XENON1T Excess: Some Possible Backgrounds

TL;DR

This paper investigates potential background sources in XENON1T that could explain the observed low-energy excess, focusing on cosmogenic and decay chain isotopes, and assesses their plausibility through spectral fitting.

Contribution

It identifies and evaluates new possible background isotopes that might contribute to the XENON1T excess, using spectral fitting to constrain their contributions.

Findings

Certain isotopes can plausibly account for the excess within rate constraints.

Multiple background sources may collectively explain the excess.

Some backgrounds are constrained or ruled out by the data.

Abstract

This work is a study of some possible background sources in the XENON1T environment which might affect the energy spectrum of electronic recoil events in the lower side and might contribute to the observed excess. We have identified some additional possible backgrounds, like $^{41}$Ca, $^{49}$V, $^{63}$Ni, $^{106}$Ru and $^{125}$Sb coming from cosmogenic production, where the former two emit monoenergetic $X$-rays and the latter three have $\beta$ decays, or isotopes, like $^{210}$Pb, from the decay chain of $^{222}$Rn emanated in liquid xenon from the materials, or isotopes, like $^{137}$Cs, produced due to neutron capture. We perform a $\chi^2$ fitting of the ER spectrum from these backgrounds along with tritium to the observed excess events by varying their individual rates to understand whether they can be present to contribute to the low energy excess or their presence is constrained from the data. We also study the possibility of simultaneous presence of more than one such backgrounds, and how this affects the rates required by individual backgrounds to explain the excess.