Search for Solar Axions Produced in $p(d,{}^3\mathrm{He})\mathrm{A}$ Reaction with Borexino Detector

Abstract

A search for 5.5-MeV solar axions produced in the $p+d\to {}^3\mathrm{He}+\mathrm{A}(5.5\mathrm{MeV})$ reaction was performed using the Borexino detector. The Compton conversion of axions to photons, $\mathrm{A}+e\to e+\gamma$; the axio-electric effect, $\mathrm{A}+e+Z\to e+Z$; the decay of axions into two photons, $\mathrm{A}\to 2\gamma$; and inverse Primakoff conversion on nuclei, $\mathrm{A}+Z\to \gamma +Z$, are considered. Model independent limits on axion-electron ($g_{Ae}$), axion-photon ($g_{A\gamma }$), and isovector axion-nucleon ($g_{3AN}$) couplings are obtained: $|g_{Ae}\times g_{3AN}|\le 5.5\times 10^{-13}$ and $|g_{A\gamma }\times g_{3AN}|\le 4.6\times 10^{-11}{\mathrm{GeV}}^{-1}$ at $m_A<$ 1 MeV (90% c.l.). These limits are 2-4 orders of magnitude stronger than those obtained in previous laboratory-based experiments using nuclear reactors and accelerators.

Comments: 11 pages, 7 figures, submitted to Phys.Rev.D