Two experiment collaborations, the g2p and EG4 collaborations, combined their complementary data on the proton’s inner structure to improve calculations of a phenomenon in atomic physics known as the hyperfine splitting of hydrogen. An atom of hydrogen is made up of an electron orbiting a proton.
The overall energy level of hydrogen depends on the spin orientation of the proton and electron. If one is up and one is down, the atom will be in its lowest energy state. But if the spins of these particles are the same, the energy level of the atom will increase by a small, or hyperfine, amount. These spin-born differences in the energy level of an atom are known as hyperfine splitting.
While it’s commonplace for many scientists to collaborate on nuclear physics experiments at the U.S. Department of Energy’s Thomas Jefferson National Accelerator Facility, it’s rarer for the lab’s individual experiments to collaborate with each other. But that’s exactly what g2p in Jefferson Lab’s Experimental Hall A and EG4 in Experimental Hall B did.