MADISON – On December 6, 2016, a high-energy material was injected into Earth from outer space near the speed of light. The ball, an antineutrino electron, broke into an electron deep inside the ice sheet at the South Pole. This crash quickly erupted grain into a shower of secondary grains, removing the sensors of the Neutrino IceCube Observatory, a large telescope buried in the Antarctic glacier.
IceCube had witnessed the Glashow reset event, a phenomenon predicted by Nobel physicist Sheldon Glashow in 1960. With this discovery, scientists further validated the Universal Model of particle physics. It also showed the ability of IceCube, which detects almost non-volatile grains called neutrinos using thousands of sensors rooted in Antarctic ice, to perform basic physics. The result was announced March 10 in Nature.
Sheldon Glashow first proposed this position in 1960 when he was a postgraduate researcher at the Niels Bohr Institute today in Copenhagen, Denmark. There, he wrote a paper in which he predicted that antineutrino – an antimatter pair of neutrinos – could interact with an electron to detect as yet undiscovered particles through a process called resonance. The key is that the antineutrino must have precise energy to produce this content.
When the proposed item, the W-minus boson, was finally discovered in 1983, it turned out to be much heavier than Glashow and his colleagues expected back in 1960. Resetting a Glashow would require a neutrino with an energy of 6.3 petaelectronvolts, nearly 1,000 times more dynamic than CERN’s Large Hadron Collider is capable of. A human cheese accelerator on Earth, conventional or designed, cannot create a neutrino with so much energy.
But the massive energy of massive black holes at the centers of galaxies and other real cosmic events can create particles with energy that cannot be created on Earth. Such a phenomenon apparently was due to the antineutrino that reached IceCube in 2016, which crashed into the Earth with an energy of 6.3 PeV – just as Glashow ‘s theory predicted.
“When Glashow was Niels Bohr ‘s postdoc, he could not have imagined that his unconventional proposal for the extraction of a W – minus boson would be effected by an antineutrino from a long galaxy from falling into the ice of Antarctica, ”said Francis Halzen, chief investigator of IceCube and professor of physics at the University of Wisconsin-Madison, IceCube’s headquarters for maintenance and operations.
Since IceCube became fully operational in May 2011, the observatory has detected hundreds of high-energy astrophysical neutrinos and has achieved a number of important results in particle astrophysics, including entered the detection of astrophysical neutropho flux in 2013 and the first identification of a source of astrophysical neutrophos in 2018. The Glashow reset event is famous for its very high energy. It is only the third event to find an IceCube with an energy greater than 5 PeV.
This result was a collaborative effort accomplished by a team of three scientists: Lu Lu from the University of Chiba in Japan, now at UW-Madison, Tianlu Yuan from UW-Madison, and Christian Haack from RWTH University Aachen, now at TU Munich.
The Glashow reset was the first individual neutrino to be confirmed to be of astrophysical origin. It will also showcase IceCube’s unique contributions to multi-person astronauts, which use light, particles and gravitational waves to explore the cosmos. The result also opens a new chapter of neutrino astronomy as it begins to separate neutrinos from antineutrinos.
“Previous measurements had not been sensitive to the difference between neutrinos and antineutrinos, so this result is the first direct measurement of the antineutrino component of the astrophysical neutrino flux,” said Lu, one of the paper’s leading analysts. seo.
“There are several properties of the astrophysical neutrinos sources that we cannot measure, such as the physical size of the accelerator and the strength of the magnetic field in the acceleration region,” said Yuan, an assistant scientist at the Wisconsin IceCube Particle Astrophysics Center and another principal analyst. “If we can determine the neutrino-to-antineutrino ratio, we can directly study these properties.”
The result also demonstrates the value of international cooperation. IceCube is run by more than 400 scientists, engineers, and staff from 53 institutions in 12 countries, together known as IceCube Collaboration. The principal investigators of this paper worked together across Asia, North America and Europe.
To validate the detection and make a definitive measurement of the neutrino-to-antineutrino ratio, IceCube Collaboration wants to see more Glashow reset. A proposed extension of the IceCube detector, IceCube-Gen2, would allow scientists to perform these steps in a statistically significant manner. The collaboration recently announced an update to the tracker that will be implemented over the next few years, the first step towards IceCube-Gen2.
Glashow, who is now a professor of physics at Boston University, confirms the need for more discoveries of his eponymous resonance events.
“To be absolutely sure, we should see another such event at the same energy as the one that was seen,” he says. “So far there is one, and sometimes there will be more.”
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This work was supported in part by the National Science Foundation (OPP-1600823 and PHY-191360 grants).
– Madeleine O’Keefe, (608) 515-3831, [email protected]
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