First measurement of the temperature dependence of muon transfer rate from the µp atoms to oxygen

We report the first measurement of the temperature dependence of muon transfer rate from µp atoms to oxygen between 100 and 300 K. Data were obtained from the X-ray spectra of delayed events in gaseous target H2/O2 exposed to a muon beam. Based on the data, we determined the muon transfer energy dependence up to 0.1 eV, showing an 8-fold increase in contrast with the predictions of constant rate in the low energy limit. This work set constraints on theoretical models of muon transfer, and is of fundamental importance for the measurement of the hyperfine splitting of µp by the FAMU collaboration.