Speaker
Santiago Peris
(U. Autonoma de Barcelona, Spain)
Description
(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)
Co-authors
Christopher Aubin
(Fordham Univ., USA)
Kim Maltman
(York Univ., Canada)
Maarten Golterman
(San Francisco State Univ., USA)
Tom Blum
(Univ. of Connecticut, USA)
