) π0. Multipole ratios $ \Re$ { S 1+ * M 1+}/| M 1+|2 and $ \Re$ { S 0+ * M 1+}/| M 1+|2 were determined in the framework of the MAID2003 model. The results are in agreement with older data. The unusally strong negative $ \Re$ { S 0+ * M 1+}/| M 1+|2 required to bring also the result of Kalleicher et al. in accordance with the rest of the data is almost excluded. [ABSTRACT FROM AUTHOR]

The electric form factor of the neutron, GE,n, has been measured at the Mainz Microtron by recoil polarimetry in the quasielasticD(¯e,e’¯n)preaction. Three data points have been extracted at squared four-momentum transfersQ2 = 0.3, 0.6 and 0.8 (GeV/c)2. Corrections for nuclear binding effects have been applied. [ABSTRACT FROM AUTHOR]

The reaction 12C(e,e'Δ0)11C →12C(e,e'pπ−)11C was investigated at the Mainz Microtron MAMI in a triple coincidence measurement using the three spectrometer setup of the A1 Collaboration. The good missing mass resolution of σm= 0.27 MeV/c2 allowed to select the events belonging to the ground state of 11C. Cutting on these events the excitation energy spectra of 12CΔ0 show evidence for two peaks of about 4 MeV width (FWHM) at 282 MeV and 296 MeV with a significance of about 4.5 standard deviations. The peaks are interpreted in a simple weak coupling model as bound Δ0 states in 12CΔ0. [ABSTRACT FROM AUTHOR]

A correction to the article titled "First measurements of the 16O(e; e0pn)14N reaction" published in the 2006 issue of the European Physical Journal is presented.

The differential cross-sections σ0 = σT + εσL , σLT , and σTT of π0 electroproduction from the proton were measured from threshold up to an additional center-of-mass energy of 40MeV, at a value of the photon four-momentum transfer of Q 2 = 0.05 GeV2/c2 and a center-of-mass angle of θ = 90° . By an additional out-of-plane measurement with polarized electrons σLT' was determined. This showed for the first time the presence of an imaginary part of the s -wave above the π+ threshold, which is usually interpreted as a unitary cusp. The predictions of the Heavy Baryon Chiral Perturbation Theory (HBChPT) are in disagreement with these data. On the other hand, the data are somewhat better predicted by the MAID phenomenological model and are in good agreement with the dynamical model DMT. [ABSTRACT FROM AUTHOR]

The electric form factor of the neutron, GE,n, has been measured at the Mainz Microtron by recoil polarimetry in the quasielasticD(¯e,e’¯n)preaction. Three data points have been extracted at squared four-momentum transfersQ2 = 0.3, 0.6 and 0.8 (GeV/c)2. Corrections for nuclear binding effects have been applied. [ABSTRACT FROM AUTHOR]