MIT Researchers Solve Decades-Old Quark Quandary

Physicists from MIT have announced that they have discovered the answer to a question that has challenged nuclear physicists for 35 years. That mystery was why do quarks move more slowly inside larger atoms? A quark is a fundamental building block of the universe.

Quarks are subatomic particles and are some of the smallest particles we know of, and they operate at higher energy levels than the protons and neutrons found with them. The assumption in scientific circles was that a quark should be indifferent to the characteristics of protons and neutrons as well as the atom it resides in as a whole.

However, in 1983 physicists at CERN observed for the first time something called the EMC effect. Scientists say that in the nucleus of an iron atom that has many protons and neutrons, quarks move significantly more slowly than quarks move in deuterium. The latter has only a single proton and neutron.

Evidence has been gathered over the years that shows the larger an atom's nucleus, the slower the quarks inside move. MIT researchers Or Hen, Barak Schmookler, and Axel Schmidt have found an explanation for EMC. The team says that the speed of the quark depends on the number of protons and neutrons that form short-range correlated pairs in the nucleus of an atom.

The more pairs, the slower the quarks move within the protons and neutrons of the atom. According to Schmidt, the protons and neutrons inside an atom pair up constantly, but only momentarily before splitting apart again. During the interaction, Schmidt believes that the Quarks have "a larger space to play." He notes that in quantum mechanics when you increase the volume over which an object is confined, it slows down. When space is tighter, the object speeds up. The larger the nucleus of an atom is, the more protons and neutrons it has, meaning slower speeds for the quark.