First Axion Results from the XENON100 Experiment

TL;DR

This work reports the first axion and axion-like particle searches with XENON100 using the axio-electric effect in liquid xenon. A profile likelihood analysis of 224.6 live days × 34 kg finds no evidence for axions, yielding a 90% CL upper limit on the axion-electron coupling $g_{Ae}$ and translating into mass bounds within the DFSZ and KSVZ frameworks. For solar axions with $m_A<1$ keV, the limit is $g_{Ae} < 7.7\times10^{-12}$, corresponding to $m_A < 0.3$ eV/$c^2$ (DFSZ) or $m_A < 80$ eV/$c^2$ (KSVZ); for galactic ALPs constituting all DM, $g_{Ae} < 1\times10^{-12}$ in the 1–40 keV/$c^2$ range, representing the best direct-detection constraint to date. These results demonstrate the continued sensitivity of large LXe detectors to low-energy electron-recoil signatures from axions and ALPs and set benchmarks for future searches in this channel.

Abstract

We present the first results of searches for axions and axion-like-particles with the XENON100 experiment. The axion-electron coupling constant, $g_{Ae}$, has been probed by exploiting the axio-electric effect in liquid xenon. A profile likelihood analysis of 224.6 live days $\times$ 34 kg exposure has shown no evidence for a signal. By rejecting $g_{Ae}$, larger than $7.7 \times 10^{-12}$ (90\% CL) in the solar axion search, we set the best limit to date on this coupling. In the frame of the DFSZ and KSVZ models, we exclude QCD axions heavier than 0.3 eV/c$^2$ and 80 eV/c$^2$, respectively. For axion-like-particles, under the assumption that they constitute the whole abundance of dark matter in our galaxy, we constrain $g_{Ae}$, to be lower than $1 \times 10^{-12}$ (90\% CL) for mass range from 1 to 40 keV/c$^2$, and set the best limit to date as well.

Figures (7)

• Figure 1: Top: Event distribution in the flattened $\mathrm{log_{10}}(S2_b/S1)$ vs. $S1$ space for science data (black points) and calibration (grey points). Straight dashed lines show the selection cut on the flattened $\mathrm{log_{10}}(S2_b/S1)$ (horizontal red lines) and the 3 PE threshold cut (red vertical line). Bottom: Global acceptance for electronic recoil events, evaluated on calibration data.
• Figure 2: Conversion function between energy recoil in keV and $S1$ in PE. The $n^{exp}$ central value and the $\pm 1 \sigma$ uncertainty are indicated with solid blue and black dashed line, respectively.
• Figure 3: Background model $N_b \times f_b$ (grey line), scaled to the correct exposure, as explained in the text. The analytic function $f_b$ is based on the $^{60}$Co and $^{232}$Th calibration data (empty blue dots), and is used in Eq.(\ref{['eq:signallike']}). The 3 PE threshold is indicated by the vertical red dashed line.
• Figure 4: Event distribution of the data (black dots), and background model (grey) of the solar axion search. The expected signal for solar axions with $m_A<$ 1 keV/c$^2$ is shown by the dashed blue line, assuming $g_{Ae}$$= 2 \times 10^{-11}$, the current best limit, from EDELWEISS-II edelweiss2013. The vertical dashed red line indicates the low $S1$ threshold, set at 3 PE. The top axis indicates the expected mean energy for electronic recoils as derived from the observed S1 signal.
• Figure 5: The XENON100 limits (90% CL) on solar axions is indicated by the blue line. The expected sensitivity, based on the background hypothesis, is shown by the green/yellow bands ($1 \sigma$/$2 \sigma$). Limits by EDELWEISS-II edelweiss2013, and XMASS xmass2013 are shown, together with the limits from a Si(Li) detector from Derbin et al. derbin2012. Indirect astrophysical bounds from solar neutrinos gondolo2009 and red giants viaux2013 are represented by dashed lines. The benchmark DFSZ and KSVZ models are represented by black lines DFSZKSVZ.