Thomas Simon Stuttard
My field of research is fundamental neutrino physics, primarily oscillations, using atmospheric neutrinos detected in the DeepCore low energy sub-array of the IceCube neutrino telescope at the South Pole.
My current research topics are...
Tau neutrino appearance
Neutrinos produced by the interactions of cosmic rays in the Earth's atmosphere may interact as a different neutrino flavor state compared to the state they were produced as, in a phenomenon known as neutrino oscillations. In the energy range 10-50 GeV, atmospheric muon neutrinos have a large probability of being detected as tau neutrinos. The DeepCore sub-array of the IceCube detector is ideally suited to the detection of neutrinos in this energy range.
Although there is a strong probability of oscillation to tau neutrinos, detecting them is difficult. The large mass of the tau neutrino suppresses the charged-current cross-section of tau neutrino interactions with the South Pole ice, making detectable events rare. Additionally, these rare events produce showers of photons in the ice that are difficult to distinguish in the detector from electron neutrino events (which are common in the atmospheric flux), and from neutral-current events of all neutrino flavours. Despite these difficulties, it is possible to measure the statistical increase in the numbers of neutrinos observed in DeepCore resulting from the appearance of tau neutrinos.
The PMNS matrix describes the mixing between neutrino mass and flavour eignestates, and as such neutrino oscillations. The primary physics goal of studying tau neutrino appearance is to measure elements of the PMNS matrix that are currently poorly constrained. In doing so, the unitarity of the PMNS matrix can be tested. A discovery of non-unitarity would indicate new physics our current understanding of neutrinos, such as previously undiscovered neutrino states, and would have wide reaching implications in high energy physics, astrophysics and cosmology.
Environmentally-induced neutrino decoherence
It has been postulated that a neutrino propagating through space-time may weakly couple to its environment in a dissipative manner. For example, this is predicted by some classes of quantum gavity models. This would result in a sharing of quantum information between the neutrino and the enviroment, in a process known as decoherence.
Assuming this coupling occurs beween the neutrino and some property of space-time itself, rather than the matter within it, phenomenologically this effect results in the damping of muon neutrino oscillation probability as a function of the distance travelled by the neutrino. The wide range of distances travelled by atmospheric neutrinos before reaching the DeepCore detector, from 10s of km for neutrinos produced directly above the South Pole to 12,000 km for neutrinos produced above the North Pole (and thus subtending the diameter of the Earth), makes DeepCore a powerful instrument for studying decoherence of this kind.
A discovery of this phenomenon could result in a paradigm shift in the understanding of space-time, as well as identifying sub-leading effects in neutrino oscillations.