MicroBooNE

MicroBooNE is an experiment at Fermilab looking for a possible signal from a short baseline neutrino (SBN) oscillation at an approximate L/E = o(1) m/MeV.

The SLAC group members have been involved in all aspects of the experiment including electronics hardware, daq, online and offline data management, software maintenance and leadership roles in data reconstruction algorithms development, and pioneering work in applying machine learning techniques to LArTPC data. Much of the expertise acquired during our involvement in MicroBooNE is now applied efficiently in ICARUS and DUNE experiments.

While the group's focus is now moving onto those tow experiments, we continue to support the low energy excess search, the flagship measurement of the experiment. In particular, we are applying deep learning techniques to extract signal from real MicroBooNE detector data.

What is "low energy excess" (LEE)? It is an anomaly of electron neutrino candidate events observed by a sibling experiment called MiniBooNE. Both MiniBooNE and MicroBooNE are on-axis with the Booster Neutrino Beamline (BNB) at Fermilab, which consists of primarily (approximately 97 to 98%) muon flavored neutrino. An observation of electron neutrino candidate with statistics above expected electron neutrino contamination in the beam indicate a possible muon flavor to electron flavor oscillation. MiniBooNE indeed measured possible excess of events that are consistent with neutrino energy between 200 to 600 MeV, so-called "low energy region". A very exciting finding!

However, an associated fundamental physics parameters, namely mixing angle and squared mass splitting, are not consistent with the standard three neutrino oscillation model for which parameters are measured by many other experiments. Further investigations are due.

Is the low energy excess an electron or photon?

This is a legitimate question since the subject energy region is dominated by a photon background originated from neutral pion and others. The MiniBooNE detector is an oil Cherenkov technology which is not good at all for distinguishing from photons unfortunately. If it were an electron, then this might have been an oscillation that involves new neutrino mass state which has small or no coupling to weak interactions, referred to as a stellar neutrino. That would be an exciting discovery! If it were photons, explanation is due still as to where this photon is originated from.

In order to make a definite conclusion to this question, MicroBooNE was proposed. Instead of an oil Cherenkov detector, a technology employed in MiniBooNE experiment, MicroBooNE experiment utilizes a liquid argon time projection chamber (LArTPC) which can essentially take 2D photographs of particle energy depositions, and can distinguish between electron vs. photon originated EM showers with high efficiency.