Title 



Measurements of the polarisation in decays
 
Author 



 
Abstract 



A sample of Z(0) > tau(+)tau() events observed in the DELPHI detector at LEP in 1991 and 1992 is analysed to measure the tau polarisation in the exclusive decay channels e nu ($) over bar nu, mu nu ($) over bar nu, pi nu, rho nu and a(l) nu. The tau polarisation is also measured with an inclusive hadronic analysis which benefits from a higher efficiency and a better systematic precision than the use of the exclusive decay modes. The results have been combined with those published on the 1990 data. A measurement of the tau polarisation as a function of production angle yields the values for the mean tau polarisation [Ptau] = 0.148 +/ 0.022 and for the Z(0) polarisation Pz = 0.136 +/ 0.027. These results are used to determine the ratio of vector to axialvector effective couplings for taus ($) over bar upsilon(tau)/($) over bar a(tau) = 0.074 +/ 0.011 and for electrons ($) over bar upsilon(e)/($) over bar a(e) = 0.068 +/ 0.014, compatible with etau universality. With the assumption of lepton universality, the ratio of vector to axialvector effective couplings for leptons ($) over bar upsilon(l)/($) over bar a(l) = 0.072 +/ 0.008 is obtained, implying a value of the effective weak mixing angle sin(2) theta(eff)(lept) = 0.2320 +/ 0.0021.   
Language 



English
 
Source (journal) 



Zeitschrift für Physik : C : particles and fields.  Berlin  
Publication 



Berlin : 1995
 
ISSN 



01709739
 
Volume/pages 



67:2(1995), p. 183201
 
ISI 



A1995RJ82200001
 
