Search for proton decay via $pto e^+pi^0$ and $pto mu^+pi^0$ with an enlarged fiducial volume in Super-Kamiokande I-IV

We have searched for proton decay via $pto e^+pi^0$ and $pto mu^+pi^0$ modes with the enlarged fiducial volume data of Super-Kamiokande from April 1996 to May 2018, which corresponds to 450 kton$cdot$years exposure. We have accumulated about 25% more livetime and enlarged the fiducial volume of the Super-Kamiokande detector from 22.5 kton to 27.2 kton for this analysis, so that 144 kton$cdot$years of data, including 78 kton$cdot$years of additional fiducial volume data, has been newly analyzed. No candidates have been found for $pto e^+pi^0$ and one candidate remains for $pto mu^+pi^0$ in the conventional 22.5 kton fiducial volume and it is consistent with the atmospheric neutrino background prediction. We set lower limits on the partial lifetime for each of these modes: $tau/B(pto e^+pi^0) > 2.4 times 10^{34}$ years and $tau/B(pto mu^+pi^0) > 1.6 times 10^{34}$ years at 90% confidence level.