Production of radioactive isotopes through cosmic muon spallation in KamLAND

Abstract

Radioactive isotopes produced through cosmic muon spallation are a background for rare-event detection in ν detectors, double-β-decay experiments, and dark-matter searches. Understanding the nature of cosmogenic backgrounds is particularly important for future experiments aiming to determine the pep and CNO solar neutrino fluxes, for which the background is dominated by the spallation production of 11 C. Data from the Kamioka liquid-scintillator antineutrino detector (KamLAND) provides valuable information for better understanding these backgrounds, especially in liquid scintillators, and for checking estimates from current simulations based upon MUSIC, FLUKA, and GEANT4. Using the time correlation between detected muons and neutron captures, the neutron production yield in the KamLAND liquid scintillator is measured to be Y n = (2.8 ± 0.3) × 10 −4 µ −1 g −1 cm 2 . For other isotopes, the production yield is determined from the observed time correlation related to known isotope lifetimes. We find some yields are inconsistent with extrapolations based on an accelerator muon beam experiment.

Improved measurements of the neutrino mixing angle θ 13 with the Double Chooz detector

“…The error includes the systematic uncertainties evaluated by varying the cuts on d, values of λ Li and binning of ∆T µ distribution. In addition, the impact of 8 He is also evaluated assuming a fraction of 8 ± 7 % based on the measurement by KamLAND [34], rescaled to account for the different energies of the cosmic muons illuminating the two experiments, and taken into account in the rate estimate and its uncertainty. In the standard IBD selection, Li candidates are rejected by the Li+He veto.…”

Cosmogenic neutron production at Daya Bay

“…The predicted yields at Daya Bay from GEANT4 and FLUKA are also shown. Experimental data is shown from Hertenberger [6], Boehm [8], Aberdeen Tunnel [10], KamLAND [4], LVD [2] with corrections from [35], and Borexino [3]. The solid line shows the power-law fit to the global data set including Daya Bay.…”

“…Muon-induced neutron and isotope production has been studied with the CERN Super Proton Synchrotron (SPS) muon beam in 2000 [1]. Studies on neutron and isotope yields in various materials in underground detectors have been performed by the INFN largevolume detector (LVD) [2], Borexino [3], KamLAND [4], and many others [5][6][7][8][9][10][11][12]. This paper reports a measurement of the neutron production rate in liquid scintillator at three different values of average muon energy by the Daya Bay Reactor Neutrino Experiment, an underground lowbackground neutrino oscillation experiment.…”

SEARCH FOR EXTRATERRESTRIAL ANTINEUTRINO SOURCES WITH THE KamLAND DETECTOR

“…The delayed event in the DC pair is generated by a 2.2 MeV γ -ray produced when the neutron captures on a proton. The mean neutron capture time is (207.5 ± 2.8) μs (Abe et al 2010). The inverse beta-decay cross-section is well approximated at the first order in 1/M (Vogel & Beacom 1999), where M is the nucleon mass.…”

“…The overall vertex reconstruction resolution is ∼12 cm / √ E (MeV) and energy resolution is 6.4%/ √ E (MeV). Energy reconstruction of positrons with E p > 7.5 MeV (i.e., E ν e > 8.3 MeV) is verified using tagged 12 B β − -decays (τ = 29.1 ms and Q = 13.4 MeV) generated via muon spallation (Abe et al 2010).…”