New machine helps scientists detect mysterious particles

After nearly a decade of preparation, scientists—including researchers from Rutgers University—have turned on a new apparatus capable of detecting a host of mysterious tiny particles.

They are in search of special, new kinds of subatomic particles that, if found, could rewrite the physical laws of the universe.

Researchers working on the Short-Baseline Near Detector (SBND) at Fermi National Accelerator Laboratory (Fermilab) in Batavia, Ill., have started up the new machine and begun detecting the neutrinos produced by Fermilab's particle accelerator beams.

Neutrinos are among the most abundant particles in the universe. About 100 trillion of them pass through a person's body every second, but they cannot be felt—the interactions of these ghostly particles with other matter are exceptionally rare. Scientists believe that these particles played a vital role in the creation of the universe.

"We think neutrinos could help us get at some huge questions, like finding a more complete theory of nature at the smallest scales, or even why our matter-filled universe exists at all," said Andrew Mastbaum, a researcher on the SBND team and an associate professor in the Department of Physics and Astronomy at the Rutgers School of Arts and Sciences.

Because of their rare interactions, neutrinos are difficult to study and that's why scientists are particularly excited about the detector.

"Having this detector up and running is a major milestone, the culmination of a monumental international effort, and the start of a really exciting chapter for the field," Mastbaum said.

SBND is part of a set of particle detectors at Fermilab that provides information on a beam of neutrinos created by the laboratory's powerful particle accelerators.

Whenever a neutrino collides with the nucleus of an atom, the interaction sends a spray of particles careening through the detector. To infer the properties of the ghostly neutrinos, physicists must account for all the particles produced during that interaction, both those visible and invisible.

Of the known elementary particles of matter, neutrinos are among the least understood. Scientists conducting previous experiments have observed some puzzling behavior that could indicate humankind's picture of fundamental physics, including its Standard Model, is incomplete.

According to current thinking, neutrinos come in three types, or what physicists refer to as flavors: muon, electron and tau. Over the past 30 years, researchers have observed anomalies suggesting the existence of a new type of neutrino, called a sterile neutrino, which isn't predicted by the Standard Model.

"SBND is a game changer because we will get to study an enormous number of neutrino interactions, finally resolve some long-outstanding experimental mysteries and have remarkable sensitivity to potential physics phenomena beyond the Standard Model," Mastbaum said.

Members of the SBND collaboration have been planning, developing models and constructing the detector for nearly a decade.

Rutgers scientists on the collaboration have worked on the machine's simulation software, data analysis tools, installation and startup, and are now involved in operations.

Among those who have contributed from Rutgers are former undergraduates Andrew Schwartz ('23) and Amy Flather ('24), postdoctoral researcher Ivan Lepetic and doctoral student Keng Lin.

"I am grateful to contribute to building this machine, knowing that each cable I connect could help unlock the secrets of the universe," said Lin, who has worked on the machine for months.

"Visualizing physics, especially particle physics, can be quite abstract, but your understanding really clicks when you're actually assembling parts of a machine and seeing the concepts come to life right at your fingertips."

The detector was built by an international collaboration of 250 physicists and engineers from Brazil, Spain, Switzerland, the United Kingdom and the United States.

In addition to searching for a fourth neutrino, scientists operating SBND have some other objectives.

SBND is expected to record 7,000 neutrino interactions a day, more than any other detector of its kind, according to collaborators on the project. The large data sample will allow researchers to study neutrino interactions with unprecedented precision.

Insights gained from the interactions will inform future experiments.

The neutrino signatures detected are just the beginning for the SBND project. The collaboration will continue operating the detector and analyzing the many millions of neutrino interactions being collected for the next several years.

"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.

Provided by Rutgers University