In a groundbreaking achievement, physicists at the Thomas Jefferson National Accelerator Facility, supported by the U.S. Department of Energy, have shattered the record for measuring parallel spin within electron beams, known as electron beam polarimetry, in nearly three decades. This milestone could potentially unlock new avenues for physics exploration. The research was published in the recent edition of "Physical Review C."
The ultra-high precision measurement was achieved during the Calcium Radius Experiment (CREX). This experiment, conducted alongside the Lead Radius Experiment (PREX-II), aims to probe the nuclei of medium and heavy atoms to gain deeper insights into their "neutron skin" structure. The neutron skin refers to the distribution of protons and neutrons within the denser regions of atomic nuclei. Lighter elements (typically those with atomic numbers of 20 or lower on the periodic table) often have an equal number of protons and neutrons. Medium and heavy atoms typically require more neutrons than protons to maintain stability.
PREX-II and CREX focused on lead-208, which has 82 protons and 126 neutrons, and calcium-48, which has 20 protons and 28 neutrons, respectively. In these atoms, an approximately equal number of protons and neutrons cluster around the core of the nucleus, while excess neutrons are pushed to the periphery, forming a "skin."
The experiment determined that lead-208 has a thicker "neutron skin," which impacts the characteristics of neutron stars, while calcium-48 has a relatively thinner skin. The precision of these measurements reached one-billionth of a nanometer.
During the CREX experiment, researchers continuously measured the polarization of the electron beam using the Compton polarimetry method, achieving an accuracy of 0.36%. This surpasses the 0.5% accuracy reported during the SLAC Large Detector (SLD) experiment.
