Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Observation of exotic meson production in the reaction $ \pi^{-} p \to
  \eta^{\prime} \pi^- p$ at 18 GeV/c   An amplitude analysis of an exclusive sample of 5765 events from the reaction
$\pi^{-} p \to \eta^{\prime} \pi^- p$ at 18 GeV/c is described. The
$\eta^{\prime} \pi^-$ production is dominated by natural parity exchange and by
three partial waves: those with $J^{PC} = 1^{-+}, 2^{++},$ and $4^{++}$. A
mass-dependent analysis of the partial-wave amplitudes indicates the production
of the $a_2(1320)$ meson as well as the $a_4(2040)$ meson, observed for the
first time decaying to $\eta^{\prime}\pi^-$. The dominant, exotic
(non-$q\bar{q}) $ $1^{-+}$ partial wave is shown to be resonant with a mass of
$1.597 \pm 0.010^{+0.045}_{-0.010}$ GeV/c^2 and a width of $0.340 \pm 0.040 \pm
0.050$ GeV/c^2 . This exotic state, the $\pi_1(1600)$, is produced with a $t$
dependence which is different from that of the $a_2(1320)$ meson, indicating
differences between the production mechanisms for the two states.

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The categories of this paper are: patt-sol
14
The categories of this paper are: math-ph
34
The categories of this paper are: chem-ph
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The categories of this paper are: dg-ga
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The categories of this paper are: plasm-ph
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The categories of this paper are: atom-ph
6
The categories of this paper are: astro-ph
0
The categories of this paper are: hep-ph
36
The categories of this paper are: cmp-lg
5
The categories of this paper are: gr-qc
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The categories of this paper are: econ
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The categories of this paper are: stat
13
The categories of this paper are: quant-ph
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The categories of this paper are: acc-phys
10
The categories of this paper are: q-bio
35
The categories of this paper are: mtrl-th