Investigating the XENON1T Low-Energy Electronic Recoil Excess Using NEST

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 3.5σ excess potentially consistent with dark matter, or with solar axions. Here, we utilize the Noble Element Simulation Technique (NEST) software to simulate the XENON1T detector, reproducing the excess. We present 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 ± 11 37 Ar decays. Furthermore, this results in new, modified background models, reducing the significance of the excess to only 1.5-2σ, at least with non-PLR methods. This is independent confirmation the excess is a real effect, but potentially explicable by known physics. Many cross-checks of our 37 Ar hypothesis are presented.

XENON1T implications for the DAMA annual modulation: The good, the bad and the ugly

“…which produces a ∼ 0.6 keV offset at E m R = 2.3 keV (marginally higher than the 0.5 keV offset considered in [43]) and rising higher at lower energies. Figure 7a (standard resolution) and Figure 7b (modified resolution) show the rate, taking into account the effect of a mismodelled energy scale as given in Eq.…”

“…The XENON1T experiment has observed an excess of electron recoil events in a combined S1 and S2 analysis near their low energy threshold of around 2 keV [4]. The statistical significance of the excess is modest, ∼ 3.5σ, and while background interpretations exist [4,43] one can also interpret the excess as a possible signal for new physics [4]. Indeed, the XENON1T excess has sparked much interest in the theoretical community, including new physics models involving axions, nonstandard neutrino properties as well as dark matter e.g.…”

“…( 8), setting p = 1.6 (N 1.103). Again, this is a purely phenomenological modification employed as a means to flatten the curve, not otherwise justified; there are better motivated modifications, such as a skewed normal distribution [43] which could be considered instead, especially if one is of the view that the ends does not justify the means.…”

“…In ref. [43] it has been argued that a slight ∼ 0.5 keV offset is plausible at around 2.3 keV rising even higher at low energies. That is, the measured 2.3 keV energy could correspond to 2.8 keV true recoil energy.…”

Decaying fermionic warm dark matter and XENON1T electronic recoil excess

“…In most of these cases, the interactions which cause the XENON1T ER events are difficult to probe in indirect search observations. Some previous works [21][22][23] have also tried to fit the observed data using various possible background models (other than the standard background B 0 [1]), leaving some small scopes for adding new signals.…”