Physics Seminar: First results of the DOSUE-RR experiment — search for dark-photon CDM in the mass range 74-110 μeV/c2

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Overview

Revealing the property of the cold dark matter (CDM) is one of the most important subjects for particle physics and cosmology. Many experiments have attempted to detect CDM for more than two decades. However, there have not been conclusive results above the mass range of GeV/c2 yet. Therefore, expanding the mass range for the CDM search is a natural strategy, and the dark photon is one of the CDM candidates. The dark photon is predicted in the context of high-scale inflation models and a part of string theories.

The dark photons convert to ordinary photons at the boundary of electromagnetic fields such as a metal surface. The frequency of the conversion photon corresponds to the mass of the dark-photon CDM owing to the energy conservation, i.e., hν = mc2. We launched a series of experiments to search for the conversion photons in the radio-wave range: DOSUE-RR (ド スエ-ダブルアール, Dark-matter Observing System for Un-Explored Radio-Range). Our target mass range for the dark-photon CDM is 10 μeV/c2–meV/c2.

For the first experiment, we developed a cryogenic millimeter-wave receiver in a frequency range 18.0–26.5 GHz, which corresponds to a dark photon mass range 74–110 μeV/c2, and succeeded in improving the experimental sensitivity from the previous study. Our first search was performed for two weeks in 2021. We did not find any significant signal of the dark-photon CDM and set the upper limit on the coupling constant between dark photons and ordinary photons. This is the most stringent constraint to date, and tighter than indirect constraints from cosmological observations. I will present our first results and future prospects of the DOSUE-RR experiment.