Study of Reconstructed 39Ar Beta Decays at the MicroBooNE Detector*

Liquid Argon Time Projection Chambers (LArTPCs) are imaging detectors that can be used to reconstruct the energies of particles and their trajectories with fine-grained resolution. One open question regarding large LArTPCs is their capability of measuring low-energy, point-like charge depositions such as those associated with interactions of low-energy supernova burst neutrinos within the detector. Given their point-like nature and low energies, naturally occurring 39Ar beta decays in LArTPCs provide a powerful resource in probing energy scales relevant for the reconstruction of supernova burst neutrinos and solar neutrinos at future large-scale LArTPC experiments such as DUNE (Deep Underground Neutrino Experiment). We present the first study of reconstructed 39Ar beta decays in a large LArTPC with data from MicroBooNE, a large (85-ton active mass) LArTPC neutrino experiment operating near the surface at Fermilab in Batavia, Illinois. The use of 39Ar beta decays as a potential calibration source in large LArTPC detectors is also discussed in detail.