Exploring antimatter: Building a position sensitive detector for antihydrogen
According to the well-known equation E=mc2, mass and energy are equivalent. If a huge amount of energy is concentrated in a tiny space, particles with certain mass are produced. These particles are always created in pairs, that is, energy can transform into matter only when the latter is accompanied by its counterpart, antimatter. The opposite holds true as well: when a particle and its antiparticle are brought together, they annihilate completely into energy. Matter and antimatter are always produced in equal amounts. Still, observations show that the Universe is entirely made of matter and there is no significant amount of antimatter. So where did all the antimatter produced in the Big Bang go? This asymmetry between matter and antimatter is still one of the greatest unsolved problems in modern physics.
To explore the properties of antimatter, scientists at CERN have built several experiments where the simplest anti-atom (antihydrogen) is produced and studied. The most recent among them is AEgIS (Antimatter experiment: gravity, interferometry, spectroscopy), whose main goal is to determine whether antihydrogen falls with the same acceleration as hydrogen. This will be the first direct measurement of a gravitational effect on antiatoms and will be carried out by sending an antihydrogen beam launched horizontally in a vacuum tube and measuring its deflection in the Earth’s gravitational field with a position sensitive timing detector. This PhD project includes development of a silicon strip detector which is part of the position sensitive timing detector for AEgIS. After traversing a certain distance, antihydrogen atoms will annihilate on its surface. In this way the detector will provide online measurement of the vertical position of the annihilation point, as well as time of flight information which is necessary to calculate the gravitational acceleration constant, g, as experienced by antihydrogen atoms. The first step towards the design of the silicon detector is understanding the annihilation process of antiprotons in silicon. Thus, part of the necessary research involves the direct detection of slow antiprotons with different silicon detectors. Analysis of these data provides valuable information on the energy released in the detector from a single annihilation. The detector system will operate at cryogenic temperatures (-200 °C or lower), so low-temperature tests of the electronics for the readout system are also performed. A significant part of my PhD project is also dedicated to simulation of antiproton annihilation in matter. The results from the annihilation data are compared to the different simulation models, which will provide some of the optimal parameters for the final detector.