arXiv subjects

William J. Marciano

Publications and source records attributed to William J. Marciano.

53 records · Page 3Linked to original sources

arXiv2001

Status of the Hadronic Contribution to the Muon (g-2) Value

With the recent interest in the measured and standard model values of the muon anomalous magnetic moment, a_mu, some confusion has arisen concerning our knowledge of the hadronic contribution to a_mu. In the dispersion integral approach to hadronic vacuum polarization effects, low energy contributions must be evaluated from data or in a model-dependent approach tested by data. At higher energies perturbative QCD has been used, sometimes in conjunction with data. The history of such evaluations is reviewed, and the prospects for further improvement are discussed. We conclude that not all published evaluations are on an equal footing or up-to-date. One must critically examine which, and how much information went into each analysis in order to determine which are more complete, and reliable.

hep-ph↗

arXiv2001

The Muon Anomalous Magnetic Moment: A Harbinger For "New Physics"

QED, Hadronic, and Electroweak Standard Model contributions to the muon anomalous magnetic moment, a_mu = (g_mu-2)/2, and their theoretical uncertainties are scrutinized. The status and implications of the recently reported 2.6 sigma experiment vs.theory deviation a_mu^{exp}-a_mu^{SM} = 426(165) times 10^{-11} are discussed. Possible explanations due to supersymmetric loop effects with m_{SUSY} \simeq 55 sqrt{tan beta} GeV, radiative mass mechanisms at the 1--2 TeV scale and other ``New Physics'' scenarios are examined.

hep-ph↗

arXiv2001

The Muon Anomalous Magnetic Moment: Standard Model Theory and Beyond

QED, Hadronic, and Electroweak Standard Model contributions to the muon anomalous magnetic moment, a_mu = (g_mu-2)/2, are reviewed. Theoretical uncertainties in the prediction a_mu^SM = 116591597(67) times 10^{-11} are scrutinized. Effects due to ``New Physics'' are described. Implications of the current experiment vs. theory constraint a_mu^exp - a_mu^SM = 453(465) times 10^{-11} and anticipated near term error reduction to +- 155 times 10^{-11} are discussed.

hep-ph↗

arXiv2000

Polarized Moller Scattering Asymmetries

The utility of polarized electron beams for precision electroweak studies is described. Parity violating Moller scattering asymmetries in e-e- --> e-e- are discussed. Effects of electroweak radiative corrections and the running sin^2(theta_W(Q^2)) are reviewed. The sensitivity of E158 (a fixed target e-e- experiment at SLAC) and future e-e- collider studies to ``new physics'' is briefly outlined.

hep-ph↗

arXiv2000

Precision Electroweak Parameters and the Higgs Mass

The status of various precisely measured electroweak parameters is reviewed. Natural relations among them are shown to constrain the Higgs mass, m_H, via quantum loop effects to relatively low values. A comparison with direct Higgs searches is made.

hep-ph↗

arXiv1999

KAON 99 - Summary and Perspective

An overview of KAON 99 with commentary is presented. Emphasis is placed on the state of CKM mixing and CP violation. The Jarlskog invariant, J_{CP}, is shown to provide a useful quantitative comparison of K and B phenomenology. The potential of future rare and ``forbidden'' decay experiments to probe O(3000 TeV) ``New Physics'' is also described.

hep-ph↗

arXiv1999

Muonium Decay

Modifications of the mu+ lifetime in matter due to muonium (M = mu+ e-) formation and other medium effects are examined. Muonium and free mu+ decay spectra are found to differ at O(alpha m_e/m_mu) from Doppler broadening and O(alpha^2 m_e/m_mu) from the Coulomb bound state potential. However, both types of corrections are shown to cancel in the total decay rate due to Lorentz and gauge invariance respectively, leaving a very small time dilation lifetime difference, (tau_M - tau_mu+)/tau_mu+ = alpha^2 m_e^2/ 2m_mu^2 \simeq 6\times 10^-10, as the dominant bound state effect. It is argued that other medium effects on the stopped mu+ lifetime are similarly suppressed.

hep-ph↗

arXiv1999

Fermi Constants and ``New Physics''

Various precision determinations of the Fermi constant are compared. Included are muon and (leptonic) tau decays as well as indirect prescriptions employing $α, m_Z, m_W, \ssthwmzms, Γ(Z\to\ell^+\ell^-)$, and $Γ(Z \to ν\bar ν)$ as input. Their good agreement tests the standard model at the $\pm 0.1%$ level and provides stringent constraints on new physics. That utility is illustrated for: heavy neutrino mixing, 2 Higgs doublet models, S, T, and U parameters and excited $W^{\ast^\pm}$ bosons (Kaluza-Klein excitations). For the last of those examples, $m_{W^\ast}\gsims 2.9$ TeV is found.

hep-ph↗

arXiv1999

Precision Electroweak Measurements and ``New Physics''

The status of several precisely measured electroweak parameters is reviewed. Natural relations among them are shown to constrain the Higgs mass, m_H, as well as various ``New Physics'' effects. Indications of an anomalous Zb anti-b coupling are discussed. Constraints on excited W^* bosons are given.

hep-ph↗

arXiv1998

Lepton anomalous magnetic moments - a theory update

Standard Model contributions to the electron, muon, and tau lepton anomalous magnetic moments, a_l=(g_l-2)/2, are reviewed and updated. The fine structure constant is obtained from the electron g_e-2 and used to refine the QED contribution to the muon g_mu-2. Recent advances in electroweak and hadronic effects on g_mu-2 are summarized. Examples of ``New Physics'' probed by the a_mu Brookhaven experiment E821 are outlined. The prediction for a_tau is also given.

hep-ph↗

arXiv1998

Electroweak radiative corrections to b --> s gamma

Two loop electroweak corrections to b --> s gamma decays are computed. Fermion and photonic loop effects are found to reduce R = BR(b --> s gamma)/BR(b --> c e nu) by 8+-2% and lead to the standard model prediction BR(B --> X_s gamma)=(3.28 +- 0.30)x10^-4 for inclusive B meson decays. Comparison of R^{theory} =(3.04 +- 0.25)x10^-3(1+0.10rho), where rho is a Wolfenstein CKM parameter, with the current experimental average R^{exp}=(2.52+-0.52)x10^-3 gives rho=-1.7+-1.9 which is consistent with -0.21<rho<0.27 obtained from other B and K physics constraints.

hep-ph↗

arXiv1998

Parity violating asymmetries at future lepton colliders

Parity violating left-right scattering asymmetries at future high energy e+e- and e-e- colliders are examined. The utility of two polarized beams for precision measurements is pointed out. Sensitivity to ``new'' short-distance physics is briefly discussed. Electroweak radiative corrections due to the running of sin^2(theta_W)(q^2) are exhibited.

hep-ph↗

arXiv1998

Coherent muon-electron conversion in muonic atoms

Transition rates for coherent muon-electron conversion in muonic atoms, mu+N --> e+N, are computed for various types of muon number violating interactions. Attention is paid to relativistic atomic effects, Coulomb distortion, finite nuclear size, and nucleon distributions. Discrepancies with previously published results are pointed out and explained. Results are presented for several elements of current and future experimental interest.

hep-ph↗

arXiv1997

Higgs Resonance Studies At The First Muon Collider

Higgs resonance signals and backgrounds at the First Muon Collider are discussed. Effects due to beam polarization and background angular distributions (forward-backward charge asymmetries) are examined. The utility of those features for improving precision measurements and narrow resonance ``discovery'' scans is described.

hep-ph↗

arXiv1996

Electroweak corrections to the muon anomalous magnetic moment

The bosonic two-loop electroweak radiative corrections to the muon's anomalous magnetic moment, $a_μ\equiv (g_μ-2)/2$, are presented. We find $Δa_μ^{\rm EW}({\rm 2\,loop\, bosonic})/ a_μ^{\rm EW}({\rm 1\,loop})\approx {α\over π}\left(-3.6 \ln\left({M_W^2\over m_μ^2}\right) +0.10 \right)\approx -0.11$ for $M_{\rm Higgs}\approx 250$ GeV. Combining that result with our previous two-loop fermionic calculation, we obtain an overall 22.6\% reduction in $a_μ^{\rm EW}$ from $195\times 10^{-11}$ to $151(4)\times 10^{-11}$. Implications for the full standard model prediction and an upcoming high precision measurement of $a_μ$ are briefly discussed. We also give the two-loop electroweak corrections to the anomalous magnetic moments of electron and tau lepton; they result in a reduction of the one-loop estimates by 35\% and 15\%, respectively.

hep-ph↗

arXiv1995

Electroweak Radiative Corrections To Polarized Møller Scattering Asymmetries

One loop electroweak radiative corrections to left-right parity violating Møller scattering ($e^-e^-\to e^-e^-$) asymmetries are presented. They reduce the standard model (tree level) prediction by 40$\pm 3$ \% where the main shift and uncertainty stem from hadronic vacuum polarization loops. A similar reduction also occurs for the electron-electron atomic parity violating interaction. That effect can be attributed to an increase of $\sin^2θ_W(q^2)$ by $3\%$ in running from $q^2=m_Z^2$ to 0. The sensitivity of the asymmetry to ``new physics'' is also discussed.

hep-ph↗

arXiv1995

Electroweak Fermion-loop Contributions to the Muon Anomalous Magnetic Moment

The two-loop electroweak corrections to the anomalous magnetic moment of the muon, generated by fermionic loops, are calculated. An interesting role of the top quark in the anomaly cancellation is observed. New corrections, including terms of order $G_μαm_t^2$, are computed and a class of diagrams previously thought to vanish are found to be important. The total fermionic correction is $-(23\pm 3) \times 10^{-11}$ which decreases the electroweak effects on $g-2$, predicted from one-loop calculations, by 12\%. We give an updated theoretical prediction for $g-2$ of the muon.

hep-ph↗