The interactions of the quarks and gluons that make up protons and neutrons are so strong that the structure of protons and neutrons is difficult to calculate from theory and must be instead measured experimentally. Neutrino experiments use targets that are nuclei made of many protons and neutrons bound together. This complicates interpreting those measurements to infer proton structure. By scattering neutrinos from the protons that are the nuclei of hydrogen atoms in the MINERvA detector, scientists have provided the first measurements of this structure with neutrinos using unbound protons.
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Source: ScienceDaily