US: 4th neutrino flavor discovery closer as Fermilab’s SBND detects 1st signals

Researchers at Fermi National Accelerator Laboratory’s Short-Baseline Near Detector (SBND) have successfully detected their first neutrino interactions.

SBND is the final component of Fermilab’s Short-Baseline Neutrino (SBN) Program and is set to play a pivotal role in unraveling a long-standing mystery in particle physics.

“It isn’t every day that a detector sees its first neutrinos,” said David Schmitz, co-spokesperson for the SBND collaboration and associate professor of physics at the University of Chicago.

“We’ve all spent years working toward this moment and this first data is a very promising start to our search for new physics.”

A new neutrino?

Neutrinos are the second most common particle in the universe, yet they remain incredibly elusive due to their weak interactions. They only respond to gravity and the weak nuclear force, making them rarely detectable.

There are three known types of neutrinos, or “flavors”: muon, electron, and tau. One of the most unusual properties of neutrinos is their ability to switch between these flavors, a process known as oscillation.

Scientists generally have well-established predictions for how many of each neutrino flavor should appear at various distances from a source. However, results from several past experiments have not aligned with these expectations.

“That could mean that there’s more than the three known neutrino flavors,” explained Fermilab scientist Anne Schukraft. “The only way we would see them is if the measurement of the number of muon, electron and tau neutrinos is not adding up like it should.”

Fermilab’s Short-Baseline Neutrino Program aims to investigate these flavor oscillations and search for evidence that might suggest the existence of a possible fourth type of neutrino.

Dark matter and more

In addition to the search for a potential fourth neutrino, the SBND has its own ambitious physics agenda. Positioned near the neutrino beam, SBND will record 7,000 interactions daily, more than any other detector of its type.

This wealth of data will enable researchers to study neutrino interactions with a level of precision never before achieved. Understanding these interactions is crucial for future experiments using liquid argon detectors, such as the upcoming Deep Underground Neutrino Experiment ( DUNE ).

However, neutrinos aren’t the only focus for SBND scientists. Due to its proximity to the particle beam, the detector may also capture unexpected phenomena.

“We will collect 10 times more data on how neutrinos interact with argon than all previous experiments combined,” said Ornella Palamara, Fermilab scientist and co-spokesperson for SBND. “So, the analyses that we do will be also very important for DUNE.”

One of the major unsolved mysteries in the Standard Model of physics is dark matter. While SBND will only be sensitive to lightweight particles, those theoretical particles could provide a first glimpse into a ‘dark sector,’ potentially offering key insights into the elusive nature of dark matter.