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(5.5MeV) 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), inverse Primakoff conversion on nuclei (A+Z→γ+Z), the Compton conversion of axions to photons (A+e→e+γ) and the axio-electric effect (A+e+Z→e+Z). Model-independent limits on product of axion–photon (gAγ), axion–electron (gAe), and isovector axion–nucleon (g3AN) couplings are obtained: |gAγ×g3AN|≤2.3×10-11GeV-1 and |gAe×g3AN|≤1.9×10-13 at mA< 1 MeV (90% c.l.). The Borexino results exclude new large regions of gAγ, and gAe coupling constants and axion masses mA, and leads to constraints on the products |gAγ×mA| and |gAe×mA| for the KSVZ- and the DFSZ-axion models.