In this contribution, we review the status and perspectives of direct neutrino mass experiments, which investigate the kinematics of β-decays of specific isotopes (3H, 187Re, 163Ho) to derive ...model-independent information on the averaged electron (anti)neutrino mass. After discussing the kinematics of β-decay and the determination of the neutrino mass, we give a brief overview of past neutrino mass measurements (SN1987a-ToF studies, Mainz and Troitsk experiments for 3H, cryobolometers for 187Re). We then describe the Karlsruhe Tritium Neutrino (KATRIN) experiment currently under construction at Karlsruhe Institute of Technology, which will use the MAC-E-Filter principle to push the sensitivity down to a value of 200 meV (90% C.L.). To do so, many technological challenges have to be solved related to source intensity and stability, as well as precision energy analysis and low background rate close to the kinematic endpoint of tritium β-decay at 18.6 keV. We then review new approaches such as the MARE, ECHO, and Project8 experiments, which offer the promise to perform an independent measurement of the neutrino mass in the sub-eV region. Altogether, the novel methods developed in direct neutrino mass experiments will provide vital information on the absolute mass scale of neutrinos.
We present the idea and proof of principle measurements for an angular-selective active filter for charged particles. The motivation for the setup arises from the need to distinguish background ...electrons from signal electrons in a spectrometer of MAC-E filter type. While a large fraction of the background electrons exhibit predominantly small angles relative to the magnetic guiding field (corresponding to a low amount of kinetic energy in the motion component transverse to the field lines, in the following referred to as transverse energy) and pass the filter mostly unhindered, signal electrons from an isotropically emitting source interact with the active filter and are detected. The concept is demonstrated using a microchannel plate (MCP) as an active filter element. When correctly aligned with the magnetic field, electrons with a small transverse energy pass the channels of the MCP without interaction while electrons with large transverse energies hit the channel walls and trigger an avalanche of secondary electrons that is subsequently detected. Due to several drawbacks of MCPs for an actual transverse energy filter, an alternative detection technique using microstructured Si-PIN diodes is proposed.
The DARWIN observatory is a proposed next-generation experiment to search for particle dark matter and for the neutrinoless double beta decay of
136
Xe. Out of its 50 t total natural xenon inventory, ...40 t will be the active target of a time projection chamber which thus contains about 3.6 t of
136
Xe. Here, we show that its projected half-life sensitivity is
2.4
×
10
27
year
, using a fiducial volume of 5 t of natural xenon and 10 year of operation with a background rate of less than 0.2 events/(t
·
year) in the energy region of interest. This sensitivity is based on a detailed Monte Carlo simulation study of the background and event topologies in the large, homogeneous target. DARWIN will be comparable in its science reach to dedicated double beta decay experiments using xenon enriched in
136
Xe.
The KArlsruhe TRItium Neutrino (KATRIN) experiment will measure the absolute mass scale of neutrinos with a sensitivity of mν = 200 meV c2 by high-precision spectroscopy close to the tritium β-decay ...endpoint at 18.6 keV. Its Windowless Gaseous Tritium Source (WGTS) is a β-decay source of high intensity (1011 s−1) and stability, where high-purity molecular tritium at 30 K is circulated in a closed loop with a yearly throughput of 10 kg. To limit systematic effects the column density of the source has to be stabilized at the 10−3 level. This requires extensive sensor instrumentation and dedicated control and monitoring systems for parameters such as the beam tube temperature, injection pressure, gas composition and so on. In this paper, we give an overview of these systems including a dedicated laser-Raman system as well as several β-decay activity monitors. We also report on the results of the WGTS demonstrator and other large-scale test experiments giving proof-of-principle that all parameters relevant to the systematics can be controlled and monitored on the 10−3 level or better. As a result of these works, the WGTS systematics can be controlled within stringent margins, enabling the KATRIN experiment to explore the neutrino mass scale with the design sensitivity.
We correct an overestimation of the production rate of
137
Xe in the DARWIN detector operated at LNGS. This formerly dominant intrinsic background source is now at a level similar to the irreducible ...background from solar
8
B neutrinos, thus unproblematic at the LNGS depth. The projected half-life sensitivity for the neutrinoless double beta decay (
0
ν
β
β
) of
136
Xe improves by
22
%
compared to the previously reported number and is now
T
1
/
2
0
ν
=
3.0
×
10
27
yr
(90% C.L.) after 10 years of DARWIN operation.
Electrostatic spectrometers utilized in high-resolution β-spectroscopy studies such as in the Karlsruhe Tritium Neutrino (KATRIN) experiment have to operate with a background level of less than 10−2 ...counts per second. This limit can be exceeded by even a small number of 219,220Rn atoms being emanated into the volume and undergoing α-decay there. In this paper we present a detailed model of the underlying background-generating processes via electron emission by internal conversion, shake-off and relaxation processes in the atomic shells of the 215,216Po daughters. The model yields electron energy spectra up to 400 keV and electron multiplicities of up to 20 which are compared to experimental data.
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