Aksijalni faktor oblika nukleona iz tvorbe elektron-pion za male q2

Results of the measurement of the transverse and longitudinal cross-section for coincident electro-production of positively charged pions on protons measured in parallel kinematics at the invariant mass of W = 1125 MeV and at three fourmomentum transfers q 2 = −0.117, −0.195 and −0.273 GeV2 are presented. An axial-mass parameter of high accuracy was extracted from a preliminary analysis of the transverse cross-section within the Mainz effective Lagrangian model of the nucleon. The value supports the prediction of the chiral perturbation theory that pion-loop corrections effectively increase the value of the axial mass extracted from pion electro-production data relative to that from neutrino scattering.Opisuju se ishodi mjerenja poprečnog i uzdužnog udarnog presjeka za višestruku elektrotvorbu pozitivnih piona u paralelnoj kinematici

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

Sljedeće mjerenje virtualnog Comptonovog raspršenja u MAMI

A new ep → epγ experiment is foreseen at MAMI in order to study the Q2 - dependence of the structure functions PLL − PT T /ǫ and PLT and the generalized polarizabilities αE(Q2 ) and βM(Q2 ) of the proton.Predviđamo novo mjerenje ep → epγ u MAMI radi proučavanja Q2 -ovisnosti strukturnih funkcija PLL − PT T /ǫ i PLT te poopćenih polarizabilnosti αE(Q2 ) i βM(Q2 ) protona

Promjene svojstava Delta u nuklearnoj sredini

In the experiments at the Mainz Microtron, MAMI, ∆0 particles in the electron scattering reactions 12C (e, e ′∆0 ) 11C have been produced in nuclear medium. The three high-resolution magnetic spectrometers of the A1 collaboration have been used in triple coincidence measurements 12C (e, e ′p π −) 11C. Indications for substantial changes of delta properties in the nuclear medium have been obtained. Because of low statistics, these results cannot yet be taken as conclusive. A new setup for measurements at MAMI with silicon detectors for proton detection, which subtend larger solid angle, is described.U eksperimentima s mikrotronom u Mainzu, MAMI, proizvodili smo u nuklearnoj sredini čestice ∆0 reakcijom 12C (e, e ′∆0 ) 11C. U okviru suradnje A1, rabili smo tri magnetska spektrometra visokog razlučivanja za trosudesna mjerenja 12C (e, e ′p π −) 11C. Podaci ukazuju na promjene svojstava delta čestica u nuklearnoj sredini. Zbog slabe statistike, ti se ishodi još ne mogu smatrati konačnima. Opisuje se i nov mjerni sustav za detekciju protona sastavljen od silicijskih detektora koji zahvaća veći prostorni kut

The Effect of the Short-Range Correlations on the Generalized Momentum Distribution in Finite Nuclei

The effect of dynamical short-range correlations on the generalized momentum distribution $n(\vec{p},\vec{Q})$ in the case of $Z=N$, $\ell$-closed shell nuclei is investigated by introducing Jastrow-type correlations in the harmonic-oscillator model. First, a low order approximation is considered and applied to the nucleus $^4$He. Compact analytical expressions are derived and numerical results are presented and the effect of center-of-mass corrections is estimated. Next, an approximation is proposed for $n(\vec{p}, \vec{Q})$ of heavier nuclei, that uses the above correlated $n(\vec{p},\vec{Q})$ of $^4$He. Results are presented for the nucleus $^{16}$O. It is found that the effect of short-range correlations is significant for rather large values of the momenta $p$ and/or $Q$ and should be included, along with center of mass corrections for light nuclei, in a reliable evaluation of $n(\vec{p},\vec{Q})$ in the whole domain of $p$ and $Q$.Comment: 29 pages, 8 figures. Further results, figures and discussion for the CM corrections are added. Accepted by Journal of Physics

Measurement of polarization-transfer to bound protons in carbon and its virtuality dependence

We measured the ratio $P_{x}/P_{z}$ of the transverse to longitudinal components of polarization transferred from electrons to bound protons in $^{12}\mathrm{C}$ by the $^{12}\mathrm{C}(\vec{e},e'\vec{p})$ process at the Mainz Microtron (MAMI). We observed consistent deviations from unity of this ratio normalized to the free-proton ratio, $(P_{x}/P_{z})_{^{12}\mathrm{C}}/(P_{x}/P_{z})_{^{1}\mathrm{H}}$, for both $s$- and $p$-shell knocked out protons, even though they are embedded in averaged local densities that differ by about a factor of two. The dependence of the double ratio on proton virtuality is similar to the one for knocked out protons from $^{2}\mathrm{H}$ and $^{4}\mathrm{He}$, suggesting a universal behavior. It further implies no dependence on average local nuclear density