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Muon g − 2 (pronounced "gee minus two") is a particle physics experiment at Fermilab to measure the anomalous magnetic dipole moment of a muon to a precision of 0.14 ppm, [1] which is a sensitive test of the Standard Model. [2] It might also provide evidence of the existence of new particles. [3] [4] [5]
The spin magnetic moment of a charged, spin-1/2 particle that does not possess any internal structure (a Dirac particle) is given by [1] =, where μ is the spin magnetic moment of the particle, g is the g-factor of the particle, e is the elementary charge, m is the mass of the particle, and S is the spin angular momentum of the particle (with magnitude ħ/2 for Dirac particles).
The g-force acting on an object under acceleration can be much greater than 1 g, for example, the dragster pictured at top right can exert a horizontal g-force of 5.3 when accelerating. The g-force acting on an object under acceleration may be downwards, for example when cresting a sharp hill on a roller coaster.
The E821 Experiment reported the following average value [8] = (). In 2024, the Fermilab collaboration "Muon g−2" doubled the accuracy of this value over the group’s previous measurements from the 2018 data set. The data for the experiment were collected during the 2019–2020 runs.
Like the North Magnetic Pole, the North Geomagnetic Pole attracts the north pole of a bar magnet and so is in a physical sense actually a magnetic south pole. It is the center of the 'open' magnetic field lines which connect to the interplanetary magnetic field and provide a direct route for the solar wind to reach the ionosphere.
The g-factor for a "Dirac" magnetic moment is predicted to be g = −2 for a negatively charged, spin-1/2 particle. For particles such as the electron, this "classical" result differs from the observed value by around 0.1%; the difference compared to the classical value is the anomalous magnetic moment.
The gravitomagnetic effect in the Cassini radioscience experiment was implicitly postulated by B. Bertotti as having a pure general relativistic origin but its theoretical value has never been tested in the experiment which effectively makes the experimental uncertainty in the measured value of gamma actually larger (by a factor of 10) than 0. ...
This singularity is the Landau pole with a negative residue, g(Λ) ≈ −Λ Landau / (β 2 (Λ − Λ Landau)).. In fact, however, the growth of g 0 invalidates Eqs. 1, 2 in the region g 0 ≈ 1, since these were obtained for g 0 ≪ 1, so that the nonperturbative existence of the Landau pole becomes questionable.