Search for Low-energy Electronic Recoil Excess in XENONnT

The XENON1T experiment achieved the lowest electronic recoil background among all dark matter experiments, namely 76+-2 events/(t y keV) below 30 keV. An excess of electronic recoils was found below 7 keV and most prominent between 2 and 3 keV. The excess could be explained by solar axions, solar neutrinos with an enhanced magnetic moment, or a trace amount of tritium background which could neither be confirmed nor rejected. The XENONnT experiment, which has replaced XENON1T, features a larger scale time projection chamber with a total of 8.5 tonnes of liquid xenon (LXe), of which 6 tonnes are active. The even lower electronic recoil background expected in XENONnT, due to the LXe self-shielding, the careful material screening and selection, and the effective removal of intrinsic contaminations such as Kr-85 and Rn-222 by cryogenic distillation, will enable more competitive searches for a variety of physics. In particular, XENONnT will be more sensitive in the search for new physics potentially associated with an excess of low-energy electronic recoils, as hinted by XENON1T. In this talk, I will review the excess electronic recoils in XENON1T and present the prospect to decipher the origin of the excess with XENONnT.