On search for eV hidden sector photons in Super-Kamiokande and CAST experiments

TL;DR

The paper investigates experimental tests for eV-scale hidden sector photons produced by solar photons via kinetic mixing. It proposes two laboratory approaches: a direct search with Super-Kamiokande exploiting γ'→γ oscillations in PMT vacuum regions, and an upgraded CAST helioscope with vacuum detectors and mirrors to focus potential regenerated photons. Both strategies yield projected sensitivities to the mixing parameter χ down to ~10^-9 for sub-eV hidden-photon masses, with SK providing competitive exclusions relative to CAST keV searches and CAST_eV extending sensitivity to lower masses beyond some laser experiments. The work emphasizes the importance of low-background, high-efficiency single-photon detection and vacuum quality, offering complementary, laboratory-based probes of hidden photons independent of astrophysical bounds.

Abstract

If light hidden sector photons exist, they could be produced through kinetic mixing with solar photons in the eV energy range. We propose to search for this hypothetical hidden photon flux with the Super-Kamiokande and/or upgraded CAST detectors. The proposed experiments are sensitive to mixing strengths as small as 10^-9 for hidden photon masses in the sub eV region and, in the case of non-observation, would improve limits recently obtained from photon regeneration laser experiments in this mass region.

Figures (3)

• Figure 1: Schematic illustration of the direct search for light hidden-sector photons in the Super-K experiment. Hidden photons penetrate the Earth and convert into visible photons inside the vacuum volume of the Super-K PMTs. This results in an increase of the counting rate of those Super-K PMTs that are 'illuminated' by the Sun from the back, in comparison with those facing the Sun. If, for instance, the Earth rotates around the Z-axis, the counting rate is a periodic function of the angle $\psi$, i.e. is daily modulated.
• Figure 2: Regions in the ($m_{\gamma '}, \chi$) plane which could be excluded by the proposed experiments: SuperK (gray region) and CAST$_{eV}$ (black). Also shown are the regions, with self explanatory labels, excluded by CAST in the keV range jr1, by LSW experiments ring7 and by searches of deviations of Coulomb's law c1c2.
• Figure 3: Schematic illustration of the direct search for solar ${\gamma '}$-flux in the CAST experiment. A vacuum pipe equipped from both sides by mirrors used to focus ordinary photons produced from ${\gamma '} \to \gamma$ oscillations on single photon detectors (SPDs). The manifestation of a signal would be an increase of the counting rate of the SPD that is 'illuminated' by the Sun compare to the other.