麻豆淫院

Nucleons, which include protons and neutrons, are the composite particles that make up atomic nuclei. While these particles have been widely studied in the past, their internal structure has not yet been fully elucidated.

These particles are known to consist of three smaller building blocks known as quarks, held together by strong nuclear force carriers called gluons. While a proton is made of two "up" quarks and one "down" quark, a neutron is made of one "up" quark and two "down" quarks.

Inside nucleons, however, one can also find many quark-antiquark pairs that continuously appear and disappear. The distribution of momentum and spin across all the different building blocks of nucleons has not yet been uncovered.

Over the past decades, some physicists have been trying to devise new experiments that could help to shed new light on the internal structure of nucleons. One of these experiments is the so-called MARATHON (MeAsurement of the F鈧傗伩/F鈧傖禆, d/u Ratio and A=3 EMC Effect in Deep Inelastic Scattering off Tritium and Helium-3 Mirror Nuclei) experiment, carried by the Jefferson Lab Hall A Tritium Collaboration.

Recently, the researchers involved in this experiment published the most precise measurement yet of the ratio of the neutron and proton structure functions (F鈧傗伩/F鈧傖禆), which essentially describes the share of momentum among quarks inside nucleons. Their paper, in 麻豆淫院ical Review Letters, opens new possibilities for testing modern models of quantum chromodynamics (QCD) and other theoretical predictions.

"This is the second publication of the MARATHON Jefferson Lab experimental project, which was initiated back by Mina Katramatou and Makis Petratos of Kent State University, Javier Gomez of Jefferson Lab and Roy Holt of Argonne National Lab," Makis Petratos, spokesperson of the JLab MARATHON experiment, told 麻豆淫院.

"The experiment had to wait for the 12 GeV energy upgrade of the Lab and a lengthy safety review process as it required the use of a radioactive tritium gas target. It was fully approved in 2011 and took data in 2018鈥攁lmost 20 years after its inception."

The first objective of the MARATHON experiment was to measure the ratio of the inelastic structure functions of individual protons and neutrons. These functions contain vital information about the momentum distributions of the up and down quark constituents of nucleons.

"Knowledge of these distributions is critical for the understanding of the internal substructure of the two nucleons in terms of quarks and gluons," said Petratos. "The latter are the carriers of the strong force of nature. The results of this part have been published in a highly cited paper in 麻豆淫院ical Review Letters."

The MARATHON experiment also had another objective: to measure the so-called EMC effect on tritium and helium-3 mirror nuclei. The EMC effect is a phenomenon discovered back in 1983 and named after the European Muon Collaboration, the team of researchers at CERN who discovered it.

"This effect demonstrates that the inelastic structure function of a nucleus is not (as was naively originally expected) equal to the sum of the inelastic structure functions of its nucleon constituents," said Petratos.

"The reason for this apparent 'modification' of a free nucleon when it is embedded in a nucleus is not yet resolved. Theorists had argued that the measurement of this effect for the tritium and helium-3 mirror nuclei would be essential for its explanation."

The target used in the experiment was developed by a team from the JLAB Target Group led by Dave Meekins, staff scientist at Jefferson Lab and co-spokesperson for the collaboration. This is the first use of such a target material in over thirty years.

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"Dave Meekins noted that 'developing and implementing the tritium target was by far the biggest challenge for this experiment. Tritium being a radioactive gas, it was critical to ensure a safe and effective design,'" said Petratos.

As part of the MARATHON experiment, the researchers bombarded gaseous tritium, helium-3 and deuterium targets with an 11 GeV beam from the JLab accelerator. This allowed them to measure and quantify inelastic electron scattering from these three nuclei.

"Scattered electrons were detected in the two state-of-the-art mass magnetic spectrometers of the Hall A Facility of the Lab made up of powerful, high volume superconducting magnets and modern radiation detection apparatus," explained Petratos.

"The most notable achievement was the acquisition of high-quality data on the inelastic structure functions of tritium and helium-3鈥攕o called mirror nuclei because the number of protons in one nucleus is equal to the number of neutrons in the other presenting a mirror effect. These measurements are considered essential for our understanding of the internal structure and dynamics of the three-nucleon systems of nature, and of the nature of nucleon-nucleon interactions inside them."

Notably, the Jefferson Lab Hall A Tritium Collaboration's measurement of the EMC effect of tritium is the first of its kind and will most likely not be collected again in the future. This measurement, along with the others they collected, could have significant implications for the study of nuclear and particle physics, as it could help to improve existing models of nucleon structure and validate theoretical predictions.

"The understanding of the nuclear EMC effect and the structure of the nuclear 'few-body' (few-nucleon) systems remains one of the most important issues of modern, high-energy nuclear physics today," added Petratos.

"It is expected that Jefferson Lab will conduct additional experimental investigations in the future and promote the development of novel theoretical ideas that will advance fundamental subatomic physics."

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