CAREER: Towards Particle Physics Discoveries With Double Cascades In IceCube and Beyond

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Particle physics has progressed over the last century by exploring new, increasing energy scales; more generally, physics has moved forward by studying physical phenomena under new, unexplored conditions. The discovery that the supposedly massless neutrino actually has a mass, inferred through the observation that the three types of neutrinos, electron, muon, and tau can change flavor, i.e. spontaneously change from one to another, is one of those phenomena. This unexpected and unexplained observation suggests that the study of neutrinos will yield additional discoveries. The PI of this project aims to explore neutrinos in yet uncharted territories and contexts to make precision measurements of neutrino interactions and discover new physics. The IceCube Neutrino Observatory at the South Pole allows studying neutrinos whose center-of-mass energy is comparable to the Large Hadron Collider at CERN, Switzerland, and whose traversed distance from production to detection can be as large as gigaparsecs (one gigaparsec equals 3.26 billion light years). Using these unique neutrinos, the PI will study neutrino flavor changes in astrophysical scales by measuring the appearance of tau neutrinos, which can be differentiated from other neutrino species by their characteristic light emission and will search for the production of heavy particles in neutrino interactions. The measurement of tau neutrinos from distant, high-energy astrophysical sources demonstrates that neutrino flavor change, which is a purely quantum mechanical phenomenon, operates on cosmic scales. Additionally, the PI will perform the first measurement of heavy particles produced in high-energy neutrino interactions, which has implications for the quark content of the proton and the existence of new neutrino species. During the implementation of this project, the PI will additionally make significant contributions to physics education and underserved communities. First, the PI will extend his current undergraduate particle physics class to incorporate elements of computational physics. These activities complement data analysis classes and expose students to modern simulation and reconstruction techniques. Second, taking advantage of his fluency in Spanish, the PI will expand existing work with a local middle school to expose Hispanic students to neutrino physics. The project includes a plan to deliver introductory lectures in Spanish to middle school students and instructors. Spanish-speaking undergraduate and graduate students will be incorporated in outreach activities and educational videos in Spanish about the physics of our project will be developed.With this award the PI plans to significantly improve the selection efficiency of astrophysical tau neutrinos and measure for the first time the production of D-mesons in high-energy atmospheric neutrino interactions. The observation of tau neutrinos is crucial as they are predominantly of astrophysical origin and prove that neutrino oscillations operate at cosmic baselines. Measuring D-meson production will constrain the proton's strange quark content. Additionally, the PI will perform the first search for heavy neutrinos produced in atmospheric neutrino interactions in the sub-TeV energy range. These heavy neutrinos are one of the leading explanations for the unexplained excess of events observed by the MiniBooNE experiment. These analyses are tied together by their common double cascade signature in IceCube, which the PI proposed to identify by developing a graph neural network. This project also prepares the PI to perform follow-up analyses on the NSF-funded and currently under-construction IceCube-Upgrade and, on a longer timescale, optimize the IceCube-Gen2 design so that it continues to have a strong particle physics program.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.