Here we present measurements of the rates of emission of single electrons from the cathode of a proportional counter filled with a mixture of Ar + CH4 (10%) at 1 bar. We interpret the results as a possible photoelectric effect associated with hidden photons (HPs). Our results set upper limits for HPs from cold dark matter (CDM). We also discuss future options for searches for HPs from CDM using a multi-cathode counter technique.

A method for registration of the coherent scattering reactor antineutrino on nuclei using a three-section low-background proportional counter was proposed. It is planned to use argon and xenon as the working substance. As has been shown on a test bench, pulse shape discrimination can effectively suppress the background from electromagnetic interference and microphonic effects in the energy range from 20 to 100 eV where the effect of coherent scattering of neutrinos on nuclei is expected with a factor of about 10³. Problems of the neutron background generated by cosmic-ray muons are analyzed. The scheme of the experimental setup is presented.

We propose a method of search for cold dark matter, which presumably consists of hidden photons, by detecting single electrons emitted from the surface of the metal cathode of a counter as a result of the conversion of hidden photons. To detect single electrons, a special multi-cathode counter has been designed. The counter allows one to discriminate the background by subtracting from the effect the dark count rate measured in a configuration with a blocking potential that prevents the drift of the cathode-emitted electrons to the central counter. The measurement results are presented and significant progress in the development of the methodology is demonstrated. Further steps to improve the method are discussed.