Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Sub-threshold states in $^{19}$Ne relevant to
  $^{18}$F(p,$\alpha$)$^{15}$O   Classical novae result from thermonuclear explosions producing several
$\gamma$-ray emitters which are prime targets for satellites observing in the
MeV range. The early 511 keV gamma-ray emission depends critically on the
$^{18}$F(p,$\alpha$)$^{15}$O reaction rate which, despite many experimental and
theoretical efforts, still remains uncertain. One of the main uncertainties in
the $^{18}$F(p,$\alpha$)$^{15}$O reaction rate is the contribution in the Gamow
window of interference between sub-threshold $^{19}$Ne states and known broad
states at higher energies. Therefore the goal of this work is to clarify the
existence and the nature of these sub-threshold states. States in the $^{19}$Ne
compound nucleus were studied at the Tandem-ALTO facility using the
$^{19}$F($^3$He,t)$^{19}$Ne charge exchange reaction. Tritons were detected
with an Enge Split-pole spectrometer while decaying protons or
$\alpha$-particles from unbound $^{19}$Ne states were collected, in
coincidence, with a double-sided silicon strip detector array. Angular
correlations were extracted and constraints on the spin and parity of decaying
states established. The coincidence yield at $E_x$ = 6.29 MeV was observed to
be high spin, supporting the conclusion that it is indeed a doublet consisting
of high spin and low spin components. Evidence for a broad, low spin state was
observed around 6 MeV. Branching ratios were extracted for several states above
the proton threshold and were found to be consistent with the literature.
R-matrix calculations show the relative contribution of sub-threshold states to
the astrophysically important energy region above the proton threshold. The
levels schemes of $^{19}$Ne and $^{19}$F are still not sufficiently well known
and further studies of the analogue assignments are needed. The tentative broad
state at 6 MeV may only play a role if the reduced proton width is large.

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The categories of this paper are: q-alg
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The categories of this paper are: alg-geom
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The categories of this paper are: stat
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The categories of this paper are: atom-ph
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The categories of this paper are: cmp-lg
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The categories of this paper are: comp-gas
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The categories of this paper are: plasm-ph
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The categories of this paper are: cond-mat
0
The categories of this paper are: hep-ph
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The categories of this paper are: q-bio
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The categories of this paper are: nucl-th
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The categories of this paper are: gr-qc
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The categories of this paper are: chao-dyn
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The categories of this paper are: adap-org
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The categories of this paper are: bayes-an
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The categories of this paper are: solv-int