A proton charge12/12/2023 His personal assumption is that past measurements have misgauged the Rydberg constant and that the current official proton size is inaccurate. Randolf Pohl, the original investigator of the puzzle, stated that while it would be "fantastic" if the puzzle led to a discovery, the most likely explanation is not new physics but some measurement artefact. Among the postulated explanations are the three-body force, interactions between gravity and the weak force, or a flavour-dependent interaction, higher dimension gravity, a new boson, and the quasi-free The uncertain nature of the experimental evidence has not stopped theorists from attempting to explain the conflicting results. The immediate concern is for other groups to reproduce the anomaly. There is as yet no conclusive reason to doubt the validity of the old data. The anomaly remains unresolved and is an active area of research. In 2019, another experiment reported a measurement of the proton size using a method that was independent of the Rydberg constant-its result, 0.833 femtometers, agreed with the smaller 2010 value once more. The result is again ~5% smaller than the previously-accepted proton radius. By measuring the energy required to excite hydrogen atoms from the 2S to the 2P state, the Rydberg constant could be calculated, and from this the proton radius inferred. In 2017 a group at the Max-Planck-Institute of Quantum Optics performed yet another experiment, this time using hydrogen atoms that had been excited by two different lasers. This experiment allowed the measurements to be 2.7 times more accurate, but also found a discrepancy of 7.5 standard deviations smaller than the expected value. in August 2016 used a deuterium atom to create muonic deuterium and measured the deuteron radius. Since 2010, additional measurements using electrons with the previous methods have slightly reduced the estimated radius to 0.8751(61) fm, but by reducing the uncertainty even more the disagreement with the muonic hydrogen experiment has worsened to over 7 σ.Ī follow-up experiment by Pohl et al. (The new measurement's uncertainty limit of only 0.1% makes a negligible contribution to the discrepancy.) The newly measured radius is 4% smaller than the prior measurements, which were believed to be accurate within 1%. The resulting radius was recorded as 0.842(1) fm, 5 standard deviations (5 σ) smaller than the prior measurements. However, the much higher mass of a muon causes it to orbit 207 times closer than an electron to the hydrogen nucleus, where it is consequently much more sensitive to the size of the proton. Conceptually, this is similar to the spectroscopy method. published the results of an experiment relying on muonic hydrogen as opposed to normal hydrogen. Consistent with the spectroscopy method, this produces a proton radius of about 0.8775(5) fm. Small particles such as electrons can be fired at a proton, and by measuring how the electrons are scattered, the size of the proton can be inferred. The nuclear method is similar to Rutherford's scattering experiments that established the existence of the nucleus. This method produces a proton radius of about 0.8768(69) fm, with approximately 1% relative uncertainty. Measurements of hydrogen's energy levels are now so precise that the accuracy of the proton radius is the limiting factor when comparing experimental results to theoretical calculations. For hydrogen, whose nucleus consists only of one proton, this indirectly measures the proton charge radius. The exact values of the energy levels are sensitive to the distribution of charge in the nucleus. The spectroscopy method uses the energy levels of electrons orbiting the nucleus. Prior to 2010, the proton charge radius was measured using one of two methods: one relying on spectroscopy, and one relying on nuclear scattering. While some believe that this difference has been resolved, this opinion is not yet universally held. New experimental results reported in the autumn of 2019 agree with the smaller measurement, as does a re-analysis of older data published in 2022. This value was challenged by a 2010 experiment using a third method, which produced a radius about 4% smaller than this, at 0.842 femtometres. Historically the proton charge radius was measured by two independent methods, which converged to a value of about 0.877 femtometres (1 fm = 10 −15 m). The proton radius puzzle is an unanswered problem in physics relating to the size of the proton.
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