Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Can a protophobic vector boson explain the ATOMKI anomaly?   In 2016, the ATOMKI collaboration announced [PRL {\bf 116}, 042501 (2016)]
observing an unexpected enhancement of the $e^+-e^-$ pair production signal in
one of the $^8$Be nuclear transitions induced by an incident proton beam on a
$^7$Li target. Many beyond-standard-model physics explanations have
subsequently been proposed. One popular theory is that the anomaly is caused by
the creation of a protophobic vector boson ($X$) with a mass around 17 MeV
[e.g., PRL\ {\bf 117}, 071803 (2016)] in the nuclear transition. We study this
hypothesis by deriving an isospin relation between photon and $X$ couplings to
nucleons. This allows us to find simple relations between protophobic
$X$-production cross sections and those for measured photon production. The net
result is that $X$ production is dominated by direct transitions induced by
$E1^X$ and $L1^X$ (transverse and longitudinal electric dipoles) and $C1^X$
(charge dipole) without going through any nuclear resonance (i.e.
Bremsstrahlung radiation) with a smooth energy dependence that occurs for all
proton beam energies above threshold. This contradicts the experimental
observations and invalidates the protophobic vector boson explanation.

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The categories of this paper are: eess
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The categories of this paper are: bayes-an
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The categories of this paper are: nlin
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The categories of this paper are: acc-phys
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The categories of this paper are: alg-geom
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The categories of this paper are: chem-ph
2
The categories of this paper are: math
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The categories of this paper are: ao-sci
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The categories of this paper are: solv-int
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The categories of this paper are: econ
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The categories of this paper are: hep-lat
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The categories of this paper are: quant-ph
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The categories of this paper are: chao-dyn
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The categories of this paper are: comp-gas
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The categories of this paper are: physics
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The categories of this paper are: adap-org