IceCube Detection of a High-Energy Particle – Antineutrino “Unmistakably of Extraterrestrial Origin”

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IceCube Neutrino Event: Hydrangea

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A visualization of the Glashow occasion taped by the IceCube detector. Each colored circle reveals an IceCube sensing unit that was activated by the occasion; red circles show sensing units activated previously in time, and green-blue circles show sensing units activated later on. This occasion was nicknamed “Hydrangea.” Credit: IceCube Collaboration

The South Pole neutrino detector saw a Glashow resonance occasion, a phenomenon forecasted by Nobel laureate physicist Sheldon Glashow in 1960 where an electron antineutrino and an electron connect to produce a W- boson.

On December 6, 2016, a high-energy particle called an electron antineutrino sped to Earth from deep space at near the speed of light bring 6.3 petaelectronvolts (PeV) of energy. Deep inside the ice sheet at the South Pole, it smashed into an electron and produced a particle that rapidly rotted into a shower of secondary particles. The interaction was recorded by a huge telescope buried in the Antarctic glacier, the IceCube Neutrino Observatory.

“We now can detect individual neutrino events that are unmistakably of extraterrestrial origin.” — Christian Haack

IceCube had actually seen a Glashow resonance occasion, a phenomenon forecasted by Nobel laureate physicist Sheldon Glashow in 1960. With this detection, researchers offered another verification of the Standard Model of particle physics. It likewise even more showed the capability of IceCube, which discovers almost massless particles called neutrinos utilizing countless sensing units embedded in the Antarctic ice, to do basic physics. The result was released today (March 10, 2021) in Nature.

Sheldon Glashow very first proposed this resonance in 1960 when he was a postdoctoral scientist at what is today the Niels Bohr Institute in Copenhagen, Denmark. There, he composed a paper in which he forecasted that an antineutrino (a neutrino’s antimatter twin) might connect with an electron to produce an as-yet undiscovered particle — if the antineutrino had simply the ideal energy — through a procedure called resonance.

When the proposed particle, the W boson, was lastly found in 1983, it ended up being much heavier than what Glashow and his coworkers had actually anticipated back in 1960. The Glashow resonance would need a neutrino with an energy of 6.3 PeV, nearly 1,000 times more energetic than what CERN’s Large Hadron Collider can producing. In truth, no human-made particle accelerator on Earth, existing or prepared, might produce a neutrino with that much energy.

IceCube Neutrino Observatory Schematic

A schematic of the in-ice part of IceCube, that includes 86 strings holding 5,160 light sensing units organized in a three-dimensional hexagonal grid. Credit: IceCube Collaboration

But what about a natural accelerator — in area? The massive energies of supermassive great voids at the centers of galaxies and other severe cosmic occasions can create particles with energies difficult to produce on Earth. Such a phenomenon was most likely accountable for the 6.3 PeV antineutrino that reached IceCube in 2016.

“When Glashow was a postdoc at Niels Bohr, he might never ever have actually thought of that his non-traditional proposition for producing the W boson would be understood by an antineutrino from a distant galaxy crashing into Antarctic ice,” states Francis Halzen, teacher of physics at the University of Wisconsin-Madison, the head office of IceCube upkeep and operations, and primary private investigator of IceCube.

Since IceCube began complete operation in May 2011, the observatory has actually discovered numerous high-energy astrophysical neutrinos and has actually produced a variety of considerable lead to particle astrophysics, consisting of the discovery of an astrophysical neutrino flux in 2013 and the very first recognition of a source of astrophysical neutrinos in 2018. But the Glashow resonance occasion is specifically notable since of its incredibly high energy; it is just the 3rd occasion discovered by IceCube with an energy higher than 5 PeV.

“This result proves the feasibility of neutrino astronomy — and IceCube’s ability to do it — which will play an important role in future multimessenger astroparticle physics,” states Christian Haack, who was a college student at RWTH Aachen while dealing with this analysis. “We now can detect individual neutrino events that are unmistakably of extraterrestrial origin.”

Antineutrino Journey

The electron antineutrino that developed the Glashow resonance occasion took a trip rather a range prior to reaching IceCube. This graphic reveals its journey; the blue dotted line is the antineutrino’s course. (Not to scale.) Credit: IceCube Collaboration

The result likewise opens a brand-new chapter of neutrino astronomy since it begins to disentangle neutrinos from antineutrinos. “Previous measurements have not been sensitive to the difference between neutrinos and antineutrinos, so this result is the first direct measurement of an antineutrino component of the astrophysical neutrino flux,” states Lu Lu, among the primary analyzers of this paper, who was a postdoc at Chiba University in Japan throughout the analysis.

“There are a number of properties of the astrophysical neutrinos’ sources that we cannot measure, like the physical size of the accelerator and the magnetic field strength in the acceleration region,” states Tianlu Yuan, an assistant researcher at the Wisconsin IceCube Particle Astrophysics Center and another primary analyzer. “If we can determine the neutrino-to-antineutrino ratio, we can directly investigate these properties.”

To validate the detection and make a definitive measurement of the neutrino-to-antineutrino ratio, the IceCube Collaboration wishes to see more Glashow resonances. A suggested growth of the IceCube detector, IceCube-Gen2, would allow the researchers to make such measurements in a statistically considerable method. The partnership just recently revealed an upgrade of the detector that will be carried out over the next couple of years, the initial step towards IceCube-Gen2.

Glashow, now an emeritus teacher of physics at Boston University, echoes the requirement for more detections of Glashow resonance occasions. “To be absolutely sure, we should see another such event at the very same energy as the one that was seen,” he states. “So far there’s one, and someday there will be more.”

Last however not least, the outcome shows the worth of worldwide partnership. IceCube is run by over 400 researchers, engineers, and personnel from 53 organizations in 12 nations, together called the IceCube Collaboration. The primary analyzers on this paper collaborated throughout Asia, North America, and Europe.

“The detection of this event is another ‘first,’ demonstrating yet again IceCube’s capacity to deliver unique and outstanding results,” states Olga Botner, teacher of physics at Uppsala University in Sweden and previous representative for the IceCube Collaboration.

“IceCube is a wonderful project. In just a few years of operation, the detector discovered what it was funded to discover — the highest energy cosmic neutrinos, their potential source in blazars, and their ability to aid in multimessenger astrophysics,” states Vladimir Papitashvili, program officer in the Office of Polar Programs of the National Science Foundation, IceCube’s main funder. James Whitmore, program officer in NSF Division of Physics, includes, “Now, IceCube amazes scientists with a rich fount of new treasures that even theorists weren’t expecting to be found so soon.”

Reference: “Detection of a particle shower at the Glashow resonance with IceCube” 10 March 2021, Nature.
DOI: 10.1038/s41586-021-03256-1

The IceCube Neutrino Observatory is moneyed mostly by the National Science Foundation (OPP-1600823 and PHY-1913607) and is headquartered at the Wisconsin IceCube Particle Astrophysics Center, a proving ground of UW-Madison in the United States. IceCube’s research study efforts, consisting of important contributions to the detector operation, are moneyed by firms in Australia, Belgium, Canada, Denmark, Germany, Japan, New Zealand, Republic of Korea, Sweden, Switzerland, the United Kingdom, and the United States. IceCube building was likewise moneyed with considerable contributions from the National Fund for Scientific Research (FNRS & FWO) in Belgium; the Federal Ministry of Education and Research (BMBF) and the German Research Foundation (DFG) in Germany; the Knut and Alice Wallenberg Foundation, the Swedish Polar Research Secretariat, and the Swedish Research Council in Sweden; and the University of Wisconsin-Madison Research Fund in the U.S.