Detecting antihydrogen annihilations in ALPHA-g for measurement of gravitational free fall
department or school: Science, Faculty of
department or school: Physics and Astronomy, Department of
data provider: DSpace
degree campus: UBCV
creator: Smith, Gareth
issued: 2025-10-02T16:22:53Z
issued: 2025
related degree: Doctor of Philosophy - PhD
degree grantor: University of British Columbia
description: Antihydrogen, the bound state of an antiproton and a positron, is an ideal system for testing fundamental symmetries between matter and antimatter. The Antihydrogen Laser PHysics Apparatus (ALPHA) at CERN has a proven history of producing and trapping antihydrogen atoms, with many precision tests of charge-parity-time (CPT) symmetry. The new ALPHA-g apparatus extends this program to a test of gravity, directly probing the applicability of the weak equivalence principle (WEP) to an antimatter system for the first time. This dissertation presents the first ALPHA-g results, which confirm that Earth's gravity acts downwards on antimatter. The ratio between the gravitational acceleration of antihydrogen and hydrogen is estimated to be ḡ/g = 0.75 ± 0.13 (statistical and systematic) ± 0.16 (simulation). This measurement depends on accurately determining the annihilation positions of antihydrogen atoms released from the ALPHA-g magnetic trap, which is accomplished using a time projection chamber (TPC) detector. To reduce the substantial background due to cosmic ray, a time-of-flight barrel scintillator (BSC) detector was also implemented. The author's primary contributions include the commissioning of the BSC, including devising and implementing time-of-flight measurements, leading to a significantly reduced background rate. Additional contributions include improving the TPC tracking algorithms to reach the required annihilation position resolution. This dissertation begins with theoretical motivations for testing the WEP using antihydrogen, followed by an overview of the ALPHA apparatus and antihydrogen production. The TPC and BSC detectors are introduced, including the event reconstruction methods, with care to highlight the author's work. Finally, the gravity measurement methodology and results, as well as future perspectives, are discussed. This first direct test of gravity on antimatter rules out a large difference in the gravitational behaviour of antimatter and matte…
aggregated CHO: https://circle.library.ubc.ca/rest/handle/2429/92478
note: Detecting Antihydrogen Annihilations inALPHA-g for Measurement ofGravitational Free FallbyGareth SmithM.Sc., The University of British Columbia, 2021B.Sc., Carleton University, 2019A DISSERTATION SUBMITTED IN PARTIAL FULFILLMENT OFTHE REQUIREMENTS FOR THE DEGREE OFDOCTOR OF PHILOSOPHYinThe Faculty of Graduate and Postdoctoral Studies(Physics)THE UNIVERSITY OF BRITISH COLUMBIA(Vancouver)September 2025© Gareth Smith 2025The following individuals certify that they have read, and recommend to theFaculty of Graduate and Postdoctoral Studies for acceptance, the disserta-tion entitled:Detecting Antihydrogen Annihilations in ALPHA-g for Measure-ment of Gravitational Free Fallsubmitted by Gareth Smith in partial fulfillment of the requirements forthe degree of Doctor of Philosophy in Physics.Examining Committee:Dr. Makoto Fujiwara, Senior Research Scientist, Particle Physics Depart-ment, TRIUMFCo-SupervisorDr. Takamasa Momose, Professor, Department of Chemistry, University ofBritish ColumbiaCo-SupervisorDr. Michael Hasinoff, Professor, Department of Physics and Astronomy,University of British ColumbiaSupervisory Committee MemberDr. Christopher Hearty, Professor, Department of Physics and Astronomy,University of British ColumbiaUniversity ExaminerDr. Andrew MacFarlane, Professor, Department of Chemistry, University ofBritish ColumbiaUniversity ExaminerDr. Michel Lefebvre, Professor, Department of Physics and Astronomy, Uni-versity of VictoriaExternal ExaminerAdditional Supervisory Committee Members:Dr. Mark Halpern, Professor, Department of Physics and Astronomy, Uni-versity of British ColumbiaSupervisory Committee MemberiiAbstractAntihydrogen, the bound state of an antiproton and a positron, is an idealsystem for testing fundamental symmetries between matter and antimat-ter. The Antihydrogen Laser PHysics Apparatus (ALPHA) at CERN has aproven history of producing and trapping antihydrogen atoms, with manyprecision tests of charge-parity-time (CPT) symmetry. The new ALPHA-gap…
has type: Thesis/Dissertation
date issued: 2025-11
is shown at: 10.14288/1.0450301
language: eng
degree discipline: Physics
provider: Vancouver : University of British Columbia Library
publisher: University of British Columbia
rights: Attribution-NonCommercial-NoDerivatives 4.0 International
rights URI: http://creativecommons.org/licenses/by-nc-nd/4.0/
scholar level: Graduate
contributor: Fujiwara, Makoto C.
contributor: Momose, Takamasa
type: Text
identifier URI: http://hdl.handle.net/2429/92478