Characterizing the energy resolution of the MicroBooNE LArTPC at the MeV scale using monoenergetic features of ${}^{208}$Tl decays

A detailed understanding of the capabilities and fidelity of low-energy reconstruction is crucial for taking advantage of MeV-scale neutrino physics opportunities in liquid argon time projection chambers (LArTPCs). This study presents a measurement of the resolution of reconstructed energy in the MicroBooNE LArTPC at $\approx 1.5$ MeV. The characterization is performed using monoenergetic signals generated by $2.614$ MeV $\gamma$-rays from ${}^{208}$Tl decays undergoing pair production in the detector. The resolution is found to be ($7.52\pm 0.78\text{(stat)}\pm 0.92\text{(syst)}$)%. This value is consistent with the MicroBooNE simulation prediction of ($9.70\pm 0.65\text{(stat)}$)% at the $1.6\sigma$ level. This study represents the first ever measurement of LArTPC energy resolution at the MeV scale and provides a pathway for monoenergetic energy calibrations in future experiments using LArTPC detectors.