In this work we present a keV-scale sterile-neutrino search with a low-tritium-activity data set of the KATRIN experiment, acquired in a commissioning run in 2018. KATRIN performs a spectroscopic ...measurement of the tritium
β
-decay spectrum with the main goal of directly determining the effective electron anti-neutrino mass. During this commissioning phase a lower tritium activity facilitated the measurement of a wider part of the tritium spectrum and thus the search for sterile neutrinos with a mass of up to
1.6
keV
. We do not find a signal and set an exclusion limit on the sterile-to-active mixing amplitude of
sin
2
θ
<
5
×
10
-
4
(
95
%
C.L.) at a mass of 0.3 keV. This result improves current laboratory-based bounds in the sterile-neutrino mass range between 0.1 and 1.0 keV.
The KATRIN experiment is designed for a direct and model-independent determination of the effective electron anti-neutrino mass via a high-precision measurement of the tritium
β
-decay endpoint ...region with a sensitivity on
m
ν
of 0.2
eV
/
c
2
(90% CL). For this purpose, the
β
-electrons from a high-luminosity windowless gaseous tritium source traversing an electrostatic retarding spectrometer are counted to obtain an integral spectrum around the endpoint energy of 18.6 keV. A dominant systematic effect of the response of the experimental setup is the energy loss of
β
-electrons from elastic and inelastic scattering off tritium molecules within the source. We determined the energy-loss function in-situ with a pulsed angular-selective and monoenergetic photoelectron source at various tritium-source densities. The data was recorded in integral and differential modes; the latter was achieved by using a novel time-of-flight technique. We developed a semi-empirical parametrization for the energy-loss function for the scattering of 18.6-keV electrons from hydrogen isotopologs. This model was fit to measurement data with a 95%
T
2
gas mixture at 30 K, as used in the first KATRIN neutrino-mass analyses, as well as a
D
2
gas mixture of 96% purity used in KATRIN commissioning runs. The achieved precision on the energy-loss function has abated the corresponding uncertainty of
σ
(
m
ν
2
)
<
10
-
2
eV
2
1
in the KATRIN neutrino-mass measurement to a subdominant level.
The KArlsruhe TRItium Neutrino experiment (KATRIN) aims to determine the effective electron (anti)-neutrino mass with a sensitivity of 0.2eV/c
2
by precisely measuring the endpoint region of the ...tritium
β
-decay spectrum. It uses a tandem of electrostatic spectrometers working as magnetic adiabatic collimation combined with an electrostatic (MAC-E) filters. In the space between the pre-spectrometer and the main spectrometer, creating a Penning trap is unavoidable when the superconducting magnet between the two spectrometers, biased at their respective nominal potentials, is energized. The electrons accumulated in this trap can lead to discharges, which create additional background electrons and endanger the spectrometer and detector section downstream. To counteract this problem, “electron catchers” were installed in the beamline inside the magnet bore between the two spectrometers. These catchers can be moved across the magnetic-flux tube and intercept on a sub-ms time scale the stored electrons along their magnetron motion paths. In this paper, we report on the design and the successful commissioning of the electron catchers and present results on their efficiency in reducing the experimental background.
The KATRIN experiment aims to measure the effective electron antineutrino mass
m
ν
¯
e
with a sensitivity of
0.2
eV
/
c
2
using a gaseous tritium source combined with the MAC-E filter technique. A ...low background rate is crucial to achieving the proposed sensitivity, and dedicated measurements have been performed to study possible sources of background electrons. In this work, we test the hypothesis that gamma radiation from external radioactive sources significantly increases the rate of background events created in the main spectrometer (MS) and observed in the focal-plane detector. Using detailed simulations of the gamma flux in the experimental hall, combined with a series of experimental tests that artificially increased or decreased the local gamma flux to the MS, we set an upper limit of
0.006
count
/
s
(90% C.L.) from this mechanism. Our results indicate the effectiveness of the electrostatic and magnetic shielding used to block secondary electrons emitted from the inner surface of the MS.
In a fusion reactor, tritium will be continuously produced in the breeding blanket and a dedicated tritium extraction and removal system (TERS) is used to recover the newly bred tritium. In the TERS ...for the solid blanket, zeolite membranes are proposed to be used to pre-concentrate HT/H2 in He before Pd/Ag membranes. Therefore, permeation experiments were carried out using two experimental facilities to determine the permeances of all hydrogen isotopologues (Q2 = H2, HD, D2, HT, DT, T2) through MFI-ZSM-5 membranes. This study aimed at investigating the existence of isotopic effects on the Q2 permeation and hence on the separation of Q2 from He. The results exhibit a strong dependency of the permeance with the mass of the isotopologue: the selectivity decreases from around 1.8 for H2/He to 1.3 for D2/He down to 1.1 for T2/He. This phenomenon is attributed to the existence of defects in the zeolite structure through which the molecules permeate according to Knudsen diffusion. These results were observed for inactive and active Q2 mixtures and no other effects related to the dipole moment of the asymmetric isotopologues (HD, HT, DT) or tritium decay were observed. Moreover, these results were obtained for three MFI-ZSM-5 membranes, showing a high reproducibility. Our results demonstrate that the pre-concentration of Q2 in He with MFI-ZSM-5 membranes appears to be challenging in the scope of the TERS.
Display omitted
•Permeation of hydrogen through MFI membranes is dependent on the isotopologues mass.•Isotopic effect due to the existence of defects in the zeolite layer.•Separation of Q2/He is highest for H2 and lowest for T2.•MFI membranes exhibit low separation performances for the tritium extraction system.
In this work we present a keV-scale sterile-neutrino search with a low-tritium-activity data set of the KATRIN experiment, acquired in a commissioning run in 2018. KATRIN performs a spectroscopic ...measurement of the tritium β-decay spectrum with the main goal of directly determining the effective electron anti-neutrino mass. During this commissioning phase a lower tritium activity facilitated the measurement of a wider part of the tritium spectrum and thus the search for sterile neutrinos with a mass of up to 1.6 keV. We do not find a signal and set an exclusion limit on the sterile-to-active mixing amplitude of $\text {sin}^{2}\: \theta<5\times 10^{-4}\: (95\%\: $C.L) at a mass of 0.3 keV. This result improves current laboratory-based bounds in the sterile-neutrino mass range between 0.1 and 1.0 keV.
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