https://www.zora.uzh.ch/id/eprint/191493/1/1-s2.0-S0370157320302556-main.pdf

The anomalous magnetic moment of the muon in the Standard Model

We compute the leading order hadronic vacuum polarization (LO-HVP) contribution to the anomalous magnetic moment of the muon, $(g_\mu-2)$, using lattice QCD Calculations are performed with four flavors of 4-stout-improved staggered quarks, at physical quark masses and at six values of the lattice spacing down to 0064~fm All strong isospin breaking and electromagnetic effects are accounted for to leading order The infinite-volume limit is taken thanks to simulations performed in volumes of sizes up to 11~fm Our result for the LO-HVP contribution to $(g_\mu-2)$ has a total uncertainty of 08\% Compared to the result of the dispersive approach for this contribution, ours significantly reduces the tension between the standard model prediction for $(g_\mu-2)$ and its measurement

Leading hadronic contribution to the muon magnetic moment from lattice QCD

We address the contribution of the $3\pi$ channel to hadronic vacuum polarization (HVP) using a dispersive representation of the $e^+e^-\to 3\pi$ amplitude. This channel gives the second-largest individual contribution to the total HVP integral in the anomalous magnetic moment of the muon $(g-2)_\mu$, both to its absolute value and uncertainty. It is largely dominated by the narrow resonances $\omega$ and $\phi$, but not to the extent that the off-peak regions were negligible, so that at the level of accuracy relevant for $(g-2)_\mu$ an analysis of the available data as model independent as possible becomes critical. Here, we provide such an analysis based on a global fit function using analyticity and unitarity of the underlying $\gamma^*\to3\pi$ amplitude and its normalization from a chiral low-energy theorem, which, in particular, allows us to check the internal consistency of the various $e^+e^-\to 3\pi$ data sets. Overall, we obtain $a_\mu^{3\pi}|_{\leq 1.8\,\text{GeV}}=46.2(6)(6)\times 10^{-10}$ as our best estimate for the total $3\pi$ contribution consistent with all (low-energy) constraints from QCD. In combination with a recent dispersive analysis imposing the same constraints on the $2\pi$ channel below $1\,\text{GeV}$, this covers nearly $80\%$ of the total HVP contribution, leading to $a_\mu^\text{HVP}=692.3(3.3)\times 10^{-10}$ when the remainder is taken from the literature, and thus reaffirming the $(g-2)_\mu$ anomaly at the level of at least $3.4\sigma$. As side products, we find for the vacuum-polarization-subtracted masses $M_\omega=782.63(3)(1)\,\text{MeV}$ and $M_\phi=1019.20(2)(1)\,\text{MeV}$, confirming the tension to the $\omega$ mass as extracted from the $2\pi$ channel.

/pdf/three-pion-contribution-to-hadronic-vacuum-polarization-3iaox9z950.pdf

Three-pion contribution to hadronic vacuum polarization

We present an update of the global fit of the Standard Model electroweak sector to latest experimental results. We include new kinematic top quark and W boson mass measurements from the LHC, a $$\sin \!^2\theta ^{\ell }_{\mathrm{eff}}$$
 result from the Tevatron, and a new evaluation of the hadronic contribution to $$\alpha (M_Z^2)$$
 . We present tests of the internal consistency of the electroweak Standard Model and updated numerical predictions of key observables. The electroweak data combined with measurements of the Higgs boson coupling strengths and flavour physics observables are used to constrain parameters of two-Higgs-doublet models.

/pdf/update-of-the-global-electroweak-fit-and-constraints-on-two-3vnx1g2dc5.pdf

Update of the global electroweak fit and constraints on two-Higgs-doublet models

Following updates in the compilation of ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}\text{hadrons}$ data, this work presents reevaluations of the hadronic vacuum polarization contributions to the anomalous magnetic moments of the electron (${a}_{e}$), muon (${a}_{\ensuremath{\mu}}$) and tau lepton (${a}_{\ensuremath{\tau}}$), to the ground-state hyperfine splitting of muonium and also updates the hadronic contributions to the running of the QED coupling at the mass scale of the $Z$ boson, $\ensuremath{\alpha}({M}_{Z}^{2})$. Combining the results for the hadronic vacuum polarization contributions with recent updates for the hadronic light-by-light corrections, the electromagnetic and the weak contributions, the deviation between the measured value of ${a}_{\ensuremath{\mu}}$ and its Standard Model prediction amounts to $\mathrm{\ensuremath{\Delta}}{a}_{\ensuremath{\mu}}=(28.02\ifmmode\pm\else\textpm\fi{}7.37)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}10}$, corresponding to a muon $g\ensuremath{-}2$ discrepancy of $3.8\ensuremath{\sigma}$.

g − 2 of charged leptons, α ( M Z 2 ) , and the hyperfine splitting of muonium

This work presents a complete reevaluation of the hadronic vacuum polarization contributions to the anomalous magnetic moment of the muon, aμhad,VP, and the hadronic contributions to the effective QED coupling at the mass of the Z boson, Δαhad(MZ2), from the combination of e+e-→hadrons cross section data. Focus has been placed on the development of a new data combination method, which fully incorporates all correlated statistical and systematic uncertainties in a bias free approach. All available e+e-→hadrons cross section data have been analyzed and included, where the new data compilation has yielded the full hadronic R-ratio and its covariance matrix in the energy range mπ≤s≤11.2  GeV. Using these combined data and perturbative QCD above that range results in estimates of the hadronic vacuum polarization contributions to g-2 of the muon of aμhad,LO VP=(693.26±2.46)×10-10 and aμhad,NLO VP=(-9.82±0.04)×10-10. The new estimate for the Standard Model prediction is found to be aμSM=(11659182.04±3.56)×10-10, which is 3.7σ below the current experimental measurement. The prediction for the five-flavor hadronic contribution to the QED coupling at the Z boson mass is Δαhad(5)(MZ2)=(276.11±1.11)×10-4, resulting in α-1(MZ2)=128.946±0.015. Detailed comparisons with results from similar related works are given.

Muon g − 2 and α ( M Z 2 ) : A new data-based analysis

We study the littlest Higgs model with T parity at the CERN LHC through pair productions of the T-odd top quark partner (T{sub -}) which decays into the top quark and the lightest T-odd particle. We identify the region of parameters favored by the electroweak and cosmological considerations. The signal and background events are simulated with fast detector simulation to study the discovery potential at the LHC. We find that the hemisphere analysis recently proposed by the CMS Collaboration is very useful to separate the signal from the tt background. We discuss the observability of the top tagged signal in the effective mass (M{sub eff}) versus the transverse missing energy (E{sub Tmiss}) plane. We show that, for all our sample parameter sets with M{sub T{sub -}}{<=}900 GeV, the excess of the signal over the background can be visible as a bump structure in the E{sub Tmiss} distribution for 50 fb{sup -1} at relatively high M{sub eff} intervals.

Hunting for the top partner in the littlest Higgs model with T parity at the CERN LHC

We use a new compilation of the hadronic $R$-ratio from available data for the process ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}\text{hadrons}$ to determine the strong coupling, ${\ensuremath{\alpha}}_{s}$. We make use of all data for the $R$-ratio from threshold to a center-of-mass energy of 2 GeV by employing finite-energy sum rules. Data above 2 GeV, for which at present far fewer high-precision experimental data are available, do not provide much additional constraint but are fully consistent with the values for ${\ensuremath{\alpha}}_{s}$ we obtain. Quoting our results at the $\ensuremath{\tau}$ mass to facilitate comparison to the results obtained from analogous analyses of hadronic $\ensuremath{\tau}$-decay data, we find ${\ensuremath{\alpha}}_{s}({m}_{\ensuremath{\tau}}^{2})=0.298\ifmmode\pm\else\textpm\fi{}0.016\ifmmode\pm\else\textpm\fi{}0.006$ in fixed-order perturbation theory, and ${\ensuremath{\alpha}}_{s}({m}_{\ensuremath{\tau}}^{2})=0.304\ifmmode\pm\else\textpm\fi{}0.018\ifmmode\pm\else\textpm\fi{}0.006$ in contour-improved perturbation theory, where the first error is statistical, and the second error reflects our estimate of various systematic effects. These values are in good agreement with a recent determination from the OPAL and ALEPH data for hadronic $\ensuremath{\tau}$ decays.

Daisuke Nomura

Papers

Muon g − 2 and α ( M Z 2 ) : A new data-based analysis

g − 2 of charged leptons, α ( M Z 2 ) , and the hyperfine splitting of muonium

Hunting for the top partner in the littlest Higgs model with T parity at the CERN LHC

Strong coupling from e + e - →hadrons below charm