Guy Wilkinson

Abstract:

We have studied the energy-energy angular correlations in hadronic final states from Z0 decay using the DELPHI detector at LEP. From a comparison with Monte Carlo calculations based on the exact second order QCD matrix element and string fragmentation we find that Λ (5) MS=104+25-20(stat.)+25-20(syst.) +3000)theor.). MeV, which corresponds to αs(91 GeV)=0.106±0.003(stat.)±0.003(syst.)+0.003 -0.000(theor). The theoretical error stems from different choices for the renormalization scale of αs. In the Monte Carlo simulation the scale of αs as well as the fragmentation parameters have been optimized to described reasonably well all aspects of multihadron production. © 1990.

Abstract:

A determination of the partial width Γc c ̄ 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*-→ D ̄0 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 Γc c ̄ Γh = 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 Γc c ̄ = 282±53 (stat.)±88(syst.) MeV. © 1990.