Ahammed, Z.
ALEPH
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Determination of the Number of Light Neutrino Species

The ALEPH collaboration Decamp, D. ; Deschizeaux, B. ; Lees, J.P. ; et al.
Phys.Lett.B 231 (1989) 519-529, 1989.
Inspire Record 282904 DOI 10.17182/hepdata.29758

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 Γ z =(2.68±0.15) GeV, and of the peak hadronic cross-section, σ had peak =(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 N v =3.27±0.30. this results rules out of the possibility of a fourth type of light neutrino at 98% CL.

2 data tables
Table 1

Selection from TPC tracks.

Table 2

Selection by calorimeters.


A Precise measurement of the average b hadron lifetime

The ALEPH collaboration Buskulic, D. ; Casper, D. ; De Bonis, I. ; et al.
Phys.Lett.B 369 (1996) 151-162, 1996.
Inspire Record 401554 DOI 10.17182/hepdata.52363

An improved measurement of the average b hadron lifetime is performed using a sample of 1.5 million hadronic Z decays, collected during the 1991–1993 runs of ALEPH, with the silicon vertex detector fully operational. This uses the three-dimensional impact parameter distribution of lepton tracks coming from semileptonic b decays and yields an average b hadron lifetime of 1.533 ± 0.013 ± 0.022 ps.

1 data table
Table 1

No description provided.