Measurement of the partial width of the decay of the Z0 into charm quark pairs

A determination of the partial width Γcc̄ of the Z0 boson into charm quark pairs is presented, based on a total sample of 36 900 Z0 hadronic decays measured with the DELPHI detector at the LEP collider. The production rate of cc̄ events is derived from the inclusive analysis of charged pions coming from the decay of charmed meson D∗+→D0π+ and D∗−→D̄0 π− where the π± is constrained by kinematics to have a low pT with respect to the axis. The probability to produce these π± from D∗± decay in cc̄ events is taken to be 0.31 ±_0.05 as measured at √s=10.55 GeV. The measured relative partial width Γcc̄Γh = 0.162± 0.030 (stat.) ±0.050 (syst.) is in good agreement with the standard moel value of 0.171. Together with our previous measurement of the total hadronic width Γh this implies Γcc̄ = 282±53 (stat.)±88(syst.) MeV