Symmetry tests and more precisely parity violation experiments using the properties of the weak interaction give us unique insight into the internal hadronic structure of matter. The Gº experiment at Jefferson Laboratory used parity violating electron scattering to probe the strange quark contribution to the electromagnetic nucleon form factors, (GMs and GEs) as well as the axial contribution, (GAe). The data taken during the experiment provide further information on the axial transition form factor of the N - $\Delta$ transition, (GANΔ), as well as the scale of the low energy constant (dΔ) characterizing the parity violating γNΔ coupling. The analysis of backward angle Gº data taken with a liquid deuterium target to deduce the parity violating asymmetry for pion photoproduction on the Δ resonance, and the first experimental constraint on the value of dΔ, are reported in this thesis. The results showed that dΔ = (8.3 ± 25.3) gπ where the uncertainty is dominated by statistics, and that 75 percent of the theory range would be excluded by this measurement at 1 sigma.

abstract: This thesis deals with the first measurements done with a cold neutron beam at the Spallation Neutron Source at Oak Ridge National Laboratory. The experimental technique consisted of capturing polarized cold neutrons by nuclei to measure parity-violation in the angular distribution of the gamma rays following neutron capture. The measurements presented here for the nuclei Chlorine ( 35Cl) and Aluminum ( 27Al ) are part of a program with the ultimate goal of measuring the asymmetry in the angular distribution of gamma rays emitted in the capture of neutrons on protons, with a precision better than 10-8, in order to extract the weak hadronic coupling constant due to pion exchange interaction with isospin change equal with one ( hπ 1). Based on theoretical calculations asymmetry in the angular distribution of the gamma rays from neutron capture on protons has an estimated size of 5·10-8. This implies that the Al parity violation asymmetry and its uncertainty have to be known with a precision smaller than 4·10-8. The proton target is liquid Hydrogen (H2) contained in an Aluminum vessel. Results are presented for parity violation and parity-conserving asymmetries in Chlorine and Aluminum. The systematic and statistical uncertainties in the calculation of the parity-violating and parity-conserving asymmetries are discussed. / Dissertation/Thesis / Ph.D. Physics 2012

Weak nucleon nucleon couplings are largely unknown because of the involved theoretical and experimental challenges. Theoretically the topic is difficult due to the non-perturbative nature of the strong interaction, which makes calculations of the couplings challenging. Experimentally, the topic is difficult given that 1) the observables are determined by ratios between strong couplings and weak couplings which differ in size by seven orders of magnitude, and 2) theoretically clean and predictable measurements are almost always restricted to simple systems that do not allow for effects that enhance the size of the asymmetry. However parity violation (PV) can be used to separate out the weak part and thus studies of PV in hadronic systems could offer a unique probe of nucleon structure. The n-3He experiment at the Spallation Neutron Source was performed to measure the parity violating asymmetry of the recoil proton momentum kp with respect to the neutron spin in the reaction n + 3He ---> p + T + 764 keV. This asymmetry is sensitive to the isospin-conserving and isospin-changing (∆I = 0, 1, 2) parts of the Hadronic Weak Interaction (HWI), and is expected to be small (~10-7). The goal of this experiment was to determine this PV asymmetry with a statistical sensitivity of 2x10-8. We also measured the parity even nuclear asymmetry proportional to kp · σn x kn for the first time for verification of nuclear theory and for confirmation of the sensitivity of our experiment to the parity violating asymmetry.

Au cours de ce travail de doctorat, nous avons d'abord étudié un aspect fondamental de la chiralité au niveau moléculaire visant à observer des différences d'énergie entre deux énantiomères provenant d'effets de violation de la parité (PV). Nous avons en particulier examiné les complexes oxorhénium chiraux dont les deux énantiomères présentent théoriquement des énergies d'absorption infrarouge différentes. Leur propriétés chiroptiques, en particulier leur dichroïsme circulaire vibrationnel (VCD), ont été examinées. D'autres complexes métalliques chiraux comme des complexes de platine portant un carbone asymétrique fluoré ont été préparés. Par ailleurs, nous avons étudié la chiralité hélicoïdale provenant de la fusion en ortho de plusieurs cycles aromatiques. Ainsi, des hélicènes portant des fonctionnalités bi-pyridines ont été synthétisés et ont montré des propriétés photophysiques et chiroptiques intéressantes. La présence d'unité chélatantes de type N^N’ ou N-C nous a permis d'étudier l'influence de la coordination de divers métaux de transition (Re(I) et Pt(II)) sur les propriétés et de concevoir de nouveaux commutateurs chiroptiques acido-basiques. / In this PhD work, we first investigated a fundamental aspect of chirality at the molecular level aiming to determine the parity violation (PV) energy difference between two enantiomers. We focused on chiral oxorhenium complexes for which the two corresponding enantiomers show theoretically different infrared absorption energies. Their chiroptical properties and especially their vibrational circular dichroism (VCD) were examined. Other chiral metal complexes such as platinum complexes bearing an asymmetric fluorinated carbon have also been prepared. Furthermore, we have investigated the helical chirality derived from the skew shape of ortho-fused aromatic ring. Indeed, helicenes bearing 2,2’-bipyridine functionalities were synthesized and they showed interesting photophysical and chiroptical properties. The presence of N^N’ or N-C chelating moieties enabled us to study the coordination effect of different transition metals (Re(I) and Pt(II)) on their properties and to conceive new acid-base triggered chiroptical switches.

The Qweak experiment has taken data to make a 2.5 percent measurement of parity violating elastic ep asymmetry in the four momentum transfer region of 0.0250 (GeV/c)2. This asymmetry is proportional to the weak charge of the proton, which is related to the weak mixing angle, sin2(thetaW). The final Qweak measurement will provide the most precise measurement of the weak mixing angle below the Z° pole to test the Standard Model prediction. A description of the experimental apparatus is provided in this dissertation. The experiment was carried out using a longitudinally polarized electron beam of up to 180 microampere on a 34.5 cm long unpolarized liquid hydrogen target. The Qweak target is not only the world’s highest cryogenic target ever built for a parity experiment but also is the least noisy target. This dissertation provides a detailed description of this target and presents a thorough analysis of the target performance. Statistical analysis of Run 1 data, collected between Feb - May 2011, is done to extract a blinded parity violating asymmetry of size--299.7 +/- 13.4 (stat.) +/- 17.2 (syst.) +/- 68 (blinding) parts-per-billion. This resulted in a preliminary proton’s weak charge of value 0.0865 +/- 0.0085, a 9% measurement. Based on this blinded asymmetry, the weak mixing angle was determined to be sin2(thetaW) = 0.23429 +/- 0.00211.

<p dir="ltr">Parity non-conversation experiments provide a method to explore the weak interaction. Precision measurements of the weak interaction will lead to more limitations on beyond the standard model theories. Our lab will use a two-color coherent control to help us to extract the small amplitude of the weak interaction between the nucleons of the cesium nucleus. In this dissertation, I will discuss how our lab is investigating the anapole moment in cesium using rf and laser fields, along with future steps to finish the measurement.</p>

The Qweak experiment has precisely determined the weak charge of the proton Qp w by measuring the parity-violating asymmetry in elastic electron-proton scattering at a low momentum transfer of Q2 = 0.0249 (GeV/c)2 . Qpw has a definite prediction in the Standard Model, and a value of sin2 θW can be extracted from it for comparison with other neutral current observables. Qweak measured the weak charge of the proton to be Qpw(P V ES) = 0.0719 ± 0.0045, which is consistent with the Standard Model value of Qp w(SM) = 0.0708 ± 0.0003. Qweak ran at the Thomas Jefferson National Accelerator Facility for two and a half years and was installed in experimental Hall C. A 180µA beam of longitudinally polarized electrons at 1.16 GeV scattered off a liquid hydrogen target of unpolarized protons. The electrons were collimated to an acceptance of 5.8◦ to 11.6◦ and then passed through a magnetic spectrometer and onto quartz Čerenkov detector bars. A detailed description of the theory and motivation behind the Qweak experiment is given. An overview of the Qweak apparatus and an in-depth discussion of the luminosity monitor performance is presented. A general overview of the Qweak analysis is also presented, with a focus on the beamline background correction, the nonlinearity measurement, and the simulation to constrain error for a rescattering effect. Also detailed here is the final, unblinded Qweak result, which determined Qpw to 6.2% and provided the highest precision measurement of sin2θW at low energy. / PHD / Q_weak is a precision-frontier accelerator driven experiment that took place at Thomas Jefferson National Accelerator Facility. Precision-frontier exists alongside the better known energy-frontier (which includes well known labs like the Large Hadron Collider) and refers to experiments which precisely measure values which are predicted by the latest theory. Deviations in these measurements help rule out theories and are used by energy-frontier experiments to know where to look for new physics. The Q_weak experiment measured the weak charge of the proton, which can be though of as the weak analog to electric charge. This value has never been measured before, and, since it is predicted to be small by current theory, is a good place to look for new physics. The value measured by this experiment indicates good agreement with the current theory. Even though there is good agreement with theory, Q_weak is an important result which will help define future physics models. In this thesis is an overview of the theoretical motivation of Q_weak, a general overview of the experimental design, in-depth discussion of the background detectors, general overview of the analysis with detailed descriptions of the several important corrections.

Weak interactions in an atomic system by external electromagnetic fields or nucleon-nucleon interaction cause perturbations in the wave-function and energy levels of electrons, which allow for transitions that are otherwise forbidden. Of particular interest are magnetic dipole (M1) transitions, Stark-induced transitions, and parity non-conserving (PNC) transitions. The PNC interaction in the hyperfine ground states is dominantly due to the anapole moment of the nucleus and there has been up-to-date only one such measurement carried out in any system; the Boulder group's ground-breaking measurement of the anapole moment in atomic cesium in 1997. Their result derived from two different hyperfine transitions, however, did not agree with the meson-coupling model from high energy physics experiments. Therefore, it is important to revisit the anapole moment through another method to cross-check the Boulder group's measurement. Our goal is to excite the nuclear-spin-dependent (NSD) PNC ground hyperfine transitions in cesium via radio-frequency (rf) and Raman excitation to directly determine the anapole moment. I present our progress toward measurement of the NSD transition in an atomic Cs beam geometry. We have developed a broadband rf cavity resonator to strongly suppress the magnetic dipole (M1) transition while enhancing the forbidden PNC electric dipole (E1) transition. We employed an injection locking scheme to generate a pair of phase-coherent Raman lasers far detuned from the cesium D2 line (852 nm) with a 9.2 GHz frequency difference. I report various measurement data from atomic signal via rf and Raman excitation. In the next generation of measurements, we will carry out interference experiments between rf and Raman transitions by varying the phase relations of the rf and Raman lasers fields. Finally, based on the measurements, I discuss a novel robust measurement technique involving interference of the Raman, M1 and E_PNC contributions.<br>

The Q-weak experiment at Thomas Jefferson National Accelerator Facility (USA) will make a precision determination of the proton weak charge with approximately 4% combined statistical and systematic uncertainties via a measurement of the parity violating asymmetry in elastic electron-proton scattering at very low momentum transfer and forward angle. This will allow an extraction of the weak mixing angle at Q^2=0.026 (GeV/c)^2 to approximately 0.3%. The weak mixing angle is a fundamental parameter in the Standard Model of electroweak interactions. At the proposed accuracy, a measured deviation of this parameter from the predicted value would indicate new physics beyond what is currently described in the Standard Model. Without deviation from the predicted value, this measurement would place stringent limits on possible extensions to the Standard Model and constitute the most precise measurement of the proton's weak charge to date. The key experimental apparatus include a liquid hydrogen target, a toroidal magnetic spectrometer and a set of eight Cerenkov detectors. The Cerenkov detectors form the main detector system for the Q-weak experiment and are used to measure the parity violating asymmetry during the primary Q-weak production runs. The Cerenkov detectors form the main subject of this thesis. Following a brief introduction to the experiment, the design, development, construction, installation, and testing of this detector system will be discussed in detail. This is followed by a detailed discussion of detector diagnostic data analysis and the corresponding detector performance. The experiment has been successfully constructed and commissioned, and is currently taking data. The thesis will conclude with a discussion of the preliminary analysis of a small portion of the liquid hydrogen data.

The goal of the Q-weak experiment is to make a measurement of the proton's weak charge ($Q^p_W = 1-4\sin^2\theta_W$) to an accuracy of ~4%. This would represent a ~0.3% determination of the weak mixing angle ($\sin^2\theta_W$) at low energy. The measurement may be used for a precision test of the Standard Model (SM) prediction on the running of $\sin^2\theta_W$ with energy scale. The Q-weak experiment operates at Thomas Jefferson National Accelerator Facility (Jefferson Lab). The experiment determines the proton's weak charge by measuring the parity violating asymmetry in elastic electron-proton scattering at low momentum transfer $Q^2 = 0.026 (GeV/c)^2$ and forward angles (~8 degree). The anticipated size of the asymmetry, based on the SM, is about 230 parts per billion (ppb). With the proposed accuracy, the experiment may probe new physics beyond Standard Model at the TeV scale. This thesis focuses on my contributions to the experiment, including track reconstruction for momentum transfer determination of the scattering process, and the focal plane scanner, a detector I designed and built to measure the flux profile of scattered electrons on the focal plane of the Q-weak spectrometer to assist in the extrapolation of low beam current tracking results to high beam current. Preliminary results from the commissioning and the first run period of the Q-weak experiment are reported and discussed.