From measurements of the cross sections for e+ e - --> hadrons and the cross sections and forward-backward charge-asymmetries for e+ e- --> e+ e-, mu+ mu- and tau+ tau- at several centre-of-mass energies around the Z0 pole with the DELPHI apparatus, using approximately 150000 hadronic and leptonic events from 1989 and 1990, one determines the following Z0 parameters: the mass and total width M(Z) = 91.177 +/- 0.022 GeV, GAMMA(Z) = 2.465 +/- 0.020 GeV, the hadronic and leptonic partial widths GAMMA(h) = 1.726 +/- 0.019 GeV, GAMMA(t) = 83.4 +/- 0.8 MeV, the invisible width GAMMA(inv) = 488 +/- 17 MeV, the ratio of hadronic over leptonic partial widths R(Z)z = 20.70 +/- 0.29 and the Born level hadronic peak cross section sigma-0 = 41.84 +/- 0.45 nb. A flavour-independent measurement of the leptonic cross section gives very consistent results to those presented above (GAMMA(t) = 83.7 +/- 0.8 MeV). From these results the number of light neutrino species is determined to be N(nu) = 2.94 +/0. 10. The individual leptonic widths obtained are: GAMMA(e) = 82.4 +/- 1.2 MeV, GAMMA(mu) = 86.9 +/- 2.1 MeV and GAMMA(tau) = 82.7 +/- 2.4 MeV. Assuming universality, the squared vector and axial-vector couplings of the Z0 to charged leptons are: VBAR(t)2 = 0.0003 +/- 0.0010 and ABAR(l)2 = 0.2508 +/- 0.0027. These values correspond to the electroweak parameters: rho(eff) = 1.003 +/- 0.011 and sin2-theta(W)eff = 0.241 +/- 0.009. Within the Minimal Standard Model (MSM), the results can be expressed in terms of a single parameter: sin2-theta(W)MSBAR = 0.2338 +/- 0.0027. All these values are in good agreement with the predictions of the MSM. Fits yield 43 < m(top) < 215 GeV at the 95% level. Finally, the measured values of GAMMA(Z) and GAMMA(inv), are used to derive lower mass bounds for possible new particles.

DETERMINATION OF Z0 RESONANCE PARAMETERS AND COUPLINGS FROM ITS HADRONIC AND LEPTONIC DECAYS

DE LOTTO, Barbara;SCURI, Fabrizio;
1991-01-01

Abstract

From measurements of the cross sections for e+ e - --> hadrons and the cross sections and forward-backward charge-asymmetries for e+ e- --> e+ e-, mu+ mu- and tau+ tau- at several centre-of-mass energies around the Z0 pole with the DELPHI apparatus, using approximately 150000 hadronic and leptonic events from 1989 and 1990, one determines the following Z0 parameters: the mass and total width M(Z) = 91.177 +/- 0.022 GeV, GAMMA(Z) = 2.465 +/- 0.020 GeV, the hadronic and leptonic partial widths GAMMA(h) = 1.726 +/- 0.019 GeV, GAMMA(t) = 83.4 +/- 0.8 MeV, the invisible width GAMMA(inv) = 488 +/- 17 MeV, the ratio of hadronic over leptonic partial widths R(Z)z = 20.70 +/- 0.29 and the Born level hadronic peak cross section sigma-0 = 41.84 +/- 0.45 nb. A flavour-independent measurement of the leptonic cross section gives very consistent results to those presented above (GAMMA(t) = 83.7 +/- 0.8 MeV). From these results the number of light neutrino species is determined to be N(nu) = 2.94 +/0. 10. The individual leptonic widths obtained are: GAMMA(e) = 82.4 +/- 1.2 MeV, GAMMA(mu) = 86.9 +/- 2.1 MeV and GAMMA(tau) = 82.7 +/- 2.4 MeV. Assuming universality, the squared vector and axial-vector couplings of the Z0 to charged leptons are: VBAR(t)2 = 0.0003 +/- 0.0010 and ABAR(l)2 = 0.2508 +/- 0.0027. These values correspond to the electroweak parameters: rho(eff) = 1.003 +/- 0.011 and sin2-theta(W)eff = 0.241 +/- 0.009. Within the Minimal Standard Model (MSM), the results can be expressed in terms of a single parameter: sin2-theta(W)MSBAR = 0.2338 +/- 0.0027. All these values are in good agreement with the predictions of the MSM. Fits yield 43 < m(top) < 215 GeV at the 95% level. Finally, the measured values of GAMMA(Z) and GAMMA(inv), are used to derive lower mass bounds for possible new particles.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11390/883634
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