![]() ![]() Muons are produced in high-energy particle accelerators by first creating While the electron is stable, the muon is not, and it decays to anĮlectron and two neutrinos with a half life of 2.2 microseconds. The muon is a fundamental leptonic particle very similar to the electron,Įxcept that the muon has a mass that is 207 times larger. ![]() Next we'll consider muon-hydrogen spectroscopy. Probing the charge distribution, but these are difficult to measure with high The momentum transferred in the scattering process is very small are best at The accuracy of the radius estimate is limited by counting statistics and Proton, are analyzed to extract the charge radius of the proton. ![]() Theseĭata, particularly the results at small momentum transfers between electron and Probes the charge structure of the proton. In this situation is the electromagnetic interaction, such scattering data Because the only significant interaction between an electron and a proton Is carefully measured by accumulating a large number of such events. Of electrons scattering in a particular direction with a particular final energy Solid target is placed in a beam of accelerated electrons, and the probability 's scattering experiments that first established the existence of the atomic Measurement methods one at a time, starting with electron scattering, which is In order to understand the puzzle in more detail, let's examine the It has become known as "The Proton Radius Puzzle". Physics community, and it has proved difficult to understand. With muons that is not included in the Standard Model? This 4% difference is large enough to represent a serious problem for the Some unsuspected difference in the interaction of protons with electrons vs. Thus, there is a discrepancy of about 4% in estimates of the protonĬharge radius given by these trusted methods. = 0.8775(5) fm, which tends to agree with the electron-hydrogen spectroscopy The results from electron scattering have greater uncertainties than the On the other hand, with somewhat more accuracy muon-hydrogen spectroscopy The problem is that as of 2010, these three methods have given at least (see below), which is conventionally assumed to be the charge radius of the Three methods have measured a quantity called r p Is from a much smaller distance), and (c) deducing it by scattering energetic (b) deducing it from the way a negative mu lepton (muon) orbits a proton (which the way an electron orbits a proton (from a considerable distance), Radius of the proton: (a) deducing it from the energy levels of the hydrogenĪtom, i.e. Experimental physicists have used three ways of measuring the charge Same electric field as a proton, both inside and outside. Latter is the radius of a sphere of distributed charge that would produce the The properties of a proton are mass, charge, spin, magnetic moment, and Gives the appearance of a single particle. Quark, bound together by the strong force so tightly that the three-body system System consisting of three fundamental particles, two up quarks and one down Universe and the nucleus of a hydrogen atom, is not really a fundamental Try at explaining a current physics development to you, my loyal readers:Īs we now understand it, the proton, the main form of matter in the Was 2,000 words really enough space to explain complicated physics ideas? Would I miss the audience with too much complexity? What if I couldn't find anything to write about? Anyhow, after thinking about it for a while I decided to do it, and the Learning to explain physics at the popular level, and I had earlier writtenīut I was not at all sure that I could do a regular column. Earlier in my career as a physicist I had decided to make a run at The responsibility of writing a 2,000 word AV column every two months. Stan asked me if I was interested in replacing Jerry, taking on Stanley Schmidt saying that Jerry Pournelle no longer wanted to do his end of I received a letter from the then- Analog-Editor In 1984 I was on a sabbatical at the Hahn-Meitner Institute in Westīerlin, in the days before the Wall came down. Is the 200 th Alternate View column that I have written for Analog. No part may be reproduced in any form without the Published in the May-June-2019 issue of Analog Science Fiction &Īnd is copyrighted ©2019 by John G. Spectroscopy, muon-hydrogen spectroscopy, electron scattering, Keywords: proton radius, electron-hydrogen Opus 200: How Big is the Proton? by John G. Opus 200: How Big is the Proton? Analog Science ![]()
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