Investigating the XENON1T Low-Energy Electronic Recoil Excess Using NEST

TL;DR

This study uses NEST simulations to reproduce the XENON1T low-energy excess, suggesting it can be explained by known physics such as argon decays, thus reducing its statistical significance.

Contribution

The paper demonstrates that the XENON1T excess can be modeled with NEST, especially via argon decays, providing an alternative explanation to dark matter or solar axions.

Findings

The excess can be reproduced by adding 31±11 ^{37}Ar decays.

Modified background models reduce the excess significance to ≤2.2σ.

The excess is likely a known physics effect, not new physics.

Abstract

The search for dark matter, the missing mass of the Universe, is one of the most active fields of study within particle physics. The XENON1T experiment recently observed a 3.5$\sigma$ excess potentially consistent with dark matter, or with solar axions. Here, we will use the Noble Element Simulation Technique (NEST) software to simulate the XENON1T detector, reproducing the excess. We utilize different detector efficiency and energy reconstruction models, but they primarily impact sub-keV energies and cannot explain the XENON1T excess. However, using NEST, we can reproduce their excess in multiple, unique ways, most easily via the addition of 31$\pm$11 $^{37}Ar$ decays. Furthermore, this results in new, modified background models, reducing the significance of the excess to $\le2.2\sigma$ at least using non-Profile Likelihood Ratio (PLR) methods. This is independent confirmation that the excess is a real effect, but potentially explicable by known physics. Many cross-checks of our $^{37}Ar$ hypothesis are presented.