The ORIGINS PhD Awards are presented annually for outstanding doctoral theses in astrophysics, nuclear and particle physics, and biophysics. The selection committee, our Cluster Emeriti, faced a difficult task this year: Among the many nominations were three particularly impressive works that are bound to leave a lasting mark in their fields. They, therefore, decided – as an exception – to award all three dissertations.
Beyond the Standard Model
The dissertation „Beyond the Standard Model physics searches with double-beta decays“ by Dr. Elisabetta Bossio uses double-beta decay to examine the predictions of the Standard Model of particle physics. Beta decay is a process of weak interaction in which a d-quark transforms into a u-quark (or vice versa); thus, a proton becomes a neutron (or vice versa, a neutron becomes a proton). Double beta decays are extremely rare, only detected in 13 atomic nuclei as two-neutrino double beta decays. The decay results in the emission of two electrons and two antineutrinos. If neutrinos are their own antiparticles - so-called Majorana particles - neutrinoless double beta decays could occur. Observing this previously hypothetical decay channel, which is “forbidden” in the Standard Model due to its changed lepton number, would be evidence of new physics beyond the Standard Model. This is precisely what Elisabetta Bossio was looking for in the GERmanium Detector Array (GERDA) data at the Laboratori Nazionali del Gran Sasso (LNGS). She led several projects that she published as lead author in renowned specialist journals. These include the determination of the half-life of the two-neutrino double beta decay of 76Ge with unprecedented accuracy and the first sensitivity study to search for light exotic fermions in double beta decays.
Aproaching the Big Bang
Dr Angelo Caravano's dissertation „Simulating the inflationary Universe: from single-field to the axion-U(1) model“ deals with the first numerical simulations of the first known expansion phase of the Universe, the so-called inflation. The theory states that in the first fractions of a second of its existence, the Universe went through a phase in which it expanded exponentially. This allowed microscopic density fluctuations, inherent in every quantum mechanical system due to the uncertainty principle, to grow to macroscopic sizes. These structures formed the basis for the further development of the cosmos, for the distribution of galaxies, the stars within them, and ultimately for our solar system and the Earth. So far, inflation has been examined with analytical models based on approximations and interpolations. Angelo Caravano's numerical simulations of the inflation phase link early and late cosmology: They offer a new and unique way to study the observable signatures of physics during inflation and draw conclusions about the initial conditions shortly after the Big Bang.
A telescope for cosmic rays
The dissertation „Modeling of the Galactic cosmic-ray antiproton flux and development of a multi-purpose active-target particle telescope for cosmic rays“ by Dr Thomas Pöschl is about modelling the production and propagation of antiprotons and antinuclei of cosmic rays in our galaxy and the development of a novel concept for a detector to measure them in space. Cosmic rays consist of high-energy particles, primarily of protons – the nuclei of the hydrogen atom. If these collide with ordinary matter, such as hydrogen and helium, antimatter can be created as antihelium-3 nuclei (two antiprotons and one antineutron). Antihelium-3 nuclei could also arise in processes involving weakly interacting dark matter. These antihelium nuclei differ from those resulting from collisions with cosmic rays because they are lower in energy. However, the low-energy antihelium-3 nuclei have an extremely low particle flux and have not yet been detected. Thomas Pöschl modelled the various galactic antiproton fluxes and developed a novel concept for a particularly sensitive detector that can measure them. In addition, he constructed algorithms that allow reconstructing the particle properties from the detector signal.