Many people learn in elementary school that the primary components that make up all matter on earth are protons, neutrons, and electrons. However, the real fundaments of atoms are smaller and much more enigmatic than the school-age narrative suggests.
The U.S. Department of Energy has renewed the $1.26 million grant allowing the physics department at New Mexico State University to continue uncovering the complex behaviors of quarks and gluons, the particles that form protons and neutrons (collectively referred to as nucleons).
NMSU Physics professors Stephen Pate and Vassilios Papavassiliou are involved with two current experiments, SpinQuest and MicroBooNE, that are transpiring at the Fermi National Accelerator Laboratory near Chicago. Graduate student Samantha Sword-Fehlberg and post-doctoral researcher Lu Ren are working on MicroBooNE while graduate research assistants Forhad Hossain, Dinupa Nawarathne, Harsha Arachchige and post-doctoral researcher Abinash Pun are working on SpinQuest.
SpinQuest is, as you might imagine, on a quest to understand the “spin” of nucleons, a peculiar property of particles that mysteriously arises from the behavior of their constituent parts. Spin, as Pate explained, is a property that makes it seem like they are spinning when they aren’t. The spin of a particle, when paired with an electrical charge, creates a magnetic field around the particle.
“The quarks and gluons conspire to create the spin of the proton,” Pate said, “but we don’t have a complete understanding of how they do that.”
Gluons, which produce a powerful field of energy that acts as a glue to hold quarks together, can create pairs of evanescent quarks and anti-quarks that are extremely elusive; they are formed by gluon energy but quickly recombine, existing only temporarily. The behavior of these “sea quarks” – as physicists call them – may be playing a more complex role in generating the spin of the nucleon.
Other experiments have clarified that the nucleon’s spin doesn’t arise from the mere spin of its constituents, raising the question of what else is at play. The team wants to see if the sea quarks are contributing to the spin of the nucleon by rotating around the center of it, like planets rotating around the sun.
“The SpinQuest experiment uses a high-energy proton beam from the Fermilab Main Injector and a ‘polarized’ target consisting of frozen ammonia,” said Papavassiliou. The target is polarized by using a strong magnetic field to arrange the protons so that their spins are aligned, pointing in the same direction. As the proton beam and target protons collide, the researchers look for quark and anti-quark interactions that give insight into their behavior within nucleons.
NMSU also participates in an international collaboration called MicroBooNE, which is short for Micro Booster Neutrino Experiment. This project consists of about 180 researchers across 36 institutions attempting to understand the properties of the neutrino, another elusive elementary particle, but one that doesn’t make up the atom.
“While much of the effort is dedicated to studying the neutrino,” Papavassiliou said, “our group focuses on using a neutrino beam to study the internal structure of the proton.” He explains that neutrinos, although still mysterious, are understood enough to be used as a probe for the properties of nucleons.
These nucleons reside in a 170-ton vessel of liquid argon that has a time-projection chamber inside. The team uses sophisticated electronics to record the immense number of interactions happening between the beam of neutrinos and the nucleons of the argon atoms.
According to Pate, this research has far-reaching applications to technological advancement, even if they aren’t immediately apparent. For example, MRI, commonly used in healthcare settings, capitalized on what we understand about how particles behave and interact. Pate posits that once physicists are trained to understand these fundamental properties, they can use their acquired skills to go out and invent new technologies that contribute to society.