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| Figure 1: (a) The CPT symmetry can be likened to a mirror that reflects spatial coordinates, flips charge and other additive quantum numbers, and reverses time. To test for cracks in this CPT mirror, physicists check whether the magnetic moment of the proton (left) has the same magnitude as that of the antiproton (right). (Technically, the moments have opposite signs due to the way magnetic moment is defined relative to the spin.) (b) To measure the antiproton’s magnetic moment, the ATRAP Collaboration measures the cyclotron and spin-flip frequencies, fc and fs, respectively. The ratio of these frequencies gives the antiproton’s magnetic moment, μp¯=-fsfcμN, in terms of the nuclear magneton μN. |
The ATRAP Collaboration has measured the magnetic moment of the antiproton more precisely than ever before, allowing a new test of CPT symmetry.
Many physical laws are indifferent to distinctions such as left or right and forwards or backwards. On rare occasions, though, a discrepancy shows up, and we say that a symmetry is broken. One symmetry that has so far avoided any signs of breaking is the so-called CPT symmetry, which equates matter and antimatter at a fundamental level. A new test of CPT symmetry involves antiprotons. Specifically, Jack DiSciacca of Harvard University and his colleagues (the ATRAP Collaboration) present the most precise measurement to date of the antiproton magnetic moment [1]. As reported in Physical Review Letters, the results match data on the proton, thus extending CPT ’s shatterproof status for the time being.
Look into a mirror and imagine the world on the other side is not just a reflection, but instead a real physical world. Should nature behave differently in this mirrored world? For decades, most physicists believed the answer was “no.” They assumed that nature was the same in a coordinate system and its mirror image, and they even gave this supposition a name: parity reversal symmetry or P symmetry. However, in 1957, the nuclear physics world was rocked when two back-to-back articles in Physical Review revealed that P symmetry was violated by nature [2, 3]. This discovery revolutionized the understanding of the weak interaction.
American Physical Society: Viewpoint: Antiprotons Reflect a Magnetic Symmetry
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