The Universe in the Mirror

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Science  22 Jul 2011:
Vol. 333, Issue 6041, pp. 386
DOI: 10.1126/science.333.6041.386-b

The concept of symmetry plays a prominent role in modern physics, and of all symmetries, C(harge)P(arity)T(ime Reversal) is the one believed to hold for every physical law: if the universe were replaced with its mirror image, particles' direction of motion reversed, and matter replaced by antimatter, an observer would not be able to tell the difference. The many tests designed to look for violations of CPT symmetry have not yet found any; one of the simplest would be to compare the basic properties of a particle and its antiparticle, which CPT symmetry implies should be the same (modulo a sign). Ulmer et al. have now made an important step in that direction: They observed spin flips of single protons (stored in a so-called Penning trap) induced by an rf magnetic field. The faint signal associated with the spin flips was detected through the coupling of the proton's spin and motional degrees of freedom. The technique could lead to precision measurements of the magnetic moments of both protons and antiprotons, enabling a new test of the CPT symmetry.

Phys. Rev. Lett. 106, 253001 (2011).

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