U of A part of global neutrino research
A new finding by scientists — including two from the University of Alberta — about the dynamics of high-energy “ghost particle” neutrinos could pave the way for a greater understanding of the structure of the Earth’s core.
Since 2010, researchers at the South Pole have been collecting data about neutrinos at the IceCube Collaboration facility, the world’s biggest neutrino detector, to gain a better understanding of one of the most elusive particles in the universe.
Neutrinos are one of the most abundant fundamental particles, but they rarely interact with anything, making them difficult to study.
That’s where IceCube comes in. The facility is a three-dimensional cubic kilometre grid of more than 5,000 ultrasensitive basketball sized light sensors drilled 21/2 km into a glacier in the Antarctic. It’s designed to monitor the highest energy neutrinos in the universe coming from cataclysmic astrophysical events.
The glacier effectively blocks the constant bombardment of cosmic radiation and allows scientists to monitor neutrinos as they pass through the Earth.
Scientists discovered during their analysis of its first year of data that the highest-energy neutrinos, instead of passing through the Earth and travelling to the ends of the universe, actually stop.
“It kind of floored me,” said project lead and University of Alberta physics professor Darren Grant.
“When you go up high enough in energy, the probability that a neutrino will interact instead of simply passing through material actually increases and if you get to a high enough energy, they will get absorbed and stop.
“This is a really beautiful measurement in many ways and it’s the first time we have seen it.”
Grant, who along with University of Alberta assistant professor Claudio Kopper are among more than 300 members from 48 institutions in 12 countries involved in the IceCube Collaboration, said the discovery was the first step in understanding the makeup of the Earth’s core.
The group is already in the stages of expanding the detector by a factor of 10 to capture more neutrinos to gain an even more detailed view of what’s below the Earth’s surface via neutrino tomography.
While geologists and geophysicists study the Earth’s core by how sound waves bend and reflect as they move through the planet, they struggle when it comes to learning much about the inner liquid layer.
Grant said that by looking at neutrinos arriving at the detector from different directions at different energies, they can effectively map the layers of the Earth’s core and outer core.
“The probability that the neutrino will interact is related to the density of the material it is going through,” he said.
“Neutrinos are seen as one of the landmark ways you could use to make a precision probe of Earth’s deep interior structure, which you can’t really do with traditional methods.”
This is a really beautiful measurement in many ways and it’s the first time we have seen it.