Calculating a proton's spin used to be an easy college assignment. In fact, Carl Gagliardi remembers answering that question when he was a physics graduate student in the 1970s. But the real answer turned out not to be simple at all. Even Gagliardi's "right" response was disproven by experiments a few years later that turned the field upside-down.
Protons are one of the three particles that make up atoms, the building
blocks of the universe. A proton's spin is one of its most basic
properties. Because protons are in part made up of quarks, scientists
presumed the proton spins were just the sum of the quark spins.
But studies in the 1980s showed that reality is far more complex. Since then, Gagliardi and other researchers have used the unique DOE Office of Science User Facilities at Thomas Jefferson National Accelerator Facility (Jefferson Lab) and Brookhaven National Laboratory to explore this fundamental phenomenon.
Investigating a Force of Nature...