Experimental searches

Last update April 14, 2024

Since the only known particles that might be tachyons are one or more of the neutrinos, most searches for tachyons involve tests whether neutrinos have either v > c or a negative mass squared. This possibility remains viable as long as no neutrinos are observed with v < c or positive squared.

Overall situation. A review of the situation for experimental searches for tachyons and for evidence that neutrinos are tachyons was published in 2022. See: R, Ehrlich, A Review of Searches for Evidence of Tachyons, Symmetry 202214(6), 1198, Symmetry | Free Full-Text | A Review of Searches for Evidence of Tachyons | HTML (mdpi.com). Further evidence was published in 2023, see:Tachyonic Neutrinos: From the Cosmic Rays to Extragalactic Supernovae, Symmetry 202315(9), 1624; https://doi.org/10.3390/sym15091624

KATRIN experiment. This experiment was designed to measure the effective mass of the electron neutrino. It has been taking data since 2019 . The first results from the KATRIN experiment in 2019 were consistent with both the existence of a single effective mass neutrino of mass under 1.1 eV, and also an exotic “3+3” neutrino model that had been proposed in 2013. This model assumes three active-sterile pairs, having specific masses, one of which is imaginary. This short paper shows how the experiment’s first results are consistent with that model. In June 2021 KATRIN published new results from a second run which lowered the value of the electron neutrino mass further to m < 0.7 eV. Again. however, those results may are consistent with the 3 + 3 model as shown here. A definitive test of the 3 + 3 model may be possible as KATRIN acquires more data, but such a test has not been carried out at the time of this writing. The most recent review of evidence for the 3 + 3 model, and tachyon searches in general can be found in the two references given in the first paragraph.

Project 8. Is an experiment that promises to yield even better resolution for the neutrino mass than KATRIN, but as of 2024 it is just beginning to take data using Cyclotron Radiation Emission Spectroscopy, as described here.

Supernovae. A direct test of the 3 + 3 model could be provided if a galactic supernova were to occur, but these occur only two or three times per century, If one did occur, and the model were correct, it follows that the masses of the three neutrinos should be obtainable based on a simple relation between their observed energies and arrival times. With regard to extragalactic supernovae, currently, only upper limits exist for neutrino bursts. Nevertheless, it is possible that existing detectors, including Super-Kamiokande IV, might observe one with a day-long search window, as suggested in the 2023 article mentioned in the first paragraph. To date there has been zero interest on the part of neutrino groups to test this possibility.  

Cosmic rays. A direct test of the possibility that electron neutrinos are tachyons would be the observation of neutrons in the cosmic rays just above the knee of the spectrum at 3 PeV.

Photo shows the interior of the KATRIN main spectrometer Credit: Michael Zacher. A 27 min video about the experiment can be found here.