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http://dx.doi.org/10.1088/1475-7516/2013/08/049

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 Y_n = (3.10±0.11)10⁻⁴ n/(μ(g/cm²)). The distance profile between the parent muon track and the neutron capture point has the average value λ = (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 μ-n distance profile and the neutron multiplicity distribution are found to be overall consistent with data.

doi:10.1088/1475-7516/2012/05/015

G. Bellini et al. (Borexino Collaboration) M. Wójcik, G. Zuzel, M. Misiaszek

Download http://iopscience.iop.org/1475-7516/2012/05/015

Abstract
We have measured the muon flux at the underground Gran Sasso National Laboratory (3800 m w.e.) to be (3.41±0.01)⋅10⁻⁴m⁻²s⁻¹ using four years of Borexino data. A modulation of this signal is observed with a period of (366±3) days and a relative amplitude of (1.29±0.07)%. The measured phase is (179±6) days, corresponding to a maximum on the 28^th of June. Using the most complete atmospheric data models available, muon rate fluctuations are shown to be positively correlated with atmospheric temperature, with an effective coefficient α_T = 0.93±0.04. This result represents the most precise study of the muon flux modulation for this site and is in good agreement with expectations.