The Gbar project, or how does antimatter fall?

Abstract

International audienceThe Einstein classical Weak Equivalence Principle states that the trajectory of a particle is independent of its composition and internal structure when it is only submitted to gravitational forces. This fundamental principle has never been directly tested with antimatter. However, theoretical models such as supergravity may contain components inducing repulsive gravity, thus violating this principle. The GBAR project (Gravitational Behaviour of Antihydrogen at Rest) proposes to measure the free fall acceleration of ultracold neutral antihydrogen atoms in the terrestrial gravitational field. The experiment consists in preparing antihydrogen ions (one antiproton and two positrons) and sympathetically cool them with Be+ ions to a few 10 mu K. The ultracold ions will then be photoionized just above threshold, and the free-fall time over a known distance measured. In this work, the GBAR project is described as well as possible improvements that use quantum reflection of antihydrogen on surfaces to use quantum methods of measurements

Lorentz andCPTtests with hydrogen, antihydrogen, and related systems

“…Several experiments have been proposed to test this idea directly using antihydrogen, including AEGIS [70], GBAR [72], ALPHA [71], and AGE [73]. While the present work is focused on the spectroscopic effects of nonminimal operators for Lorentz and CPT violation in flat spacetime, we offer in this subsection a few comments about the role of nonminimal operators in the gravitational couplings of antihydrogen.…”

“…A number of collaborations have as goal the precision spectroscopy of antihydrogen, including the Antihydrogen Laser Physics Apparatus (ALPHA) collaboration [19], the Atomic Spectroscopy and Collisions Using Slow Antiprotons (ASACUSA) collaboration [20], and the Antihydrogen Trap (ATRAP) collaboration [21]. Several studies of the gravitational response of antihydrogen are under development, including ones by the Antihydrogen Experiment: Gravity, Interferometry, Spectroscopy (AEGIS) collaboration [70], the ALPHA collaboration [71], and the Gravitational Behavior of Antihydrogen at Rest (GBAR) collaboration [72]. A proposal for an Antimatter Gravity Experiment (AGE) also exists [73].…”

On the existence of exotic matter in classical Newtonian mechanics

“…Nevertheless, it has yet to be proven experimentally for example that antimatter does not antigravitate, because of the inherent difficulty in isolating and carrying out gravitational measurements on antimatter. It is only recently that it has been possible to isolate significant quantities of antihydrogen, and a number of experiments are underway [19][20][21] to determine whether the principle of equivalence holds for antimatter. The sensitivity of these experiments is not yet sufficiently high to answer this question but it is hoped that a definitive answer will be forthcoming in due course.…”

Charged particle reflection by a planar artificially structured boundary with electrostatic plugging

“…[7][8][9][10][11] The ALPHA and ATRAP experiments simultaneously synthesize and confine antihydrogen in Penning traps that are located within neutral atom traps. 7,8 In Penning traps, the presence of a strong magnetic field in the region where antihydrogen is formed reduces the three-body recombination rate by roughly an order of magnitude as compared to the rate when there is no magnetic field present.…”