• Number 309  |
• April 12, 2010

Femto-scale Freedom

Some of the most tightly bound objects in the universe can at times appear to roam freely. Scientists have debated whether this is a fact of nature or a fluke limited to the objects they were studying. Now, nuclear physicists at DOE's Jefferson Lab have an answer.

In probing the building blocks of matter, subatomic particles that are bound tightly together deep inside the nucleus of the atom can appear on average as if they are roaming free. This phenomenon, known as quark-hadron duality, specifically pertains to quarks and the particles they build, such as protons (which are hadrons).

While quark-hadron duality has been observed in the proton for decades, it has only recently been conclusively observed in the neutron. A team of nuclear physicists used a newly developed technique to extract accurate neutron cross sections from experimental data. The data were obtained from experiments involving the nuclei of two different hydrogen isotopes: one with nuclei that contained one proton and another that contained a proton and a neutron.

The observation of quark-hadron duality in the neutron has excited the team, because prior to their discovery it was not clear whether quark-hadron duality was the result of accidental cancellations between quark charges in the proton (which do not occur for the neutron) or whether it arose from fundamental principles of the force that binds quarks together. The team now hopes to build upon its findings to obtain a description of protons and neutrons based on their fundamental constituents, even in kinematic regions where this was previously deemed unachievable.

[Kandice Carter, 757.269.7263,
kcarter@jlab.org]