Measurement of the spectral functions of axial - vector hadronic tau decays and determination of alpha(S)(M**2(tau))

ALEPH Collaboration, The and Barate, R. and Betteridge, Andrew and Bowdery, Christopher and Colrain, Paul and Finch, Alexander and Foster, Frank and Hughes, Gareth and Jones, Roger and Williams, Mark (1998) Measurement of the spectral functions of axial - vector hadronic tau decays and determination of alpha(S)(M**2(tau)). The European Physical Journal C (EPJ C) - Particles and Fields, 4 (3). pp. 409-431. ISSN 1434-6052

Abstract

An analysis based on 124 000 selected τ pairs recorded by the ALEPH detector at LEP provides the vector (V) and axial-vector (A) spectral functions of hadronic τ decays together with their total widths. This allows the evaluation of finite energy chiral sum rules that are weighted integrals over the (V−A) spectral functions. In addition, a precise measurement of αs along with a determination of nonperturbative contributions at the τ mass scale is performed. The experimentally and theoretically most robust determination of αs(M2τ) is obtained from the (V+A) fit that yields αs(M2τ)=0.334±0.022 giving αs(M2Z)=0.1202±0.0027 after the extrapolation to the mass of the Z boson. The approach of the Operator Product Expansion (OPE) is tested experimentally studying the evolution of the τ hadronic widths to masses smaller than the τ mass.