Search for high energy 5.5 MeV solar axions with the complete Borexino dataset

A search for solar axions and axion-like particles produced in the p+d→ ³He+A~(5.5 ~MeV) p + d → 3 He + A ( 5.5 MeV ) reaction was performed using the complete dataset of the Borexino detector (3995 days of measurement live-time). The following interaction processes have been considered: axion decay into two photons (A→ 2γ ) ( A → 2 γ ) , inverse Primakoff conversion on nuclei (A+Z→ γ +Z ( A + Z → γ + Z ), the Compton conversion of axions to photons (A+e→ e+γ ) ( A + e → e + γ ) and the axio-electric effect (A+e+Z→ e+Z ( A + e + Z → e + Z ). Model-independent limits on product of axion–photon ( gAγ g A γ ), axion–electron ( gAe g Ae ), and isovector axion–nucleon ( g3AN g 3 A N ) couplings are obtained: |gAγ× g3AN| ≤ 2.3× 10⁻¹¹ GeV⁻¹ | g A γ × g 3 A N | ≤ 2.3 × 10 - 11 GeV - 1 and |gAe× g3AN| ≤ 1.9× 10⁻¹³