The status of JSNS2 and JSNS2-II

Abstract

The search for sterile neutrinos is one of the hottest topics in neutrino physics in this decade. JSNS2 (J-PARC Sterile Neutrino Search at the J-PARC Spallation Neutron Source) and the second phase of the experiment JSNS2-II aim to search for neutrino oscillations with Delta m square near 1 eV2 at the J-PARC Materials and Life Science Experimental Facility (MLF). With the 1 MW of 3 GeV proton beam created by Rapid Cycling Synchrotron (RCS) and spallation neutron target, an intense neutrino beam from muon decay at rest is available. Neutrinos come predominantly from mu+ decay: mu+ -> e+ + numubar + nue. The oscillation searched for is numubar to nue, which is detected via the inverse beta decay interaction: nuebar + p -> e+ + n, followed by gammas from neutron capture of Gd. The JSNS2 detector (and the near detector in the JSNS2-II) with a fiducial volume of 17 tonnes is located 24 m away from the mercury target. The new far detector of the JSNS2-II that is being newly constructed is located outside the MLF building with the baseline of 48 m. This far detector has a 32 tonnes of the fiducial volume. These experiments directly test the LSND anomaly. Additional physics programs include the cross section measurements with neutrinos with order 10 MeV from muon decay at rest and with monochromatic 236 MeV from kaon decay at rest. These are important for the potential observation of a supernova explosion using neutrinos and nuclear physics. JSNS2 started data taking in 2020 and the accumulated Proton-On-Target (POT) is 1.45 x 10^{22}. The far detector of JSNS2-II is under the construction. This article describes the status of these experiments.