Measurement of In-Medium Modifications of Proton Form-Factors

Brecelj, Tilen (author), Širca, Simon (mentor)

Measurements of the polarization transfer in the reactions of the type $A(\vec{e},e'\vec{p})A-1$, where the polarization is transferred from incident polarized electrons to free or bound target protons, are a relatively new method used for the investigation of the nucleon structure and different nuclear effects by means of spin degrees of freedom. So far polarization transfer measurements have been performed on $^1\text{H}$, $^2\text{H}$, $^4\text{He}$ and $^{16}\text{O}$. The aim of my doctoral research was to perform the first polarization transfer measurement on $^{12}\text{C}$ and analyse the collected data. In this work the theoretical background, the experimental setup, the data analysis and the results of the measurement of the polarization transfer in the $^{12}\text{C}(\vec{e},e'\vec{p})^{11}\text{B}$ process are presented. The experimentally obtained polarization transfer to protons ejected from $^{12}\text{C}$ is compared to the theoretically predicted polarization transfer as only theoretical models, which can reproduce the experimental data to a large extent, can provide a good understanding of the underlying physics processes influencing the measured quantities. Furthermore, the results obtained in the discussed experiment are compared also to the results of polarization transfer measurements performed on other atomic nuclei. The experimental data is usually presented as the ratio of the transverse and the longitudinal components of the polarization transfer to bound protons divided by the same ratio obtained for free protons. If this double-ratio is presented in the virtuality domain the mutual agreement between the experimental data obtained on different nuclei is unexpectedly good, although different experiments have been performed at different experimental setups. This implies that the discussed technique is suitable for the investigation of the interactions of the atomic nucleus with the embedded protons. In addition, the results of the polarization transfer measurements performed on $^{12}\text{C}$ cover a large kinematic range and were obtained with unprecedented precision. They may thus be helpful in developing theoretical models for the description of the polarization transfer, different nuclear phenomena and the influence of the atomic nucleus to the structure of the embedded protons.

• Language: English
• Keywords: polarized beam, elastic electron scattering, inelastic electron scattering to specific states, inelastic electron scattering to continuum, lepton-induced reactions, electric and magnetic charged-particle spectrometers, tracking and position-sensitive
• Work type: Doctoral dissertation
• Typology: 2.08 - Doctoral Dissertation
• Organization: FMF - Faculty of Mathematics and Physics
• Year: 2018
• PID: 20.500.12556/RUL-101577
• COBISS.SI-ID: 3208548
• Publication date in RUL: 18.06.2018

Secondary language

• Language: Slovenian

Abstract

Meritve prenosa polarizacije v reakcijah tipa $A(\vec{e},e'\vec{p})A-1$, kjer vpadni polariziran elektron izbije prost ali vezan tarčni proton, pri čemer pride do prenosa polarizacije, so relativno nova metoda, ki se uporablja za raziskovanje strukture nukleonov in različnih jedrskih pojavov s pomočjo spinskih prostostnih stopenj. Doslej so bile meritve prenosa polarizacije izvedene na $^1\text{H}$, $^2\text{H}$, $^4\text{He}$ in $^{16}\text{O}$. Cilj moje doktorske raziskave je bil izvedba prve meritve prenosa polarizacije na protone vezane v $^{12}\text{C}$ in analiza pridobljenih podatkov. V tem delu so predstavljeni teoretično ozadje, eksperimentalna postavitev, analiza podatkov ter rezultati meritve prenosa polarizacije v procesu $^{12}\text{C}(\vec{e},e'\vec{p})^{11}\text{B}$. Eksperimentalno pridobljena prenesena polarizacija na protone izbite iz $^{12}\text{C}$ je primerjana s teoretično napovedano preneseno polarizacijo, saj lahko samo s teoretičnimi modeli, ki dobro opišejo eksperimentalne rezultate, razumemo fizikalne procese, ki vplivajo na izmerjene količine. Poleg tega je v tem delu predstavljena tudi primerjava rezultatov, pridobljenih v obravnavanem eksperimentu, z rezultati, pridobljenimi na drugih atomskih jedrih. Rezultati meritev prenosa polarizacije so običajno predstavljeni kot količnik razmerja med prečno in vzdolžno komponento prenesene polarizacije na vezane protone ter istega razmerja pridobljenega na prostih protonih. Če je to dvojno razmerje predstavljeno v odvisnosti od virtualnosti, se eksperimentalni rezultati pridobljeni na različnih jedrih medsebojno nepričakovano dobro ujemajo, čeprav so bili različni eksperimenti izvedeni pri različnih eksperimentalnih postavitvah. To nakazuje na primernost obravnavane metode za raziskovanje interakcij atomskega jedra z vezanimi protoni. Poleg tega se rezultati meritve prenosa polarizacije izvedene na $^{12}\text{C}$ raztezajo čez veliko kinematično območje in so podani z doslej še nedoseženo natančnostjo. Ti rezultati bodo zato lahko v pomoč pri izdelavi teoretičnih modelov za opis prenosa polarizacije, različnih jedrskih pojavov ter vpliva atomskega jedra na strukturo vezanih protonov.

• Keywords: polariziran snop, elastično elektronsko sipanje, neelastično elektronsko sipanje v specifična stanja, neelastično elektronsko sipanje v kontinuum, z leptoni povzročene reakcije, električni in magnetni spektrometri za nabite delce, sledilni detektorji