Search Results (17 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.

The rate of nuclear muon capture by the proton has been measured using a new technique based on a time projection chamber operating in ultraclean, deuterium-depleted hydrogen gas, which is key to avoiding uncertainties from muonic molecule formation. The capture rate from the hyperfine singlet ground state of the μp atom was obtained from the difference between the μ^- disappearance rate in hydrogen and the world average for the μ⁺ decay rate, yielding Λ_S=725.0±17.4  s^-1, from which the induced pseudoscalar coupling of the nucleon, g_P(q²=-0.88m_μ²)=7.3±1.1, is extracted.

The mean life of the positive muon has been measured to a precision of 11 ppm using a low-energy, pulsed muon beam stopped in a ferromagnetic target, which was surrounded by a scintillator detector array. The result, τ_μ=2.197 013(24)  μs, is in excellent agreement with the previous world average. The new world average τ_μ=2.197 019(21)  μs determines the Fermi constant G_F=1.166 371(6)×10^-5  GeV^-2 (5 ppm). Additionally, the precision measurement of the positive-muon lifetime is needed to determine the nucleon pseudoscalar coupling g_P.

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.

We present a measurement of the longitudinal spin cross section asymmetry for deep-inelastic muon-nucleon interactions with two high transverse momentum hadrons in the final state. Two methods of event classification are used to increase the contribution of the photon-gluon fusion process to above 30%. The most effective one, based on a neural network approach, provides the asymmetries A_p^lN→lhhX=0.030±0.057(stat)±0.010(syst) and A_d^lN→lhhX=0.070±0.076(stat)±0.010(syst). From these values we derive an averaged gluon polarization ΔG/G=-0.20±0.28(stat)±0.10(syst) at an average fraction of nucleon momentum carried by gluons 〈η〉=0.07.

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 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.

We present the results of the spin asymmetries A₁ of the proton and the deuteron in the kinematic region extending down to x=6×10^-5 and Q²=0.01 GeV². The data were taken with a dedicated low x trigger, which required hadron detection in addition to the scattered muon, so as to reduce the background at low x. The results complement our previous measurements and the two sets are consistent in the overlap region. No significant spin effects are found in the newly explored region.

We present a next-to-leading order QCD analysis of the presently available data on the spin structure function g₁ including the final data from the Spin Muon Collaboration. We present results for the first moments of the proton, deuteron, and neutron structure functions, and determine singlet and nonsinglet parton distributions in two factorization schemes. We also test the Bjorken sum rule and find agreement with the theoretical prediction at the level of 10%.

We present the final results of the spin asymmetries A₁ and the spin structure functions g₁ of the proton and the deuteron in the kinematic range 0.0008<x<0.7 and 0.2<Q²<100 GeV². For the determination of A₁, in addition to the usual method which employs inclusive scattering events and includes a large radiative background at low x, we use a new method which minimizes the radiative background by selecting events with at least one hadron as well as a muon in the final state. We find that this hadron method gives smaller errors for x<0.02, so it is combined with the usual method to provide the optimal set of results.

We have measured the spin-dependent structure function g₁^p in inclusive deep-inelastic scattering of polarized muons off polarized protons, in the kinematic range 0.003<x<0.7 and 1 GeV²<Q²<60 GeV². A next-to-leading order QCD analysis is used to evolve the measured g₁^p(x,Q²) to a fixed Q₀². The first moment of g₁^p at Q₀²=10 GeV² is Γ₁^p=0.136±0.013 (stat) ±0.009 (syst) ±0.005 (evol). This result is below the prediction of the Ellis-Jaffe sum rule by more than two standard deviations. The singlet axial charge a₀ is found to be 0.28±0.16. In the Adler-Bardeen factorization scheme, Δg≃2 is required to bring ΔΣ in agreement with the quark-parton model. A combined analysis of all available proton, deuteron, and ³He data confirms the Bjorken sum rule.