Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Photoproduction ofeta-pi pairs off nucleons and deuterons   Quasi-free photoproduction of $\pi\eta$-pairs has been investigated from
threshold up to incident photon energies of 1.4 GeV, respectively up to
photon-nucleon invariant masses up to 1.9 GeV. Total cross sections, angular
distributions, invariant-mass distributions of the $\pi\eta$ and meson-nucleon
pairs, and beam-helicity asymmetries have been measured for the reactions
$\gamma p\rightarrow p\pi^0\eta$, $\gamma n\rightarrow n\pi^0\eta$, $\gamma
p\rightarrow n\pi^+\eta$, and $\gamma n\rightarrow p\pi^-\eta$ from nucleons
bound inside the deuteron. For the $\gamma p$ initial state data for free
protons have also been analyzed. Finally, the total cross sections for
quasi-free production of $\pi^0\eta$ pairs from nucleons bound in $^3$He nuclei
have been investigated in view of final state interaction (FSI) effects. The
experiments were performed at the tagged photon beam facility of the Mainz MAMI
accelerator using an almost $4\pi$ covering electromagnetic calorimeter
composed of the Crystal Ball and TAPS detectors. The shapes of all differential
cross section data and the asymmetries are very similar for protons and
neutrons and agree with the conjecture that the reactions are dominated by the
sequential $\Delta^{\star}3/2^-\rightarrow\eta\Delta(1232)\rightarrow\pi\eta N$
decay chain, mainly with $\Delta(1700)3/2^-$ and $\Delta(1940)3/2^-$. The
ratios of the magnitude of the total cross sections also agree with this
assumption. However, the absolute magnitudes of the cross sections are reduced
by FSI effects with respect to free proton data.

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The categories of this paper are: atom-ph
28
The categories of this paper are: alg-geom
31
The categories of this paper are: ao-sci
10
The categories of this paper are: q-bio
25
The categories of this paper are: patt-sol
4
The categories of this paper are: cond-mat
35
The categories of this paper are: mtrl-th
21
The categories of this paper are: adap-org
13
The categories of this paper are: quant-ph
37
The categories of this paper are: supr-con
30
The categories of this paper are: q-alg
27
The categories of this paper are: comp-gas
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The categories of this paper are: dg-ga
22
The categories of this paper are: chao-dyn
2
The categories of this paper are: math
7
The categories of this paper are: hep-th