1,797 research outputs found

### Tau Decay Determination of the Strange Quark Mass

The recent ALEPH measurements of the inclusive Cabibbo--suppressed decay
width of the $\tau$ and several moments of its invariant mass distribution are
used to determine the value of the strange quark mass. We obtain, in the
$\bar{\rm MS}$ scheme, $m_s(M_\tau^2) = (119\pm 24)$ MeV, which corresponds to
$m_s(1 {\rm GeV}^2) = (164 \pm 33) {\rm MeV}, m_s(4 {\rm GeV}^2) = (114\pm 23)
{\rm MeV}$.Comment: 5pages. Invited talk at QCD'99 (Montpellier, July 1999

### Chiral low-energy constants from tau data

We analyze how the recent precise hadronic tau-decay data on the V-A spectral
function and general properties of QCD such as analyticity, the operator
product expansion and chiral perturbation theory (ChPT), can be used to improve
the knowledge of some of the low-energy constants of ChPT. In particular we
find the most precise values of L_{9,10} (or equivalently l_{5,6}) at order p^4
and p^6 and the first phenomenological determination of C_87 (c_50).Comment: Proceedings of the 6th International Workshop on Chiral Dynamics
(Bern, Switzerland, July 6-10, 2009). 9 pages, 3 figure

### The Hadronic Light-by-Light Contribution to the Muon Anomalous Magnetic Moment: Where do we stand?

We review the status of the hadronic light-by-light contribution to the muon
anomalous magnetic moment and critically compare recent calculations. We also
study in detail which momentum regions the pi^0 exchange main contribution
originates. We also argue that a_\mu^{light-by-light} = (11 \pm 4) \times
10^{-10} encompasses the present understanding of this contribution and comment
on some directions to improve on that.Comment: 16 pages, 9 figure

### Yukawa coupling and anomalous magnetic moment of the muon: an update for the LHC era

We study the interplay between a soft muon Yukawa coupling generated
radiatively with the trilinear A-terms of the minimal supersymmetric standard
model (MSSM) and the anomalous magnetic moment of the muon. In the absence of a
tree-level muon Yukawa coupling the lightest smuon mass is predicted to be in
the range between 750 GeV and 2700 GeV at 2 sigma, if the bino mass M_1 is
below 1 TeV. Therefore, a detection of a smuon (in conjunction with a sub-TeV
bino) at the LHC would directly imply a non-zero muon Yukawa coupling in the
MSSM superpotential. Inclusion of slepton flavor mixing could in principle
lower the mass of one smuon-like slepton below 750 GeV. However, the
experimental bounds on radiative lepton decays instead strengthen the lower
mass bound, with larger effects for smaller M_1, We also extend the analysis to
the electron case and find that a light selectron close to the current
experimental search limit may prove the MSSM electron Yukawa coupling to be
non-zero.Comment: 6 pages, 2 figures, references added, version accepted for
publication in PR

### High Efficiency Positron Accumulation for High-Precision Measurements

Positrons are accumulated within a Penning trap designed to make more precise
measurements of the positron and electron magnetic moments. The retractable
radioactive source used is weak enough to require no license for handling
radioactive material and the radiation dosage one meter from the source gives
an exposure several times smaller than the average radiation dose on the
earth's surface. The 100 mK trap is mechanically aligned with the 4.2 K
superconducting solenoid that produces a 6 tesla magnetic trapping field with a
direct mechanical coupling.Comment: 7 pages, 9 figure

### Determination of |V_us| from hadronic tau decays

The recent update of the strange spectral function and the moments of the
invariant mass distribution by the OPAL collaboration from hadronic tau decay
data are employed to determine |V_us| as well as m_s. Our result,
|V_us|=0.2208\pm0.0034, is competitive to the standard extraction of |V_us|
from K_e3 decays and to the new proposals to determine it. Furthermore, the
error associated to our determination of |V_us| can be reduced in the future
since it is dominated by the experimental uncertainty that will be eventually
much improved by the B-factories hadronic tau data. Another improvement that
can be performed is the simultaneous fit of both |V_us| and m_s to a set of
moments of the hadronic tau decays invariant mass distribution, which will
provide even a more accurate determination of both parameters.Comment: 6 pages. Invited talk given by E.G. at the XXXXth Rencontres de
Moriond on Electroweak Interactions and Unified Theories, La Thuile, Italy,
5-12 Mar 200

### Measuring the muon's anomalous magnetic moment to 0.14 ppm

The anomalous magnetic moment (g-2) of the muon was measured with a precision
of 0.54 ppm in Experiment 821 at Brookhaven National Laboratory. A difference
of 3.2 standard deviations between this experimental value and the prediction
of the Standard Model has persisted since 2004; in spite of considerable
experimental and theoretical effort, there is no consistent explanation for
this difference. This comparison hints at physics beyond the Standard Model,
but it also imposes strong constraints on those possibilities, which include
supersymmetry and extra dimensions. The collaboration is preparing to relocate
the experiment to Fermilab to continue towards a proposed precision of 0.14
ppm. This will require 20 times more recorded decays than in the previous
measurement, with corresponding improvements in the systematic uncertainties.
We describe the theoretical developments and the experimental upgrades that
provide a compelling motivation for the new measurement.Comment: 5 pages, 1 figure, presented at International Nuclear Physics
Conference 2010 (INPC 2010

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