Reacción a "Highest-energy cosmic neutrino detected to date"
Carlos Pobes
Postdoctoral researcher of the Q-MAD group at the Institute of Nanoscience and Materials of Aragon (INMA)
The recent outcome of the KM3NeT collaboration is certainly surprising. It is exciting, but it is so exceptional that it forces us to be cautious. There are several explanations for such an extraordinary event, and all of them have a low a priori probability.
The most natural explanation (that it is the first neutrino of cosmogenic origin, the well-known GZK background) clashes with the difficulty that IceCube (the other operational neutrino telescope) has not detected any event. The article itself discusses this possibility, which would have a probability of about 1 % (one must think that IceCube currently has a volume 10 times larger and has been taking data for 10 times longer).
Another possibility is that it is an astrophysical source [which would arrive in a punctual way and not uniformly and from all directions, as would the one we call cosmogenic], but of the possible candidates identified, no anomalous activity has been observed in any of them with other instruments.
One last possibility remains. The collaboration has made a very rigorous analysis of the data and in fact has taken 2 years to publish the result, but the energy value assigned to this event is an estimate that depends on many intermediate processes, each of them affected by certain uncertainties. It is possible that they have all 'aligned' to produce an abnormally high signal even though the original neutrino was of significantly lower energy and therefore less exceptional.
In any case, the solution to the enigma lies in accumulating more data, particularly once KM3NeT reaches its final size. It should be noted that IceCube itself is starting campaigns to expand its volume as well, so hopefully we will have an answer to this problem in the remainder of the decade. Of course, these are exciting times for astrophysics and cosmology; we are living live the birth of a new way of looking at the universe, and this event confirms that KM3NeT is already a reality. My sincere congratulations to the collaboration.