IceCube
The IceCube Neutrino Observatory is a neutrino detector located in the Antarctic continent at the geographical South Pole. It is the realization of a long dream that started in the mid-eighties of detecting high-energy astrophysical neutrinos. These high-energy neutrinos carry about a million times the energy of a proton, and their sources still unidentified.
To achieve this feat, the IceCube collaboration, comprised of about three hundred scientists in more than forty institutions and spread around twelve countries, has instrumented one cubic kilometer of ultra-clear ice with light detectors called DOMs. Each DOM, initials for Digital Optical Module, is a basketball-size independent detector enclosed in a pressure resisting vessel containing one photomultiplier tube. These extremely sensitive light detectors capture the light produced by ultra-high energy particles' interacting in the deep ice.
The figure on the left shows the number of events triggered in a couple of microseconds in IceCube. Many of these events are muons (electrons more massive brothers) produced in cosmic-ray air showers in the south pole atmosphere. For every million interaction of cosmic-ray produced muon, one neutrino will make a recognizable signal in our detector.
All of IceCube's neutrinos are very special, but we can group them by origin. The most special and rare ones are from high-energy astrophysical sources. Those types of neutrinos are detected at a rate of about ~30 per year. These very-high-energy neutrinos can be a gateway to new physics, as we discussed in here and here.
The other ones are produced in cosmic-ray showers in the Earth atmosphere and thus are named atmospheric neutrinos. IceCube detects more than 30 000 of these neutrinos per year. My work involves using these neutrinos to constrain new neutrino phenomena.
IceCube Upgrade and IceCube-Gen2
The current IceCube experiment will grow in this upcoming decade. The expansion will happen in two stages that serve two distinct and complementary physics purposes. The first stage, called the IceCube-Upgrade, consists of seven new strings concentrated in the innermost part of the IceCube detector called DeepCore. Together with these new strings, a series of calibration devices will be installed. The increased light capture by the new sensors and expected improved characterization of the glacier ice obtained by using the new calibration devices, will improve the reconstruction and particle identification of sub-100 GeV events. In this energy range, IceCube can observe atmospheric neutrinos' oscillations, which are mainly given by muon-neutrino to tau-neutrino conversion. These allow a unique opportunity to study tau neutrino interactions and probe the neutrino mixing matrix's unitary.
Also, the construction of the IceCube-Upgrade is an ideal stage to test next-generation detectors. These will be deployed in the second stage of expansion, known as IceCube-Gen2. This extension is optimized to obtain a large sample of high-energy neutrinos, which are expected to be predominantly of astrophysical origin. IceCube was a discovery experiment that opened the door and lay the ground to start doing neutrino astronomy; IceCube-Gen2 will allow us to detect currently subthreshold sources.
Phenomenology
Phenomenology can be related to its Greek root phenomena. In particle physics, it is the interface between experimental observation and complete theories. It is like standing on a stony cliff within the deepest fog and stretching out one foot and hands to try to feel the more firm land ahead. One's hands are guided by theoretical intuition and understanding, but the back feet should never leave the stone's certainty. This act of balance is phenomenology.
My phenomenology work revolves around neutrinos and their potential undiscovered partners. The Standard Model of particle physics, which is our current theoretical paradigm, does not predict neutrinos to be massive. But they are. Working under the hypothesis that this is because neutrinos are involved in some new undiscovered physics is part of my main work. My work in phenomenology is to find ways to make this explicit by thinking about new observables in IceCube, as well as ongoing neutrino experiments such as Super-Kamiokande, Nova, MiniBooNE, or microBooNE, or new proposed experiments such as IsoDAR, Hyper-Kamiokande, JUNO, or DUNE. I collaborate with my theory colleagues to connect their models with signatures we can detect in these experiments in this work. An example is shown in the diagram above, where heavy neutral leptons (HNL) can be produced from neutrino interaction leading to novel signatures in neutrino detectors.
Global fits to the neutrino data
Neutrino physics has become a worldwide effort with experiments in the United States (FermiLab), in Europe (CERN), Asia (Daya-Bay, SuperKamiokande, RENO), and to the south pole with IceCube, ANITA, and others. To study neutrino flavor conversion, it is essential to have detectors at different energies and distances. Having different ratios of energies to distances is the only way we can disentangle the oscillation frequencies. It is also important to have detectors of different designs, proving complementary strengths and covering each other's weaknesses. Using this information, we can obtain the flavor composition of the three massive neutrinos.
Though the three-neutrino paradigm seems to explain the bulk of the neutrino data, deviations from our standard three-neutrino picture have been observed in the last decades. First, by the Los Alamos-based LSND neutrino experiment. This experiment looked for unexpected flavor transition from muon-neutrino flavor to electron-neutrino flavor in the 90s. LSND observed such phenomena, but its main conclusion -- which is the existence of a new neutrino species -- contradicts the lack of observation in other experiments. A follow-up experiment, based at Fermilab, called MiniBooNE reported an excess of electron-neutrino-like events compatible with their observation. To understand how to resolve the tension between negative and positive evidence for new particles leads us, we need to aggregate the information from these different experiments. My group's work on global fits to the neutrino data is done in close collaboration with Conrad's group at MIT and Shaevitz's group at Columbia University. The figure below shows some of the experiments that we include in our latest global analysis.