KATRIN

The Karlsruhe Tritium Neutrino Experiment ( KATRIN ), the direct determination of the mass of the electron antineutrino to the destination. The experiment is set up currently (2013 ) at the Karlsruhe Institute of Technology and is 2015 at the earliest record to measuring mode.

KATRIN will measure the beta spectrum of the decay of tritium in the region of maximum energy with a sensitivity of 0.2 eV. This KATRIN will surpass the previous, similar experiments in Mainz and Troitsk an order of magnitude; they had delivered an upper limit of 2.1 eV for the mass.

Motivation

In the Standard Model of elementary particle physics, the known neutrino species were νe, νμ and ντ first as massless accepted. Various experiments with atmospheric (Super - Kamiokande ), solar ( GALLEX, Homestake, SNO ) and reactor neutrinos ( Double Chooz ) point out, however, that the neutrino rest mass is different from zero. All these experiments demonstrate neutrino oscillations and therefore measure mass squared distance such as, but not the absolute neutrino masses. Experiments such as KATRIN and its predecessor experiments, however, possible to determine the absolute masses of the so-called mass eigenstates associated with the measurable masses of e, μ and τ - neutrino via the Maki - Nakagawa- Sakata mixing matrix.

The precise knowledge of the neutrino mass is needed to decide between the many different models that are used to attempt to give the neutrinos over the previous standard model going beyond a mass. The result may also shed light on, have contributed to the emergence of large-scale structures in the universe to what extent neutrinos as "hot dark matter" ( HDM).

Knowing the mass of the three mass eigenstates, it is also possible to distinguish three possible types of neutrino mass spectrum:

• Normal hierarchy:
• Inverted hierarchy:
• Quasi- degenerate hierarchy:

KATRIN thereby entering the first experiment in the realm of quasi- degenerate hierarchy.

Implementation

Starting point of the experiment is the tritium beta decay, in which an electron and an electron antineutrino are emitted. The decay energy of 18.6 keV are divided between two particles. If the neutrino is massless, there is no lower limit on the neutrino energy, and the energy spectrum of emitted electrons reaches to the maximum of 18.6 keV. For non-zero neutrino mass and the neutrino, however, must bear at least its rest energy, so this energy is missing in the electron energy spectrum. By precise measurement of the spectrum close to the maximum energy, the neutrino mass on the difference between the theoretical curve ( for ) and the measured spectrum can be determined.

Only electrons are useful for the experiment, which are emitted with almost maximum energy of the tritium source. Low-energy electrons are therefore filtered out. The energy of about 18.6 keV must be measured to be about 1 eV exactly, so with an energy resolution of better than 0.005 percent. This can not be achieved by simple particle. Two successively arranged spectrometers are used instead of actual detector, which together achieve this high resolution while maintaining a sufficient luminosity. Both spectrometers operate as so-called MAC -E - Filter (Magnetic Adiabatic Collimation combined with on Electrostatic filter), in which the electrons are selected according to their energy through a reverse voltage. In smaller Vorspektrometer is already greatly reduced by a voltage in the range of -18 kV, the electron flow; the tension in the main spectrometer is varied for the measurement of the spectrum in the range of -18.6 kV. The aim is to reach a total an energy resolution of 0.93 eV. The main spectrometer using superconducting magnet coils capable of a magnetic flux density of several Tesla

The detector used for the detection of the electron has only an energy resolution of 200 eV. Because of the previous energy selection here not particularly high resolution is necessary, and the lower resolution helps in the suppression of background signals.

The electron flow is reduced by the two filters of 1010 s / s on the tritium source to about 1 s / s at the detector. To achieve meaningful results, therefore, several measurement periods with a duration of three months will be needed, in which especially the reverse voltage in the spectrometer to a few ppm must be accurately recorded.

To prevent corruption of the measurement by not coming from the tritium beta decay electrons - such as a cosmic ray - all the main spectrometer is lined with a double shield. The voltage applied to these electrodes is slightly smaller than the voltage applied to the tank wall, that is, approximately 18.6 kV to 18.4 kV over the wall. Through this counter-voltage electrons are dislodged from the wall to slow down and do not penetrate to the detector before.

Others

The 200 -tonne, 24 m long vacuum tank with a diameter of 10 m for the KATRIN main spectrometer was manufactured by MAN DWE GmbH in Deggendorf in Regensburg. The experiment but will be established at the Karlsruhe Institute of Technology and carried out, since this is where the tritium laboratory at KIT Campus North (formerly Forschungszentrum Karlsruhe) is Europe's only appropriate for the experiment tritium source. The tank, however, was too large to be transported over highways can. He was over the Danube, the Black Sea, the Mediterranean, the Atlantic, the English Channel, the North Sea and the Rhine to Leopoldshafen near Karlsruhe by ship and finally on 25 November 2006 to the last 6.8 kilometers by low loader heavy transport in four and a half hours brought by Leopoldshafen to the research center. This detour was about 8600 km towards the shorter route of 350 km on the road.