Neutrino and Rare Events

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The Columbia neutrino and rare events group at Nevis Labs is involved in a number of accelerator-based neutrino experiments, all of which involve the same detection technology, that of a liquid argon time projection chamber (LArTPC). The group is also involved in an astro-article project that proposes to use the same LArTPC detector technology as a Compton telescope for MeV gamma-ray observations.

MicroBooNE is a neutrino experiment at Fermilab that is investigating neutrino properties and interactions using the Fermilab booster neutrino beam. It is a follow-up experiment to the MiniBooNE experiment, which also ran in the Fermilab booster neutrino beam. MiniBooNE observed an enhanced number of low energy events over expectation with characteristics that imply the events have an outgoing electron or photon. Since electron neutrinos produce electrons in their charged current interactions, one interpretation is that these extra events are due to more electron neutrino interactions than expectation. An alternative explanation is that they are due to an unexpected number of neutrino events producing photons in the final state. In either case, the anomalous MiniBooNE signal may be from some type of new physics either within or beyond the current particle physics model.

MicroBooNE has the capability to detect and study neutrino interactions using a time projection chamber (TPC) filled with 175 tons of liquid argon. This detector has excellent spatial and energy resolution and is able to differentiate between an electron from an electron neutrino interaction and a photon from other types of neutrino interactions; an electron produces an ionization trace originating at the main interaction vertex, while a photon travels some distance from the vertex before converting to an e+e- pair and producing a trace. MicroBooNE’s superb pattern recognition capabilities also allow improved measurements of several neutrino cross sections. MicroBooNE is also a test bed for future very large (~10-100 kton) liquid argon detectors, such as DUNE, which is planned for studies of CP violation in neutrino interactions, baryon number violation through proton decay searches, and supernova neutrino detection. MicroBooNE provides R\&D on liquid argon purity, mechanical configurations and electronic readout designs, including triggering.

The Columbia neutrino and rare events group at Nevis Labs were prime members involved in the design and construction of the readout electronics for the MicroBooNE detector. The group has also led MicroBooNE's first search for a single-photon excess, investigating the MiniBooNE anomaly. The group is involved in improving pattern recognition and selection analysis procedures to distinguish between neutrino interactions and background events and between electrons, photons, and e+e- pairs from non-photon sources. Part of this involves applying “deep learning” techniques, such as convolutional neural nets that use machine learning to train computers to recognize and isolate features in images such as those from the MicroBooNE liquid argon TPC. The group’s prime physics topic is investigating the MiniBooNE low energy excess and neutrino oscillation to sterile neutrinos using MicroBooNE in combination with the other detectors at Fermilab.

MicroBooNE has recently completed its data taking mode and has collected the full data set needed for its physics goals. This summer will be an intense time for looking at the data, improving neutrino event reconstruction and selection software, and carrying out additional low energy excess search studies, and producing more MicroBooNE physics results. We plan for several REU students to be based at Nevis Labs and be involved in all of these efforts, along with possibly helping with electronics commissioning for the upcoming SBND experiment, the near detector for the Short-Baseline Neutrino (SBN) program, or simulation studies for the future DUNE and proposed GRAMS experiments.

Contact persons: Georgia Karagiorgi and Mike Shaevitz