Séminaires

# New lattice QCD calculation of the hadronic vacuum polarization contribution to the muon magnetic moment

## by Laurent Lellouch (CPT Marseille)

Europe/Paris
Description

Charged-lepton magnetic moments play a special role in probing the standard model (SM) of particle physics, which is complementary to direct searches for new physics at the energy frontier. In particular, the experimental value of the anomalous contribution to the muon magnetic moment, $a_\mu=(g_\mu-2)/2$, has exhibited a persistent discrepancy of over 3 standard deviations with the SM prediction, ever since the very precise measurement made at Brookhaven National Lab in the early 2000s. This is particularly enticing, because it could indicate the presence new, fundamental physics.  At present, theoretical and experimental uncertainties are comparable in size. However, a new experiment underway at Fermilab, and another one planned at J-PARC, are aiming to reduce the error on the measurement of $a_\mu$ by a factor of 4. To fully leverage these future measurements, and possibly claim the presence of new fundamental physics, it is imperative to check the SM prediction with independent methods and to reduce its uncertainties. After an introduction and a discussion of the current experimental and theoretical status of $a_\mu$, I will present a new lattice QCD calculation of the contribution to this quantity that most limits the precision of its SM prediction.  Surprisingly, our result eliminates the need to invoke new physics to explain the current measurement of $a_\mu$.

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