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Neste trabalho estudamos a estrutura do nucleon para grande x de Bjorken e pequeno Q2. Nesta região é preciso considerar correções nas funções de estrutura, de origem cinemática e dinâmica. Nos concentramos nas correções de origem cinemática, para as funções de estrutura não polarizadas, que surgem devido a massa do nucleon (mp) ser finita, essa correção é comumente chamada de Correções da Massa do Alvo (TMC). Revisamos a abordagem tradicionalmente utilizada e fizemos uma análise do problema inerente que se tem ao utilizar este tratamento (inclusão de regiões não físicas x > 1), verificando a existência de uma inconsistência nesse método. Nossa solução para evitarmos este problema foi realizar uma expansão nas funções de estrutura com TMC ordem por ordem em m2 p=Q2, estudando numericamente a convergência da serie obtida. Desta forma evitamos o problema da abordagem tradicional. / In this work we study the nucleon structure for large Bjorken x and low Q2. In such region is necessary to consider corrections on the structure functions, with by using kinematics and dynamics origins. We focus our study in the corrections of kinematic origin, for non-polarized structure functions, which cames from the nite nucleon mass (mp) and it is generally known by Target Mass Corrections (TMC). We review the traditional approach and perform an analysis of the inherent problem that has been in this treatment (inclusion of non-physical regions x > 1), which provides the inconsistency of this method. Our solution to avoid this problem was to perform an expansion order by order in m2 p=Q2 on the structure functions with TMC and perform the numerical study of the convergence of the series obtained. By this way we avoid the problem of the traditional approach.

Neste trabalho estudamos a estrutura do nucleon para grande x de Bjorken e pequeno Q2. Nesta região é preciso considerar correções nas funções de estrutura, de origem cinemática e dinâmica. Nos concentramos nas correções de origem cinemática, para as funções de estrutura não polarizadas, que surgem devido a massa do nucleon (mp) ser finita, essa correção é comumente chamada de Correções da Massa do Alvo (TMC). Revisamos a abordagem tradicionalmente utilizada e fizemos uma análise do problema inerente que se tem ao utilizar este tratamento (inclusão de regiões não físicas x > 1), verificando a existência de uma inconsistência nesse método. Nossa solução para evitarmos este problema foi realizar uma expansão nas funções de estrutura com TMC ordem por ordem em m2 p=Q2, estudando numericamente a convergência da serie obtida. Desta forma evitamos o problema da abordagem tradicional. / In this work we study the nucleon structure for large Bjorken x and low Q2. In such region is necessary to consider corrections on the structure functions, with by using kinematics and dynamics origins. We focus our study in the corrections of kinematic origin, for non-polarized structure functions, which cames from the nite nucleon mass (mp) and it is generally known by Target Mass Corrections (TMC). We review the traditional approach and perform an analysis of the inherent problem that has been in this treatment (inclusion of non-physical regions x > 1), which provides the inconsistency of this method. Our solution to avoid this problem was to perform an expansion order by order in m2 p=Q2 on the structure functions with TMC and perform the numerical study of the convergence of the series obtained. By this way we avoid the problem of the traditional approach.

No description available.

The resonance spectrum of the nucleon gives direct information on the dynamics and interactions of its constituents. This offers an important challenge to the theoretical models of nucleon structure, including the emerging Lattice QCD predictions, conformal field theories and more phenomenological, QCD-based approaches. Although the various models predict different features for the excitation spectra, the experimental information is currently of too poor quality to differentiate between these models. Pion photoproduction from the nucleon is a powerful probe of the spectrum as most resonances are expected to couple to the pion decay channel. However, cross-sections alone are not sensitive enough to allow identification of the underlying excitation spectrum, as the resonances have energy widths larger than their separations. A major world effort is underway to additionally measure polarisation observables in the production process. For a model-independent analysis a “complete” set of single- and doublepolarisation observables needs to be measured in experiments involving polarised beams, targets and a means of determining recoil nucleon polarisation. In particular, the beam asymmetry is a critical observable for the constraint of partial wave analyses (PWA) used to extract the nucleon excitation spectrum from the data. Almost all of the available world data on the beam asymmetry has been taken on the proton, with the neutron dataset sparse, containing only three experiments at fixed angles and in a limited photon energy range. The lack of extensive data on the neutron is a major deficiency, as different resonances have very different electromagnetic couplings to the proton and neutron. As a result, the data from the two targets will have very different relative contributions from, and sensitivities to, the spectrum of nucleon resonances. Moreover, neutron data is essential for the separation of the isoscalar and isovector components of the reaction amplitudes. This thesis presents a very high statistics measurement of the photon beam asymmetry on the neutron with close-to-complete angular coverage and a wide range of invariant mass (1610 – 2320 MeV) extending over the third resonance region, where the excitation spectrum is particularly ill defined. The experiment was conducted at the Thomas Jefferson National Accelerator Facility (JLab) using a tagged, linearly polarised photon beam, a liquid deuterium target and the CEBAF Large Acceptance Spectrometer (CLAS). The quality and quantity of the data has allowed an invariantmass resolution of 10 MeV and an angular resolution of 0.1 in the cosine of the centre-of-mass pion production angle, θ. Good agreement is evident in the regions where there is kinematic overlap with sparse previous data. Comparison of the new data is made with the two main partial wave analyses, SAID andMAID. Significant discrepancy is observed at backward θ with SAID (across most of the energy range) and MAID (up to ∼ 1750 MeV) and also below ∼ 35◦ in θ with both analyses. This extensive new dataset will help significantly to constrain partial wave analyses and will be a crucial part of the current world effort to use meson photoproduction to tackle long-standing uncertainties in the fundamental excitation spectrum of the nucleon. As a first step towards this the refitting of the SAID partial wave analysis incorporating the new data was carried out and shows very significant changes in the properties of the magnetic P11, P13, D13, D35, F15, G17 and G19 partial waves.

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.

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.

Jointly-supervised doctoral thesis Title: Nucleon spin structure studies in Drell-Yan process at COMPASS Author: Jan Matoušek Department I: Department of Low Temperature Physics, Faculty of Mathem- atics and Physics, Charles University Department II: Department of Physics, University of Trieste Supervisor I: prof. Miroslav Finger (Department I) Supervisor II: prof. Anna Martin (Department II) Abstract: The nucleon structure is presently described by Transverse Momentum Depend- ent (TMD) Parton Distribution Functions (PDFs), which generalise the collinear PDFs, adding partonic spin and transverse momentum degrees of freedom. The recent HERMES and COMPASS data on hadron production in deep inelastic scattering (SIDIS) of leptons off transversely polarised nucleons have provided a decisive validation of this framework. Nevertheless, the TMD PDFs should be studied in complementary reactions, like pp hard scattering and Drell-Yan pro- cesses. In particular the Sivers TMD PDF, which encodes the correlation between the nucleon transverse spin and quark transverse momentum and appears in the Sivers Transverse Spin Asymmetry (TSA), is expected to have opposite sign in Drell-Yan and SIDIS. In 2015 COMPASS measured for the first time the Drell- Yan process on a transversely polarised target π− p↑ → µ− µ+ X to test...

Quantum Chromodynamics (QCD) is generally assumed to be the fundamental theory underlying nuclear physics. In recent years there is progress towards investigating the nucleon structure from first principles of QCD. Although this structure is best revealed in Deep Inelastic Scattering, a consistent analysis has to be performed in a fully non-perturbative scheme. The only known method for this purpose are lattice simulations. We first sketch the ideas of Monte Carlo simulations in lattice gauge theory. Then we comment in particular on the issues of chiral symmetry and operator mixing. Finally we present our results for the Bjorken variable of a single quark, and for the second Nachtmann moment of the nucleon structure functions.

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