Abstract
Studies of antimatter are important for understanding our universe at a fundamental level. There are still unsolved problems, such as the matter-antimatter asymmetry in the universe. The AEgIS experiment at CERN aims at measuring the gravitational fall of antihydrogen in order to determine the gravitational force on antimatter. The proposed method will make use of a position-sensitive detector to measure the annihilation point of antihydrogen. Such a detector must be able to tag the antiproton, measure its time of arrival and reconstruct its annihilation point with high precision in the vertical direction. This work explores a new method for tagging antiprotons and reconstructing their annihilation point. Antiprotons from the Antiproton Decelerator at CERN were used to obtain data on direct annihilations on the surface of a silicon pixel sensor with Timepix3 readout. These data were used to develop and verify a detector response model for annihilation of antiprotons in this detector. Using this model and the antiproton data it is shown that a tagging efficiency of 50± 10% and a vertical position resolution of 22 ± 0.5 μm can be obtained.
Highlights
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A full detector response model based on FLUKA was developed
A tagging efficiency of 50 ± 10% is estimated with cuts of at least 70 pixels and at least 1 prong, while the false tagging rate is 1% with the same cuts
Summary
An antiproton annihilation with an atomic nucleon creates on average in total 5 pions (charged and neutral) per annihilation [11]. In addition to the antiprotons, fragments and pions from annihilations occurring in the vacuum window of GRACE, and on the walls and electrodes inside GRACE can reach the detector. These particles create secondary clusters which contaminate the data. Secondary clusters are defined as clusters caused by nuclear fragments or pions originating from annihilations taking place elsewhere than in the detector itself. An annihilation cluster can be recognized as a region with high-energy depositions, possibly with tracks originating from its center These tracks, from here on called prongs, are caused by pions or nuclear fragments traveling in the plane of the detector. The false tagging rate is defined as the probability of mistagging a secondary cluster as an annihilation cluster
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