New evidence of a fourth ultra-high energy neutrino has been detected by the IceCube experiment located at the South Pole. This is the highest-energy neutrino discovered up to date. The IceCube experiment is a project developed with the help received from Berkeley Lab researchers. Scientists from Berkeley Lab currently contribute with analysis for data accumulate by the experiment.
The new neutrino particle has been detected by researchers at Rheinisch-Westfälische Technische Hochschule Aachen University in Germany. The German scientists were conducting a new search for astrophysical muon neutrinos with the aim to confirm through their analysis previous IceCube measurements of other astrophysical neutrinos. The researchers participating at the astrophysical particles analysis were not looking, in particular, to find new types of neutrinos and the discovery of the ultra-high-energy neutrino was an unexpected bonus.
Scientists hope that ultra-high-energy neutrinos could point to sources of cosmic rays such as hypernova star explosions or supermassive black holes at the centers of galaxies. However, the most recent neutrino finding, according to Berkeley Lab's Spencer Klein, is not coming to confirm their expectations but rather only "deepens the mystery" of cosmic ray origins.
The new neutrino was discovered when a muon trail was observed by an array of 5,160 optical detectors. The special electronics for the research were designed and built by Berkeley Lab engineers and scientists. According to astrophysicists, muons are heavy relatives of electrons. They are emitted when a muon neutrino interacts with an atomic nucleus.
The recently detected muon has a high energy of about 2600 trillion electron volts. At such high energy level, it could have only had as a source an ultra-high-energy neutrino. The muon track long for several kilometers was too long for IceCube to capture the entire trace. It is possible that the actual neutrino energy was several times higher than detected.
A neutrino can point to the origin of cosmic rays that are suspected to come from ultra-high-energy sources outside our Milky Way galaxy. These charged particles inside the cosmic rays arrive at Earth only after following follow twisted, chaotic paths circling around magnetic field lines in space. Scientists believe that the ultra-high-energy neutrinos are coming from the same sources as cosmic rays. However, these neutrinos differ in that they are neutral and they travel in straight lines.
According to Gary Binder, a Nuclear Science Division graduate student who conducted a recent analysis of previous IceCube data, the results suggest that ultra-high-energy neutrinos have a source more conventional cosmic rays such as supermassive black holes. Klein added that the issue of the origins of cosmic rays and ultra-high-energy neutrinos is far from settled.