Prospects for studies of the free fall and gravitational quantum states of antimatter

Dufour, G.; Reynaud, S.; Crivelli, P.; Debu, P.; Wall, T.E.; Cassidy, D.B.; Lambrecht, A.; Voronin, A.Yu.; Nesvizhevsky, V.V.

doi:10.1155/2015/379642

Article
Report number	arXiv:1409.0705
Title	Prospects for studies of the free fall and gravitational quantum states of antimatter
Author(s)	Dufour, G. (College de France ; Paris, Lab. Kastler Brossel) ; Cassidy, D.B. (University Coll. London) ; Crivelli, P. (Zurich, ETH) ; Debu, P. (IRFU, SPP, Saclay) ; Lambrecht, A. (College de France ; Paris, Lab. Kastler Brossel) ; Nesvizhevsky, V.V. (Laue-Langevin Inst.) ; Reynaud, S. (College de France ; Paris, Lab. Kastler Brossel) ; Voronin, A.Yu. (Lebedev Inst.) ; Wall, T.E. (University Coll. London)
Publication	2015
Imprint	01 Sep 2014
Number of pages	16
Note	This work reviews contributions made at the GRANIT 2014 workshop on prospects for the observation of the free fall and gravitational quantum states of antimatter Comments: This work reviews contributions made at the GRANIT 2014 workshop on prospects for the observation of the free fall and gravitational quantum states of antimatter
In:	Adv. High Energy Phys. 2015 (2015) 379642
DOI	10.1155/2015/379642
Subject category	General Relativity and Cosmology ; quant-ph ; General Theoretical Physics ; physics.atom-ph ; Other Fields of Physics ; gr-qc ; General Relativity and Cosmology
Accelerator/Facility, Experiment	CERN AD ; AD-7
Abstract	Different experiments are ongoing to measure the effect of gravity on cold neutral antimatter atoms such as positronium, muonium and antihydrogen. Among those, the project GBAR in CERN aims to measure precisely the gravitational fall of ultracold antihydrogen atoms. In the ultracold regime, the interaction of antihydrogen atoms with a surface is governed by the phenomenon of quantum reflection which results in bouncing of antihydrogen atoms on matter surfaces. This allows the application of a filtering scheme to increase the precision of the free fall measurement. In the ultimate limit of smallest vertical velocities, antihydrogen atoms are settled in gravitational quantum states in close analogy to ultracold neutrons (UCNs). Positronium is another neutral system involving antimatter for which free fall under gravity is currently being investigated at UCL. Building on the experimental techniques under development for the free fall measurement, gravitational quantum states could also be observed in positronium. In this contribution, we review the status of the ongoing experiments and discuss the prospects of observing gravitational quantum states of antimatter and their implications.
Copyright/License	arXiv nonexclusive-distrib. 1.0

$The positron trapping mechanism (from \cite{Grandemange2013}). The horizontal axis is the position along the trap axis. The left vertical axis is the voltage seen by particles. The magnetic field strength is shown by the green curve, with the scale on the right vertical axis. In blue, the electron potential well filled with electrons is drawn , reducing the apparent voltage shown by black curve with the value on the left vertical axis. In red is shown the positron potential well. When a positron bunch arrives, the entrance electrode voltage is low (dashed dotted line). It is then increased and positrons go back and forth (it is depicted by red arrows) between this gate and the downstream part of the trap. They pass many times through the electron plasma, and are eventually slowed down and fall into their well. The presence of residual $\mathrm{H} _{\mathrm{2}} ^{\mathrm{+}}$ helps the final catching of positrons.$ $The accumulation of positrons (from \cite{Grandemange2013}).$