Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Pion electromagnetic form factor from full lattice QCD   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,
$\langle r^2_v\rangle$. 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
$\langle r^2_s\rangle$.

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The categories of this paper are: q-bio
15
The categories of this paper are: nucl-ex
4
The categories of this paper are: cond-mat
25
The categories of this paper are: patt-sol
22
The categories of this paper are: chao-dyn
28
The categories of this paper are: alg-geom
19
The categories of this paper are: eess
0
The categories of this paper are: hep-ph
27
The categories of this paper are: comp-gas
16
The categories of this paper are: stat
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The categories of this paper are: math
12
The categories of this paper are: nucl-th
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The categories of this paper are: hep-ex
31
The categories of this paper are: ao-sci
20
The categories of this paper are: acc-phys
34
The categories of this paper are: chem-ph