The XVI edition of Neutrino Telescopes is over and it is the time for some summing up – which I feel completely unsuited to do, as I was just an observer there. As you know, my field is high-energy collider physics, and neutrino physics has become a very different thing since the discovery of neutral currents 42 years ago. Anyway, I decided I would collect here a few random thoughts on the status of the field, as seen from my very skewed viewpoint...
First of all, I am really envious of the degree of activity, the large number of interesting experiments, the many complementary sides that can be taken to attack the problem of understanding the riddles posed by the physics of neutrinos. Collider physics pales in comparison, with only few experiments really capable of producing breakthroughs. The reason of this difference is that in trying to break the Standard Model and finding new physics beyond it, collider physicists are condemned to look only in one direction, that of the smallest distance scales and highest collision energies. Sure, we can also try to step on some effect measured in the physics of B hadrons, or find something extraordinary in other low-energy endeavours - but few of us believe that's what Nature (the bitch, not the magazine) has in store for us. In contrast, the field of neutrino physics is still in its infancy: after the discovery of neutrino oscillations in 1998 there is still a lot to learn, and many parameters to measure. Those parameters are tightly interconnected by the theory, but surprisingly decoupled in the experimentally accessible ways to determine them.
Experimental techniques are also quite varied as the source of neutrinos is not one and the same: we can study reactor (anti)neutrinos, solar neutrinos, cosmic-ray-originated atmospheric neutrinos; or we can produce them with accelerators, and there too, one may distinguish short and long-baseline setups, which are sensitive to different propagation properties of the neutrino beams; and there one can study appearance or disappearance of neutrino flavors. But one can also study geo-neutrinos, learning about the core of our planet; or astrophysical sources of neutrinos, cosmogenic neutrinos. And one can detect supernova explosions with the neutrino fluxes. It is astounding how rich is the physics program and how varied the implications of measurements of the properties of just one particle -well, one kind of particle, but actually three, or more of them.
Another reason to be enthusiastic is the incredibly large scale of some of the experiments – IceCube, Pingu, Km3Net, and Juno are some notable examples. These are real telescopes looking at the cosmos, the sun, and our planet as well. It is remarkable how we can exploit the ice of the south polar cap as a detector, or the water of the marine depths. Equally awesome is to know how detectors weighing just a few kilograms can compete in determining crucial properties of neutrinos: these are the solid-state experiments looking for neutrinoless double-beta decays. Of course, you do not need large dimensions when your process of interest is neutrinoless!
It is also quite interesting to remain in touch with the development of neutrino studies because of the tight interconnections with cosmology: dark matter searches use partly the same experimental techniques, and are now getting sensitive to the region where we should really start to detect a signal from weakly-interacting massive particles. If we see no signal in the next generation of searches, we may have to revise our general understanding of the universe, as the “cosmic miracle” of a weak neutral particle produced in the big bang with just the right abundance and mass to explain dark matter away, ending up in the exact mass region of the electroweak scale, will cease to provide a motivation for that explanation. And of course, cosmogenic neutrinos may provide further evidence of our model of the cosmos, or create new questions.
Overall, it was a lot of fun for me to listen to the many talks at Neutrino Telescopes XVI. All were of very high quality, thanks to the careful job of the organizing committee. The latter must also be acknowledged for flawlessly organizing a very pleasant week, with a splendid venue and excellent food, and with a successful poster session.
If you want to know more about the conference, read excerpts from all posters presented there, or an account on selected topics, please visit the conference blog at http://neutel11.wordpress.com . The site will remain on but "dormant" for the next couple of years, until the XVII edition will take place.