Ortho-positronium observation in the Double Chooz experiment
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Abe-2014-Ortho-positronium ob.pdf
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Author(s)
Double Chooz collaboration
Spitz, Joshua B.
Winslow, Lindley
Conrad, Janet Marie
Terao, Kazuhiro
Date Issued
October 2014
Journal
Journal of High Energy Physics
Publisher
Springer-Verlag Berlin Heidelberg
Citation
Abe, Y., J. C. dos Anjos, J. C. Barriere, E. Baussan, I. Bekman, M. Bergevin, T. J. C. Bezerra, et al. “Ortho-Positronium Observation in the Double Chooz Experiment.” J. High Energ. Phys. 2014, no. 10 (October 2014).
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Final published version
Abstract
The Double Chooz experiment measures the neutrino mixing angle θ13 by detecting reactor ν¯e via inverse beta decay. The positron-neutron space and time coincidence allows for a sizable background rejection, nonetheless liquid scintillator detectors would profit from a positron/electron discrimination, if feasible in large detector, to suppress the remaining background. Standard particle identification, based on particle dependent time profile of photon emission in liquid scintillator, can not be used given the identical mass of the two particles. However, the positron annihilation is sometimes delayed by the ortho-positronium (o-Ps) metastable state formation, which induces a pulse shape distortion that could be used for positron identification. In this paper we report on the first observation of positronium formation in a large liquid scintillator detector based on pulse shape analysis of single events. The o-Ps formation fraction and its lifetime were measured, finding the values of 44% ± 12% (sys.) ± 5% (stat.) and 3.68ns ± 0.17ns (sys.) ± 0.15ns (stat.) respectively, in agreement with the results obtained with a dedicated positron annihilation lifetime spectroscopy setup.
MIT Department
Massachusetts Institute of Technology. Department of Physics
Massachusetts Institute of Technology. Laboratory for Nuclear Science
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DOI of Published Version
https://doi.org/10.1007/JHEP10(2014)032
