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International audience; Understanding the structure of the nucleon (proton and neutron) is a critical problem in physics. Especially challenging is to understand the spin structure when the Strong Interaction becomes truly strong. At energy scales below the nucleon mass (~1 GeV), the intense interactions of the quarks and gluons inside the nucleon makes them highly correlated. Their coherent behavior causes the emergence of effective hadronic degrees of freedom (hadrons are composite particles made of quarks and gluons) which are necessary to understand the nucleon properties. Theoretically studying this subject requires approaches employing non-perturbative techniques or using hadronic degrees of freedom, e.g. chiral effective field theory (chiEFT). Here, we present measurements sensitive to the neutron's spin precession under electromagnetic fields. The observables, the generalized spin-polarizabilities delta_LT and gamma_0, which quantify the nucleon spin's precession, were measured at very low energy-momentum transfer squared Q^2 corresponding to probing distances of the size of the nucleon. Our Q^2 values match the domain where chiEFT calculations are expected to be applicable. The calculations have been conducted to high degrees of sophistication, including that of the so-called "gold-plated" observable, delta_LT. Surprisingly however, our data show a strong discrepancy with the chiEFT calculations. This presents a challenge to the current description of the neutron's spin properties.

A given outcome of radiotherapy treatment can be modeled by analyzing its correlation with a combination of dosimetric, physiological, biological, and clinical factors, through a logistic regression fit of a large patient population. The quality of the fit is measured by the combination of the predictive power of this particular set of factors and the statistical significance of the individual factors in the model. We developed a genetic algorithm (GA), in which a small sample of all the possible combinations of variables are fitted to the patient data. New models are derived from the best models, through crossover and mutation operations, and are in turn fitted. The process is repeated until the sample converges to the combination of factors that best predicts the outcome. The GA was tested on a data set that investigated the incidence of lung injury in NSCLC patients treated with 3DCRT. The GA identified a model with two variables as the best predictor of radiation pneumonitis: the V30 (p=0.048) and the ongoing use of tobacco at the time of referral (p=0.074). This two-variable model was confirmed as the best model by analyzing all possible combinations of factors. In conclusion, genetic algorithms provide a reliable and fast way to select significant factors in logistic regression analysis of large clinical studies.

In this thesis, we present the results of the experiment E99-007, which measured the ratio of the electric to magnetic form factors of the proton to the four momentum transfer square Q2 = 5.6 GeV2, by recoil polarimetry. Data were taken in 2000 at the Thomas Jefferson National Accelerator Facility in Virginia, USA. A 4.6 GeV polarized electron beam was scattered off a cryogenic hydrogen target. The polarization of the recoil proton was measured in the Focal Plane Polarimeter, located after one of the two High Resolution Spectrometers in Hall A. The ratio of the transverse to longitudinal components of the recoil proton polarization is proportional to the ratio of the form factors. Elastic events were selected by detecting the scattered electron in a large acceptance lead-glass calorimeter. The main result of this experiment is the linear decrease of the form factor ratio with increasing Q2, corresponding to different spatial distributions of the electric charge and the magnetization. Numerous theoretical calculations show that relativistic effects, such as mixing of spin states due to Lorentz boosts, are important to account for the observed data in this critical intermediate kinematic region.; Dans cette thèse sont présentés les résultats de l'expérience E99-007, qui a mesuré le rapport des facteurs de forme électrique et magnétique du proton, jusqu'au quadri-moment de transfert Q2 = 5.6 GeV2, par polarisation de recul. Les données ont été prises en 2000 au Thomas Jefferson National Accelerator Facility en Virginie, Etats-Unis. Un faisceau d'électrons polarisés de 4.6 GeV a été diffusé sur une cible d'hydrogène liquide. La polarisation du proton de recul était mesurée dans le Polarimètre du Plan Focal, situé à l'extrémité de l'un des deux Spectromètres à Haute Résolution du Hall A. Le rapport des composantes transverse et longitudinale de la polarisation du proton de recul est proportionnel au rapport des facteurs de forme. Les événements élastiques étaient identifiés en détectant l'électron diffusé dans un calorimètre en verre au plomb de grande acceptance. Le résultat principal de cette expérience est la décroissance linéaire du rapport des facteurs de forme quand Q2 augmente, correspondant à des distributions spatiales différentes de la charge électrique et de la magnétisation. De nombreux calculs théoriques montrent que des effets relativistes, comme le mélange des états de spin dûs à des transformations de Lorentz, doivent être pris en compte pour expliquer les résultats observés dans cette région cinématique critique.