Quantification of GR effects in muon g-2, EDM and other spin precession experiments

Abstract

Recently, Morishima, Futamase and Shimizu published a series of manuscripts, putting forward arguments, based on a post-Newtonian approximative calculation, that there can be a sizable general relativistic (GR) correction in the experimental determination of the muon magnetic moment based on spin precession, i.e., in muon g-2 experiments. In response, other authors argued that the effect must be much smaller than claimed. Further authors argued that the effect exactly cancels. Also, the known formulae for de Sitter and Lense-Thirring effect do not apply due to the non-geodesic motion. All this indicates that it is difficult to estimate from first principles the influence of GR corrections in the problem of spin propagation. Therefore, in this paper we present a full general relativistic calculation in order to quantify this effect. The main methodology is the purely differential geometrical tool of Fermi-Walker transport over a Schwarzschild background. Also the Larmor precession due to the propagation in the electromagnetic field of the experimental apparatus is included. For the muon g-2 experiments the GR correction turns out to be very small, well below the present sensitivity. However, in other similar storage ring experimental settings, such as electric dipole moment (EDM) search experiments, where the so-called frozen spin method is used, GR gives a well detectable effect, and should be corrected for. All frozen spin scenarios are affected which intend to reach a sensitivity of 0.1 microradians/second for the spin precession in the vertical plane.

arXiv commentFinal, published version. Conclusions: no measurable GR effect for g-2 experiments, but significant GR effect for EDM (frozen spin) experiments, growing unboundedly with Lorentz factor

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• Geometric post-Newtonian description of massive spin-half particles in curved spacetime
• Difference of measured proton and He3 EDMs: a reduced systematics test of T-reversal invariance
• On systematic and GR effects on muon $g-2$ experiments