A direct measurement of the invisible width of the Z from single photon counting

D. Buskulic, I. De Bonis, D. Decamp, P. Ghez, C. Goy, J. P. Lees, M. N. Minard, B. Pietrzyk, F. Ariztizabal, P. Comas, J. M. Crespo, M. Delfino, I. Efthymiopoulos, E. Fernandez, M. Fernandez-Bosman, V. Gaitan, Ll Garrido, T. Mattison, A. Pacheco, C. PadillaA. Pasual, D. Creanza, M. de Palma, A. Farilla, G. Iaselli, G. Maggi, S. Natali, S. Nuzzo, M. Quattromini, A. Ranieri, G. Raso, F. Romano, F. Ruggieri, G. Selvaggi, L. Silvestris, P. Tempesta, G. Zito, Y. Chai, H. Hu, D. Huang, X. Huang, J. Lin, T. Wang, Y. Xie, D. Xu, R. Xu, J. Zhang, L. Zhang, W. Zhao, E. Blucher, G. Bonvicini, J. Boudreau, D. Casper, H. Drevermann, R. W. Forty, G. Ganis, C. Gay, R. Hagelberg, J. Harvey, J. Hilgart, R. Jacobsen, B. Jost, J. Knobloch, I. Lehraus, T. Lohse, M. Maggi, C. Markou, M. Martinez, P. Mato, H. Meinhard, A. Minten, A. Miotto, R. Miquel, H. G. Moser, P. Palazzi, J. R. Pater, J. A. Perlas, J. F. Pusztaszeri, F. Ranjard, G. Redlinger, L. Rolandi, J. Rothberg, T. Ruan, M. Saich, D. Schlatter, M. Schmelling, F. Sefkow, W. Tejessy, I. R. Tomalin, R. Veenhof, H. Wachsmuth, S. Wasserbaech, W. Wiedenmann, T. Wildish, W. Witzeling, J. Wotschack, Z. Atjaltouni, F. Badaud, M. Bardadin-Otwinowska, R. El Fellous

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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.). © 1993.
Original languageEnglish
Pages (from-to)520-534
JournalPhysics Letters B
Volume313
Issue number3-4
DOIs
Publication statusPublished - 2 Sep 1993

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