1,514 research outputs found
Hadronic \tau decays and QCD
Hadronic decays of the lepton provide a clean source to study hadron
dynamics in an energy regime dominated by resonances, with the interesting
information captured in the spectral functions. Recent results on exclusive
channels are reviewed. Inclusive spectral functions are the basis for QCD
analyses, delivering an accurate determination of the strong coupling constant
and quantitative information on nonperturbative contributions. Strange decays
yield a determination of the strange quark mass.Comment: 13 page
e+e- results from BABAR and implications for g-2
The BABAR collaboration has nearly completed a program of precise
measurements of the cross sections for the dominant channels of e+e- -->
hadrons from threshold to an energy of 3-5 GeV using the initial-state
radiation (ISR) method, i.e. the measurement of the cross sections e+e- -->
gamma hadrons with the energetic photon detected at large angle to the beams.
These data are used as input to vacuum polarization dispersion integrals, in
particular the hadronic contribution to the muon g-2 anomaly. In addition to
the recently measured pi+pi- cross section, giving the dominant contibution,
many multihadronic channels have been investigated, with some recent examples
presented here. We give preliminary results for the process e+e- -->
K+K-(gamma) using 232 fb-1 of data collected with the BABAR detector at e+e-
center-of-mass energies near 10.6 GeV. The lowest-order contribution to the
hadronic vacuum polarization term in the muon magnetic anomaly is obtained for
this channel: amu-KK-LO=(22.95 +-0.14(stat) +-0.22(syst)) 10^-10, which is
about a factor of three more precise than the previous world average value.Comment: 4 pages, 5 figures, talk given at the Tau Workshop, September 2012,
Nagoy
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 \ee annihilation cross section into hadrons by the CMD-2
Collaboration. The agreement between \ee and spectral functions in the
channel is found to be much improved. Nevertheless, significant
discrepancies remain in the center-of-mass energy range between 0.85 and .The deviations from the measurement at BNL are found to be
(1.9 ) and (0.7 ) for the \ee- and -based estimates,
respectively, where the second error is from the nonhadronic contributions and
the third one from the BNL measurement. Taking into account the mass splitting determined from the measured spectral functions
increases the -based estimate and leads to a worse discrepancy between
the two estimates.Comment: 9 pages, 7 figures, proceedings of the SIGHAD03 workshop (Pisa,
October 2003) on e+e- annihilation cross sections at low energ
Progress on R measurement through ISR with BaBar
The status of the ISR analysis with BaBar is presented. Preliminary results
are given on the process e+e- --> 2pi+ 2pi- and J/psi decays including a
determination of its total width and the branching ratios into 2pi+ 2pi-, K+ K-
pi+ pi-, and 2K+ 2K- modes.Comment: 6 pages, 6 figures, proceedings of the SIGHAD03 workshop (Pisa,
October 2003) on e+e- annihilation cross sections at low energ
Comments on "An Update of the HLS Estimate of the Muon g-2"by M.Benayoun {\it et al.}, arXiv:1210.7184v3
In a recent paper \cite{benayoun} M.Benayoun {\it et al.} use a specific
model to compare results on the existing data for the cross section of the
process and state conclusions about the
inconsistency of the BABAR results with those from the other experiments. We
show that a direct model-independent comparison of the data at hand contradicts
this claim. Clear discrepancies with the results of Ref. \cite{benayoun} are
pointed out. As a consequence we do not believe that the lower value and the
smaller uncertainty obtained for the prediction of the muon magnetic anomaly
are reliable results.Comment: 7 pages,2 figures, comment
The hadronic contribution to (g-2) of the muon
The evaluation of the hadronic contribution to the muon magnetic anomaly
is revisited, taking advantage of new experimental data on
annihilation into hadrons: SND and CMD-2 for the channel, and
\babar for multihadron final states. Discrepancies are observed between KLOE
and CMD-2/SND data, preventing one from averaging all the results. The
long-standing disagreement between spectral functions obtained from
decays and annihilation is still present, and not accounted by
isospin-breaking corrections, for which new estimates have been presented. The
updated Standard Model value for based on annihilation data is
now reaching a precision better than experiment, and it disagrees with the
direct measurement from BNL at the 3.3 level, while the -based
estimate is in much better agreement. The / discrepancy, best
revealed when comparing the measured branching fraction for to its prediction from the isospin-breaking-corrected
spectral function, remains a serious problem to be understood.Comment: 9 pages, 7 figures, invited talk at the Tau06 International Workshop,
Pisa, September 19-22 200
Spectral functions from Hadronic Tau Decays and QCD
Hadronic decays of the lepton provide a clean environment to study
hadron dynamics in an energy regime dominated by resonances, with the
interesting information captured in the spectral functions. Recent results from
ALEPH on exclusive channels are presented, with some emphasis on the \pi \piz
final state which plays a crucial role for the determination of the hadronic
contribution to the muon anomalous magnetic moment. Inclusive spectral
functions are the basis for QCD analyses, delivering an accurate determination
of the strong coupling constant, quantitative information on nonperturbative
contributions and a measurement of the mass of the strange quark.Comment: 14 pages, 18 figures, invited talk at the Tau02 Workshop, Santa Cruz,
Sept. 200
Measurement of Branching Fractions in Tau Decays
Full LEP-I data collected by the ALEPH detector during 1991-1995 running are
analyzed in order to measure the decay branching fractions. The analysis
follows the global method used in the published study based on 1991-1993 data,
with several improvements, especially concerning the treatment of photons and
's. Extensive systematic studies are performed, in order to match the
large statistics of the data sample corresponding to 327148 measured and
identified decays. Preliminary values for the branching fractions are
obtained for the 2 leptonic channels and 11 hadronic channels defined by their
respective numbers of charged particles and 's. Using previously
published ALEPH results on final states with charged and neutral kaons,
corrections are applied so that branching ratios for exclusive final states
without kaons are derived. Some physics implications of the results are given,
in particular concerning universality in the leptonic charged weak current,
isospin invariance in decays, and the separation of vector and
axial-vector components of the total hadronic rate.Comment: Invited Talk at Tau02 International Workshop, Sept. 10-13 2002, Santa
Cruz, California, 19 pages, 13 figure
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