In a paper recently published in Nature Communications, a team of Temple University physicists describe a new method for measuring the charge radius of neutrons that represents a substantial advance over previous methodologies dating back to the 1990s.
Together with protons, neutrons constitute the nuclei of atoms and, as such, are cornerstones in the depiction of the visible universe. "Neutrons are of significant importance, not only for understanding the foundation of nuclear physics but for also understanding cosmology, the science of the creation and development of the universe," says the principal investigator Nikolaos Sparveris, associate professor of physics.
Despite this critical importance, for the past two decades the indirect method of measuring the neutron charge radius followed by the Particle Data Group—an international collaboration of particle physicists from 26 countries charged with summarizing particle physics—compiled measurements that disagree due to unresolved systematic discrepancies.
Based, in part, on measurements conducted at both the Thomas Jefferson National Accelerator Facility in Newport News, Virginia—where Sparveris previously was a staff scientist holding a bridge position with Temple University—and the Mainz Microtron particle accelerator in Mainz, Germany, the Temple physicists have developed a more direct and accurate method that specifically targets nucleons. "It addresses the current discrepancies and opens up the path for higher precision measurements, which we intend to further pursue," says Sparveris.
The new methodology is the culmination of a series of experiments spanning many years. Sparveris, a native of Greece, has been pondering this issue for most of this century, beginning when he was a doctoral student and postdoctoral research associate at the University of Athens, and then as a postdoctoral associate at the Massachusetts Institute of Technology. He joined the Temple Physics Department as an assistant professor in 2010.
The latest research was funded by the U.S. Department of Energy's Office of Science, Office of Nuclear Physics. The co-authors of the research paper include, from the Temple Physics Department, Assistant Professor Martha Constantinou; Zein-Eddine Meziani, a Temple adjunct and a senior scientist at the Argonne National Laboratory in Illinois; and Hamza Atac, a Temple PhD graduate who is now a post-doctoral fellow working in Sparveris' laboratory. Michael Paolone, a former research assistant professor at Temple who is now an assistant professor of physics at New Mexico State University in Las Cruces, is also a co-investigator.