Direct Searches for Hidden-Photon Dark Matter with the SHUKET Experiment

Hidden photons are dark matter candidates motivated by theories beyond the standard model of particle physics. They mix with conventional photons, and they can be detected through the very weak electromagnetic radiation they induce at the interface between a metal and the air. SHUKET [search for U(1) dark matter with an electromagnetic telescope] is a dedicated experiment sensitive to the hidden photon-induced signal. The results from a hidden photon search campaign are reported, with no significant detection of a dark matter signal. Exclusion limits are derived from the observed noise fluctuations in a 5–6.8 GHz frequency range, corresponding to a hidden photon mass region ranging from 20.8 to $28.3\mu \mathrm{eV}$. SHUKET is currently the most sensitive instrument in this mass range, and the obtained limits on the kinetic mixing term constrain significantly dark matter models inspired from string theory.

Figure 1

Top: Principle of the SHUKET experiment. Bottom left: Picture of the spherical cap; reflective patches are to help with the alignment procedure. Bottom right: Horn antenna with the shielding.

Figure 2

Power density measured in the SHUKET experiment before cleaning. The ON distribution is shifted upwards by a factor 1.5 to improve readability. The insets show two distributions of residuals (ON-OFF) on 100-MHz bands between 5.5 and 5.6 GHz (left) and 6.5 and 6.6 GHz (right).

Figure 3

Detail of the distribution of residuals around 6.4 GHz, together with a $3\sigma$-excluded dark matter signal.

Figure 4

95% confidence level upper limits on the dark matter signal power. The vertical line at 6.331 GHz corresponds to the narrow band search.

Figure 5

95% confidence level upper limits on the hidden photon kinetic mixing term (red curve).