Science & Technology

Physicists Cast Doubt on Neutrino Theory – Exotic Subatomic Particle May Not Exist at All

Neutrino Animation Concept

Exotic subatomic particles, sterile neutrinos, are no-shows in experiments, growing doubts about their existence.

College of Cincinnati physicists, as a part of a world analysis crew, are elevating doubts in regards to the existence of an unique subatomic particle that failed to point out up in twin experiments.

UC Faculty of Arts and Sciences affiliate professor Alexandre Sousa and assistant professor Adam Aurisano took half in an experiment at the Fermi Nationwide Accelerator Laboratory looking for sterile neutrinos, a suspected fourth “taste” of neutrino that will be a part of the ranks of muon, tau, and electron neutrinos as elementary particles that make up the recognized universe.

Discovering a fourth kind of neutrino can be big, Sousa mentioned. It might redefine our understanding of elementary particles and their interactions in what’s generally known as the Normal Mannequin.

UC affiliate professor Alexandre Sousa holds a neutrino mannequin that adjustments colour when tossed within the air to display how neutrinos change “taste.” Credit score: Joseph Fuqua II/UC Artistic + Model

Researchers in two experiments known as Daya Bay and MINOS+ collaborated on complementary tasks in an intense effort to seek out sterile neutrinos utilizing a few of the world’s most superior and exact instruments.

“We apparently don’t see any proof for them,” Aurisano mentioned.

“It’s an necessary consequence for particle physics. It supplies an nearly definitive reply to a query that has been lingering for over 20 years.” — Alexandre Sousa, UC affiliate professor of physics

The examine was revealed within the journal Bodily Evaluate Letters and was featured in Physics Journal, revealed by the American Bodily Society.

“It’s an necessary consequence for particle physics,” Sousa mentioned. “It supplies an nearly definitive reply to a query that has been lingering for over 20 years.”

The analysis builds on earlier research that provided tantalizing prospects for locating sterile neutrinos. However the brand new outcomes counsel sterile neutrinos may not have been answerable for the anomalies researchers beforehand noticed, Aurisano mentioned.

Experiments at Fermilab collect a lot information that it takes supercomputers to investigate it. Credit score: Photograph/Reidar Hahn/Fermilab

“Our outcomes are incompatible with the sterile neutrino interpretation of the anomalies,” he mentioned. “So these experiments take away a chance – the main chance – that oscillations into sterile neutrinos solely clarify these anomalies.”

UC assistant professor Adam Aurisano. Credit score: College of Cincinnati

Neutrinos are tiny, so tiny they’ll’t be damaged down into one thing smaller. They’re so small that they move by way of nearly all the pieces — mountains, lead vaults, you — by the trillions each second at nearly the velocity of sunshine. They’re generated by the nuclear fusion reactions powering the solar, radioactive decays in nuclear reactors or within the Earth’s crust, and in particle accelerator labs, amongst different sources.

And as they journey, they usually transition from one kind (tau, electron, muon) to a different or again.

However theorists have steered there could be a fourth neutrino that interacts solely with gravity, making them far tougher to detect than the opposite three that additionally work together with matter by way of the weak nuclear drive.

The experiment Daya Bay consists of eight detectors arrayed round six nuclear reactors outdoors Hong Kong. MINOS+ makes use of a particle accelerator in Illinois to shoot a beam of neutrinos 456 miles by way of the curvature of the Earth to detectors ready in Minnesota.

“We’d all have been completely thrilled to seek out proof for sterile neutrinos, however the information we’ve got collected to date don’t help any sort of sterile neutrino oscillation,” mentioned Pedro Ochoa-Ricoux, affiliate professor at the College of California, Irvine.

Fermilab’s MINOS+ experiment makes use of two neutrino detectors 450 miles aside in Illinois and Minnesota. Credit score: Fermilab

Researchers anticipated to see muon neutrinos seemingly vanish into skinny air once they transitioned into sterile neutrinos. However that’s not what occurred.

“We anticipated to see muon neutrinos oscillating to sterile neutrinos and disappear,” Aurisano mentioned.

Regardless of the findings, Aurisano mentioned he thinks sterile neutrinos do exist, at least in some type.

“I believe sterile neutrinos are extra possible than to not exist at excessive energies. On the very starting of the universe, you’d anticipate there can be sterile neutrinos,” he mentioned. “With out them, it’s exhausting to clarify elements of neutrino mass.”

However Aurisano is skeptical about discovering gentle sterile neutrinos that many theorists anticipated them to seek out within the experiments.

“Our experiment disfavors gentle or lower-mass sterile neutrinos,” he mentioned.

Sousa mentioned a few of his analysis was truncated considerably by the worldwide COVID-19 pandemic when Fermilab shut down accelerator operations months sooner than anticipated. However researchers continued to make use of huge supercomputers to look at information from the experiments, even whereas working from residence through the quarantine.

“It’s one of many blessings of excessive power physics,” Aurisano mentioned. “Fermilab has all the info on-line and the computing infrastructure is unfold out world wide. So so long as you’ve gotten the web you’ll be able to entry all the info and all of the computational amenities to do the analyses.”

Nonetheless, Aurisano mentioned it takes some adjusting to do business from home.

“It was simpler after I had devoted hours at the workplace. It’s a problem generally to do business from home,” he mentioned.

Reference: “Improved Constraints on Sterile Neutrino Mixing from Disappearance Searches within the MINOS, MINOS+, Daya Bay, and Bugey-3 Experiments” by P. Adamson et al. (Daya Bay Collaboration, MINOS+ Collaboration), 10 August 2020, Bodily Evaluate Letters.
DOI: 10.1103/PhysRevLett.125.071801

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