Looking at the Neutrino Sky

In June, ICTP and The Italian Institute for Nuclear Research co-sponsored a workshop on cosmic rays and neutrinos called "Looking at the Neutrino Sky--NUSKY 2011."  About 90 participants attended the week-long event, which featured 40 presentations given by the main players in the field, and intensive discussion sessions.

The talks covered all substantial aspects of the production, propagation and detection of high energy cosmic neutrinos.

The neutrino sky "seen" by detectors such as ANTARES and IceCube is the atmospheric shining, day and night, by neutrinos. IceCube, based in Antarctica, has already detected more than 100,000 atmospheric neutrino events. But scientists hope to detect something more: astrophysical neutrinos. Once produced, astrophysical neutrinos can travel cosmological distances and reach the Earth practically without interactions and deviations (except from gravitational lensing), thus carrying unique information on sources of cosmic rays, their acceleration and composition. The detectors could help scientists learn more about far away neutrino sources like supernovae, gamma ray bursters, and active galactic nuclei--the most energetic phenomena in the Universe--and maybe even dark matter.

One highlight of the workshop was the discussion of preliminary data from IceCube, which was a recurring topic throughout many of the talks.  So far, no astrophysical neutrino events have been identified, but even this negative result is of great importance. The programme's final speaker was the principle investigator at IceCube, Francis Halzen from the University of Wisconsin in the United States.  Halzen spoke about the challenges involved in building the detector and about his hopes and expectations for its future.  

In the theoretical part of the workshop, a wide range of topics was discussed. For example, Alexander Kusenko, professor of physics and astronomy at UCLA, spoke about the necessity of a holistic, multi-messenger approach to active galactic nuclei studies. He also argued that the increasing fraction of heavy nuclei with energy, as seen by the Pierre Auger Cosmic Ray Observatory in Argentina, may testify (due to the difference in diffusion times for protons and nuclei) for galactic sources of cosmic rays, probably unusual supernovae, hypernovae or gamma ray bursters. When cosmic rays interact with protons and photons of different energies they produce astrophysical neutrinos.

A main conclusion from the workshop is that further collection of data from detectors will have serious impact on the understanding of the neutrino sky.

For details on the workshop, visit its website.