MINERvA
I work primarily at Fermilab's MINERvA experiment.
The Standard Model predicts that neutrinos must be massless, but the discovery of neutrino oscillations (Nobel Prize in Physics 2015!) showed that neutrinos do have small, nonzero masses - definite confirmation that the Standard Model is not the final physical theory. My thesis topic hones in on the elusive Heavy Neutral Leptons (HNLs), which are a type of sterile neutrinos - that is, they couple to the Standard Model only by mixing with the active "left-handed" neutrino flavours. These particles are hypothesized to mix primarily with heavy "right-handed" neutrino mass eigenstates, and very little with the light, active ones.
HNLs have many properties that make them appealing; for example, detection of an HNL would shed much light on the seesaw mechanism by which the currently known neutrino types acquire their mass (by the "seesaw" mechanism, so named because the heavier the right-handed neutrinos are, the lighter the left-handed ones). Sterile neutrinos can also, perhaps, account for dark matter in the Universe, since they don't couple with the Standard Model. They may explain why there is more matter than antimatter in the observable Universe; lastly, the detection of an HNL decaying could tell physicists whether neutrinos are their own antiparticles or not.
I am undertaking the first Beyond-the-Standard-Model search at MINERvA, using data taken from the powerful NuMI beam from 2013 to 2019. This large quantity of data, in addition to the high energy of neutrinos produced by the beam, makes MINERvA a good candidate for observing HNL in previously unexplored mass regions. In the context of this search, I am involved in the production and organisation of special samples within the experiment, and have developed a utility for converting GENIE v3 generator predictions to a format that can be passed through to our detector simulation which uses GENIE v2.
Together with my supervisor, Dr. Xianguo Lu, and members of the GENIE core group, we have implemented a fully functional and factorisable "BeamHNL" module that allows the user to generate signal samples of HNL decays, in the context of an effective field theory describing mesons coupling directly to neutrinos. This addition to the GENIE generator (forming part of the v3.4.0 release, tagged on March 10th, 2023) lets users specify their input fluxes as records of neutrino-producing hadrons, and their detectors via ROOT geometry files. We have described our method and the generator in Phys. Rev. D 107 (2023) 055003.
I am currently working on selecting HNL events, generated with BeamHNL and passed through the detailed MINERvA detector simulation, and separating them from the Standard Model background.
Previous work
Before starting my D.Phil., I completed the MSc in Mathematical and Theoretical Physics at Oxford in 2019-20, writing my final dissertation on the status of obtaining cosmological bounds to the sum of absolute masses of the neutrino species by looking at the history of formation of large-scale structure in the Universe. Cosmic neutrinos are very abundant, and the more massive they are, the more they free-stream after they decouple from the Cosmic Microwave Background (CMB). Thus, they suppress the formation of structure on small position (large momentum) scales, leaving observable effects on the power spectra of both the CMB and the local (much less ancient) Universe.
This information is complementary to present-day oscillation experiments, which are sensitive to the mass splittings \(\Delta m^{2}_{ij}\); the larger the mass \(M := \sum_{i}m_{\nu_{i}}\)is, the greater the suppression.
I first graduated from the National Technical University of Athens, where I studied applied physics with a specialisation in particle and computational physics. Before graduating, I worked at CERN as a summer student in the group of Prof. Theodoros Alexopoulos, where I was responsible for implementing a multi-cluster track reconstruction algorithm for charged particles passing through the planes of a Micromegas detector.
Conference talks I've given
- Path to Dark Sector Discoveries at Neutrino Experiments, June 5-7, 2023. I presented BeamHNL, including a work-in-progress upgrade that will allow the user to specify the production and decay rates of HNL using an xml interface.
- UK HEP forum: Neutrinos: What? Where from? Where to?, November 22-23, 2022. I presented the BeamHNL simulation addon to the popular GENIE neutrino generator.
- International School of Nuclear Physics 43rd Course: Neutrinos in Cosmology, in Astro-, Particle- and Nuclear Physics, Erice, Sicily, September 16-22, 2022. I attended the School and presented BeamHNL.
- International Conference on High Energy Physics, Bologna, July 6-13, 2022. I shared new results from the MINERvA experiment with the community, focusing on our experiment's in situ flux constraint using Inverse Muon Decay events, on the measurement of the coherent pion production cross section in various nuclear targets, and on high-statistics muon analyses as probes of neutrino generators.
- New Perspectives (remote), Fermilab, June 16-17 and 22-23, 2022. I presented the MINERvA search for Heavy Neutral Leptons in the N4 --> μ + π channel.
- Lake Louise Winter Institute, Lake Louise, Canada, February 20-26, 2022. I presented new and upcoming MINERvA results.