IceCube Neutrino Observatory event may be caused by a tau neutrino

IceCube Neutrino Observatory event may be caused by a tau neutrino
The IceCube Neutrino Observatory detector © Sven Lidstrom, IceCube-NSF via https://icecube.wisc.edu/

Theoretical physicists calculate the origin of a high-energy particle track captured by the IceCube Neutrino Observatory.

The IceCube Neutrino Observatory detector, a research centre located at the South Pole to detect neutrinos emanating from the cosmos, allows the detection of high-energy neutrinos by IceCube made viable completely new options for explaining how our universe works.

Dr Ranjan Laha of Johannes Gutenberg University Mainz (JGU), Germany, said: “These neutrinos with their considerable energy are cosmic messengers we have never encountered before, and it is extremely important that we understand exactly what they are telling us.”

Working in collaboration with a colleague at Stanford University in the USA, the Mainz-based physicist has put forward a new hypothesis on what this interstellar message carrier might be.

The two physicists have calculated that what has been detected could be the track of a high-energy tau particle that transited the IceCube detector.

What are Neutrino particles?

Neutrinos are particles that have very little or no mass, enabling them to pass through material almost unnoticed, making them extremely difficult to detect. Yet, for this very same reason, these elusive particles are particularly important to science because they originate from exploding stars and other high-energy astrophysical phenomena that then travel to Earth.

In the case of the IceCube Neutrino Observatory, the individual detector elements are buried in the Antarctic ice and distributed across an ice volume of a cubic kilometre, where they are well protected against the effects of possible interference.

The project team reported the detection of high-energy neutrinos from space for the first time in 2013. Numerous related events have been registered since then.

High-energy track

In June 2014, the IceCube sensors detected a particle with extraordinarily high energy. Calculations showed that the particle deposited 2.6 petaelectron-volts (PeV), in other words, 2.6 quadrillion electron-volts.

In comparison, collisions between protons in the Large Hadron Collider (LHC) at CERN, the world’s largest particle accelerator, occur at an energy of just 13 trillion electron-volts.

The questions around this track began, with the main one being ‘what sort of netrino would leave behind this track’. There are three types of neutrino:

  • Electrons;
  • Muons; and
  • Tau neutrinos.

The investigations at the IceCube Neutrino Observatory

According to the university, the two physicists first based their investigations on the standard assumption that the track had been produced by a muon.

Following collision with an atom nucleus, a muon neutrino would have been transformed into a muon and would have been captured by the optical sensors of the IceCube detector. Instead, the two researchers propose that the track could be that of a high-energy tau lepton.

To be registered by the detector with an energy of 2.6 PeV, the supposed tau neutrino would have to have had an initial energy of at least 50 PeV.

Laha explained: “A tau particle that can pass through a detector with a length of one kilometer without decaying and furthermore releasing energy of 2.6 PeV must originate from a neutrino with significantly greater energy,

“Assuming this is the case, this opens up completely unexpected possibilities, namely that astrophysics should start looking for neutrinos with energy of up to 100 PeV.”

The two researchers also came to the conclusion that the 2.6 PeV event was probably caused by a component of the neutrino spectrum previously unknown to astrophysicists.

Laha concluded: “We still don’t really know what caused the 2.6 PeV track. It is generally assumed to be a transiting muon. We show that it is also possible to be a transiting tau particle.

“We consider this event so significant that we believe it should be examined more closely. And we need more data to be able to discover more and decode this message sent us by the cosmos.”

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