Subsequent measurements by various research teams have produced mixed results regarding the size of the proton. In 2013, an international team confirmed their earlier 2010 measurement, concluding that the proton’s radius is 0.84 femtometers, a discrepancy of 7 sigma. Later, in 2016, another experiment replaced the electron with a muon in a deuterium atom—an isotope containing a neutron. This aimed to observe how the presence of a neutron might change the perception of the proton’s charge, and results aligned with the 2010 finding.
However, experiments using regular hydrogen yielded contradictory outcomes. A 2017 study reaffirmed the 2010 measurement, while a 2018 study indicated a larger value that contradicted it. In 2019, scientists from York University conducted an electron-based measurement, seeking to reconcile these differences, and found a proton radius of 0.833 femtometers, consistent with the earlier smaller value.
The latest research involved measurements of hydrogen atoms in a vacuum chamber, where lasers controlled the electrons and tracked energy transitions. These observations suggested that the proton’s radius is approximately 0.84 femtometers, reaffirming the 2010 findings that started this debate.
Juan Rojo, a physicist at Vrije University Amsterdam who was not involved in the studies, commented that the proton radius should be a consistent value across different methods of measurement. He noted that the recent papers offer diverse methods arriving at the same conclusion, contributing valuable insights to an ongoing scientific discussion.
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