A refined reference Earth model for the geoneutrino studies at Borexino

First experimental measurements of geoneutrinos by Borexino and KamLAND collaborations have revealed its importance to constrain the radiogenic heat production in the Earth and to test various geological paradigms. The geoneutrino flux is determined by amount and distribution of heat producing elements (HPEs: U, Th and K) in the Earth’s interior. With the aim of studying the signal at Borexino a global model of the Earth and a local model of the crust around Gran Sasso National Laboratories (LNGS) were built. Thickness of the global crust was calculated by combining three existing geophysical models and it yields an average crustal thickness of 34.4±4.1 km in the continents and 8.0±2.7 km in the oceans. In situ seismic velocity provided by CRUST 2.0 allowed to estimate the average composition of the deep continental crust by using updated compositional databases for amphibolite and granulite facies rocks and ultrasonic velocities measurements. Mantle was divided into three reservoirs of HPEs. Geophysical data presented in the literature is used to build a three dimensional model of the area around LNGS. Amount HPE in various crustal reservoirs is analyzed by collecting and measuring composition of representative rocks. Monte Carlo simulation is used to predict the signal and to propagate the asymmetrical uncertainties. The predicted signal at Borexino is equal to 35.5(+4.4 -2.9)TNU. 7 TNU reduction of the signal is caused by a gradual refining of the previous models and is discussed in the text. A new compilation of operating experience of commercial nuclear reactors all around the world was built. It is used to evaluate the antineutrino background from nuclear reactors at Borexino with the time resolution of one month in the last four years.