Ortho-positronium observation in the double chooz experiment

Abe, Y, Dos Anjos, J C, Barriere, J C, Baussan, E, Bekman, I, Bergevin, M, Bezerra, T J C, Bezrukov, L, Blucher, E, Buck, C, Busenitz, J, Cabrera, A, Caden, E, Camilleri, L, Carr, R, The Double Chooz collaboration, and others, (2014) Ortho-positronium observation in the double chooz experiment. Journal of High Energy Physics, 2014. a32 1-14. ISSN 1126-6708

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The Double Chooz experiment measures the neutrino mixing angle θ13 by detecting reactor ¯νe 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 orthopositronium (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 3.68 ns ± 0.17 ns (sys.) ± 0.15 ns (stat.) respectively, in agreement with the results obtained with a dedicated positron annihilation lifetime spectroscopy setup.

Item Type: Article
Keywords: Neutrino Detectors and Telescopes
Schools and Departments: School of Mathematical and Physical Sciences > Physics and Astronomy
SWORD Depositor: Mx Elements Account
Depositing User: Mx Elements Account
Date Deposited: 16 Nov 2021 10:06
Last Modified: 16 Nov 2021 10:15
URI: http://sro.sussex.ac.uk/id/eprint/102902

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