Telling Solar Neutrinos from Solar Axions When You Can't Shut Off the Sun

Understand

The XENON1T experiment recently reported an excess of events at low electron recoil energies, which may be due to interactions of solar neutrinos inside the detector via a large neutrino magnetic moment.

• We point out that a $^{51}$Cr neutrino source placed close to the detector can directly test this hypothesis.