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Article overview
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Pion electromagnetic form factor from full lattice QCD | Jonna Koponen
; Francis Bursa
; Christine T. H. Davies
; Rachel J. Dowdall
; G. Peter Lepage
; | Date: |
20 Oct 2017 | Abstract: | We present the first calculation of the pion electromagnetic form factor at
physical light quark masses. This form factor parameterises the deviations from
the behaviour of a point-like particle when a photon hits the pion. These
deviations result from the internal structure of the pion and can thus be
calculated in QCD. We use three sets (different lattice spacings) of $n_f =
2+1+1$ lattice configurations generated by the MILC collaboration. The Highly
Improved Staggered Quark formalism (HISQ) is used for all of the sea and
valence quarks. Using lattice configurations with $u$/$d$ quark masses very
close to the physical value is a big advantage, as we avoid the chiral
extrapolation. We study the shape of the vector ($f_+$) form factor in the
$q^2$ range from $0$ to $-0.15$~GeV$^2$ and extract the mean square radius,
$langle r^2_v
angle$. The shape of the vector form factor and the resulting
radius is compared with experiment. We also discuss the scalar form factor and
radius extracted from that, which is not directly accessible to experiment. We
have also calculated the contributions from the disconnected diagrams to the
scalar form factor at small $q^2$ and discuss their impact on the scalar radius
$langle r^2_s
angle$. | Source: | arXiv, 1710.7467 | Services: | Forum | Review | PDF | Favorites |
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