X-ray searches for decaying sterile neutrinos with the Micro-X and XQC sounding rockets

Abstract

The nature of dark matter is a major question in modern physics. Cosmological measurements have motivated the existence of matter beyond the standard model, but thus far there has not been a definitive observation of any particular candidate. One proposed particle is the sterile neutrino, a counterpart of the observed active neutrino with right-handed chirality. A recent detection of an unidentified X-ray emission line has been suggested as a possible signal of sterile neutrino decay, but requires more observations with high-resolution spectroscopy to fully explore the nature of the line. In the first half of this thesis, we present the results from a search for a similar unidentified line, using data from the X-ray Quantum Calorimeter (XQC) sounding rocket.

The XQC microcalorimeter array provides superior energy resolution to current satellite instruments and its wide field of view is well suited for observations of the Milky Way dark matter halo which would provide an all-sky signal. This analysis does not find evidence of an emission line, but also does not exclude the signal seen in other targets, motivating a re-flight of the instrument targeting near the center of the galaxy where the signal strength is expected to be greater. In the second half of this thesis, we present a summary of the Micro-X sounding rocket and its development into a flight instrument. Micro-X is an X-ray microcalorimeter, which uses sensitive thermometry to perform high-resolution spectroscopy with superior resolution to other non-dispersive techniques.

The Micro-X array employs Transition Edge Sensors, which provide improved resolution and larger array sizes than the Si thermistor detectors used in previous instruments, along with SQUID multiplexing for readout and is the first instrument to employ either of these technologies in a space environment. We also describe the results of its first flight, which took place on July 22, 2018 in which it attempted to observe the Cassiopeia A supernova remnant. While a failure of the attitude control system meant that no astronomy could be done with this flight, it was still useful for evaluating the instrument performance in anticipation of future flights.