proton charge radius from electron scattering

In 2010, atomic physicists announced results from a new method. These two different methods yielded a radius of about 0.88 femtometers. Nuclei that have typically been observed include hydrogen (with one proton) or deuterium (with a proton and a neutron). In atomic spectroscopy measurements, the transitions between energy levels by electrons are observed (in the form of photons that are given off by the electrons) as they orbit a small nucleus. In electron-scattering experiments, electrons are shot at the protons, and the proton’s charge radius is determined by the change in path of the electrons after they bounce off, or scatter from, the proton.

Prior to 2010, the most precise measurements of the proton’s radius came from two different experimental methods. Yet, an unexpected result from an experiment to measure the size of this cloud, in terms of its root-mean-square charge radius, has united atomic and nuclear physicists in a flurry of activity to re-examine this basic quantity of the proton. The ubiquitous proton, which sits at the heart of every atom, has been the subject of numerous studies and experiments aimed at revealing its secrets. Gasparian is an Armenian physicist who got his PhD from the Yerevan Physics Institute in Armenia.Īll visible matter in the universe is built on a cloud of three quarks bound together with strong force energy. “We are happy that years of hard work of our collaboration is coming to an end with a good result that will help critically toward solution of the so-called proton radius puzzle,” says Ashot Gasparian, a professor at North Carolina A&T State University and the experiment’s spokesperson. The new value for the proton radius that was obtained is 0.831 fm, which is smaller than the previous electron-scattering value of 0.88 fm and is in agreement with recent muonic atomic spectroscopy results.

The result, recently published in the journal Nature, is one of the most precise measured from electron-scattering experiments. Using the first new method in half a century for measuring the size of the proton via electron scattering, the PRad collaboration has produced a new value for the proton’s radius in an experiment conducted at the Department of Energy’s Thomas Jefferson National Accelerator Facility.

Proton charge radius from electron scattering