Search results for "Anomalous magnetic dipole moment"
showing 10 items of 91 documents
Rho resonance, timelike pion form factor, and implications for lattice studies of the hadronic vacuum polarization
2020
We study isospin-1 P-wave ππ scattering in lattice QCD with two flavors of O(a) improved Wilson fermions. For pion masses ranging from mπ=265 MeV to mπ=437 MeV, we determine the energy spectrum in the center-of-mass frame and in three moving frames. We obtain the scattering phase shifts using Lüscher’s finite-volume quantization condition. Fitting the dependence of the phase shifts on the scattering momentum to a Breit-Wigner form allows us to determine the corresponding ρ mass mρ and gρππ coupling. By combining the scattering phase shifts with the decay matrix element of the vector current, we calculate the timelike pion form factor, Fπ, and compare the results to the Gounaris-Sakurai repr…
Heavy mass expansion, light-by-light scattering through pointlike quanta, and the anomalous magnetic moment of the muon
2003
Contributions from light-by-light scattering to ${(g}_{\ensuremath{\mu}}\ensuremath{-}2)/2,$ the anomalous magnetic moment of the muon, are mediated by the exchange of charged fermions or scalar bosons. Assuming large masses M, pointlike couplings for the virtual particles and employing the technique of large mass expansion, analytical results are obtained for virtual fermions and scalars in the form of a series in ${(m}_{\ensuremath{\mu}}{/M)}^{2}.$ This series is well convergent even for the case ${M=m}_{\ensuremath{\mu}}.$ For pointlike virtual fermions, the expansion confirms published analytical formulas. For virtual scalars, the result can be used to evaluate the contribution from poi…
Experimental constraints on the coupling of the Higgs boson to electrons
2015
In the standard model (SM), the coupling of the Higgs boson to electrons is real and very small, proportional to the electron mass. New physics could significantly modify both real and imaginary parts of this coupling. We discuss experiments which are sensitive to the Higgs-electron coupling and derive the current bounds on new physics contributing to this coupling. The strongest constraint follows from the ACME bound on the electron electric dipole moment (EDM). We calculate the full analytic two-loop result for the electron EDM and show that it bounds the imaginary part of the Higgs-electron coupling to be less than 1.7 x 10^-2 times the SM electron Yukawa coupling. Deviations of the real…
Muon Anomaly from Lepton Vacuum Polarization and The Mellin--Barnes Representation
2008
We evaluate, analytically, a specific class of eighth--order and tenth--order QED contributions to the anomalous magnetic moment of the muon. They are generated by Feynman diagrams involving lowest order vacuum polarization insertions of leptons $l=e,\mu$, and $\tau$. The results are given in the form of analytic expansions in terms of the mass ratios $m_e/m_\mu$ and $m_\mu/m_\tau$. We compute as many terms as required by the error induced by the present experimental uncertainty on the lepton masses. We show how the Mellin--Barnes integral representation of Feynman parametric integrals allows for an easy analytic evaluation of as many terms as wanted in these expansions and how its underlyi…
A dispersive estimate of scalar contributions to hadronic light-by-light scattering
2021
We consider the contribution of scalar resonances to hadronic light-by-light scattering in the anomalous magnetic moment of the muon. While the $f_0(500)$ has already been addressed in previous work using dispersion relations, heavier scalar resonances have only been estimated in hadronic models so far. Here, we compare an implementation of the $f_0(980)$ resonance in terms of the coupled-channel $S$-waves for $\gamma^*\gamma^*\to \pi\pi/\bar K K$ to a narrow-width approximation, which indicates $a_\mu^{\text{HLbL}}[f_0(980)]=-0.2(2)\times 10^{-11}$. With a similar estimate for the $a_0(980)$, the combined effect is thus well below $1\times 10^{-11}$ in absolute value. We also estimate the …
Cosmology with a very light Lμ − Lτ gauge boson
2019
In this paper, we explore in detail the cosmological implications of an abelian L − L gauge extension of the Standard Model featuring a light and weakly coupled Z′. Such a scenario is motivated by the longstanding ∼ 4σ discrepancy between the measured and predicted values of the muon’s anomalous magnetic moment, (g − 2) , as well as the tension between late and early time determinations of the Hubble constant. If sufficiently light, the Z′ population will decay to neutrinos, increasing the overall energy density of radiation and altering the expansion history of the early universe. We identify two distinct regions of parameter space in this model in which the Hubble tension can be significa…
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 r…
1978
Abstract 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…
HADRONIC CROSS SECTION MEASUREMENT AT BES-III
2014
Measurements of the R ratio are closely related to two pre quantities, the anomalous magnetic moment of the muon (g - 2), and the value of the electromagnetic fine structure constant [Formula: see text]. Hadronic contributions to both quantities can be derived via dispersion integrals, using experimental R data as input. For the phenomenological evaluations of these contributions, different energy ranges of hadronic cross section data are required. At BES-III, Initial State Radiation (ISR) from an existing Ψ(3770) dataset will be used for measurements of hadronic cross sections below [Formula: see text], while for higher energies a dedicated energy scan program will be performed up to [For…
Leptons and QCD
2015
Three important QCD-related aspects of the τ and μ dynamics are reviewed: the determination of the strong coupling from the hadronic tau decay width, leading to the updated value αs(mτ2)=0.331±0.013; the measurement of |Vus| through the Cabibbo-suppressed decays of the τ, and the Standard Model prediction for the muon anomalous magnetic moment.
Real and Virtual Compton Scattering (experiments)
1999
This paper deals with Real and Virtual Compton Scattering off the proton at threshold and the way to deduce information about the nucleon polarizabilities.