Spectroscopy of geoneutrinos from 2056 days of Borexino data

We report an improved geoneutrino measurement with Borexino from 2056 days of data taking. The present exposure is (5.5±0.3)×1031  proton×yr. Assuming a chondritic Th/U mass ratio of 3.9, we obtain 23.7+6.5−5.7(stat)+0.9−0.6(sys) geoneutrino events. The null observation of geoneutrinos with Borexino alone has a probability of 3.6×10−9 (5.9σ). A geoneutrino signal from the mantle is obtained at 98% C.L. The radiogenic heat production for U and Th from the present best-fit result is restricted to the range 23–36 TW, taking into account the uncertainty on the distribution of heat producing elements inside the Earth.