I belong to this group, as I am sure many others are as well. Some people use it to locate areas they have lived or traveled, while others use it to visit remote places of the planet that one would not otherwise be able to see. The program, which utilizes satellite imagery and aerial photographs to map the earth in amazing detail, can be used for a variety of reasons. Jon Butterworth’s book Smashing Physics is available as “Most Wanted Particle” in Canada & the US and was on the shortlist for the Royal Society Winton Prize for Science Books, though it lost out on Thursday to Gaia Vince’s excellent Adventures in the Anthropocene.By now, most of you have either downloaded or are at least aware of Google Earth. ¹ Assuming the mass and the charge are distributed in the same way throughout the snooker ball. If the disagreement with the Standard Model grows as the precision increases, the muon g-2 experiment may give us the first definite signpost on the way to answering some of the big questions in physics which are left open by the Standard Model. Ultimately we need to know the field to better than 1 part in ten million.” Photograph: Mark Lancaster/FermilabĪs Mark Lancaster, my colleague at UCL who also works on the experiment, says: “This really marks the start of the experiment’s data-taking. The little “shim-cart” between the magnet’s pole pieces, limbering up to start its measurements of the magnetic field. A special ‘shim-cart’ has been built to make the measurements: The size of the shims is machined to an accuracy well below the width of a human hair. Over a thousand special low-carbon steel ‘shims’ have been installed on the magnet’s pole pieces, to improve the uniformity of the magnetic field by a factor of a hundred. (There is more information on how the whole experiment works here.)Īfter very careful moving and reassembly of the base of the magnet - “like building a 750-ton Swiss watch,” according to Chris Polly, the project manager for the experiment - the magnet has now been cooled down. When muons orbit in the field, their magnetic dipoles oscillate, and from those oscillations, g can be measured. The magnet is designed to produce a strong, uniform magnetic field. It was moved from Brookhaven, where the most precise measurement so far was made, to Fermilab, because Fermilab has more intense sources of muons, and so an even more precise measurement can be made there. Measurements began this week at Fermilab’s super-precise, second-hand magnet. This really marks the start of the experiment’s data-taking. Some of them could even have masses so high that they cannot be seen directly at the LHC, but their influence could be observed in the muon g, and specifically g-2, the tiny difference from the Dirac prediction which is due to these quantum loops. If the measurement does not agree with the theory, this might be because new particles, not present in the Standard Model, are going round those loops. The point is that the reason that g is not exactly 2 is that quantum corrections, involving other particles, going round tiny, transient loops, come into play. That is enough of a discrepancy to motivate lots of effort to both calculate and measure the value more precisely. But more interestingly, the theory and the experiment disagree in the case of the muon, by about 3.4 sigma. It is less precisely measured than the electron, as one might expect since muons are less common than electrons and harder to store. The value for the muon is very similar, −2.00233184178 with an uncertainty of about 0.0000000012.
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