Detecting Antihydrogen Annihilations in ALPHA-g for Measurement of Gravitational Free Fall

Event Date:
2025-07-11T12:30:00
2025-07-11T15:00:00
Event Location:
TRIUMF MOB Conference Room - 4004 Wesbrook Mall
Speaker:
Gareth Smith, Departmental Defense
Related Upcoming Events:
Grad Theses
Intended Audience:
Everyone
Event Information:

Abstract:
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 g/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 rays, a time-of-flight barrel scintillator (BSC) detector was also implemented. The author’s primary contributions include the commission 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 matter, furthering our understanding of the fundamental matter-antimatter symmetry, and laying the foundation for future precision WEP tests using antimatter.
 

Add to Calendar 2025-07-11T12:30:00 2025-07-11T15:00:00 Detecting Antihydrogen Annihilations in ALPHA-g for Measurement of Gravitational Free Fall Event Information: Abstract: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 g/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 rays, a time-of-flight barrel scintillator (BSC) detector was also implemented. The author’s primary contributions include the commission 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 matter, furthering our understanding of the fundamental matter-antimatter symmetry, and laying the foundation for future precision WEP tests using antimatter.  Event Location: TRIUMF MOB Conference Room - 4004 Wesbrook Mall