Improved limits on solar axions and bosonic dark matter from the CDEX-1B experiment using the profile likelihood ratio method

TL;DR

This paper reports improved constraints on solar axions and bosonic dark matter using low-threshold germanium detector data analyzed with the profile likelihood ratio method, enhancing sensitivity below 0.8 keV.

Contribution

The study introduces a more sensitive analysis technique and lower energy threshold, leading to tighter limits on axion and dark matter couplings compared to previous experiments.

Findings

Set new upper limits on axion-electron coupling $g_{Ae}$

Placed constraints on bosonic dark matter below 0.8 keV

Achieved an energy threshold of 160 eV, improving sensitivity

Abstract

We present the improved constraints on couplings of solar axions and more generic bosonic dark matter particles using 737.1 kg-days of data from the CDEX-1B experiment. The CDEX-1B experiment, located at the China Jinping Underground Laboratory, primarily aims at the direct detection of weakly interacting massive particles using a p-type point-contact germanium detector. We adopt the profile likelihood ratio method for analysis of data in the presence of backgrounds. An energy threshold of 160 eV was achieved, much better than the 475 eV of CDEX-1A with an exposure of 335.6 kg-days. This significantly improves the sensitivity for the bosonic dark matter below 0.8 keV among germanium detectors. Limits are also placed on the coupling $g_{Ae} < 2.48 \times 10^{-11}$ from Compton, bremsstrahlung, atomic-recombination and de-excitation channels and $g^{eff}_{AN} \times g_{Ae} < 4.14 \times 10^{-17}$ from a $^{57}$Fe M1 transition at 90\% confidence level.