Lattice calculation of the short and intermediate time-distance hadronic vacuum polarization contributions to the muon magnetic moment using twisted-mass fermions

Alexandrou, C.; Bacchio, S.; Dimopoulos, P.; Finkenrath, J.; Frezzotti, R.; Gagliardi, G.; Garofalo, M.; Hadjiyiannakou, K.; Kostrzewa, B.; Jansen, K.; Lubicz, V.; Petschlies, M.; Sanfilippo, F.; Simula, S.; Urbach, C.; Wenger, U. (2023). Lattice calculation of the short and intermediate time-distance hadronic vacuum polarization contributions to the muon magnetic moment using twisted-mass fermions. Physical review. D - particles, fields, gravitation, and cosmology, 107(7) American Physical Society 10.1103/PhysRevD.107.074506

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We present a lattice determination of the leading-order hadronic vacuum polarization (HVP) contribution to the muon anomalous magnetic moment, a HVP μ, in the so-called short and intermediate time-distance windows, a SDμ and aWμ, defined by the RBC/UKQCD Collaboration [Phys. Rev. Lett. 121, 022003 (2018)]. We employ gauge ensembles produced by the Extended Twisted Mass Collaboration (ETMC) with Nf=2+1+1 flavors of Wilson-clover twisted-mass quarks with masses of all the dynamical quark flavors tuned close to their physical values. The simulations are carried out at three values of the lattice spacing equal to
≃0.057, 0.068 and 0.080 fm with spatial lattice sizes up to L≃7.6fm. For the short-distance window we obtain a SDμ(ETMC)=69.27(34)×10−10, which is consistent with the recent dispersive value of aSDμ(e+e−)=68.4(5)×10−10 [, Phys. Lett. B 833, 137313 (2022)]. In the case of the intermediate window we get the value aWμ(ETMC)=236.3(1.3)×10−10, which is consistent with the result aWμ(BMW)=236.7(1.4)×10−10 [, Nature (London) 593, 51 (2021)] by the BMW Collaboration as well as with the recent determination by the CLS/Mainz group of aWμ(CLS)=237.30(1.46)×10−10 [, Phys. Rev. D 106, 114502 (2022)]. However, it is larger than the dispersive result of aWμ(e+e−)=229.4(1.4)×10−10 by approximately 3.6 standard deviations. The tension increases to approximately 4.5 standard deviations if we average our ETMC result with those by BMW and CLS/Mainz. Our accurate lattice results in the short and intermediate windows point to a possible deviation of the
e+e− cross section data with respect to Standard Model predictions in the low- and intermediate-energy regions but not in the high-energy region.

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