A. V. Kumpan

Observation of coherent elastic neutrino-nucleus scattering

A 14.6-kilogram sodium-doped CsI scintillator is used to detect a neutrino scattering process with a 6.7σ confidence level. Nailing down an elusive process Detecting neutrinos—elementary particles that barely interact with other matter—usually requires detectors of enormous size. A particular interaction of neutrinos with atomic nuclei, called the coherent elastic neutrino-nucleus scattering (CEνNS), is predicted to occur with relatively high probability, and it could be used to drastically reduce the size of neutrino detectors. However, observing this interaction requires a source of low-energy neutrinos and detectors that contain nuclei of optimal mass. Akimov et al. observed CEνNS with a 6.7σ confidence by using a comparatively tiny, 14.6-kg sodium-doped CsI scintillator exposed to neutrinos from a spallation neutron facility (see the Perspective by Link). The discovery places tighter bounds on exotic, beyond-the-standard-model interactions involving neutrinos. Science, this issue p. 1123; see also p. 1098 The coherent elastic scattering of neutrinos off nuclei has eluded detection for four decades, even though its predicted cross section is by far the largest of all low-energy neutrino couplings. This mode of interaction offers new opportunities to study neutrino properties and leads to a miniaturization of detector size, with potential technological applications. We observed this process at a 6.7σ confidence level, using a low-background, 14.6-kilogram CsI[Na] scintillator exposed to the neutrino emissions from the Spallation Neutron Source at Oak Ridge National Laboratory. Characteristic signatures in energy and time, predicted by the standard model for this process, were observed in high signal-to-background conditions. Improved constraints on nonstandard neutrino interactions with quarks are derived from this initial data set.

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.

The COHERENT Experiment at the Spallation Neutron Source

The COHERENT collaborations primary objective is to measure coherent elastic neutrino-nucleus scattering (CEvNS) using the unique, high-quality source of tens-of-MeV neutrinos provided by the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory (ORNL). In spite of its large cross section, the CEvNS process has never been observed, due to tiny energies of the resulting nuclear recoils which are out of reach for standard neutrino detectors. The measurement of CEvNS has now become feasible, thanks to the development of ultra-sensitive technology for rare decay and weakly-interacting massive particle (dark matter) searches. The CEvNS cross section is cleanly predicted in the standard model; hence its measurement provides a standard model test. It is relevant for supernova physics and supernova-neutrino detection, and enables validation of dark-matter detector background and detector-response models. In the long term, precision measurement of CEvNS will address questions of nuclear structure. COHERENT will deploy multiple detector technologies in a phased approach: a 14-kg CsI[Na] scintillating crystal, 15 kg of p-type point-contact germanium detectors, and 100 kg of liquid xenon in a two-phase time projection chamber. Following an extensive background measurement campaign, a location in the SNS basement has proven to be neutron-quiet and suitable for deployment of the COHERENT detector suite. The simultaneous deployment of the three COHERENT detector subsystems will test the

Measurement of single-electron noise in a liquid-xenon emission detector

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

dependence of the cross section and ensure an unambiguous discovery of CEvNS. This document describes concisely the COHERENT physics motivations, sensitivity and plans for measurements at the SNS to be accomplished on a four-year timescale.

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

A technique for studying single-electron noise in emission detectors that are intended for detection of rare processes with small energy releases is developed. Examples of possible applications are experiments for search of dark matter in the Universe and detection of reactor antineutrinos via coherent neutrino scattering at heavy xenon nuclei. We present the first results of studying the nature of single-electron noise in a liquid-xenon emission detector and consider possible ways to suppress it.

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

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.

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

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.

The RED-100 two-phase emission detector

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.

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

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.