Can the electron be converted into neutrino

07/05/2001 11:15

How heavy is a neutrino?

Inge Arnold Press, Communication and Marketing department
Research Center Karlsruhe in the Helmholtz Association

Karlsruhe Research Center before a large-scale experiment to determine the neutrino mass

An important experiment in basic physical research is in the starting blocks at the Karlsruhe Research Center: Over the next five years, the Karlsruhe Tritium Neutrino Experiment KATRIN will be set up here with international participation. The aim of the DM 25 million project is to answer one of the most important questions in modern physics: How heavy are neutrinos, the most volatile of all elementary particles? The determination of the neutrino mass would be of the greatest importance for both cosmology and high-energy physics.

We have known since June of this year at the latest that neutrinos have a mass. Indeed, this is the result of a group of American, Canadian and British researchers. They examined neutrinos that come from the sun and proved that different types of neutrinos can transform into one another (so-called neutrino oscillations). This is only possible if the different types of neutrinos do not all have the same mass.
How heavy the neutrinos actually are, however, the researchers could not clarify with their experiment. Pioneering experiments in recent years at the University of Mainz and at the Institute for Nuclear Research in Troitsk near Moscow indicate upper limits of 2 electron volts for the electron neutrino. (For comparison: the electron, the lightest component of an atom, is 250 times heavier with a mass of 511 electron volts.) With the planned experiment KATRIN, the neutrino mass can still be measured even if it is ten times smaller than the previous upper limit.
KATRIN uses the effect on the basis of which the physicist Wolfgang Pauli predicted the neutrino as early as 1931 (the first direct measurement was not possible until 1957): During beta decay in atomic nuclei, a neutron is converted into a proton and an electron. The resulting electron has no fixed energy, but can have any energies up to an upper limit that corresponds to the total energy released. Since the same total energy is always released during the beta decay of a certain atom, another particle has to carry the energy difference between the electron and total energy: the neutrino. From the precise observation of the energy spectrum of the electrons in the vicinity of the total energy, conclusions can now be drawn about the neutrino mass. If the neutrino has a mass and thus carries a minimum amount of energy with it, the spectrum will be modified in relation to a continuous energy distribution.
As a beta emitter, KATRIN will use tritium, a form of hydrogen that decays with a half-life of 12.3 years. During the beta decay of tritium, a total energy of 18,600 electron volts is released, which is distributed between the electron and the neutrino. The neutrinos are not detectable. The electrons are examined for their energy in the heart of KATRIN, a huge electrostatic spectrometer, and then detected in a semiconductor detector. The central spectrometer will have a diameter of 7 meters and a length of 20 meters, the total length of the experiment will be 60 meters.
"The Karlsruhe Research Center has ideal conditions for carrying out such a large-scale experiment," explains Johannes Bl├╝mer, Head of the Institute for Nuclear Physics at the Karlsruhe Research Center and Professor at the Institute for Experimental Nuclear Physics at the University of Karlsruhe. "The Tritium Laboratory is a unique European laboratory for demanding tritium handling. We also have many years of experience with high vacuum and cryogenics in large scientific apparatus, as well as the know-how and infrastructure for the construction and operation of such systems. "
For this reason, an international collaboration involving universities in Karlsruhe, Mainz and Fulda as well as research institutions in the Czech Republic (Prague), USA (Seattle) and Russia (Troitsk) has chosen the Karlsruhe Research Center as the location for the experiment. Other international research institutes have already expressed their interest in collaborating.
Joachim Hoffmann July 4th 2001

Criteria of this press release:
Mathematics, Physics / astronomy
transregional, national
Research projects