New Results on α s from DELPHI

Abstract

Recent studies of the strong coupling α s using the DELPHI detector at LEP [1, 2] are reviewed. For the analysis of the data at \(\sqrt s = {M_z}\) recorded in 1994, a large number of shape observables and their dependence on the event orientation are measured and compared to theoretical calculations in \(O\left( {\alpha _s^2} \right)\). The adjustment of the renormalization scale μ, turns out to be of major importance. Only a poor description of the data can be achieved if the so-called physical scale μ 2 = Q 2 is applied, whereas a combined fit of α s and the renormalization scale value yields an excellent description of the high statistics data. For these scale values perfect consistency of the fit values of α s (Mz) is obtained for all event shape observables considered. The running of α s is measured from the DELPHI data at \(\sqrt s = 130Gev - 172GeV\). Here an analytical power ansatz for the hadronization corrections is compared with hadronization corrections obtained by using Monte Carlo generators.