Građa nukleona iz mjerenja elektrotvorbe piona u MAMIju

Recent pion electro-production experiments of the A1 Collaboration at MAMI are presented. The threshold data in the p(e,e′p)π 0 and d(e,e′d)π 0 channels reveal the chiral dynamics of the pion-nucleon system at low energies. Measurements of the neutral channel in the ∆ region address the issue of the pion cloud, while the p(e,e′π +)n channel gives access to the axial structure of the nucleon.Predstavljamo nedavna mjerenja elektrotvorbe piona Suradnje A1 u MAMIju. Podaci oko pragova kanala p(e, e′ p)π 0 i d(e, e′ d)π 0 otkrivaju kiralnu dinamiku sustava pion-nukleon na niskim energijama. Mjerenja neutralnog kanala u području ∆ rezonancije daju uvid u strukturu pionskog oblaka, a kanal p(e, e′π +)n u aksijalnu građu nukleona

Uloga pionskog oblaka u nukleonskim faktorima oblika

In the linear sigma model and in the chromodielectric model, it is shown how the pion cloud enhances the electric polarizability, the electroexcitation of the ∆ and the axial form factor, and how it reduces the magnetic polarizability.U linearnom sigma modelu i u kromodielektričnom modelu se pokazuje kako pionski oblak povećava električnu polarizivnost, elektrouzbudu ∆ i aksijalni faktor oblika, te kako smanjuje magnetsku polarizivnost

Recoil polarization and beam-recoil double polarization measurement of \eta electroproduction on the proton in the region of the S_{11}(1535) resonance

The beam-recoil double polarization P_{x'}^h and P_{z'}^h and the recoil polarization P_{y'} were measured for the first time for the p(\vec{e},e'\vec{p})\eta reaction at a four-momentum transfer of Q^2=0.1 GeV^2/c^2 and a center of mass production angle of \theta = 120^\circ at MAMI C. With a center of mass energy range of 1500 MeV < W < 1550 MeV the region of the S_{11}(1535) and D_{13}(1520) resonance was covered. The results are discussed in the framework of a phenomenological isobar model (Eta-MAID). While P_{x'}^h and P_{z'}^h are in good agreement with the model, P_{y'} shows a significant deviation, consistent with existing photoproduction data on the polarized-target asymmetry.Comment: 4 pages, 1 figur