The cross-section for e+e− -> hadrons in the vicinity of the Z boson peak has been measured with the ALEPH detector at the CERN Large Electron Positron collider, LEP. Measurements of the Z mass, M_Z= (91.174 +/- 0.070) GeV, the Z width Gamma_Z=(2.68 +/- 0.15) GeV, and of the peak hadronic cross-section, Sigma_hadpeak=(29.3 +/- 1.2) nb, are presented. With the constraints of the standard electroweak model, the number of light neutrino species is found to be Nnu=3.27+/- 0.30. this results rules out of the possibility of a fourth type of light neutrino at 98% CL.
Determination of the Number of Light Neutrino Species
CIOCCI, MARIA AGNESE;G. BATIGNANI;FERRANTE, ISIDORO;FIDECARO, FRANCESCO;F. FORTI;MESSINEO, ALBERTO MARIA;TONELLI, GUIDO EMILIO;G. TRIGGIANI;
1989-01-01
Abstract
The cross-section for e+e− -> hadrons in the vicinity of the Z boson peak has been measured with the ALEPH detector at the CERN Large Electron Positron collider, LEP. Measurements of the Z mass, M_Z= (91.174 +/- 0.070) GeV, the Z width Gamma_Z=(2.68 +/- 0.15) GeV, and of the peak hadronic cross-section, Sigma_hadpeak=(29.3 +/- 1.2) nb, are presented. With the constraints of the standard electroweak model, the number of light neutrino species is found to be Nnu=3.27+/- 0.30. this results rules out of the possibility of a fourth type of light neutrino at 98% CL.File in questo prodotto:
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