Search for Supernova Relic Neutrinos

Core-collapse supernovae are amongst the most energetic events in the Universe. A single supernova will outshine an entire galaxy, yet the light is less than 1% of the energy that is released. The vast majority of energy released in a supernova (99%) is emitted in the form of neutrinos, a 'ghostly' particle that almost never interacts with matter. Over thirty years ago, 24 neutrinos were detected from Supernova 1987A; these have provided most of what we currently know about supernovae.

Neutrinos from the next galactic supernova are currently on their way to Earth. When they arrive, we will study them to greatly advance our knowledge of how massive stars die. However, it is impossible to predict how many years (or decades) it will be before this happens.

While we wait it is also possible to search for the signal from extra-galactic supernovae in an attempt to do neutrino cosmology. Core-collapose supernovae are believed to have started in the universe shortly after star formation began. Thus, there should exist a diffuse background of neutrinos throughout all of space, originating from all of the supernovae that have previously exploded. These particles are called 'supernova relic neutrinos', and we can use them to learn about the history of supernova explosions in the universe and related cosmological quantities, such as the star formation rate and cosmic chemical evolution.

Previous searches for supernova relic neutrinos have been performed, but the signal has been masked by terrestrial backgrounds. The Super-Kamiokande (SK) detector will soon be upgraded with gadolinium and re-christened as SK-Gd. With the aid of gadolinium tagging, SK-Gd will be able to identify the supernova relic neutrinos and minimise the terrestrial backgrounds, making it very likely that the supernova relic neutrinos will finally be detected in the next few years.

This PhD will involve travel to Japan for participation in the SK-Gd experiment, including calibration of the detector following gadolinium loading. It will also involve data reduction, simulation, and analysis, ultimately aimed at producing the first successful observation of the supernova relic neutrinos.