![]() Once data taking was complete, the collaboration worked to carefully analyze the data. The outgoing electrons were collected and measured with the hall’s left and right High Resolution Spectrometers. ![]() The targets included helium-3 and three isotopes of hydrogen, including tritium. The experiment sent 10.59 GeV (billion electron-volt) electrons into four different targets in Experimental Hall A. “That’s part of the mission of the lab: There’s nothing so important that we can sacrifice safety.” Tritium being a radioactive gas, we needed to ensure safety above everything,” Meekins explained. “For this individual experiment, clearly the biggest challenge was the target. The more than 130 members of the MARATHON experimental collaboration overcame many hurdles to carry out the experiment.įor instance, MARATHON required the high-energy electrons that were made possible by the 12 GeV CEBAF Upgrade Project that was completed in 2017, as well as a specialized target system for tritium. ![]() These two quantities may be related to the distribution of up and down quarks inside the nuclei,” Petratos said.įirst conceived in a summer workshop in 1999, the MARATHON experiment was finally carried out in 2018 in Jefferson Lab’s Continuous Electron Beam Accelerator Facility, a DOE user facility. “It turns out that if we measure the ratio of cross sections in these two nuclei, we can access the structure functions of protons relative to neutrons. “We used the simplest mirror nuclei system that exists, tritium and helium-3, and that’s why this system is so interesting,” said David Meekins, a Jefferson Lab staff scientist and a co-spokesperson of the MARATHON experiment. Credit: Thomas Jefferson National Accelerator Facility Two state of the art particle detector systems, the High Resolution Spectrometers in Jefferson Lab’s Experimental Hall A, were instrumental in collecting data in the MARATHON experiment. This is why they are known as mirror nuclei. If you could ‘mirror’ transform helium-3 by converting all protons into neutrons and neutrons into protons, the result would be tritium. While helium-3 has two protons and one neutron, tritium has two neutrons and one proton. The physicists chose to focus on the nuclei of helium-3 and tritium, which is an isotope of hydrogen. In the recently completed MARATHON experiment, nuclear physicists compared the results of deep inelastic scattering experiments for the first time in two mirror nuclei to learn about their structures. Today, experiments continue to fine-tune this process to tease out ever more detailed information. These experiments have fueled nuclear physicists’ understanding of the role of quarks and gluons in the structures of protons and neutrons. Since those first experiments five decades ago, deep inelastic scattering experiments have been performed around the world at various laboratories. The huge particle detector systems that collect the electrons that emerge from these collisions measure their momenta – a quantity that includes the electrons’ mass and velocity. “When we say deep inelastic scattering, what we mean is that nuclei bombarded with electrons in the beam break up instantly thereby revealing the nucleons inside them when the scattered electrons are captured with state-of-the art particle detection systems,” explained Gerassimos (Makis) Petratos, a professor at Kent State University and the MARATHON experiment’s spokesperson and contact person. The quarks and gluons within protons and neutrons are probed using high-energy electrons that travel deep inside of them. These groundbreaking experiments ushered in a new age of deep inelastic scattering.
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