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Optimization of Spherical Proportional Counter Backgrounds and Response for Low Mass Dark Matter Search

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Optimization of Spherical Proportional Counter Backgrounds and Response for Low Mass Dark Matter Search Optimization of spherical proportional counter backgrounds and response for low mass dark matter search by Alexis Brossard A thesis submitted to the Physics, engineering physics and astronomy department in conformity with the requirements for the degree of Ph.D. Queen's University Kingston, Ontario, Canada Universit´eParis-Saclay Saint-Aubin, France March 2020 Copyright c Alexis Brossard, 2020 To my grandparents. i Abstract The NEWS-G collaboration uses Spherical Proportional Counters to search for Weakly Interacting Massive Particles (WIMP). The first detector, SEDINE, developed for this goal is a 60 cm diameter sphere installed at the Laboratoire Souterrain de Modane in France. In 2015, the collaboration took a run with neon as the target mate- rial for an exposure of 9.7 kg · days. This run allowed new limits to be set on the spin-independent WIMP-nucleon cross-sections with 90% confidence upper limit of −37 2 2 σSI < 4:4 × 10 cm for a 0:5 GeV=c WIMP. The study of the background events observed during this run shows that it is dominated by the presence of the 210Pb decay chain in the different materials composing the detector, its shielding, and on the inner surface of the sphere. The experience acquired in running the detector SEDINE and the analysis of its data allowed procedures to be developed to mitigate radioactive contaminations and the resulting background events in the experiment. For the next detector a more stringent selection of radio-pure materials surrounding the detector is carried out. The radioactive background affecting the experimental set up is then estimated via the measurements of material radioactive contaminations and the simulation of the different components. The development of new sensors al- lows a better homogeneity of the detector response and improved data acquisition in a larger detector. The new detector is a 140 cm diameter copper sphere, to be ii installed at SNOLAB in Canada in 2020. Its performances will be also enhanced by the development of new methods of signal characterisation and energy calibration. iii R´esum´e Les compteurs proportionnels sph´eriques sont utilis´espour la recherche de mati`ere noire par la collaboration NEWS-G depuis 2013 avec le d´etecteurSEDINE install´e au Laboratoire Souterrain de Modane. Ce premier d´etecteura permis d'´etablirune nouvelle limite de la section efficace d'interaction WIMP-nucl´eonpour des WIMPs de masse inf´erieur`a0.6 GeV=c2. Depuis, la collaboration travaille `ala mise au point d'un nouveau d´etecteur.Cette th`esese concentre sur deux aspects am´elior´espour le second d´etecteur.L'´etudedu bruit de fond observ´epar SEDINE a permis de conclure que celui-ci est domin´epar le pr´esencede la chaine de d´esint´egrationdu 210Pb sur les surfaces et dans les mat´eriauxcomposant le d´etecteuret son blindage. Ceci a permis de s´electionnerdes mat´eriaux et des proc´ed´esde fabrication permettant de r´eduirele bruit de fond du prochain d´etecteur.Le second d´eveloppement concerne l'anode du d´etecteur.Plac´eeau centre de la sph`ere,l'anode assure la formation du signal. Les derniers d´eveloppements montrent la capacit´ede ce composant `aassurer la d´etection d'´electronsuniques en ´etant stable et avec une bonne r´esolution. iv Acknowledgments I would like first to thanks my supervisor Gilles Gerbier for bringing me to Canada to live this great adventure. Acquiring knowledge from all your wise advice and discussions is a great honour. Thanks for your trust and your kindness. Working with you during these years elevated me both in term of my scientific knowledge and as a human being. I greatly thanks my co-supervisor Ioannis Giomataris for welcoming me on France. Working with you was very rewarding and I am glad to have acquired some of your invaluable knowledge of gas detectors. I want to thank my fellows student at Queen's University Marie Vidal, George Savvidis, and a special mention for Paco Vazquez de Sola Fernandez who shared the past five years with me. You are a great co-worker, I wish you all best in your future post-doc, I will miss you and your invaluable math skills. Many thanks to the most brilliant student Daniel Durnford, the P.I. of the next dark matter experiment which will discover dark matter if NEWS-G has not already done so. All my thanks to the great people who paved my way during this adventure. Thanks to Sabine Roth and Alvine Kamaha. Many thanks to Ali Dastgheibi-Fard, for all your advice and the knowledge acquired and your welcome at the LSM. Thanks a lot to Jean-Fran¸coisCaron who reviewed this manuscript, thanks too your good eyes and your precisions. Your help was extremely precious. An enormous thanks to v Quentin Arnaud, the best of all. Never has having a beer and a cigarette been so instructive. I wish you all best for you great coming career. Thanks to the best lab chief Philippe Gros. Thank you for your time, your kindness, for all you taught to me. All the time we have spend together was extremely valuable. I want to address a warm thanks to all members of the NEWS-G collaboration. Many thanks to Julie McDonald for her kindness and all the time she gave me. Thanks to Ioannis Katisoulas and Michel Gros for welcoming me two times in Saclay. Thanks to Michel Zampaolo for welcoming me in Modane and Thierry Zampieri for the hiking with me in the beautiful `Vall´eede la Maurienne`. Thanks a lot to the members in Grenoble, and particularity to Jean-Fran¸coisMuraz for his kindness and patience allowing me for understand all the details of his amazing Comimac. A great thanks to the members from Royal Military College of Canada for the 37Ar supply, without which the sensor development at Queen's would not have been possible. Many thanks to Eric Hoppe for the invaluable skill of electroplating. Last but not least, a great thanks to Maurice Chapellier. Working with you is a real pleasure. My knowledge about radioactivity and electronics would not be the same without you. I want to thanks all the roommates I met over these years. You are awesome dudes and have been a familly. Thanks to Rango, Florie, August, Ginnie, Eydis, Ethan, Kyle, Joabe, Ivan and all that I may forget. Also a great thanks to Chanpreet Amole who is the best officemate, see you soon under the sun. Merci beaucoup `ama famille, mes parents Catherine et Charles qui m'ont toujours soutenu et ´epaull´edepuis tout petit et durant toute mes ann´eesd'´etude.Si j'en suis l`aaujourd'hui c'est gr^ace`avous. Un ´enormemerci `amon fr`ereThibaut qui a ´et´e le meilleur compagnon de route depuis le ber¸ceau, sa femme No´emie et leurs enfants vi Zo´eet Louis. Je suis tr`esimpatient de rentrer vous retrouver en France. Et pour finir, un grand merci `ames meilleurs amis Alexis et Alexandra. Grandir avec vous durant toute ces ann´eesa ´et´ela plus incroyable des exp´eriences. Je vous dit `abient^otpour venir rencontrer votre petite qui arrive. vii Contents Abstract ii R´esum´e iv Acknowledgments v Contents viii List of Tables xii List of Figures xiii Chapter 1: Introduction 1 Chapter 2: Dark matter 4 2.1 Introduction . 4 2.2 Evidence for dark matter . 5 2.2.1 Velocity of galaxies in the Coma cluster . 5 2.2.2 Rotation curve of galaxies . 6 2.2.3 Galaxy cluster merging . 9 2.2.4 Cosmic microwave background anisotropy . 10 2.3 Dark matter candidates . 13 2.3.1 MOND . 13 2.3.2 MACHOS . 14 2.3.3 Non-baryonic dark matter . 14 2.4 Search for WIMPs . 17 2.4.1 Production . 17 2.4.2 Indirect detection . 18 2.4.3 Direct detection . 20 2.5 State of the art of WIMP direct detection . 35 2.6 Discussion . 38 viii Chapter 3: The spherical proportional counter 39 3.1 Interaction of particles with matter . 40 3.1.1 Charged particles . 41 3.1.2 Photons . 44 3.1.3 Neutrons . 50 3.1.4 Ionization yield . 52 3.2 Gaseous proportional counter . 55 3.2.1 Primary ionization . 57 3.2.2 Thermal diffusion of charged particles . 58 3.2.3 Drift and diffusion of ions in an electric field . 60 3.2.4 Drift and diffusion of electrons in an electric field . 62 3.2.5 Electron loss effect . 64 3.2.6 Charge multiplication . 67 3.2.7 Simulation of electron drift . 72 3.3 Specification of the SPC . 74 3.3.1 Detector description . 74 3.3.2 The ideal electric field . 75 3.3.3 Response of the detector, induced pulses . 77 3.3.4 Charge induced by electrons and ions . 81 3.3.5 Ballistic deficit . 82 3.3.6 Pulse treatment . 83 3.3.7 Gain of the detector . 84 3.3.8 Pulse shape discrimination . 85 3.3.9 Electronic noise . 86 3.4 Importance of the sensor and electric field corrector . 88 3.5 Discussion, SPC for dark matter search . 91 Chapter 4: Background of the SEDINE detector 92 4.1 Introduction . 92 4.2 The SEDINE detector . 93 4.3 First WIMP search run . 94 4.4 Assessing the O2 contamination and field anisotropy . 95 4.4.1 O2 contamination in the gas . 96 4.4.2 Electric field anisotropy in the avalanche region . 100 4.5 22Na calibration, physical events selection . 107 4.6 Background of the physics run . 109 4.6.1 Calibration .
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