4,583 research outputs found

### New Results on the Hadronic Contributions to alpha(M_Z) and to (g-2)_mu

We reevaluate the dispersion integrals of the leading order hadronic
contributions to the running of the QED fine structure constant alpha(s) at
s=M_Z^2, and to the anomalous magnetic moments of the muon and the electron.
Finite-energy QCD sum rule techniques complete the data from e+e- annihilation
and tau decays at low energy and at the cc-bar threshold. Global quark-hadron
duality is assumed in order to resolve the integrals using the Operator Product
Expansion wherever it is applicable.
We obtain delta_alpha_had(M_Z) = (276.3 +/- 1.6)x10^{-4} yielding
alpha^{-1}(M_Z) = 128.933 +/- 0.021, and a_mu^had = (692.4 +/- 6.2)x10^{-10}
with which we find for the complete Standard Model prediction a_mu^SM =
(11659159.6 +/- 6.7)x10^{-10}. For the electron, the hadronic contribution
reads a_e^had = (187.5 +/- 1.8)x10^{-14}.Comment: 16 pages, 3 figure

### Two-photon exchange model for production of neutral meson pairs in e+e- annihilation

A vector-dominance two-photon exchange model is proposed to explain the
recently observed production of $\rho^0\rho^0$ and $\rho^0\phi$ pairs in
$e^+e^-$ annihilation at 10.58 GeV with the BaBar detector. All the observed
features of the data --angular and decay distributions, rates-- are in
agreement with the model. Predictions are made for yet-unobserved final states.Comment: 7 pages, 2 figures, 1 tabl

### Recent progress on isospin breaking corrections and their impact on the muon g-2 value

We describe some recent results on isospin breaking corrections which are of
relevance for predictions of the leading order hadronic contribution to the
muon anomalous magnetic moment (amuhadLO) when using tau lepton data. When
these corrections are applied to the new combined data on the pi^+pi^0 spectral
function, the prediction for amuhadLO based on tau lepton data gets closer to
the one obtained using e^+e^- data.Comment: 6 pages, 3 figures, Proceedings of the PhiPsi09 Workshop, Oct. 13-16,
2009, Beijing, China. Some typos corrected, and the FSR correction used in a
previous work is added to Table

### The hadronic contribution to $(g-2)_\mu$

The evaluation of the hadronic contribution to the muon magnetic anomaly $a_\mu$Â is reviewed, including a new estimate using precise results on the $\pi^+\pi^-$ spectral function from the KLOE Collaboration. It is found that the KLOE data confirm to some extent the previous $e^+e^-$ annihilation data in this channel, and accentuate the disagreement with the isospin-breaking-corrected spectral function from $\tau^-\to\pi^+\pi^0\nu_\tau$ decays. Correcting for the empirical difference in the mass of the charged and the neutral $\rho$ locally improves, but does not resolve this discrepancy. A preliminary reevaluation (including the KLOE data) of the e^+e-^-based Standard Model prediction of $a_\mu$Â results in a deviation of 2.7 standard deviations from the BNL measurement

### Updated Estimate of the Muon Magnetic Moment Using Revised Results from e+e- Annihilation

A new evaluation of the hadronic vacuum polarization contribution to the muon
magnetic moment is presented. We take into account the reanalysis of the
low-energy e+e- annihilation cross section into hadrons by the CMD-2
Collaboration. The agreement between e+e- and tau spectral functions in the pi
pi channel is found to be much improved. Nevertheless, significant
discrepancies remain in the center-of-mass energy range between 0.85 and 1.0
GeV, so that we refrain from averaging the two data sets. The values found for
the lowest-order hadronic vacuum polarization contributions are a_mu[had,LO] =
(696.3 +- 6.2[exp] +- 3.6[rad])e-10 (e+e- -based) and a_mu[had,LO] = (711.0 +-
5.0[exp] +- 0.8[rad] +- 2.8[SU2])e-10 (tau-based), where the errors have been
separated according to their sources: experimental, missing radiative
corrections in e+e- data, and isospin breaking. The corresponding Standard
Model predictions for the muon magnetic anomaly read a_mu = (11,659,180.9 +-
7.2[had] +- 3.5[LBL] +- 0.4[QED+EW])e-10 (e+e- -based) and a_mu = (11,659,195.6
+- 5.8[had] +- 3.5[LBL] +- 0.4[QED+EW])e-10 (tau-based), where the errors
account for the hadronic, light-by-light (LBL) scattering and electroweak
contributions. The deviations from the measurement at BNL are found to be (22.1
+- 7.2 +- 3.5 +- 8.0)e-10 (1.9 sigma) and (7.4 +- 5.8 +- 3.5 +- 8.0)e-10 (0.7
sigma) for the e+e- and tau-based estimates, respectively, where the second
error is from the LBL contribution and the third one from the BNL measurement.Comment: 14 pages, 7 figures (to be submitted to Phys Lett B

### Study of $e^+e^-$ collisions with a hard initial state photon at BABAR

A study of several 3- and 4-body hadronic final states ($\pi^+\pi^-\pi^0, \pi^+\pi^-\pi^+\pi^-, K^+K^-\pi^+\pi^- and K^+K^-K^+K^-$) accompanied by a hard photon is presented. These states are produced from $e^+e^-$ collisions at the c.m. energy near the \UPSILON (4S) resonance using a $90 fb^-1$ data sample collected with the BABAR detector at the PEP-II collider. The invariant mass of the hadronic final state determines the virtual photon energy, so that the data can be compared with direct $e^+e^-$ cross sections. Cross sections have been obtained from threshold up to 4.5 GeV with systematic errors at the 5% level. The accuracy of the results is comparable with the best direct $e^+e^-$ results overall, but achieves amuch better precision in 1.4-2.5 GeV region where data are sparse. In addition to light meson spectroscopy these data can be used to improve the determination of R -the ratio of $e^+e^-\to$ hadrons cross section to $e^+e^-\to \mu^+\mu^-$ - and thereby to impact the understanding of the recent $(g-2)_\mu$Â measurement through a better evaluation of the hadronic vacuum polarization contribution. The ISR technique also gives access to $J/\psi$ production and allows one to measure branching ratios into 3- and 4-body final states above at a level of precision that is typically better than that obtained in the combined earlier measurements

### Detection of gravitational wave bursts by interferometric detectors

We study in this paper some filters for the detection of burst-like signals
in the data of interferometric gravitational-wave detectors. We present first
two general (non-linear) filters with no {\it a priori} assumption on the
waveforms to detect. A third filter, a peak correlator, is also introduced and
permits to estimate the gain, when some prior information is known about the
waveforms. We use the catalogue of supernova gravitational-wave signals built
by Zwerger and M\"uller in order to have a benchmark of the performance of each
filter and to compare to the performance of the optimal filter. The three
filters could be a part of an on-line triggering in interferometric
gravitational-wave detectors, specialised in the selection of burst events.Comment: 15 pages, 8 figure

### Status of the Fermilab Muon (g-2) Experiment

The New Muon $(g-2)$ Collaboration at Fermilab has proposed to measure the
anomalous magnetic moment of the muon, $a_\mu$, a factor of four better than
was done in E821 at the Brookhaven AGS, which obtained $a_\mu = [116 592 089
(63)] \times 10^{-11}$ $\pm 0.54$ ppm. The last digit of $a_{\mu}$ is changed
from the published value owing to a new value of the ratio of the
muon-to-proton magnetic moment that has become available. At present there
appears to be a difference between the Standard-Model value and the measured
value, at the $\simeq 3$ standard deviation level when electron-positron
annihilation data are used to determine the lowest-order hadronic piece of the
Standard Model contribution. The improved experiment, along with further
advances in the determination of the hadronic contribution, should clarify this
difference. Because of its ability to constrain the interpretation of
discoveries made at the LHC, the improved measurement will be of significant
value, whatever discoveries may come from the LHC.Comment: Proceedings of the PhiPsi09, Oct. 13-16, 2009, Beijing, China, 4
pages 2 figures. Version 2 includes Fermilab report number, minor corrections
and one additional referenc

### Strange Quark Mass from the Invariant Mass Distribution of Cabibbo-Suppressed Tau Decays

Quark mass corrections to the tau hadronic width play a significant role only
for the strange quark, hence providing a method for determining its mass. The
experimental input is the vector plus axial-vector strange spectral function
derived from a complete study of tau decays into strange hadronic final states
performed by ALEPH. New results on strange decay modes from other experiments
are also incorporated. The present analysis determines the strange quark mass
at the Mtau mass scale using moments of the spectral function. Justified
theoretical constraints are applied to the nonperturbative components and
careful attention is paid to the treatment of the perturbative expansions of
the moments which exhibit convergence problems. The result obtained,
m_s(Mtau^2) = (120 +- 11_exp +- 8_Vus +- 19_th) MeV = (120^+21_-26) MeV, is
stable over the scale from Mtau down to about 1.4 GeV. Evolving this result to
customary scales yields m_s(1 GeV^2) = (160^+28_-35) MeV and m_s(4 GeV^2) =
(116^+20_-25) MeV.Comment: LaTex, 8 pages, 4 figures (EPS

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