Atom Optical Tools for Antimatter Experiments

The direct measurement of the gravitational acceleration of antimatter in the earth's field, which represents a test of the weak equivalence principle, is in the focus of several ongoing experimental attempts. This thesis investigates tools and techniques known from the field of atom optics that can be utilised for such a measurement with antihydrogen atoms as envisioned by the AEgIS collaboration. A first experimental step is presented, in which a detection due to an electromagnetic force acting on antiprotons is measured with a moiré deflectometer. This device, which can be described with classical particle trajectories, consists of two gratings and a spatially resolving detector. Key elements of this measurement are the use of an emulsion detector with high spatial resolution and an absolute reference technique based on an interferometric fringe pattern of light, which is not deflected by forces. For future realisations, a new detection and evaluation scheme to measure gravity based on a three-grating system enclosed by a vertex-reconstructing detector is discussed. This allows the use of a grating periodicity that is smaller than the resolution of the detector while making efficient use of the particle flux. Smaller periodicities are favourable to increase the inertial sensitivity of the measurement apparatus but require to take effects of diffraction into account. To explore this near-field regime with antimatter, a Talbot-Lau interferometer for antiprotons is proposed and its possible experimental implementation is discussed

Measuring the gravitational free-fall of antihydrogen

Antihydrogen holds the promise to test, for the first time, the universality of free-fall with a system composed entirely of antiparticles. The AEgIS experiment at CERN’s antiproton decelerator aims to measure the gravitational interaction between matter and antimatter by measuring the deflection of a beam of antihydrogen in the Earths gravitational field (g¯¯¯). The principle of the experiment is as follows: cold antihydrogen atoms are synthesized in a Penning-Malberg trap and are Stark accelerated towards a moiré deflectometer, the classical counterpart of an atom interferometer, and annihilate on a position sensitive detector. Crucial to the success of the experiment is the spatial precision of the position sensitive detector. We propose a novel free-fall detector based on a hybrid of two technologies: emulsion detectors, which have an intrinsic spatial resolution of 50 nm but no temporal information, and a silicon strip / scintillating fiber tracker to provide timing and positional information. In 2012 we tested emulsion films in vacuum with antiprotons from CERN’s antiproton decelerator. The annihilation vertices could be observed directly on the emulsion surface using the microscope facility available at the University of Bern. The annihilation vertices were successfully reconstructed with a resolution of 1–2 μmon the impact parameter. If such a precision can be realized in the final detector, Monte Carlo simulations suggest of order 500 antihydrogen annihilations will be sufficient to determine g¯¯¯with a 1 % accuracy. This paper presents current research towards the development of this technology for use in the AEgIS apparatus and prospects for the realization of the final detector.ISSN:0304-3843ISSN:0304-3834ISSN:1572-954

The AEgIS Experiment

The AEgIS experiment aims at performing the first test of the Weak Equivalence Principle of General Relativity in the antimatter sector by measuring the gravitational acceleration acting on a beam of cold antihydrogen to a precision of 1%. The installation of the apparatus is making good progress and large parts were taken into operation. Parasitic detector tests during the beamtime in December 2012 gave essential input for an optimal moiré deflectometer and the detector layout necessary to perform the gravity measurement.ISSN:0304-3843ISSN:0304-3834ISSN:1572-954

AEgIS experiment: Towards antihydrogen beam production for antimatter gravity measurements

AEgIS (Antimatter Experiment: Gravity, Interferometry, Spectroscopy) is an experiment that aims to perform the first direct measurement of the gravitational acceleration g of antihydrogen in the Earth’s field. A cold antihydrogen beam will be produced by charge exchange reaction between cold antiprotons and positronium excited in Rydberg states. Rydberg positronium (with quantum number n between 20 and 30) will be produced by a two steps laser excitation. The antihydrogen beam, after being accelerated by Stark effect, will fly through the gratings of a moiré deflectometer. The deflection of the horizontal beam due to its free fall will be measured by a position sensitive detector. It is estimated that the detection of about 103 antihydrogen atoms is required to determine the gravitational acceleration with a precision of 1%. In this report an overview of the AEgIS experiment is presented and its current status is described. Details on the production of slow positronium and its excitation with lasers are discussed

Positron Manipulation and Positronium Laser Excitation in AEgIS

International audienceProduction of antihydrogen by using the charge exchange reaction, as proposed by AEgIS (Antimatter Experiment: gravity, Interferometry, Spectroscopy), requires the formation of a dense cloud of positronium atoms excited to Rydberg states. In this work, the recent advances in AEgIS towards this result are described. Namely, the manipulation of positrons to produce bunches containing more than 10$^{8}$ particles and the laser excitation of positronium to Rydberg states, using n=3 as intermediate level, are presented