We reevaluate the hadronic vacuum polarisation contributions to the muon magnetic anomaly and to the running of the electromagnetic coupling constant at the
Z
-boson mass. We include newest
e
+
e
-
→
...hadrons
cross-section data together with a phenomenological fit of the threshold region in the evaluation of the dispersion integrals. The precision in the individual datasets cannot be fully exploited due to discrepancies that lead to additional systematic uncertainty in particular between BABAR and KLOE data in the dominant
π
+
π
-
channel. For the muon
(
g
-
2
)
/
2
, we find for the lowest-order hadronic contribution
(
694.0
±
4.0
)
·
10
-
10
. The full Standard Model prediction differs by
3.3
σ
from the experimental value. The five-quark hadronic contribution to
α
(
m
Z
2
)
is evaluated to be
(
276.0
±
1.0
)
·
10
-
4
.
We reevaluate the hadronic vacuum polarisation contributions to the muon magnetic anomaly and to the running of the electromagnetic coupling constant at the
Z
-boson mass. We include newest
e
+
e
-
→
...hadrons
cross-section data (among others) from the BABAR and VEPP-2000 experiments. For the muon
(
g
-
2
)
/
2
we find for the lowest-order hadronic contribution
(
693.1
±
3.4
)
×
10
-
10
, improving the precision of our previous evaluation by 21%. The full Standard Model prediction differs by
3.5
σ
from the experimental value. The five-quark hadronic contribution to
α
(
m
Z
2
)
is evaluated to be
(
276.0
±
0.9
)
×
10
-
4
.
We reevaluate the hadronic contributions to the muon magnetic anomaly, and to the running of the electromagnetic coupling constant at the Z-boson mass. We include new π.sup.+π.sup.- cross-section ...data from KLOE, all available multi-hadron data from BABAR, a reestimation of missing low-energy contributions using results on cross sections and process dynamics from BABAR, a reevaluation of all experimental contributions using the software package HVPTools together with a reanalysis of inter-experiment and inter-channel correlations, and a reevaluation of the continuum contributions from perturbative QCD at four loops. These improvements lead to a decrease in the hadronic contributions with respect to earlier evaluations. For the muon g-2 we find lowest-order hadronic contributions of (692.3 ± 4.2) x 10.sup.-10 and (701.5 ± 4.7) x 10.sup.-10 for the e.sup.+e.sup.--based and r -based analyses, respectively, and full Standard Model predictions that differ by 3.6σ and 2.4σ from the experimental value. For the e.sup.+e.sup.--based five-quark hadronic contribution to a(M|) we find Δα.sup.(5).sub.had(M.sup.2.sub.Z) = (274.9 ± 1.0) x 10.sup.-4. The reduced electromagnetic coupling strength at M.sub.Z leads to an increase by 12 GeV in the central value of the Higgs boson mass obtained by the standard Gfitter fit to electroweak precision data.
An update of the ALEPH non-strange spectral functions from hadronic
τ
decays is presented. Compared to the 2005 ALEPH publication, the main improvement is related to the use of a new method to unfold ...the measured mass spectra from detector effects. This procedure also corrects a previous problem in the correlations between the unfolded mass bins. Results from QCD studies and for the evaluation of the hadronic vacuum polarisation contribution to the anomalous muon magnetic moment are derived using the new spectral functions. They are found in agreement with published results based on the previous set of spectral functions.
A
bstract
Three different approaches to precisely describe the Adler function in the Euclidean regime at around 2 GeVs are available: dispersion relations based on the hadronic production data in
e
+
...e
−
annihilation, lattice simulations and perturbative QCD (pQCD). We make a comprehensive study of the perturbative approach, supplemented with the leading power corrections in the operator product expansion. All known contributions are included, with a careful assessment of uncertainties. The pQCD predictions are compared with the Adler functions extracted from
Δ
α
QED
had
(
Q
2
), using both the DHMZ compilation of
e
+
e
−
data and published lattice results. Taking as input the FLAG value of
α
s
, the pQCD Adler function turns out to be in good agreement with the lattice data, while the dispersive results lie systematically below them. Finally, we explore the sensitivity to
α
s
of the direct comparison between the data-driven, lattice and QCD Euclidean Adler functions. The precision with which the renormalisation group equation can be tested is also evaluated.
(ProQuest: ... denotes formulae and/or non-USASCII text omitted; see image) An update of the ALEPH non-strange spectral functions from hadronic ... decays is presented. Compared to the 2005 ALEPH ...publication, the main improvement is related to the use of a new method to unfold the measured mass spectra from detector effects. This procedure also corrects a previous problem in the correlations between the unfolded mass bins. Results from QCD studies and for the evaluation of the hadronic vacuum polarisation contribution to the anomalous muon magnetic moment are derived using the new spectral functions. They are found in agreement with published results based on the previous set of spectral functions.
The determination of αS from τ decays revisited Davier, M.; Descotes-Genon, S.; Höcker, A. ...
The European physical journal. C, Particles and fields,
08/2008, Letnik:
56, Številka:
3
Journal Article
Recenzirano
Odprti dostop
We revisit the determination of
α
S
(
m
τ
2
) using a fit to inclusive
τ
hadronic spectral moments in light of (1) the recent calculation of the fourth-order perturbative coefficient
K
4
in the ...expansion of the Adler function, (2) new precision measurements from BABAR of e
+
e
−
annihilation cross sections, which decrease the uncertainty in the separation of vector and axial-vector spectral functions, and (3) improved results from BABAR and Belle on
τ
branching fractions involving kaons. We estimate that the fourth-order perturbative prediction reduces the theoretical uncertainty, introduced by the truncation of the series, by 20% with respect to earlier determinations. We discuss to some detail the perturbative prediction of two different methods: fixed-order perturbation theory (FOPT) and contour-improved perturbative theory (CIPT). The corresponding theoretical uncertainties are studied at the
τ
and
Z
mass scales. The CIPT method is found to be more stable with respect to the missing higher order contributions and to renormalization scale variations. It is also shown that FOPT suffers from convergence problems along the complex integration contour. Nonperturbative contributions extracted from the most inclusive fit are small, in agreement with earlier determinations. Systematic effects from quark-hadron duality violation are estimated with simple models and found to be within the quoted systematic errors. The fit based on CIPT gives
α
S
(
m
τ
2
)=0.344±0.005±0.007, where the first error is experimental and the second theoretical. After evolution to
M
Z
we obtain
α
S
(
M
Z
2
)=0.1212±0.0005±0.0008±0.0005, where the errors are respectively experimental, theoretical and due to the evolution. The result is in agreement with the corresponding N
3
LO value derived from essentially the
Z
width in the global electroweak fit. The
α
S
(
M
Z
2
) determination from
τ
decays is the most precise one to date.
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_muhad,LO = (696.3 +- 6.2exp +- 3.6rad)e-10 (e+e- -based) and a_muhad,LO = (711.0 +- 5.0exp +- 0.8rad +- 2.8SU2)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 +- 7.2had +- 3.5LBL +- 0.4QED+EW)e-10 (e+e- -based) and a_mu = (11,659,195.6 +- 5.8had +- 3.5LBL +- 0.4QED+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.
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