APS physics logoPositronium signature in organic liquid scintillators for neutrino experiments
D. Franco, G. Consolati, and D. Trezzi
Phys. Rev. C 83, 015504
Published 27 January 2011 [6 pages] doi: 10.1103/PhysRevC.83.015504
Preprint: arXiv:1011.5736


Electron antineutrinos are commonly detected in liquid scintillator experiments via inverse β decay by looking at the coincidence between the reaction products: neutrons and positrons. Prior to positron annihilation, an electron-positron pair may form an orthopositronium (o-Ps) state, with a mean lifetime of a few nanoseconds.  Even if the o-Ps decay is speeded up by spin-flip or pick-off effects, it may introduce distortions in the photon emission time distribution, crucial for position reconstruction and pulse shape discrimination algorithms in antineutrino experiments. Reversing the problem, the o-Ps-induced time distortion represents a new signature for tagging antineutrinos in liquid scintillator.  In this article, we report the results of measurements of the o-Ps formation probability and lifetime for the most used solvents for organic liquid scintillators in neutrino physics (pseudocumene, linear alkyl benzene, phenylxylylethane, and dodecane).  We characterize also a mixture of pseudocumene +1.5 g/l of 2,5-diphenyloxazole, a fluor acting as wavelength shifter.  In the second part of the article, we demonstrate that the o-Ps-induced distortion of the scintillation photon emission time distributions represent an optimal signature for tagging positrons on an event by event basis, potentially enhancing the antineutrino detection.


Positronium signature in organic liquid scintillators for neutrino experiments
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