V.V. Sosnovtsev

Prospects for observation of neutrino-nuclear neutral current coherent scattering with two-phase Xenon emission detector

We propose to detect and to study neutrino neutral current coherent scattering off atomic nuclei with a two-phase emission detector using liquid xenon as a working medium. Expected signals and backgrounds are calculated for two possible experimental sites: the Kalinin Nuclear Power Plant in the Russian Federation and the Spallation Neutron Source at the Oak Ridge National Laboratory in the U.S.A. Both sites have advantages as well as limitations. The experiment looks feasible at either location.

Experimental study of ionization yield of liquid xenon for electron recoils in the energy range 2.8–80 keV

We present the results of the first experimental study of ionization yield of electron recoils with energies below 100 keV produced in liquid xenon by the isotopes: 37Ar, 83mKr, 241Am, 129Xe, 131Xe. It is confirmed by a direct measurement with 37Ar isotope (2.82 keV) that the ionization yield is growing up with the energy decrease in the energy range below ~ 10 keV accordingly to the NEST predictions. Decay time of scintillation at 2.82 keV is measured to be 25 +/- 3 ns at the electric field of 3.75 kV/cm.

RED-100 detector for the first observation of the elastic coherent neutrino scattering off xenon nuclei

The RED-100 (Russian Emission Detector) is being constructed for the experiment to search for elastic coherent neutrino scattering off atomic nuclei. This fundamental process was predicted several decades ago by the Standard Model of electroweak interactions but has not been discovered yet. The RED-100 is a two-phase emission xenon detector containing ~200 kg of the liquid Xe (~ 100 kg of that is in a fiducial volume). One of the possible sites to carry out the experiment is the SNS (Spallation Neutron Source) facility at Oak Ridge National Laboratory, USA. SNS is the worlds most intense pulsed source of neutrinos and unique place to study neutrino properties. The energy spectrum of neutrinos produced at the SNS extends up to ~ 50 MeV and satisfies coherence condition. These neutrinos give kinetic energies of Xe recoils up to a few tens of keV where the response of nuclear recoils is well-known from neutron calibrations of dark matter detectors. The detector will be deployed in the basement under the experimental hall at a distance of ~30 meters from the SNS target. The expected signal and background (neutron and gamma) are estimated for this specific location. The detector details, current status and future plans are provided.

Noise characteristics of low-background Hamamatsu R11410-20 photomultiplier tubes

The RED-100 two-phase liquid xenon emission detector is developed today for the experiment aimed at searching for elastic coherent neutrino scattering off atomic nuclei. The main elements of the photodetector system of the RED-100 detector are Hamamatsu R11410-20 photomultiplier tubes (PMTs) dedicated for low-background experiments and liquid xenon environment. The basic characteristics of the PMTs are investigated, in particular, noise pulses and afterpulses, which may cause difficulties in searching for rare events. Amplitude distributions of the noise pulses and time distributions of the afterpulses, as well as the dependences of the noise pulse rate on the PMT bias voltage and the temperature are presented.

A Two-Phase Emission Liquid Xe Detector for Study of Low-Ionization Events at the Research Reactor IRT MEPhI

A two-phase emission detector containing 5 kg of liquid Xe is installed at the horizontal experimental channel of the research nuclear reactor IRT MEPhI to measure the liquid Xe response to nuclei recoils with kinetic energies below 1 keV. Preliminary tests have demonstrated that ≥ 15 μs electron lifetime in liquid Xe and ~ 10 photoelectrons single ionization electron signal are achieved. These parameters are sufficient to detect and identify events at the single electron level.

A controllable voltage divider for Hamamatsu R11410-20 photomultipliers for use in the RED 100 emission detector

A control circuit for the operation of Hamamatsu R11410-20 photomultiplier tubes (PMTs), which is intended for use in the RED 100 liquid-xenon emission detector, was developed. To prevent the photocathode degradation due to intense flashes that are associated with signals from high-energy cosmic-ray muons, the circuit forms a voltage pulse that is fed to the PMT photocathode and “blocks” the interelectrode gap between the photocathode and the first dynode. Thus, electron current through this gap is stopped for some time, which suffices for the complete collection of ionization electrons in the RED 100 detector after a cosmic muon passes its sensitive volume. The parameters of the circuit are selected such that the PMT relaxation time after the termination of a blocking pulse, which is determined by the transient processes in the divider, is ∼200 μs for a divider with a total resistance of 20 MΩ. This is acceptable for the intended application of the RED 100 detector in an experiment on the search for coherent neutrino scattering off xenon nuclei.

The RED-100 two-phase emission detector

The RED-100 experimental setup, which is designed to detect elastic coherent neutrino scattering off xenon nuclei, is described. One specific feature of this setup is the possibility of using it in above ground experiments. The setup is based on the RED-100 two-phase emission detector in which liquid xenon is used as a working medium for detection of rare events. The results of the technical run with the setup are presented. These are the evidence of the normal operation of all systems and the readiness of the setup for carrying out an experiment.

Characterization of the low-background Hamamatsu R11410- 20 cryogenic PMTs for the RED100 detector

The RED100 two-phase liquid xenon emission detector for neutrino coherent scattering experiments is equipped with 38 Hamamatsu R11410-20 photomultiplier tubes capable to operate at cryogenic temperatures and made of low background materials. A dedicated characterization procedure has been carried out for each PMT unit to be installed into the detector. The results presented here include single photoelectron analysis, gain curves for a wide range of the bias voltage values, data on dark count rate for 34 PMT samples. Peculiar noise characteristics of selected PMT units are analysed and discussed.

Purification of liquid xenon with the spark discharge technique for use in two-phase emission detectors

A procedure for spark-discharge purification of a liquid xenon sample with a mass of 55 kg is described. The average lifetime of ionization electrons before capture by electronegative impurities in liquid xenon increased from ≤ 0.1 μs to ≥ 50 μs for an electric field of 50–500 V/cm as a result of the procedure. The xenon purified with this method is intended for use in the RED-100 detector for observation of the process of coherent elastic neutrino scattering off xenon nuclei.

Performance of Hamamatsu R11410-20 PMTs under intense illumination in a two-phase cryogenic emission detector

Hamamatsu R11410-20 PMTs are used in the RED-100 two-phase xenon emission detector built to search for the rare process of coherent elastic neutrino-nucleus scattering using intense artificial neutrino flux. We demonstrate how to adapt the PMTs for their operation under strong illumination caused by electroluminescent signals from gamma and cosmogenic muon backgrounds which are significant at shallow depth experimental sites. The PMT linearity is demonstrated for signals in the dynamic range from 1 to 2*104 photoelectrons. Impact of a photoelectric effect at the PMT first dynode to the capabilities of the RED-100 photodetection system is studied and quantified.