Determination of event shape distributions and αsb from events at LEP

In hadronic Z0 decays collected by the OPAL experiment at LEP, event shape variables such as jet rates, jet masses, thrust and the energy-energy correlation for$$Z^0 \to b\bar b$$ events are compared to those for all flavours using secondary vertex information to tag the b quarks. The measured distributions are found to be well described by anO"(αs) calculation for heavy quarks as well as by parton shower simulations. We also determine the ratio of the strong coupling constant for b quarks and all quarks, αsb/αsincl, from these distributions. We find$$\alpha _s^b /\alpha _s^{incl} = 0.994 \pm 0.005_{ - 0.012}^{ + 0.010} ,$$ where the errors are the statistical and systematic errors. The result can be converted into the ratio for b quarks relative to the complementary flavours udsc αsb/αsudsc=0.992±0.007-0.015+0.013.