Physicists reported that the IceCube neutrino observatory detectors for the first time detected the formation of the W-boson when high-energy antineutrinos interact with electrons. This phenomenon, known as the Glashow Resonance, was theoretically predicted over 60 years ago. The research results are published in the journal Nature.
Scientists registered the first high-energy astrophysical neutrinos at the IceCube under-ice neutrino observatory, located near the South Pole, in 2013.
In 2016, IceCube detectors detected a high-energy particle called an electron antineutrino, which came to Earth from space at a speed close to the speed of light, with an energy of 6.3 PETA-electron volts (PeV). Deep inside the ice sheet of Antarctica, it collided with an electron, and this collision generated a stream of secondary particles – W-bosons, which were captured by the IceCube detector filaments immersed in the ice.
The possibility of such interaction of high-energy antineutrinos with electrons was theoretically predicted in 1960 by the American physicist and Nobel Prize winner Sheldon Glashow. The particle that should appear during this interaction, the W-boson, was discovered by physicists at CERN in 1983, but it turned out that it is much heavier than Glashow predicted, and its formation from antineutrinos requires energy of at least 6.3 PeV – this is almost 1000 times more than the Large Hadron Collider at CERN is capable of producing. In fact, no artificial particle accelerator on Earth, current or planned, can create neutrinos with such high energy.
And IceCube has already discovered hundreds of high-energy astrophysical neutrinos since its full operation in May 2011 and has yielded a number of other significant results in particle astrophysics, including the discovery of an astrophysical neutrino flux in 2013 and the first identification of an astrophysical neutrino source in 2018. But the confirmation of Glashow’s resonance is especially noteworthy because of its extremely high energy. This is only the third over 5 PeV event detected by IceCube.
“Gleshaw could not even imagine that his unconventional assumption about the formation of the W-boson would be confirmed in the collision of an antineutrino from a distant galaxy with Antarctic ice,” – quoted in a press release from the University of Wisconsin-Madison, the words of one of the leaders of the study, Francis Halzen ), Director of the Institute for Particle Physics in Wisconsin-Madison, where IceCube’s maintenance and operations headquarters are located.
According to the authors, the result obtained not only provided another confirmation of the Standard Model of elementary particle physics but also opened a new stage in the development of neutrino astronomy, when physicists, using instrumental methods, can separate neutrinos from antineutrinos.
“This result proves the feasibility of neutrino astronomy and highlights the important role of IceCube in future multidimensional astronomical particle physics,” says co-author Christian Haack. “We can now detect individual neutrino events that are clearly extraterrestrial.”
“Previous measurements were not sensitive to the difference between neutrinos and antineutrinos, so this result is the first direct measurement of the antineutrino component of astrophysical neutrino flux,” adds another IceCube collaborator, Ph.D. student Lu Lu at Chiba University in Japan.
To measure the quantitative ratio of neutrinos to antineutrinos, IceCube scientists plan to register as many Glashow resonances as possible. The planned expansion of the detector – IceCube-Gen2 – will allow scientists to make such measurements in a statistically significant way.