12:00–1:00 pm
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STUDY OF EXCESS ELECTRONIC RECOIL EVENTS IN XENON1T
XENON1T is a ton-scale, liquid-xenon particle detector primarily designed to search for dark matter. However, due to its unprecedentedly low background level, large detector mass, and low energy threshold, it is sensitive to a multitude of phenomena not described by the Standard Model (SM) of particle physics. In this work, we use XENON1T to search for electronic recoils induced by (1) solar axions, (2) a neutrino magnetic dipole moment, and (3) bosonic dark matter.
While searching for these three signals, we stumbled upon an interesting feature in the XENON1T data, an excess of events with energies in the 1—7 keV range. To determine the robustness of this excess, we studied in detail the event reconstruction and energy threshold of the XENON1T detector and characterized all known sources of background according to their energy spectra and temporal dependencies. Based on these studies, we conclude that the data are not compatible with the background model prediction and, with a statistical significance greater than 3σ, are suggestive of an additional background component or potentially new physics.
We then considered a number of other potential backgrounds. Trace amounts of tritium may be a possible explanation, but is discounted by the measured purity of the liquid xenon. Finally, we interpreted the excess within the context of potential beyond-the-SM physics. Of all hypotheses considered, the solar axion model best describes the feature in the data; however, a neutrino magnetic moment and 2.3-keV bosonic dark matter are both consistent with the data as well. With the next phase of the XENON program, the larger and more sensitive XENONnT, being commissioned now, we should know soon whether this result represents a severely unlucky statistical fluke, a previously unconsidered source of background, or an exciting hint of new physics.
Committee:
Luca Grandi (Chair)
Juan Collar
Liantao Wang
William Irvine
Evan will be starting a postdoc at UC San Diego, jointly advised by Liang Yang and Kaixuan Ni, where he will continue working with liquid xenon technology to search for a variety of rare phenomena, including dark matter, solar axions, neutrinoless double-beta decay, and a neutrino magnetic moment.