P.M. Hattersley

Final report on the CERN muon storage ring including the anomalous magnetic moment and the electric dipole moment of the muon, and a direct test of relativistic time dilation

A comprehensive description of the muon storage ring and its operation is given, and the final results of the experiment are presented and discussed. The anomalous magnetic moments of positive and negative muons are found to be aμ+ = 1165911(11) × 10−9 and aμ− = 1165937(12) × 10−9 giving an average value for muons of aμ = 1165924(8.5) × 10−9. The electric dipole moments were also measured with the results Dμ+= (8.6 ± 4.5) × 10−9e · cm and Dμ− = (0.8 ± 4.3) × 10−19e · cm. Under the assumption of the CPT theorem these yield a weighted average of Dμ = (3.7 ± 3.4) × 10−19e · cm. Finally the time transformation of special relativity is shown to be valid to (0.8 ± 0.7) × 10−3 at γ ≅ 29.3. All the errors quoted here are one standard deviation and contain both statistical and systematic effects.

The anomalous magnetic moment of positive and negative muons

Abstract The anomalous g -factor a ≡ ( g −2)/2 has been measured for muons of both charges in the Muon Storage Ring at CERN. The two results, a μ + = 1165910(12) × 10 −9 and a μ − = 1165936(12) × 10 −9 , are in good agreement with each other, and combine to give a mean a μ = 1165922(9) × 10 −9 , which is very close to the most recent theoretical prediction 1165921(10) × 10 −9 . For the experimental results, the total statistical and systematic error is given. The measurements thus confirm the remarkable QED calculation plus hadronic contribution, and serve as a precise verification of the CPT theorem for muons.

New limits on the electric dipole moment of positive and negative muons

New measurements of the electric dipole moment muons of both charges have been made in the Muon Storage Ring at CERN. The values found are Dmu +=(8.6+or-4.5)*10-19 e cm Dmu -=(0.8+or-4.3)*10-19 e cm (errors are of one standard deviation). It is concluded, at 95% confidence level, that mod Dmu mod <or=1.05*10-18 e cm.

New Measurement of (g-2) of the Muon

The electron and the muon are the only charged particles which do not participate in the strong interaction, at present not fully understood nor amenable to rigorous calculation. Therefore measurements on the electron or muon in isolation, and on the μ+e− system (muonium) can give information on the fine structure constant α, free of doubts about the underlying theory. For the electron the anomalous magnetic moment ae = (g-2)/2 is a known function of α, and in principle provides the purest determination of this quantity. The corresponding quantity aμ for the muon cannot yet be measured so accurately, and the theory is subject to corrections due to the strong and weak interactions which are not accurately known. Nevertheless aμis important in the discussion of the fundamental constants for three reasons: (a) gμ ≡2(1 + aμ) is needed for calculating a from the hyperfine splitting in muonium; (b) aμ verifies quantum electrodynamics (QED) at high q2 ~(20 GeV/c)2 making it very unlikely that the theory will be at fault in the low q2 region appropriate for other measurements of fundamental constants; (c) corrections to ae and aμ due to modifications of QED, or to couplings to new fields in most cases satisfy1) the rule △ae = (me/mμ) △aμ. So the verification of aμ to 25 ppm validates ae to a much higher accuracy, thus ensuring that ae gives a good measure of α.

The πd scattering length from Kα X-rays

Abstract X-rays from the K α transition (2P → 1S) of the π − d mesic atom have been observed. Their energy, 2592.8 −2.0 +1.6 , has been measured by the critical absorber technique, using the M V absorption edge in bismuth. The strong interaction shift in the 1S state is −4.8 eV, corresponding to a scattering length a ( π d) = −(0.052 −0.017 +0.022 ) m π −1 , in agreement with recent calculations. The intensity ratio K α /K total = 0.548 ± 0.015.

Production and testing of limited streamer tubes for the end-cap muon subdetector of OPAL

Abstract The construction and testing of plastic streamer tubes for use as a large-area muon detector at OPAL are described. The use of extruded Noryl coated with a new carbon-loaded vinyl resistive paint is found to give tubes that behave in a uniform and reliable manner.

Evaluation of LiNbO3 optical amplitude modulators for use in analogue electro-optic readout links from HEP particle detectors

Abstract The use of lithium niobate optical intensity modulators for reading out analogue data from HEP particle detector elements has been evaluated. Two such devices designed for operation in the 1300 nm telecoms band have been tested with several different laser light sources. A systematic study has been undertaken to quantify possible noise sources in the optical link and their impact on the overall operation of the link. A dynamic range of ∼ 200:1 has been measured for a maximum nonlinearity of 1% and a minimum peak signal to rms noise ratio of 3:1, with the modulator biased at its quadrature point.