Muon-induced neutron and pion production in an organic liquid scintillator at a shallow depth

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Abstract
The production of fast neutrons and pions by inelastic interactions of cosmic-ray muons in an organic liquid scintillator has been investigated. A detector filled with 190 liters of a 0.09% gadolinium-loaded liquid scintillator was installed in the Stanford Underground Facility, at an underground depth of approximately 20 meters water equivalent. The detector served as the target material for hadron production. Our measurements find a single-neutron production yield of (4.3±0.3±0.8)×10−5 neutrons per muon g/cm2 and a double-neutron production yield of (1.6±0.2±0.5)×10−5 double neutrons per muon g/cm2. We measured a π+ production yield of (3.5±0.2±0.7)×10−6 pions per muon g/cm2. Nearly all the π+ produced were accompanied by neutrons. These yields were dependent on the energy threshold of the muon trigger, revealing an enhancement associated with hadronic showers initiated by muons. The production yield due to nonshowering muons was lower: 2×10−5 neutrons per muon g/cm2, with a single-to-double neutron multiplicity ratio of roughly 4:1. The nonshowering muon π+ production probability was 2.5×10−6 pions per muon g/cm2, with about half of these nonshowering π+ events accompanied by neutrons.

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