Abstract
The ALPHA experiment has recently entered an expansion phase of its experimental programme, driven in part by the expected benefits of conducting experiments in the framework of the new AD + ELENA antiproton facility at CERN. With antihydrogen trapping now a routine operation in the ALPHA experiment, the collaboration is leading progress towards precision atomic measurements on trapped antihydrogen atoms, with the first excitation of the 1S–2S transition and the first measurement of the antihydrogen hyperfine spectrum (Ahmadi et al. 2017 Nature 541, 506–510 (doi:10.1038/nature21040); Nature 548, 66–69 (doi:10.1038/nature23446)). We are building on these successes to extend our physics programme to include a measurement of antimatter gravitation. We plan to expand a proof-of-principle method (Amole et al. 2013 Nat. Commun. 4, 1785 (doi:10.1038/ncomms2787)), first demonstrated in the original ALPHA apparatus, and perform a precise measurement of antimatter gravitational acceleration with the aim of achieving a test of the weak equivalence principle at the 1% level. The design of this apparatus has drawn from a growing body of experience on the simulation and verification of antihydrogen orbits confined within magnetic-minimum atom traps. The new experiment, ALPHA-g, will be an additional atom-trapping apparatus located at the ALPHA experiment with the intention of measuring antihydrogen gravitation.This article is part of the Theo Murphy meeting issue ‘Antiproton physics in the ELENA era’.
Highlights
Antimatter and gravity are central players in two of the great outstanding debates in physics today
(b) Antihydrogen gravitation proof-of-principle measurement. The second such question we addressed along these lines was that of antimatter gravitation [18]
ALPHA has developed a set of computational tools for dynamical tracking of antihydrogen and charged particle orbits in the relatively large traps used in its antihydrogen experiments
Summary
Antimatter and gravity are central players in two of the great outstanding debates in physics today. The question of antimatter and gravitation arose in the early part of the twentieth century with the idea of antigravity—namely that matter and antimatter would repel each other gravitationally As a concept, this has largely been ruled out, but antimatter gravitation is held as an important system for use in testing the Einstein equivalence principle and nonNewtonian models of gravity [5]. As for what scale differences between matter and antimatter gravitation might manifest, modern theory runs the gambit between large violations being possible (approximately tens of per cent) to limits below 10−5% [6,7] As this particular question has not been addressed empirically to date, it is paramount to measure the actual behaviour of antihydrogen to help guide and set limits on these various theoretical frameworks. In addition to the effort proposed by ALPHA and described below, this is considered a sufficiently important investigation that at least two other collaborations (AEgIS and GBAR) operating at the Antiproton Decelerator (AD) facility are actively pursuing antimatter gravitation measurements [8,9]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
