MicroBooNE

MicroBooNE is a liquid argon time projection chamber (LArTPC) at Fermilab in Batavia, Illinois. It is located in the Booster Neutrino Beam (BNB) beamline where neutrinos are produced by colliding protons from Fermilab's booster-accelerator to a beryllium target; this produces many short-lived particles that decay into neutrinos. The neutrinos then pass through solid ground (to filter out particles that are not neutrinos from the beam) through another experiment called ANNIE (under construction as of 2018), then solid ground, then through the Short Baseline Near Detector (SBND, in construction, expected to begin operation 2022), then ground again and arrive at the MicroBooNE detector 470 meters downrange from the target. After MicroBooNE the neutrinos continue to MiniBooNE detector and to the ICARUS detector.

MicroBooNE's two main physics goals are to investigate the MiniBooNE low-energy excess and neutrino-argon cross sections.[1][2] As part of the Short Baseline Neutrino program (SBN), it will be one of a series of neutrino detectors along with the new Short-Baseline Near Detector (SBND) and moved ICARUS detector.

MicroBooNE was filled with argon in July 2015 and began data taking.[3] The collaboration announced that they had found evidence of the experiment's first neutrino interactions in November 2015.[4] As of 2020, the detector was operating.[5]

In October 2021 the results of the first three years of operation were reported. Analyses examined the MiniBooNE low-energy excess, one under a single photon hypothesis[6][7] and under an electron hypothesis.[8][9] No evidence for either of these explanations was found.

The Fermilab press release accompanying the October 2021 results [9] stated that the electron hypothesis test dealt "a blow to a theoretical particle known as the sterile neutrino." This statement was false since the MicroBooNE paper did not provide fits to sterile neutrino models.[8] Theorists reacted negatively to the press release, publishing papers saying:

• "It is premature to conclude that MicroBooNE has killed light sterile neutrinos when, in fact, their data is pointing towards them."[10] and
• "We show quantitatively that MicroBooNE results, while a promising start, unquestionably do not probe the full parameter space of sterile neutrino models hinted at by MiniBooNE and other data."[11]

The key issue noted in these papers is a mild deficit of electron interactions in the MicroBooNE data [8] that can be interpreted as a signature of electron flavor oscillation to sterile neutrinos.

MicroBooNE collected five years of physics data, ending its run in 2021 as the longest continually running liquid argon time projection chamber to date.[12]