Physicists in Syracuse University’s College of Arts and Sciences are playing a key role in the ongoing study of neutrinos, one of the Universe’s smallest, most elusive particles.
Mitchell Soderberg, assistant professor of physics, is leading a team of University researchers involved with a multinational experiment called MicroBooNE. Short for “Micro Booster Neutrino Experiment,” MicroBooNE is based at the Fermi National Accelerator Laboratory (Fermilab), near Chicago, where more than one hundred participating scientists are expected to study the properties of neutrino interactions. On Oct. 15, they hit pay-dirt, observing MicroBooNE's first neutrino interaction.
“Because neutrinos have no charge and very little mass, they rarely interact with other particles,” says Soderberg, who studies the behavior of neutrinos. “In fact, most of them pass through the Earth without ever being disturbed or detected. They do occasionally, however, collide with a single atom. When that happens, we can study the interaction to learn more about the properties of neutrinos and their role in the Universe.”
One of only a couple in the world, the accelerator complex at Fermilab creates an intense beam of neutrinos that is directed at a nearby detector, which observes and records the interactions. Because neutrinos interact so weakly with matter, the detectors have to be large, so as to increase the chances of detection. They also should be underground, so other forms of background radiation in the Earth’s atmosphere, such as cosmic rays, do not fake the signature of the collision process.
“When a neutrino hits the nucleus of an argon atom in the detector, it creates a collision that sprays subatomic particle debris,” says Soderberg, adding that Fermilab’s accelerator can spit out billions of neutrinos a second. “By tracking the particles in the debris, we’re able to reveal the type and properties of the neutrinos that produced them.”
Although the existence of neutrinos was first postulated in 1930, another 26 years would pass before the particles, themselves, were first experimentally observed. Today, scientists agree there are three types, or flavors, of neutrinos, and that they continuously oscillate among these flavors while hurtling through space.
Because neutrinos are emitted in huge numbers by stars, including the sun, their behavior may hold clue’s to the Universe’s past, present, and future.
“For years, scientists have wondered why they haven't been able to detect the predicted number of neutrinos from the sun, which produces huge quantities of [neutrinos] during solar fusion,” he says. “We now understand that the solar neutrino flux has appeared to be low because the neutrino detector used in the original experiments was sensitive to only one of the three flavors.”
At Syracuse, Soderberg supervises the efforts of three graduate students, one undergraduate, and a postdoctoral research associate. Two years ago in the Physics Building, his team made and tested thousands of wires for MicroBooNE’s detector. The wires collect signals from the collisions of neutrinos with argon atoms. The signals are then converted into high-resolution images of particle tracks.