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A direct measurement of theZ 0 invisible width by single photon counting

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Zeitschrift für Physik C Particles and Fields

Abstract

The OPAL detector at LEP is used to measure the branching ratio of theZ 0 into invisible particles by measuring the cross section of single photon events ine + e collisions at centre-of-mass energies near theZ 0 resonance. In a data sample of 5.3 pb−1, we observe 73 events with single photons depositing more than 1.5 GeV in the electromagnetic calorimeter, with an expected background of 8±2 events not associated with invisibleZ 0 decay. With this data we determine theZ 0 invisible width to be 0.50±0.07±0.03 GeV, where the first error is statistical and the second systematic. This corresponds to 3.0±0.4±0.2 light neutrino generations in the Standard Model.

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OPAL Collaboration., Akrawy, M.Z., Alexander, G. et al. A direct measurement of theZ 0 invisible width by single photon counting. Z. Phys. C - Particles and Fields 50, 373–384 (1991). https://doi.org/10.1007/BF01551449

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