Karlsruhe Neutrino Volume Experiment Has Been Turned On

The Washington Post tells us that the Karlsruhe Tritium Neutrino Experiment (KATRIN) was turned on today.



Karlsruhe looks luxurious. At to the lowest degree the 1715 palace does. Just to live on sure, the metropolis is only miles East from the Easternmost signal of France.

The experiment costs €60 1000000 i.e. $66 1000000 as well as has the lead a opportunity – maybe the greatest lead a opportunity with the experiments inwards the close futurity – to mensurate the absolute masses of the neutrinos.




The gist of the experiment is a spectrometer that weighs 200 SI tons. This spectrometer volition carefully mensurate the unloosen energy of the electrons that are emitted inwards a beta decay.




The focus volition live on on the electrons that accept the maximum kinematically allowed energy. In those decays, the smallest sum of unloosen energy is left for the neutrinos. By carefully studying the maximum unloosen energy of the electrons, inside \(1\eV\) or several of them, the experiment volition decide the minimum unloosen energy of the neutrinos i.e. their balance mass.

Because i wants to accept equally low-energy electrons equally possible, as well as thus that the hypothetical neutrino majority is the highest possible fraction of this energy, they picked the tritium (very heavy hydrogen) whose beta-decay leaves a really small-scale sum of unloosen energy for the electron as well as the neutrino. Just to live on sure, the total unloosen energy of the electron as well as the antineutrino is \(18.6\keV\) which is really depression inwards comparing with the energies inwards nuclear physics – nosotros unremarkably beak virtually several \({\rm MeV}\).



The spectrometer when it was transported 10 years ago.

Note that because the neutrino oscillations accept been observed to exist, nosotros know that the neutrinos mostly accept nonzero masses (which must ultimately come upwardly from or as well as thus non-renormalizable interactions beyond the Standard Model!). However, the oscillations alone let us to decide the differences of the squared majority eigenvalues such as\[

\Delta m_{ij}^2 = m^2_i - m^2_j, \quad i,j=1,2,3

\] as well as non the absolute shift. The actual lowest eigenvalue of \(m_i^2\) could live on much smaller than both differences of the squared masses (and maybe fifty-fifty zero), or comparable to the lower difference, or comparable to the larger one, or much greater than the differences. We only don't know. If the relevant neutrino majority is significantly larger than \(1\eV\), the experiment should live on able to come across it. One powerfulness approximate that this bully lawsuit is unlikely because the square roots of \(\Delta m_{ij}^2\) are closer to \(0.01\eV\) or fifty-fifty \(0.001\eV\). Neutrinos much heavier than \(1\eV\) would hateful that all the majority eigenstates are almost degenerate. It's possible but such a degeneracy could live on considered unnatural as well as unlikely.

Even inwards the optimistic case, in that place volition likely live on or as well as thus doubtfulness virtually the neutrino masses because the experiment volition likely non fully settle the enquiry whether the neutrino masses are Dirac, Majorana, or mixed.