The MARATHON experiment has produced the most precise measurement to date of the ratio between the neutron and proton structure functions, offering a new way to test models of quantum chromodynamics. This two-decade-long project addresses fundamental questions about the internal composition of nucleons (protons and neutrons), which, despite being known to consist of quarks and gluons, still hold many secrets regarding the distribution of momentum and spin among their components.
Key Findings and Innovations
The experiment’s primary achievement is the first-ever measurement of the EMC effect in tritium. The EMC effect, discovered in 1983, describes the phenomenon where the structure of nucleons inside an atomic nucleus is different from that of free ones—a puzzle that still lacks a complete theoretical explanation. To achieve this, researchers used “mirror nuclei” (tritium and helium-3), which allowed for a precise comparison of nucleon-nucleon interactions. The project also overcame significant technical hurdles, notably the creation of a specialized cryogenic, radioactive tritium gas target, the first of its kind developed in over three decades.
Significance and Future Implications
The high-precision data from MARATHON is vital for refining theoretical models of nucleon structure and verifying predictions of quantum chromodynamics. The results provide crucial insights into the EMC effect and the dynamics of few-nucleon systems, which are key challenges in modern high-energy nuclear physics. This work highlights the patience and determination required for fundamental research and sets the stage for future experiments at Jefferson Lab to further unravel the basic nature of matter.
Mentoring question
The MARATHON experiment took over two decades from its conception to the final results. How does this long-term commitment to a single, fundamental question challenge the common expectation for rapid innovation and immediate returns in science and technology?
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