We report results from searches for new physics with low-energy electronic recoil data recorded with the XENON1T detector. With an exposure of 0.65 tonne-years and an unprecedentedly low background rate of 76 +- 2 (stat) events/(tonne*year*keV) between 1 and 30 keV, the data enables competitive searches for solar axions, an enhanced neutrino magnetic moment using solar neutrinos, and bosonic dark matter. An excess over known backgrounds is observed below 7 keV, rising towards lower energies and prominent between 2 and 3 keV. The solar axion model has a 3.5 sigma significance, and a three-dimensional 90% confidence surface is reported for axion couplings to electrons, photons, and nucleons. The neutrino magnetic moment signal is similarly favored over background at 3.2 sigma. Both results are in tension with stellar constraints. The excess can also be explained by beta decays of tritium at 3.2 sigma significance with a trace amount that can be neither confirmed nor excluded with current knowledge of production and reduction mechanisms. The significances of the solar axion and neutrino magnetic moment hypotheses are decreased to 2.1 sigma and 0.9 sigma, respectively, if an unconstrained tritium component is included in the fitting.

Mr. Jingqiang Ye received his bachelor of science degree from Zhejiang University in 2014 and is a graduate student in the physics department of University of California, San Diego, under the supervision of Prof. Kaixuan Ni. He joined the XENON Collaboration in 2015. His research interests include searches for WIMP dark matter, axions, and other new physics beyond the Standard Model, as well as noble liquid detector development.