Study of the muon-induced neutron background with the LVD detector

Abstract

LVD [1] is a neutrino telescope located in the Hall A of the Gran Sasso INFN laboratory; it consists of an array of 840 scintillator counters for a total mass of about 1000 tons. The detector is also equipped with a tracking system to reconstruct muons. Neutrons can be recognized through their interactions on protons which originate two subsequent pulses in a scintillator counter: a prompt signal due to the proton and a delayed signal due to the 2.2 MeV gamma ray from the neutron capture; the time delay distribution between the two pulses has an exponential shape with mean value 180 μs. The double signature can be seen in LVD by means of two different discrimination threshold; a high energy threshold, at about 7 MeV for the external counters (43%) and at about 4 MeV for the internal ones (57%), better shielded, for the proton recoil; a low energy threshold, at about 1 MeV and active for 1 ms after the high one, to allow the detection of the γ from the neutron capture. Taking into account the energy transfer in the interaction between neutron and proton, the proton quenching and the value of the high energy threshold of the detector, the neutrons with the double signature have energies greater than about 20 MeV. 3. Analysis and Results