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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References
S.Weinberg: Phys. Rev. Lett. 19 (1967) 1264; A. Salam: Elementary particle theory, p. 367. N. Svartholm (ed.). Stockholm: Almquist and Wiksells 1969; S.L. Glashow, J. Iliopoulos, L. Maiani: Phys. Rev. D2 (1970) 1285
D. Yu. Bardin et al.: Berlin-Zeuthen preprint PHE 89-19, 1989
OPAL collaboration: contribution by T. Mori, 25th International conference on high energy physics, Singapore 1990; OPAL Coll.: M. Z. Akrawy et al.: Phys. Lett. B240 (1990) 497
C. Jarlskog: Phys. Lett. B 241 (1990) 579
ALEPH Coll.: D. Decamp et al.: Z. Phys. C—Particles and Fields 48 (1990) 365; DELPHI Coll.: P. Abreu et al.: contribution to 25th International conference on high energy physics, Singapore, CERN-PPE/90-119, 1990; L3 Coll.: B. Adeva et al.: Phys. Lett. B249 (1990) 341
A.D. Dolgov, L.B. Okun, V.I. Zakharov: Nucl. Phys. B41 (1972) 197; E. Ma, J. Okada: Phys. Rev. Lett. 41 (1978) 287; K.J.F. Gaemers, R. Gastmans, F.M. Renard: Phys. Rev. D19 (1979) 1605; G. Barbiellini, B. Richter, J.L. Siegrist: Phys. Lett. 106B (1981) 414
L. Trentadue et al.: In: Z. Physics at LEP1. G. Altarelli (ed.), CERN 89-08 (1989) 129
MAC Coll.: W.T. Ford et al.: Phys. Rev. D33 (1986) 3472; H. Wu: Ph.D. Thesis, Universität Hamburg, 1986; CELLO Coll.: H.-J. Behrend et al.: Phys. Lett. 215B (1988) 186; ASP Coll.: C. Hearty et al.: Phys. Rev. D39 (1989) 3207
VENUS Coll.: K. Abe et al.: Phys. Lett. 232B (1989) 431
OPAL Coll.: K. Ahmet et al.: submitted to Nucl. Instr. and Meth., CERN-PPE/90-114, August 1990 xx
J. Allison et al.: Comp. Phys. Comm. 47 (1987) 55; R. Brun et al.: GEANT 3, Report DD/EE/84-1, CERN (1989)
D. Karlen: Nucl. Phys. B289 (1987) 23
R. Battacharya, J. Smith, G. Grammer: Phys. Rev. D15 (1977) 3267; J. Smith, J.A.M. Vermaseren, G. Grammen. Phys. Rev. D15 (1977) 3280
OPAL Coll.: M.Z. Akrawy et al.: submitted to Phys. Lett., CERN-PPE/90-189, December 1990
R. Miquel, C. Mana, M. Martinez: Z. Phys. C — Particles and Fields 48 (1990) 309; F.A. Berends et al.: Nucl. Phys. B301 (1988) 583
F.A. Berends, R. Kleiss: Nucl. Phys. B186 (1981) 22
W.G.J. Langeveld: Ph.D. Thesis, Rÿksuniversiteit Utrecht, 1986.
S. Jadach et al.: to be published in Comp. Phys. Comm.; xx T. Sjöstrand, M. Bengtsson: Comp. Phys. Comm. 43 (1987) 367; G. Marchesini, B.R. Webber; Nucl. Phys. B310 (1988) 461
O. Nicrosini, L. Trentadue: Nucl. Phys. B318 (1989) 1
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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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DOI: https://doi.org/10.1007/BF01551449