A precise measurement of the anomalous g value, aµ = (g − 2)/2, for the positive muon has been made at the Brookhaven Alternating Gradient Synchrotron. The result a µ + = 11 659 202(14)(6) × 10 −10 (1.3 ppm) is in good agreement with previous measurements and has an error one third that of the combined previous data. The current theoretical value from the standard model is aµ(SM)= 11 659 159.6(6.7) × 10 −10 (0.57 ppm) and aµ(exp)−aµ(SM) = 43(16) × 10 −10 in which aµ(exp) is the world average experimental value.PACS number: 14.60.Ef 13.40.EmPrecise measurement of the anomalous g value, a µ = (g−2)/2, of the muon provides a sensitive test of the standard model of particle physics and new information on speculative theories beyond it. Compared to the electron, the muon g value is more sensitive to standard model extensions, typically by a factor of (m µ /m e ) 2 . In this Letter we report a measurement of a µ for the positive muon from Brookhaven AGS experiment 821, based on data collected in 1999.The principle of the experiment, previous results, and many experimental details have been given in earlier publications [1,2]. Briefly, highly polarized µ + of 3.09 GeV/c from a secondary beamline are injected through a superconducting inflector [3] into a storage ring 14.2 m in diameter with an effective circular aperture 9 cm in diameter. The superferric storage ring [4] has a homogeneous magnetic field of 1.45 T, which is measured by an NMR system relative to the free proton NMR frequency [5,6]. Electrostatic quadrupoles provide vertical focusing. A pulsed magnetic kicker gives a 10 mrad deflection which places the muons onto stored orbits. The muons start in 50 ns bunches and debunch with a decay time of about 20 µs due to their 0.6% momentum spread. Positrons are detected using 24 lead/scintillating fiber electromagnetic calorimeters [7] read out by waveform digitizers. The waveform digitizer and NMR clocks were phase-locked to the Loran C frequency signal.The muon spin precesses faster than its momentum rotates by an angular frequency ω a in the magnetic field B weighted over the muon distribution in space and time. The quantity a µ iswhere ω a is unaffected by the electrostatic field for muons with γ = 29.3. Parity violation in the decay µ + → e +ν µ ν e causes positrons to be emitted with an angular and energy asymmetry. Because of the Lorentz boost, the positron emission angle with respect to the muon spin direction in the muon rest frame is strongly coupled to its energy in the laboratory frame. The number of decay positrons with energy greater than E is described byin which the time dilated lifetime γτ ≈ 64.4 µs. Some 140 g − 2 periods of 4.37 µs were observed. Most experimental aspects of the data taking in 1999 were the same as in 1998 [1]. However, some improvements were made. Care was taken in tuning the AGS ejection system to minimize background from any extraneous proton beam extracted during the muon storage time. Scintillating fiber detectors which could be moved in and out of the storage region were u...

A new highly sensitive method of looking for electric dipole moments of charged particles in storage rings is described. The major systematic errors inherent in the method are addressed and ways to minimize them are suggested. It seems possible to measure the muon EDM to levels that test speculative theories beyond the standard model. PACS numbers: 13.40. Em, 12.60.Jv, 14.60.Ef, 29.20.Dh The existence of a permanent electric dipole moment (EDM) for an elementary particle would violate parity (P) and time reversal symmetry (T) [1]. Therefore under the assumption of CPT invariance, a non-zero EDM would signal CP violation. In the standard model, the electron EDM is < 10 −38 e · cm [2] with the muon EDM scaled up by the mass ratio m µ /m e , a factor of 207, but some new theories predict much larger values [3,4]. For example, ref.[4] predicts the muon EDM could be as large as 5 × 10 −23 e · cm, while the electron EDM is predicted to be ∼ 10 −28 e · cm, an order of magnitude below the present limit [5]. The current 95% confidence limit for the muon EDM is 10 −18 e·cm [6]. This paper discusses a new way of using a magnetic storage ring to measure the EDM of the muon, which also can be applied to other charged particles.To measure the EDM experimentally, the particle should be in an electric field which exerts a torque on the dipole and induces an observable precession of its spin. If the particle is charged this electric field inevitably accelerates the particle; it will move to a region where the field is zero or leave the scene. An example is the nucleus at the center of an atom in equilibrium; the net force and therefore the net electric field at the nucleus must average to zero according to Schiff's theorem [7]. Any applied external electric field will be shielded from the nucleus by the electrons in the atom. The overall effect is to suppress the EDM signal, making it more difficult to measure. The suppression would be total but for the many known exceptions to Schiff's theorem when weak and strong forces, weak electron-nucleon forces, finite particle sizes, and relativistic effects are included. Suppression of the EDM signal by Schiff's theorem is completely avoided in a magnetic storage ring [8,9] such as proposed here, because the particle is not in equilibrium; there is a net centripetal force, and this force is entirely supplied by a net electric field as seen in the muon rest frame.In particular, when a muon of velocity β = v/c and relativistic mass factor γ = (1 − β 2 ) − 1 2 is circulating in a horizontal plane due to a vertical magnetic field B, it will according to a Lorentz transformation experience both an electric and a magnetic field, E * and B * , in its own rest frame. The so-called motional electric field, E * = γc β × B, can be much larger than any practical applied electric field. Its action on the particle supplies the radial centripetal force, Thomas spin precession, and spin precession due to any non-vanishing EDM. B * produces precession due to the muon magnetic moment. The combined spi...

Three independent searches for an electric dipole moment (EDM) of the positive and negative muons have been performed, using spin precession data from the muon g À 2 storage ring at Brookhaven National Laboratory. Details on the experimental apparatus and the three analyses are presented. Since the individual results on the positive and negative muons, as well as the combined result, d ¼ ð0:0 AE 0:9Þ Â 10 À19 e cm, are all consistent with zero, we set a new muon EDM limit, jd j < 1:8 Â 10 À19 e cm (95% C.L.). This represents a factor of 5 improvement over the previous best limit on the muon EDM.

No abstract

No abstract

No abstract

The muon anomalous magnetic moment has been measured in a new experiment at Brookhaven. Polarized muons were stored in a superferric ring, and the angular frequency difference, v a , between the spin precession and orbital frequencies was determined by measuring the time distribution of highenergy decay positrons. The ratio R of v a to the Larmor precession frequency of free protons, v p , in the storage-ring magnetic field was measured. We find R 3.707 220͑48͒ 3 10 23. With m m ͞m p 3.183 345 47͑47͒ this gives a m 1 1 165 925͑15͒ 3 10 29 (613 ppm), in good agreement with the previous CERN measurements for m 1 and m 2 and of approximately the same precision.

No abstract