Search

The anomalous magnetic moment of the muon, $ a_\mu$, is a unique quantity that allows high-precision tests of the Standard Model. Currently, a difference of 3 to 4 standard deviations is observed between the prediction of the Standard Model and the most precise measurement performed. We present a review of the Standard Model calculations of $ a_\mu$. The principles and history of $ a_\mu$ experiments are presented, and the recent measurement at the Brookhaven National Laboratory, USA, is described in detail. Prospects for further improving the accuracy of both calculations and measurements of $ a_\mu$ are discussed.

The total cross section for ???hadrons was measured as a function of the invariant massW of the system (1.25 to 4.25 GeV) at thee+e--collider VEPP-4 with the detector MD-1. For the first time the data were obtained by detecting both scattered leptons with almost zero emission angles. The mean squared four momentum transfer 2> is -0.005 GeV2, the rmsW resolution is 100–250 MeV. The data on the mean charged multiplicity C> are well described by the function C>=(1.62 ±0.37)+(1.83±0.45)·ln(W(GeV)). TheW dependence of the total cross section is consistent with the theoretical prediction s(nb)=240+270/W(GeV).

Results of the search for rare radiative decay modes of the ?-meson performed with the Neutral Detector at the VEPP-2M collider are presented. For the first time upper limits for the branching ratios of the following decay modes have been placed at 90% confidence level: $$\begin{gathered} B(\phi \to \eta '\gamma )< 4 \cdot 10^{ - 4} , \hfill \\ B(\phi \to \pi ^0 \pi ^0 \gamma )< 10^{ - 3} , \hfill \\ B(\phi \to f_0 (975)\gamma )< 2 \cdot 10^{ - 3} , \hfill \\ B(\phi \to H\gamma )< 3 \cdot 10^{ - 4} , \hfill \\ \end{gathered} $$ whereH is a scalar (Higgs) boson with a mass 600 MeVH<1000 MeV, the real measurement isB(f?H?)·B(H?2p0)<0.8·10-4, the quoted result is model dependent, as explained in the text, $$\begin{gathered} B(\phi \to a\gamma ) \cdot B(a \to e^ + e^ - )< 5 \cdot 10^{ - 5} , \hfill \\ B(\phi \to a\gamma ) \cdot B(a \to \gamma \gamma )< 2 \cdot 10^{ - 3} , \hfill \\ \end{gathered} $$ wherea is a particle with a low mass and a short lifetime, $$B(\phi \to a\gamma )< 0.7 \cdot 10^{ - 5} ,$$ wherea is a particle with a low mass not observed in the detector.

The anomalous magnetic moment of the muon, aμ, is a unique quantity that allows high-precision tests of the Standard Model. Currently, a difference of 3 to 4 standard deviations is observed between the prediction of the Standard Model and the most precise measurement performed. We present a review of the Standard Model calculations of aμ. The principles and history of aμexperiments are presented, and the recent measurement at the Brookhaven National Laboratory, USA, is described in detail. Prospects for further improving the accuracy of both calculations and measurements of aμare discussed.