Analysis of Roper Resonance N(1440) in Pion Electroproduction Process $p(e,e'p)\pi^0$Štajner, Samo (Avtor) Širca, Simon (Mentor) elementary particle physicsnuclear reactionselectron scatteringRoper resonanceelectroproductioncoincidence experimentspolarizationresponse functionshelicity amplitudesElectroproduction of pseudoscalar mesons on free nucleons is a very efficient and most sensitive tool for exploration of nucleon resonances. The lowest lying excited nucleon state with positive parity is the resonance $P_{11}(1440)$, also known as the Roper resonance. Due to its unusual characteristics it has been a source of controversy since the day of its discovery. We have performed a recoil-polarization experiment, where helicity dependent proton polarizations $P_x′$ and $P_z′$ as well as helicity-independent component $P_y$ have been measured in the $p(\vec{e},e′\vec{p})\pi^0$ pion electroproduction process. We have extracted the polarization components in a single kinematic point at four-momentum transfer $Q^2 \simeq 0.1$~GeV$^2$, center-of-mass emission angle $\theta_p^\ast \simeq 90^\circ$, and invariant mass $W \simeq 1440$ MeV. This work represents the first precise measurement of double-polarization observables in the energy region of the Roper resonance. We have compared the extracted polarization components with the state-of-the-art electroproduction models MAID and DMT, as well as with the full-scale partial-wave analysis SAID. We have identified the MAID model predictions as the most adequate and performed a model-dependent extraction of the Roper’s scalar electroexcitation amplitude $S_{1/2}$ .20172018-02-02 07:15:02Doktorsko delo/naloga99560VisID: 87108COBISS_ID: 3168612sl