The WEAX experiment

Abstract

Einstein's weak equivalence principle (WEP) states that gravitational mass is identical to inertial mass. This hypothesis has withstood experimental tests to an impressive accuracy of one part in 1011. Various hypotheses based on theory and observations with matter suggest violations of WEP for antimatter may exist anywhere from the one part in 106 to the 200% level. An observed violation at any level would have a profound impact, e.g. it would offer an explanation as to why matter and antimatter are so distinctly separated in the cosmos. We propose a precise test of WEP for antiprotons in microgravity. We expect to test WEP for antimatter to about one part in 106, and foresee that additional advancements of several orders of magnitude in precision could follow with further technical developments.

Gravity effects on antimatter in the standard-model extension

“…22 Improved measurements are in preparation or have been suggested, including tests using a Moiré accelerometer, 23 trapped antihydrogen, 24 antihydrogen interferometry, 25, 26 gravitational quantum states, 27 and tests in space. 28 Such experiments could obtain special sensitivities to the SME coefficients (a w eff ) µ and (c w ) µν since the sign of (a w eff ) µ reverses under CPT, while the sign of (c w ) µν does not. Hence antimatter experiments could place cleaner constrains on certain combinations of SME coefficients than can be obtained with matter and could in principle observe novel behaviors stemming from Lorentz violation in the SME.…”

“…While the above tests with ordinary, neutral matter yield numerous sensitivities to Lorentz violation, versions of the tests highlighted above performed with antimatter, charged particles, and second-and third-generation particles can yield sensitivities to Lorentz and CPT violation that are otherwise impossible or difficult to achieve. Reference 12 considers gravitational experiments with antihydrogen, 22,23,24,25,26,27,28,29 charged-particle interferometry, 30,26 ballistic tests with charged particles, 31 and signals in muonium free fall. 32 Positronium may also offer an interesting possibility.…”

Antimatter-gravity couplings, and Lorentz symmetry

“…An recent direct measurement of the fall of antihydrogen by the ALPHA collaboration has placed initial direct limits on differences in the freefall rate of matter and antimatter [31]. A number of methods for improved measurements are in preparation or have been suggested including tests using a Moiré accelerometer [32], trapped antihydrogen [33], antihydrogen interferometry [34,35], gravitational quantum states [36], and tests in space [37]. As an example of the expected sensitivity of work in preparation, the AEGIS experiment [32] and the GBAR [33] experiment both expect sensitivity at the percent level.…”

Fundamental Physics in Space: A guide to present projects

“…Since it is very difficult to produce and store a reasonable amount of antimatter, and since tests of the free fall of charged particles are accompanied by huge experimental problems, until now no experiments have been carried out for testing the WEP for antimatter. Nevertheless, space experiments have been proposed recently (WEAX, p. 139 and [58,59]).…”