Search Results (16 total)

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-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_μ=(0.0±0.9)×10^-19e cm, are all consistent with zero, we set a new muon EDM limit, |d_μ|<1.8×10^-19e cm (95% C.L.). This represents a factor of 5 improvement over the previous best limit on the muon EDM.

The spin precession frequency of muons stored in the (g-2) storage ring has been analyzed for evidence of Lorentz and CPT violation. Two Lorentz and CPT violation signatures were searched for a nonzero Δω_a(=ω_a^μ+-ω_a^μ-) and a sidereal variation of ω_a^μ±. No significant effect is found, and the following limits on the standard-model extension parameters are obtained: b_Z=-(1.0±1.1)×  10^-23  GeV; (m_μd_Z0+H_XY)=(1.8±6.0)×10^-23  GeV; and the 95% confidence level limits bˇ_⊥^μ+<  1.4×10^-24  GeV and bˇ_⊥^μ-<2.6×10^-24  GeV.

A “resonance method” of measuring the electric dipole moment (EDM) of nuclei in storage rings is described, based on two new ideas: (1) Oscillating particles’ velocities in resonance with spin precession, and (2) alternately producing two sub-beams with different betatron tunes—one sub-beam to amplify and thus make it easier to correct ring imperfections that produce false signals imitating EDM signals, and the other to make the EDM measurement.

We present the final report from a series of precision measurements of the muon anomalous magnetic moment, a_μ=(g-2)/2. The details of the experimental method, apparatus, data taking, and analysis are summarized. Data obtained at Brookhaven National Laboratory, using nearly equal samples of positive and negative muons, were used to deduce a_μ(Expt)=11659208.0(5.4)(3.3)×10^-10, where the statistical and systematic uncertainties are given, respectively. The combined uncertainty of 0.54 ppm represents a 14-fold improvement compared to previous measurements at CERN. The standard model value for a_μ includes contributions from virtual QED, weak, and hadronic processes. While the QED processes account for most of the anomaly, the largest theoretical uncertainty, ≈0.55  ppm, is associated with first-order hadronic vacuum polarization. Present standard model evaluations, based on e⁺e^- hadronic cross sections, lie 2.2–2.7 standard deviations below the experimental result.

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.

The anomalous magnetic moment of the negative muon has been measured to a precision of 0.7 ppm (ppm) at the Brookhaven Alternating Gradient Synchrotron. This result is based on data collected in 2001, and is over an order of magnitude more precise than the previous measurement for the negative muon. The result a_μ^-=11 659 214(8)(3)×10^-10 (0.7 ppm), where the first uncertainty is statistical and the second is systematic, is consistent with previous measurements of the anomaly for the positive and the negative muon. The average of the measurements of the muon anomaly is a_μ(exp)=11 659 208(6)×10^-10 (0.5 ppm).

A measurement of the deflection of a laser beam in a modulated magnetic field with a prototype apparatus has produced an upper limit on the charge of the photon of 8.5×10^-17e. It is shown that an improved apparatus could attain a sensitivity of 10^-21e.

A higher precision measurement of the anomalous g value, a_μ=(g-2)/2, for the positive muon has been made at the Brookhaven Alternating Gradient Synchrotron, based on data collected in the year 2000. The result a_μ⁺=11 659 204(7)(5)×10^-10 (0.7 ppm) is in good agreement with previous measurements and has an error about one-half that of the combined previous data. The present world average experimental value is a_μ(expt)=11 659 203(8)×10^-10 (0.7 ppm).

A novel, single shot, nondestructive scheme to measure the bunch length of submillimeter relativistic electron bunches using the electro-optical method is described. In this scheme, the birefringence induced by the electric field of the electrons converts the temporal characteristics of the bunch to a spatial intensity distribution of an optical pulse. Electric field characteristics, induced birefringence, and retardation are calculated for a few typical electron beam parameters and criteria limiting the resolution are established.

A precise measurement of the anomalous g value, a_μ  =  (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 a_μ(SM)  =  11 659 159.6(6.7)×10^-10 (0.57 ppm) and a_μ(exp)-a_μ(SM)  =  43(16)×10^-10 in which a_μ(exp) is the world average experimental value.

A new measurement of the positive muon’s anomalous magnetic moment has been made at the Brookhaven Alternating Gradient Synchrotron using the direct injection of polarized muons into the superferric storage ring. The angular frequency difference ω_a between the angular spin precession frequency ω_s and the angular orbital frequency ω_c is measured as well as the free proton NMR frequency ω_p. These determine R=ω_a/ω_p=3.707 201(19)×10^-3. With μ_μ/μ_p=3.183 345 39(10) this gives a_μ⁺=11 659 191(59)×10^-10 (±5 ppm), in good agreement with the previous CERN and BNL measurements for μ⁺ and μ^-, and with the standard model prediction.

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, ω_a, between the spin precession and orbital frequencies was determined by measuring the time distribution of high-energy decay positrons. The ratio R of ω_a to the Larmor precession frequency of free protons, ω_p, in the storage-ring magnetic field was measured. We find R  =  3.707 220(48)×10^-3. With μ_μ/μ_p  =  3.183 345 47(47) this gives a_μ⁺  =  1 165 925(15)×10^-9 ( ±13 ppm), in good agreement with the previous CERN measurements for μ⁺ and μ^- and of approximately the same precision.

We have searched for a flux of axions produced in the Sun by exploiting their conversion to x rays in a static magnetic field. The signature of a solar axion flux would be an increase in the rate of x rays detected in a magnetic telescope when the Sun passes within its acceptance. From the absence of such a signal we set a 3σ limit on the axion coupling to two photons g_aγγ≡1/M<3.6×10^-9 GeV^-1, provided the axion mass m_a<0.03 eV and <7.7×10^-9 GeV^-1 for 0.03 <m_a<0.11 eV.

A microwave cavity experiment designed to search for the signal from cosmic axions converting in an external magnetic field covered the mass range (4.5-16.3)×10^-6 eV, corresponding to the frequency range from 1.09 to 3.93 GHz. Upper limits on the coupling and abundance of nonrelativistic galactic axions have been measured; these limits yield a coupling which is 1-2 orders of magnitude higher than that predicted by the Dine-Fischler-Srednicki model. Also presented are limits on axions with a continuum spectrum, limits on the presence of a wide axion line at the frequency of the 21-cm hydrogen emission line, and limits on the production of pseudoscalar particles by photons in the cavity interacting with the magnetic field.

We report preliminary results from a search for galactic axions in the frequency range 1.09<f_a<1.22 GHz. For an axion linewidth Γ_a≤200 Hz we obtain the experimental limit (g_aγγ/m_a)²ρ_a<1.4×10^-41. The theoretical prediction is (g_aγγ/m_a)²ρ_a=3.9×10^-44 with ρ_a=300 MeV/cm³. We have also searched for the presence of a continuous spectrum of light pseudoscalar particles; if we assume that the above ρ_a is contained between the upper and lower frequencies of our search, then we find that g_aγγ<2×10^-30 MeV^1/2 cm^3/2≃10^-11 GeV^-1.