Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The size of the pion from full lattice QCD with physical $u$, $d$, $s$
  and $c$ quarks   We present the first calculation of the electromagnetic form factor of the
$\pi$ meson at physical light quark masses. We use configurations generated by
the MILC collaboration including the effect of $u$, $d$, $s$ and $c$ sea quarks
with the Highly Improved Staggered Quark formalism. We work at three values of
the lattice spacing on large volumes and with $u$/$d$ quark masses going down
to the physical value. We study scalar and vector form factors for a range in
space-like $q^2$ from 0.0 to -0.1 $\mathrm{GeV}^2$ and from their shape we
extract mean square radii. Our vector form factor agrees well with experiment
and we find $\langle r^2 \rangle_V = 0.403(18)(6) \,\mathrm{fm}^2$. For the
scalar form factor we include quark-line disconnected contributions which have
a significant impact on the radius. We give the first results for SU(3)
flavour-singlet and octet scalar mean square radii, obtaining: $\langle r^2
\rangle_S^{\mathrm{singlet}} = 0.506(38)(53) \mathrm{fm}^2$ and $\langle r^2
\rangle_S^{\mathrm{octet}} = 0.431(38)(46) \mathrm{fm}^2$. We discuss the
comparison with expectations from chiral perturbation theory.

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The categories of this paper are: nucl-ex
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The categories of this paper are: econ
28
The categories of this paper are: alg-geom
35
The categories of this paper are: mtrl-th
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The categories of this paper are: patt-sol
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The categories of this paper are: chem-ph
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The categories of this paper are: q-fin
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The categories of this paper are: funct-an
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The categories of this paper are: q-bio
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The categories of this paper are: nlin
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The categories of this paper are: hep-th
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The categories of this paper are: adap-org
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The categories of this paper are: dg-ga
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The categories of this paper are: math-ph
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The categories of this paper are: solv-int
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The categories of this paper are: acc-phys