by Astronomers using the IceCube observatory, buried deep within the ice of the south pole, have detected seven candidates for mysterious and alien “particle ghosts” streaming through Earth. The signals suggest that these particles are astrophysical tau neutrinos; they act as important messengers between powerful, high-energy celestial events and us.
Neutrinos are charged particles of no less than mass that blast through space at speeds approaching that of light. Oddly enough, given those parameters, a neutrino hardly interacts with anything. In fact, about 100 trillion of them pass through our bodies every second. We can not tell. If you were a human-sized neutrino detector, you would have to wait about 100 years for a neutrino to interact with a particle in your body. Neutrons are called “ghost particles” for good reason.
High-energy neutrinos from cosmic sources at the edge of the Milky Way are called “astrophysical neutrinos”, and they come in three flavors, or generations: Electron neutrinos, muon neutrinos and tau neutrinos. All of these phantom particles are, as you’d expect, extremely elusive, but IceCube’s mission is to put them aside. In 2013, the observatory made its first detection of astrophysical neutrinos, and now it appears to have discovered astrophysical tau neutrinos in particular that could serve as a new type of cosmic messenger.
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“The detection of seven candidate tau neutrino events in the data, combined with the very low amount of expected background, allows us to claim that backgrounds are very likely conspiring to produce seven tau neutrino imposters,” Doug Cowen , a joint study. leader and professor of physics at Penn State University said in a statement. “The discovery of astrophysical tau neutrinos also provides strong confirmation of the earlier IceCube discovery of the diffuse astrophysical neutrino flux.”
Trapped under the ice
To detect neutrinos as they pass through Earth, IceCube uses strings of golden spheres called digital optical modules, or DOMs, embedded in the ice. In total, the observatory has placed 5,160 DOM deep within the Antarctic ice, waiting for a neutrino to interact with molecules in the ice and produce charged particles. These charged particles emit blue light as they travel through the ice themselves – the DOMs register this light.
Specifically, when high-energy astrophysical tau neutrinos interact with molecules, they create characteristic light emissions, including a characteristic double cascade event that produces two peaks in light levels detected by DOMs.
In the past, IceCube has managed to find tantalizing hints of those tau-neutrino signatures, but Cowen and his colleagues were trying to find the elusive particles.
IceCube can detect other neutrino flavors in real time, but the facility currently cannot do this for tau neutrinos. Instead, hunting down these particular cosmic ghosts requires going through decades of archival data. But instead of going full Scooby-Doo and hunting down these phantoms themselves, the team trained what it called “image-enhanced convolutional neural networks” to sift through nearly 10 years of IceCube data. collected between 2011 and 2020 to search for the. tau-neutrino signatures.
This led to the detection of seven strong tau neutrino candidates.
The team is keeping open the possibility that these detections are the result of misidentification, but Cowen explained that the chance that the background detected by DOM is mimicking this signal is only 1 in 3.5 million.
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Only three sets of DOM detectors were used in the current results, but future analyzes will rely on more of these icy, golden pearls. This will not only increase the sample of detected tau neutrinos, but could help scientists conduct the first ever three-generation study of neutrino oscillations. This is the phenomenon by which neutrinos change flavors as they travel over vast cosmological distances.
Understanding neutrino oscillations could be the key to determining how these ghost particles are generated, what events cause them in space in the first place, and why they migrate to to the generations to come over time.
“Overall, this exciting discovery opens up the exciting possibility of leveraging tau neutrinos to discover new physics,” Cowen concluded.
The team’s research appears on the arXiv paper repository and has been accepted for publication in the journal Physical Review Letters.
