25 research outputs found
Neutron-induced background in the CONUS experiment
CONUS is a novel experiment aiming at detecting elastic neutrino nucleus
scattering in the fully coherent regime using high-purity Germanium (Ge)
detectors and a reactor as antineutrino () source. The detector setup
is installed at the commercial nuclear power plant in Brokdorf, Germany, at a
very small distance to the reactor core in order to guarantee a high flux of
more than 10/(scm). For the experiment, a good
understanding of neutron-induced background events is required, as the neutron
recoil signals can mimic the predicted neutrino interactions. Especially
neutron-induced events correlated with the thermal power generation are
troublesome for CONUS. On-site measurements revealed the presence of a thermal
power correlated, highly thermalized neutron field with a fluence rate of
(74530)cmd. These neutrons that are produced by nuclear
fission inside the reactor core, are reduced by a factor of 10 on
their way to the CONUS shield. With a high-purity Ge detector without shield
the -ray background was examined including highly thermal power
correlated N decay products as well as -lines from neutron
capture. Using the measured neutron spectrum as input, it was shown, with the
help of Monte Carlo simulations, that the thermal power correlated field is
successfully mitigated by the installed CONUS shield. The reactor-induced
background contribution in the region of interest is exceeded by the expected
signal by at least one order of magnitude assuming a realistic ionization
quenching factor of 0.2.Comment: 28 pages, 28 figure
Constraints on elastic neutrino nucleus scattering in the fully coherent regime from the CONUS experiment
We report the best limit on coherent elastic scattering of electron antineutrinos emitted from a nuclear reactor off germanium nuclei. The measurement was performed with the CONUS detectors positioned at 17.1m from the 3.9GWth reactor core of the nuclear power plant in Brokdorf, Germany. The antineutrino energies of less than 10 MeV assure interactions in the fully coherent regime. The analyzed dataset includes 248.7 kgd with the reactor turned on and background data of 58.8 kgd with the reactor off. With a quenching parameter of k = 0.18 for germanium, we determined an upper limit on the number of neutrino events of 85 in the region of interest at 90% confidence level. This new CONUS dataset disfavors quenching parameters above k = 0.27, under the assumption of standard-model-like coherent scattering of the reactor antineutrinos
First upper limits on neutrino electromagnetic properties from the CONUS experiment
We report first constraints on neutrino electromagnetic properties from neutrino-electron scattering using data obtained from the CONUS germanium detectors, i.e. an upper limit on the effective neutrino magnetic moment and an upper limit on the effective neutrino millicharge. The electron antineutrinos are emitted from the 3.9 GW reactor core of the Brokdorf nuclear power plant in Germany. The CONUS low background detectors are positioned at 17.1 m distance from the reactor core center. The analyzed data set includes 689.1 kgd collected during reactor ON periods and 131.0 kgd collected during reactor OFF periods in the energy range of 2 to 8 keV. With the current statistics, we are able to determine an upper limit on the effective neutrino magnetic moment at 90% confidence level. From this first magnetic moment limit we can derive an upper bound on the neutrino millicharge of q
Full background decomposition of the CONUS experiment
The CONUS experiment is searching for coherent elastic neutrino nucleus scattering of reactor anti-neutrinos with four low energy threshold point-contact high-purity germanium spectrometers. An excellent background suppression within the region of interest below 1keV (ionization energy) is absolutely necessary to enable a signal detection. The collected data also make it possible to set limits on various models regarding beyond the standard model physics. These analyses benefit as well from the low background level of ~10dkgbelow 1keV and at higher energies. The low background level is achieved by employing a compact shell-like shield, that was adapted to the most relevant background sources at the shallow depth location of the experiment: environmental gamma-radiation and muon-induced secondaries. Overall, the compact CONUS shield including the active anti-coincidence muon-veto reduces the background by more than four orders of magnitude. The remaining background is described with validated Monte Carlo simulations which include the detector response. It is the first time that a full background decomposition in germanium operated at reactor-site has been achieved. Next to remaining muon-induced background, Pb within the shield and cryostat end caps, cosmogenic activation and air-borne radon are the most relevant background sources. The reactor-correlated background is negligible within the shield. The validated background model together with the parameterization of the noise are used as input to the likelihood analyses of the various physics cases
Large-size sub-keV sensitive germanium detectors for the CONUS experiment
Intense fluxes of reactor antineutrinos offer a unique possibility to probe
the fully coherent character of elastic neutrino scattering off atomic nuclei.
In this regard, detectors face the challenge to register tiny recoil energies
of a few keV at the maximum. The CONUS experiment was installed in 17.1 m
distance from the reactor core of the nuclear power plant in Brokdorf, Germany,
and was designed to detect this neutrino interaction channel by using four 1
kg-sized point contact germanium detectors with sub-keV energy thresholds. This
report describes the unique specifications addressed to the design, the
research and development, and the final production of these detectors. It
demonstrates their excellent electronic performance obtained during
commissioning under laboratory conditions as well as during the first two years
of operation at the reactor site which started on April 1, 2018. It highlights
the long-term stability of different detector parameters and the achieved
background levels of the germanium detectors inside the CONUS shield setup.Comment: (18 pages, 12 figures