Ultra High Energy Neutrinos

Ultra High Energy Neutrino Astronomy

Until the early twentieth century our kowledge of the universe was limited to studying only the visible part of the electromagnetic spectrum. As time progressed techniques were developed to exploit the whole of the electromagnetic spectrum (radio, infrared, visible, ultraviolet, x-ray, and most recently gamma rays), but all of these techniques are limited in the knowledge that they can achieve.

However, exploiting the electromagnetic sprectrum is not the only way to study the universe. The universe can also be studied by looking at particles that arrive at Earth from astrophysical sources, this field of study is aptly named astro-particle physics. And for the highest energies, the particle of interst is the neutrino.

The detection of neutrinos from distant sources and with centre-of-mass collision energies beyond the LHC is a new and emerging field and one which is of interest to both astrophysicists and particle physicists. High energy neutrinos offer the opportunity to probe the universe over cosmological distances and probe physics beyond the Standard Model in a manner complementary to conventional astronomical probes and the LHC.

Why UHE Neutrino?

Whereas nuclear energy (MeV) neutrino astronomy has been well established, the low cross section and poor angular resolution of MeV neutrinos has always been a problem in advancing the techniques to much beyond the Sun. With the exception of the 1987 supernova (SN1987A), no neutrinos from outside the solar system have ever been observed. Indeed, no neutrinos with energies much beyond 100 TeV have yet been observed from any source.

What are the Aims of Neutrino Astronomy?

High-energy astronomy has been much advanced with the invention of the gamma ray telescope, but the range of modern high-energy gamma ray telescopes is limited. This is because of attenuation of gamma rays from distant sources. At a few hundred TeV, gamma rays do not survive the journey from the centre of our galaxy. At 1014eV they interact with the cosmic background radiation. UHE neutrino astronomy is aiming for much higher energies (>1020), and look at these energies into cosmological interesting distances. A single ultra high energy (UHE) neutrino with an energy of 3x1020 eV has the same energy as the tennis ball from a Federer 1st serve, but they occur less frequently. Cosmic rays of this energy are predicted to impact the earth at a rate of 1 per century per km2. This low rate and the fact that neutrinos interact only weakly with matter makes the detection of UHE neutrinos very challenging. One either needs to instrument a large region with many detectors or have a few detectors that can detect over a very large region.

At UCL we are involved two collaborations that exploit the Askaryan effect to detect neutrinos via their interaction in ice or water. The ANITA experiment is seeking to detect UHE neutrinos via the radio Askaryan signal using antennas on a balloon that will fly over the Antarctic ice. The ACORNE collaboration is performing R&D to utilise the acoustic Askaryan signal produced when UHE neutrinos interact with water with a view to establishing a large scale acoustic UHE neutrino detector.

Last Modified : 14:39:00 09 Nov 2011