The AEGIS experiment at CERN Kellerbauer, A.; Allkofer, Y.; Amsler, C. ...
Hyperfine interactions,
05/2012, Letnik:
209, Številka:
1-3
Journal Article
Recenzirano
After the first production of cold antihydrogen by the ATHENA and ATRAP experiments ten years ago, new second-generation experiments are aimed at measuring the fundamental properties of this ...anti-atom. The goal of AEGIS (Antimatter Experiment: Gravity, Interferometry, Spectroscopy) is to test the weak equivalence principle by studying the gravitational interaction between matter and antimatter with a pulsed, cold antihydrogen beam. The experiment is currently being assembled at CERN’s Antiproton Decelerator. In AEGIS, antihydrogen will be produced by charge exchange of cold antiprotons with positronium excited to a high Rydberg state (
n
> 20). An antihydrogen beam will be produced by controlled acceleration in an electric-field gradient (Stark acceleration). The deflection of the horizontal beam due to its free fall in the gravitational field of the earth will be measured with a moiré deflectometer. Initially, the gravitational acceleration will be determined to a precision of 1%, requiring the detection of about 10
5
antihydrogen atoms. In this paper, after a general description, the present status of the experiment will be reviewed.
The AEgIS experiment 1 aims at directly measuring the gravitational acceleration g on a beam of cold antihydrogen (H) to a precision of 1%, performing the first test with antimatter of the (WEP) Weak ...Equivalence Principle. The experimental apparatus is sited at the Antiproton Decelerator (AD) at CERN, Geneva, Switzerland. After production by mixing of antiprotons with Rydberg state positronium atoms (Ps), the H atoms will be driven to fly horizontally with a velocity of a few 100 ms super(-1) for a path length of about 1 meter. The small deflection, few tens of mu m, will be measured using two material gratings (of period ~ 80 mu m) coupled to a position-sensitive detector working as a moire deflectometer similarly to what has been done with matter atoms 2. The shadow pattern produced by the H beam will then be detected by reconstructing the annihilation points with a spatial resolution (~ 2 mu m) of each antiatom at the end of the flight path by the sensitive-position detector. During 2012 the experimental apparatus has been commissioned with antiprotons and positrons. Since the AD will not be running during 2013, during the refurbishment of the CERN accelerators, the experiment is currently working with positrons, electrons and protons, in order to prepare the way for the antihydrogen production in late 2014.
The AEg¯ $\overline {\rm{g}}$IS experiment 1 aims at directly measuring the gravitational acceleration g on a beam of cold antihydrogen (H¯$\overline {\rm{H}}$) to a precision of 1%, performing the ...first test with antimatter of the (WEP) Weak Equivalence Principle. The experimental apparatus is sited at the Antiproton Decelerator (AD) at CERN, Geneva, Switzerland. After production by mixing of antiprotons with Rydberg state positronium atoms (Ps), the H¯$\overline {\rm{H}}$ atoms will be driven to fly horizontally with a velocity of a few 100 ms−1 for a path length of about 1 meter. The small deflection, few tens of μm, will be measured using two material gratings (of period ∼ 80 μm) coupled to a position-sensitive detector working as a moiré deflectometer similarly to what has been done with matter atoms 2. The shadow pattern produced by the H¯$\overline {\rm{H}}$ beam will then be detected by reconstructing the annihilation points with a spatial resolution (∼ 2 μm) of each antiatom at the end of the flight path by the sensitive-position detector. During 2012 the experimental apparatus has been commissioned with antiprotons and positrons. Since the AD will not be running during 2013,during the refurbishment of the CERN accelerators, the experiment is currently working with positrons, electrons and protons, in order to prepare the way for the antihydrogen production in late 2014.
We describe a system designed to re-bunch positron pulses delivered by an accumulator supplied by a positron source and a Surko-trap. Positron pulses from the accumulator are magnetically guided in a ...0.085T field and are injected into a region free of magnetic fields through a μ-metal field terminator. Here positrons are temporally compressed, electrostatically guided and accelerated towards a porous silicon target for the production and emission of positronium into vacuum. Positrons are focused in a spot of less than 4mm FWTM in bunches of ∼8ns FWHM. Emission of positronium into the vacuum is shown by single shot positron annihilation lifetime spectroscopy.
The aim of the AEg̅IS experiment is to measure the gravitational acceleration for anti-hydrogen in the Earth's gravitational field, thus testing the Weak Equivalence Principle, which states that all ...bodies fall with the same acceleration independent of their mass and composition. AEg̅IS will make use of a gravity module which includes a silicon detector, in order to measure the deflection of anti-hydrogen from a straight path due to the Earth's gravitational field, by detecting the annihilation position on its surface. A position resolution better than 10 μm is required to determine the gravitational acceleration with a precision better than 10%. The work presented here is part of a study of different silicon sensor technologies to realise a silicon anti-hydrogen detector for the AEg̅IS experiment at CERN. We here focus on the study of a 3D pixel sensor with FE-I4 readout, originally designed for the ATLAS detector at the LHC, and compare it to a previous monolithic planar detector studied, the MIMOTERA. The direct annihilation of low energy anti-protons (~ 100 keV) takes place in the first layers and we show that the charged annihilation products (pions and nuclear fragments) can be detected by such a sensor. The present study aims at understanding the signature of an annihilation event in a 3D silicon sensor, in order to assess the accuracy that can be achieved by such a sensor in the reconstruction of the position of annihilation, when the same happens directly on the detector surface. We also present a comparison between experimental data and GEANT4 simulations and previous data obtained with a silicon imaging detector. These results are being used to determine the geometrical and process parameters to be adopted by the silicon annihilation detector to be installed in AEg̅IS.
AEgIS (Expérience sur l'Antimatière: Gravité, Interférométrie, Spectrométrie) est une expérience approuvée par le CERN qui vise une étude globale de la physique de l'anti-hydrogène. Dans AEgIS, ...l'anti-hydrogène sera produit par des réactions d'échange de charges d'anti-protons froids avec des atomes de positronium excités dans un état de Rydberg (n > 20). Dans la première phase de l'expérience, l'accélération est contrôlée par un gradient de champ électrique (effet Stark); une mesure subséquente en chute libre dans un déflectomètre de Moiré nous fournira un test du principe d'équivalence faible. Dans une deuxième phase, l'anti-hydrogène sera ralenti, confiné et refroidi par laser pour des études de CPT et de spectroscopie de précision. Après une description générale de l'expérience, nous passons ici en revue l'état d'avancement des travaux en accordant une attention particulière à la production et l'excitation des atomes de positronium.
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