Cosmogenic Backgrounds in Borexino at 3800 m water-equivalent depth

TL;DR

This paper measures and analyzes muon-induced backgrounds in the Borexino detector at Gran Sasso, providing experimental data on neutron yields, isotope production, and muon-neutron correlations, and compares results with Monte Carlo simulations.

Contribution

It offers the first detailed measurements of cosmogenic backgrounds in Borexino and evaluates the accuracy of simulation models like Fluka and Geant4.

Findings

Muon-induced neutron yield Yn = (3.10±0.11)×10^{-4} n/μ(g/cm^2)

Average muon-neutron distance λ = (81.5±2.7)cm

General agreement between data and simulations, with some discrepancies in 11C yield

Abstract

The solar neutrino experiment Borexino, which is located in the Gran Sasso underground laboratories, is in a unique position to study muon-induced backgrounds in an organic liquid scintillator. In this study, a large sample of cosmic muons is identified and tracked by a muon veto detector external to the liquid scintillator, and by the specific light patterns observed when muons cross the scintillator volume. The yield of muon-induced neutrons is found to be Yn =(3.10+-0.11)10-4 n/({\mu} (g/cm2)). The distance profile between the parent muon track and the neutron capture point has the average value {\lambda} = (81.5 +- 2.7)cm. Additionally the yields of a number of cosmogenic radioisotopes are measured for 12N, 12B, 8He, 9C, 9Li, 8B, 6He, 8Li, 11Be, 10C and 11C. All results are compared with Monte Carlo simulation predictions using the Fluka and Geant4 packages. General agreement between data and simulation is observed for the cosmogenic production yields with a few exceptions, the most prominent case being 11C yield for which both codes return about 50% lower values. The predicted {\mu}-n distance profile and the neutron multiplicity distribution are found to be overall consistent with data.