### Conveners

#### Session 6: g-2

- Massimo Passera (INFN Padova)

#### Session 6: g-2

- Rafel Escribano (UAB (Barcelona) and IFAE/BIST (Barcelona))

#### Session 6: g-2

- Harvey Meyer (Johannes Gutenberg University Mainz)

#### Session 6: g-2

- Johan Bijnens

Nearly twenty years ago a team from Brookhaven National Lab measured the anomalous part of the muon's dipole moment ($a_\mu$) finding a ~three-sigma discrepancy against contemporary Standard Model predictions. The mystery lingered for a time as there were no further measurements, but within a few years a small dedicated team set into motion a plan to revive the technique at Fermilab. This team...

With the Fermilab g-2 experiment’s first measurement of the muon anomalous magnetic moment ($a_\mu$), announced on 7 April 2021, the difference between the new experimental average and the Muon g-2 Theory Initiative’s Standard Model prediction now stands at $4.2\sigma$. Experimental measurements of $a_\mu$ are expected to improve drastically in the coming years. In order to maximize the impact...

The recent Fermilab result has confirmed the long standing discrepancy between the direct measurement and the Standard Model (SM) prediction of the anomalous magnetic moment of the muon aμ=(gµ-2)/2. The possibility to improve the SM prediction using data-driven approaches has motivated the BESIII collaboration to embark on a dedicated experimental program. The high statistics data samples...

The recent result from the Fermilab experiment on the anomalous magnetic moment of the muon ($g-2$) has revived the interest on this observable, that exhibits an interesting —and persistent— $4\sigma$ discrepancy with respect to its theoretical value.

Future runs at Fermilab will help deciphering the nature of such discrepancy, but that will require a commensurate improvement on the theory...

In my talk, I will present a dispersive estimate of the $f_0(980)$ contribution to $(g-2)_\mu$. The performed analysis is a coupled-channel extension of the previous work, where $f_0(500)$ has already been addressed. Important ingredients are $\gamma^*\gamma^*\to \pi \pi$ and $\gamma^*\gamma^*\to K\bar{K}$ S-wave helicity amplitudes which rely on the novel unitarizaiton scheme for studying...

KLOE-2, the continuation of the KLOE experiment at the Frascati $\phi-$factory, completed its data-taking by acquiring about 5 fb$^{-1}$ at the $\phi$ meson peak.

One of its distinctive feature is the possibility to study $e^+e^- \to \gamma^{\ast}\gamma^{\ast}e^+e^-\to \pi^0 e^+e^-$ processes by tagging final state leptons with two stations installed in both arms of the DA$\Phi$NE...

The hadronic light-by-light contribution to the muon g-2 can now

be calculated using first principles lattice QCD+QED methods. Independent results from two collaborations are available. I will review the status and recent developments.

We study the HLbL contribution to g-2 in the kinematic region where the three loop momenta are large. We show how, even when the fourth photon is in the static limit, the massless quark loop gives the leading term of an operator product expansion. Power corrections are found to be small. Gluonic corrections are also included and the expansion is found to be well-behaved at relatively...

The largest part of the hadronic-vacuum-polarization (HVP) contribution to the muon anomalous magnetic moment is due to the intermediate state of two pions. Analyticity and unitarity do not only allow us to write this contribution in terms of the pion vector form factor (VFF), but also constrain the VFF itself. I will discuss fits of a dispersive representation of the pion VFF to $e^+e^-$...

We review the isospin-breaking and electromagnetic corrections to the $\tau^-\to\pi^-\pi^0\nu_\tau$ decays, which are used as an input to the two-pion contributions to the hadronic vacuum polarization (at LO) of the anomalous magnetic moment ($a_\mu$). We extend previous analyses by Cirigliano et al. working with ChPT with resonances. As an outcome, we improve the agreement between this...

We discuss a method for calculating the heavy quark vacuum polarisation contribution to the muon anomalous magnetic moment, $a_\mu$, using perturbative QCD up to ${\cal O}\left(\alpha_s^3\right)$. This approach is independent of $e^+e^-$ cross-section data allowing a fully theoretical evaluation of these contributions. This method confirms an existing result at lower orders in $\alpha_s$ and...

We present a continuum determination of a_mu^SIB, the strong isospin-breaking contribution to a_mu, the anomalous magnetic moment of the muon, using ChPT and the formulation of a_mu as a weighted integral of the electromagnetic current two-point function over Euclidean Q^2. Flavor-breaking hadronic tau decay sum rules are shown to provide a determination of a key higher-order chiral LEC...

The SM predicts zero values of CPV & TV in the decays of tau leptons except \tau^- \to \nu K^0_S [\pi,\pi\pi]. With neutrino oscillations I would give the golden medals for CPV & TV. I think that tau decays can get bronze medals in \tau^- \to \nu K [pi, \pi\pi, \eta]. Their hadronic final states are enough `complex'.