360 research outputs found

    Studying neutron structure at Jefferson Lab through electron scattering off the deuteron, using CLAS12 and the Central Neutron Detector

    Get PDF
    Generalised Parton Distributions (GPDs) offer a way of imaging nucleons through 3D tomography. They can be accessed experimentally in processes such as Deeply Virtual Compton Scattering (DVCS) and Deeply Virtual Meson Production (DVMP), where a high energy electron scatters from a quark inside a nucleon and a high energy photon or meson is produced as a result. Jefferson Lab has recently completed its energy upgrade and Hall B houses the new, large-acceptance CLAS12 detector array optimised for measurements of DVCS and DVMP in the newly accessible kinematic regime. Measurements on the proton and neutron are complementary and both are necessary to facilitate access to the full set of GPDs and enable their flavour separation. Neutron DVCS and DVMP are possible with the use of a deuteron target ‚Äď the first CLAS12 experiment with which has started taking data this year. To enable exclusive reconstruction of DVCS and neutral-meson DVMP, a dedicated detector for recoiling neutrons ‚Äď the Central Neutron Detector (CND) ‚Äď was integrated into CLAS12. We present the first CLAS12 deuteron-target experiment, with a focus on the performance of the CND

    Timelike Compton Scattering with CLAS12 at Jefferson Lab

    No full text
    International audienceGeneralized Parton Distributions (GPDs) describe the correlations between the longitudinal momentum and the transverse position of the partons inside the nucleon. At leading order, four quark helicity conserving GPDs per quark flavor describe the nucleon structure. For their direct relation to the angular momentum contribution of partons to the spin of the nucleon and to the pressure distribution in the nucleon, GPDs have been at the center of many experimental programs. GPDs have been studied mainly using Deeply Virtual Compton Scattering (DVCS). Here we highlight the measurement of the time-reversal conjugate process of DVCS, Timelike Compton Scattering (TCS), using data taken by CLAS12. The experimental measurement of the TCS angular asymmetry will provide new information on the real part of GPDs.This proceeding assesses the current status of the TCS analysis andpresents preliminary results based on CLAS12 data

    √Čtude de la structure du nucl√©on avec CLAS12 √† Jefferson Lab : diffusion Compton de genre temps et le d√©tecteur central de neutron

    No full text
    The nucleons, protons and neutrons, are the main constituents of visible matter in the universe. Their structure, three valence quarks surrounded by a cloud of sea quarks and gluons, is described by the theory of quantum chromodynamics (QCD). However, the properties of QCD cannot be computed perturbatively at energies comparable to the nucleon mass. Hence, structure functions were adopted to model the inner structure of nucleons. The Generalized Partons Distributions (GPD), were introduced in the 90's to provide a description of the nucleon in terms of both the transverse position and the longitudinal momentum of its quarks and gluons. These functions contain a large amount of information and are closely related to the nucleon spin and mechanical architecture. Their experimental measurement is a key element for the understanding of fundamental properties of matter. The main focus of this thesis is to provide new data for GPD studies, with a first-time measurement of Timelike Compton Scattering at Jefferson Lab with the CLAS12 detector.This thesis is divided in three parts. The first part presents the theory of GPDs, current models and their link with physical processes that can be experimentally measured. The relation between GPDs and experimental observables is discussed, and the concept of Compton Form Factors (CFF) is introduced. In addition, the link between the spin and the mechanical properties of the nucleon, as well as the possibility of performing a 3D imaging of the nucleon with GPDs is highlighted.The second part of the manuscript is dedicated to the work I performed on the Central Neutron Detector (CND). The CND is a plastic scintillator barrel built to increase the neutron detection capabilities of CLAS12 in its central region. After presenting the physical motivations for the building of this detector, its hardware implementation, calibration, reconstructions and simulation aspects are detailed. At the end of this part, the CND performances using real data are measured and compared to its design specifications.Finally, the third part covers the experimental measurement of the photo-production of a lepton pair off the proton, the Timelike Compton Scattering process (TCS). This reaction offers an insight on some properties of GPDs which are not well constrained by the reactions measured so far, in particular the real part of CFFs. The experimental setup used for data taking is described. The subsequent data processing and analysis is explained, and results for three different observables are shown.Les protons et les neutrons sont les constituants principaux de la matière visible de l'univers. Leur structure, constituée de trois quarks de valence baignés dans un nuage de quarks de la mer et de gluons, est régis par la théorie de la chomodynamique quantique (QCD). Cependant, aux énergies comparables à la masse du nucléon, les propriétés de QCD ne peuvent pas être calculées par des méthodes perturbatives. Des fonctions de structure doivent être utilisées pour pouvoir décrire les nucléons. Les distributions de parton généralisées (GPD) sont un ensemble de fonctions de structure, introduites dans le courant des années 90. Elles modélisent la position transverse et le moment longitudinal des quarks et des gluons, les constituants élémentaires des nucléons. La phénoménologie de ces fonctions est très singulière. Elles sont en particulier étroitement liées à la structure de spin et aux propriétés mécaniques des nucléons. La mesure des GPDs est donc un élément déterminant dans la compréhension de la structure élémentaire de la matière. Le but de cette thèse est de fournir de nouvelle donnée pour l'étude des GPDs, en particulier avec la mesure inédite de la diffusion Compton de genre temps avec le détecteur CLAS12 à Jefferson Lab.Cette thèse est divisée en trois parties. Dans la première partie, la théorie des GPDs et leur modélisation est présentée. Le lien entre ces fonctions et des réactions mesurables est aussi établi, le concept de facteurs de forme Compton (CFF) est notamment introduit. De plus, les relations entre les GPDs et les différentes contributions des quarks au spin du nucléon, la correspondance entre la partie réelle des CFFs et les propriétés mécaniques du nucléons et enfin la possibilité de réaliser une image 3D du nucléon sont mises en lumière.La seconde partie du manuscrit est consacrée au travail que j'ai réalisé sur le détecteur central de neutrons de CLAS12 (CND). Le CND est un détecteur cylindrique formé par des scintillateurs en plastique. Il a été conçu pour augmenter les capacités de détection des neutrons dans la partie centrale de CLAS12. Après avoir présenté les motivations physiques de la construction du CND, le design, la procédure de calibration, de reconstruction et de simulation sont expliqués. Enfin, les performances du CND, mesurées à partir de données réelles sont comparées aux spécifications du design initial.Enfin, dans la dernière partie, la mesure expérimentale de la réaction de photo-production d'une pair de lepton sur le proton, ou diffusion Compton de genre temps (TCS) est exposée. Cette réaction permet d'accéder à des propriétés des GPDs encore mal connues, comme la partie réelle des CFFs. Le dispositif expérimental utilisé pour cette expérience est d'abord présenté. L'analyse de données est ensuite détaillée et les résultats obtenus sont présentés et discutés

    Deeply virtual Compton scattering on the neutron with positron beam

    No full text
    International audienceMeasuring DVCS on a neutron target is a necessary step to deepen our understanding of the structure of the nucleon in terms of Generalized Parton Distributions (GPDs). The combination of DVCS observables on neutron and proton targets allows to perform a flavor decomposition of the Compton Form Factors (CFFs), which are related to integrals of GPDs. Moreover, neutron-DVCS plays a complementary role to DVCS on a transversely polarized proton target in the determination of the CFF of the GPD E, the least known and constrained GPD that enters Ji‚Äôs angular momentum sum rule. A measurement of the beam-charge asymmetry (BCA) in the e¬Īd‚Üíe¬Īnő≥(p)e^{\pm } d\rightarrow e^{\pm }n\gamma (p) reaction can significantly impact the experimental determination of the real CFFs of the E and, to a lesser extent, H~\widetilde{H} CFFs

    Infection des bovins par Neospora caninum : Deux années d'observations dans l'Ouest de la France

    No full text
    National audienceSeveral studies on the epidemiology of the protozoa Neospora caninum in cattle in Western France were performed using a serological analysis (ELISA) and a biomolecular method (PCR). In the Calvados region, 26 percent of abortions were found to be N. caninum serological positive. From 3 to 48 percent of cattle of more than 7 months of age were found to be seropositive in a sample of 13 farms in the West. Study of the serological status of dogs on these farms did not determine their role in the epidemiology of the disease. The first evidence of the parasite in an aborted foetus in France was realised by PCR testin

    Software Tools for Hybrid Quality Control for the CMS Phase-2 Outer Tracker Upgrade

    No full text
    ABSTRACT: Fifty thousand hybrid circuits of five different types will be manufactured for the Phase-2 Upgrade of the CMS Outer Tracker. These circuits must undergo a strict quality control process, composed of functional testing and visual inspection, before they can be assembled into modules. The hybrids will be functionally tested first at the manufacturing site. Afterwards, they will be visually inspected and functionally tested again at CERN or at collaborating institutes. Results from these processes will be stored in the CMS production database. This paper presents the software tools developed to carry out these tasks

    Center of Mass Motion of Short-Range Correlated Nucleon Pairs studied via the A (e,e\u27pp) Reaction

    No full text
    © 2018 American Physical Society. Short-range correlated (SRC) nucleon pairs are a vital part of the nucleus, accounting for almost all nucleons with momentum greater than the Fermi momentum (kF). A fundamental characteristic of SRC pairs is having large relative momenta as compared to kF, and smaller center of mass (c.m.) which indicates a small separation distance between the nucleons in the pair. Determining the c.m. momentum distribution of SRC pairs is essential for understanding their formation process. We report here on the extraction of the c.m. motion of proton-proton (pp) SRC pairs in carbon and, for the first time in heavier and ansymetric nuclei: aluminum, iron, and lead, from measurements of the A(e,e\u27pp) reaction. We find that the pair c.m. motion for these nuclei can be described by a three-dimensional Gaussian with a narrow width ranging from 140 to 170 MeV/c, approximately consistent with the sum of two mean-field nucleon momenta. Comparison with calculations appears to show that the SRC pairs are formed from mean-field nucleons in specific quantum states
    • ‚Ķ
    corecore