2-9 July 2014
Valencia, Spain
Europe/Madrid timezone

Fits and Related Systematics for the Hadronic Vacuum Polarization on the Lattice

5 Jul 2014, 13:10
Sala 6+7 ()

Sala 6+7

Oral presentation Lattice QCD Lattice QCD


Santiago Peris (U. Autonoma de Barcelona, Spain)


(See Attached file.) In order to test the systematic error coming from the extrapolation at low $Q^2$ carried out in present lattice determinations of the hadronic vacuum polarization contribution to the muon anomalous magnetic moment, we employ a physically motivated model for the isospin-one non-strange vacuum polarization function $\Pi(Q^2)$ [1]. The model is based on the OPAL experimental vector-channel spectral function for energies below the $\tau$ mass and a successful parametrization, including perturbation theory and a model for quark-hadron duality violations, for higher energies. Using the same covariance matrix and $Q^2$ values as in a recent lattice simulation, we then generate fake data for $\Pi(Q^2)$. The fake data is then used to extrapolate to low $Q^2$ and evaluate the hadronic vacuum polarization contribution to the muon anomalous magnetic moment, after which the result is compared to the exact model value. From this comparison we unravel a systematic error much larger than the few-percent total error sometimes claimed for such extractions in the literature. We find that errors deduced from fits using a Vector Meson Dominance ansatz are misleading, typically turning out to be much smaller than the actual discrepancy between the fit and exact model results. The use of a sequence of multipoint Pade approximants appears to provide a safer fitting strategy [2]. Alternatively, the use of one-point Pades based on the coefficients of the Taylor expansion of $\Pi(Q^2)$ at $Q^2=0$ could also prove effective, as recently emphasized in Ref. [3], but only if these coefficients are accurately known, not only for the $s,c$ quarks but also for $u$ and $d$. BIBLIOGRAPHY [1] M.~Golterman, K.~Maltman and S.~Peris, ``Tests of hadronic vacuum polarization fits for the muon anomalous magnetic moment,'' Phys. Rev. D88, 114508 (2013) [arXiv:1309.2153 [hep-lat]]. [2] C.~Aubin, T.~Blum, M.~Golterman and S.~Peris, ``Model-independent parametrization of the hadronic vacuum polarization and g-2 for the muon on the lattice,'' Phys. Rev. D86, 054509 (2012) [arXiv:1205.3695 [hep-lat]]. [3] B.~Chakraborty, C.~T.~H.~Davies, G.~C.~Donald, R.~J.~Dowdall, J.~Koponen, G.~P.~Lepage and T.~Teubner, ``The strange and charm quark contributions to the anomalous magnetic moment of the muon,'' arXiv:1403.1778 [hep-lat].

Primary author

Santiago Peris (U. Autonoma de Barcelona, Spain)


Christopher Aubin (Fordham Univ., USA) Kim Maltman (York Univ., Canada) Maarten Golterman (San Francisco State Univ., USA) Tom Blum (Univ. of Connecticut, USA)

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