The ALEPH detector at LEP is used to study single photon events in e+e- collisions at the Z resonance. In a total data sample of 15.7 pb−1 taken in 1990 and 1991 scanning the resonance, 400 events were recorded where each has a single deposition of more than 1.5 GeV measured in the polar angular region | cosθγ | < 0.74 of the electromagnetic calorimeter. It is shown that this number of events cab be accounted for by known processes. After subtraction of background events, the invisible width of the Z is determined to be 45 ± 34(stat.) ± 34(syst.) MeV. Using Z. resonance parameters derived by ALEPH, the corresponding number oflight neutrino generations is found to be 2.68 ± 0.20(stat.) ± 0.20(syst.).
A direct measurement of the invisible width of the Z from single photon counting / ALEPH Collaboration;D. Buskulic;I. De Bonis;D. Decamp;P. Ghez;C. Goy;J. -P. Lees;M. -N. Minard;B. Pietrzyk;F. Ariztizabal. - In: PHYSICS LETTERS. SECTION B. - ISSN 0370-2693. - ELETTRONICO. - 313:(1993), pp. 520-534. [10.1016/0370-2693(93)90027-F]
A direct measurement of the invisible width of the Z from single photon counting
FOCARDI, ETTORE;
1993
Abstract
The ALEPH detector at LEP is used to study single photon events in e+e- collisions at the Z resonance. In a total data sample of 15.7 pb−1 taken in 1990 and 1991 scanning the resonance, 400 events were recorded where each has a single deposition of more than 1.5 GeV measured in the polar angular region | cosθγ | < 0.74 of the electromagnetic calorimeter. It is shown that this number of events cab be accounted for by known processes. After subtraction of background events, the invisible width of the Z is determined to be 45 ± 34(stat.) ± 34(syst.) MeV. Using Z. resonance parameters derived by ALEPH, the corresponding number oflight neutrino generations is found to be 2.68 ± 0.20(stat.) ± 0.20(syst.).
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