First measurement of quasi-elastic $\mathrm{\Lambda }$ baryon production in muon anti-neutrino interactions in the MicroBooNE detector

We present the first measurement of the cross section of Cabibbo-suppressed $\mathrm{\Lambda }$ baryon production, using data collected with the MicroBooNE detector when exposed to the neutrinos from the Main Injector beam at the Fermi National Accelerator Laboratory. The data analyzed correspond to $2.2\times {10}^{20}$ protons on target of neutrino mode running and $4.9\times {10}^{20}$ protons on target of anti-neutrino mode running. An automated selection is combined with hand scanning, with the former identifying five candidate $\mathrm{\Lambda }$ production events when the signal was unblinded, consistent with the GENIE prediction of $5.3\pm 1.1$ events. Several scanners were employed, selecting between three and five events, compared with a prediction from a blinded Monte Carlo simulation study of $3.7\pm 1.0$ events. Restricting the phase space to only include $\mathrm{\Lambda }$ baryons that decay above MicroBooNE’s detection thresholds, we obtain a flux averaged cross section of $2.0_{-1.7}^{+2.2}\times {10}^{-40}$ cm${}^2\mathrm{/}$Ar, where statistical and systematic uncertainties are combined.