Determination of the structure of (tau)decays in the reaction e(sup +)e(sup -) (yields) (tau)(sup +)(tau)(sup -) (yields) (rho)(sup +) anti (nu)(sub (tau))(rho)(sup -)(nu)(sub (tau)) and a precision measurement of the (tau)-neutrino helicity

摘要

Using the ARGUS detector at the DORIS II storage ring we have investigated the Lorentz structure of the electroweak interaction in semi-hadronic (tau) decays. Spin correlations in the process e(sup +)e(sup -)(yields)(tau)(sup +)(tau)(sup -)(yields) anti (nu)(sub (tau))(pi)(sup +)(pi)(sup 0) (nu)(sub (tau))(pi)(sup -)(pi)(sup 0) are exploited for a measurement of the normalized product of the vector (g(sub V)) and axial vector (g(sub A)) couplings of the (tau) lepton, (gamma)(sub AV)=2 Re(l brace)g(sub A)g(sub V)*(r brace)/(vertical stroke g(sub V)vertical stroke (sup 2)+vertical stroke g(sub A)vertical stroke (sup 2)). The correlations are sensitive to the product of the couplings in both (tau) decays: (gamma)(sub AV)(sup 2)=(gamma)(sub AV)((tau)(sup -)(yields)(nu)(sub (tau))W(sup -))(gamma)(sub AV)((tau)(sup +)(yields) anti (nu)(sub (tau))W(sup +)), which can be interpreted as the product of the neutrino helicities: (gamma)(sub AV)(sup 2)=-h((nu)(sub (tau)))h( anti (nu)(sub (tau))). The measured value, (gamma)(sub AV)(sup 2)=1.044(+-)0.057(+-)0.060, determines the relative sign of the neutrino helicities. Assuming CP invariance, the absolute value (l brace)(gamma)(sub AV)(r brace)=1.022(+-)0.028(+-)0.030 was found to be in excellent agreement with the Standard Model. The contribution of scalar (g(sub S)) or pseudoscalar (g(sub P)) couplings was also investigated. No evidence for a scalar-like coupling was found. (orig.) (ERA citation 20:006714)