Test of New Readout Electronics for the BONuS12 Experiment

For decades, electron-proton scattering experiments have been providing a large amount of data on the proton structure function. However, because of the instability of free neutrons, fewer experiments have been able to study the neutron structure function. The BONuS collaboration at Jefferson Laboratory addresses this challenge by scattering electrons off a deuterium target, using a RTPC capable of detecting the low-momentum spectator protons near the target. Events of electrons scattering on almost free neutrons are selected by constraining the spectator protons to very low momenta and very backward scattering angles. In 2005, BONuS successfully measured the neutron structure with scattering electrons of up to 5.3 GeV energy. An extension of this measurement has been approved using the newly upgraded 12 GeV electron beam and CLAS12 (CEBAF Large Acceptance Spectrometer). For this new set of measurements, a new RTPC detector using GEM trackers is being developed to allow measurements of spectator protons with momenta as low as 70 MeV/c. The new RTPC will use a new readout electronic system, which is also used by other trackers in CLAS12. This thesis will present the first tests of this electronics using a previously built RTPC of similar design

Photoproduction of K+K− meson pairs on the proton

The exclusive reaction γp→pK+K− was studied in the photon energy range 3.0–3.8  GeV and momentum transfer range 0.6<−t<1.3  GeV2. Data were collected with the CLAS detector at the Thomas Jefferson National Accelerator Facility. In this kinematic range the integrated luminosity was approximately 20  pb−1. The reaction was isolated by detecting the K+ and the proton in CLAS, and reconstructing the K− via the missing-mass technique. Moments of the dikaon decay angular distributions were extracted from the experimental data. Besides the dominant contribution of the ϕ meson in the P wave, evidence for S−P interference was found. The differential production cross sections dσ/dt for individual waves in the mass range of the ϕ resonance were extracted and compared to predictions of a Regge-inspired model. This is the first time the t-dependent cross section of the S-wave contribution to the elastic K+K− photoproduction has been measured

Servant Leadership, Trust, and the Organizational Commitment of Public Sector Employees in China

Servant leaders strive selflessly and altruistically to assist others before themselves, work to develop their followers to their greatest potential, and seek to benefit the wider community. This paper examines the trust-based mechanisms by which servant leadership influences organizational commitment in the Chinese public sector, using data from a survey of civil servants. Quantitative analysis shows that servant leadership strongly influences affective and normative commitment, while having no impact on continuance commitment. Furthermore, we find that affective trust rather than cognitive trust is the mechanism by which servant leadership induces higher levels of commitment. Our findings suggest that in a time of decreasing confidence levels in public leaders, servant leadership behavior may be used to reestablish trust and create legitimacy for the Chinese civil service

Étude de la structure du nucléon avec CLAS à Jefferson Lab : Diffusion Compton Profondément Virtuelle sur l'azote

One of the most important unresolved questions of quantum chromo-dynamic (QCD) is the formation of nuclei and the nature of the nucleon-nucleon interaction in term of fundamental degrees of freedom, i.e. quarks and gluons. In particular, the modification of the nucleon structure function in the nuclear medium (EMC effect) is still a mystery 30 years after its discovery. We propose to study this question using the Generalized Parton Distribution (GPD) framework. The GPDs are structure functions correlating the longitudinal momentum and transverse position of partons. The GPDs are accessible through exclusive reactions such as the Deeply Virtual Compton Scattering (DVCS). The study of DVCS on nuclei is a new way to study the interactions between quarks in the nuclear medium. DVCS on helium-4 was measured at Jefferson Lab (USA) using the CLAS detector and the 6 GeV polarized electron beam. This work extends our knowledge of nuclei by analyzing the incoherent DVCS process on nitrogen. We used the CLAS experiment data which successfully measured the DVCS process on polarized protons, using an ammonia (NH₃) polarized target. This work will detail the procedure used to subtract the proton background from the ammonia target in order to analyze the incoherent DVCS channel on nitrogen. Beam-spin asymmetries of the incoherent DVCS process on nitrogen will be presented et compared to the helium-4 results.L'une des plus importantes questions non résolues de la chromodynamique quantique (QCD) est la formation des noyaux et la nature de l'interaction nucléon-nucléon à partir de ses degrés de libertés fondamentaux : les quarks et les gluons. En particulier, la modification de la structure en quark des nucléons dans le milieu nucléaire (effet EMC) est toujours un mystère plus de 30 ans après sa découverte. Nous proposons d'étudier ce problème à l'aide du formalisme des distributions de partons généralisées (GPD). Les GPDs sont des fonctions de structure corrélant l'impulsion longitudinale et la position transversale des partons. Les GPDs sont accessibles via des réactions exclusives comme la diffusion Compton profondément virtuelle (DVCS). L'étude du DVCS dans les noyaux est une nouvelle façon d'étudier les interactions entre les quarks dans le milieu nucléaire. Le DVCS sur l'helium-4 a été mesuré au Jefferson Lab (aux États-Unis), utilisant le détecteur CLAS et un faisceau d'électrons polarisé à 6 GeV. Ce travail approfondit notre connaissance des noyaux en analysant la réaction DVCS incohérent sur l'azote. Les données utilisées sont celles de l’expérience CLAS qui ont mesuré avec succès le processus DVCS sur des protons polarisés et utilisant une cible polarise d'ammoniac (NH₃). Ce travail détaillera la procédure utilisée pour soustraire le background proton de la cible d'ammoniac afin d'analyser le canal DVCS incohérent sur l'azote. Les asymétries faisceau-spin du processus DVCS incohérent sur l'azote seront présentées et comparées aux résultats de l'helium-4

Development of a Compton telescope calorimeter module for MeV-range gamma-ray astronomy

International audienceGamma-ray astronomy in the MeV energy range shows a lack of sensitivity compared to other gamma-ray energy bands. Several space observatory projects are proposed to space agencies to fill this gap. The COMCUBE CubeSat project will focus on the measurement of the polarization of the prompt emission of gamma-ray bursts (GRBs) which can provide an understanding of the physics of ultra-relativistic jets. Furthermore, the linear polarization of distant gamma-ray sources could be a probe to study the fundamental physics related to the Lorentz invariance violation. A Compton telescope is particularly well-suited for that purpose. We develop an instrument including double-sided silicon strip detectors and scintillation crystals coupled to a pixelated photodetector. The incoming photon undergoes an inelastic scattering in one or several layers of a position-sensitive silicon strip detector before being absorbed in a position-sensitive calorimeter based on inorganic scintillators. The measurement of both positions and energy deposits enables the determination of the photon’s source direction. It also enables measurement of the linear polarization of the incident gamma-rays. In this contribution, we present the results of the extensive work we have carried out to develop the calorimeter and its integration into a Compton telescope prototype. We conclude by showing the first image and polarization measurements

Grey Tracks as Probes of Hadronization Dynamics

Energetic quarks liberated from hadrons in nuclear deep-inelastic scattering propagate through the nuclear medium, interacting with it via several processes. These include quark energy loss and nuclear interactions of forming hadrons. One manifestation of these interactions is the enhanced emission of low-energy charged particles, referred to as grey tracks. We use the theoretical components of the BeAGLE event generator to interpret grey track signatures of parton transport and hadron formation by comparing its predictions to E665 data. We extend the base version of BeAGLE by adding four different options for describing parton energy loss. The E665 data we used consists of multiplicity ratios for fixed-target scattering of 490 GeV muons on Xe normalized to deuterium as a function of the number of grey tracks. We compare multiplicity ratios for E665 grey tracks to the predictions of BeAGLE, varying the options and parameters to determine which physics phenomena can be identified by these data. We find that grey tracks are unaffected by modifications of the forward production. Thus their production must be dominated by interactions with hadrons in the backward region. This offers the advantage that selecting certain particles in the forward region is unlikely to bias a centrality selection. We see a strong correlation between the number of grey tracks and the in-medium path length. Our energy loss model does not reproduce the suppression observed in the projectile region. We see an underprediction of the proton production rate in backward kinematics, suggesting that a stronger source of interaction with the nuclear medium is needed for accurate modeling. These results lay an important foundation for future spectator tagging studies at both Jefferson Lab and at the Electron-Ion Collider, where neutron and proton grey track studies will be feasible down to very small momenta

The qq q -majority efficiency of positional rules

According to a given quota q, a candidate a is beaten by another candidate b if at least a proportion of q individuals prefer b to a. The q-Condorcet efficiency of a voting rule is the probability that the rule selects a q-Condorcet winner (q-CW), that is any candidate who is never beaten under the q-majority. Closed form representations are obtained for the q-Condorcet efficiency of positional rules (simple and sequential) in three-candidate elections. This efficiency is significantly greater for sequential rules than for simple positional rules

Adhesive bond testing between composite laminates by laser shockwave loading

"Assembling materials by adhesive bonding has several advantages compared to other joining methods such as the use of fasteners or welding. Fasteners require drilling holes in the parts to be joined and both fastening and welding require significant investment in machinery. For metals, welded joints also generally produce a mechanically weaker heat affected zone. Adhesive bonding also has significant advantages for polymer-matrix composites. Drilling through composites has the drawback of cutting load-bearing fibers with adverse effects of possible delamination and excessive tool wear. It may also be economically advantageous to bond several small parts to make a large structure instead of having it co-cured. However, for all materials, the use of adhesive bonding for loadbearing structures is impeded by the absence of reliable nondestructive methods that can guarantee the strength of the joint, and in particular are able to very reliably identify the presence of near zerostrength \u201ckissing bonds\u201d [1]. Kissing bonds are undetectable by conventional ultrasonic inspection since the return echo from the interface in the pulse-echo technique does not depend upon the bond strength and only requires mechanical contact between the adherends. This is also the case for the transmitted echo. Although there have been many attempts to develop other ultrasonic approaches, such as using waves that propagate essentially along the bond line, none of these approaches has succeeded in detecting a weak bond other than those that are weakened by defects such disbonds or porosity [1-3]. These defects can be detected by the well established ultrasonic inspection technique and in the case of porosity, also by x-ray radiography. Among possible causes of weak bonds are contamination of surfaces prior to bonding, inadequate surface preparation, degradation of the adhesive from improper storage, and inadequate mixing ratio for two-part adhesives. In all these cases, there can be good mechanical contact without defects, combined with poor mechanical strength, undetectable by established ultrasonic inspection techniques. Ultrasonic techniques only apply weak stresses to the bond line and such weak stresses cannot reveal characteristics that are only apparent by applying significant stresses, like in destructive tests. Therefore, a reliable technique to identify such weak bonds requires application of a strong tensile stress across the bond line. A convenient approach that has been previously studied for evaluating the dhesion of coatings to their substrate and fibers to their matrix uses a pulsed laser to generate a large amplitude wave (shockwave) that propagates throughout the material [4-9]. This wave, being initially in compression, is converted by reflection on the back surface of the sample into a strong tensile wave that can pry apart the sample and disbond the assembly. This approach has been more recently extended to proof testing of adhesive bonds between carbon-epoxy laminates [10,11]. To probe bond strength, higher and higher tensile stress loading is applied by increasing the laser pulse energy step by step. A \u201cgood\u201d joint will be unaffected under a given stress level whereas a weaker one will be damaged, allowing this method to evaluate the bond strength. The principle of the method is described next in more detail. We then describe how the ethod is implemented, the instrumentation that has been developed and the fabrication of weak bond test specimens. Finally we present some results and indicate erspectives and future developments.Peer reviewed: YesNRC publication: Ye