Studies of hadronic event structure in e+e- annihilation from 30 to 209GeV with the L3 detector

Abstract

In this Report, QCD results obtained from a study of hadronic event structure in high energy e+e− interactions with the L3 detector are presented. The operation of the LEP collider at many different collision energies from 91 to 209 GeV offers a unique opportunity to test QCD by measuring the energy dependence of different observables. The main results concern the measurement of the strong coupling constant, alpha_s, from hadronic event shapes and the\ud study of effects of soft gluon coherence in charged particle multiplicity and momentum distributions

Efficient matrix-element matching with sector showers

“…One also notes that the two matched calculations (global and sector) are consistent with each other. As a second cross check, we include some comparisons to LEP event-shape data at √ s = m Z , using light-flavor (udsc) data taken by the L3 collaboration [52]. In all cases, we include tree-level matching through Z → 5 partons, the default in Vincia.…”

“…A first illustration of this is given in the left-hand panes of figures 18 and 19, in which we compare the sector and global shower implementations in Vincia to measurements of the Thrust and D-parameter event-shape variables, which arise at O(α s ) and O(α 2 s ) respectively (see [52] for a definition). For reference, the C parameter, qualitatively similar to Thrust, is included in appendix A, as are the Wide and Total Jet Broadening parameters.…”

“…Normalized D-parameter distribution. Vincia compared to L3 data for light-flavor Z decays [52]. Left: sector (thin) vs. global (thick) showers, using default (global) Vincia tune.…”

“…Figure 20. Normalized charged-particle-mutiplicity (top) and momentum-fraction (bottom) distributions, with the latter using x = x p = 2|p|/ √ s. Vincia compared to L3 data for light-flavor Z decays [52]. Left: sector (thin) vs. global (thick) showers, using default (global) Vincia tune.…”

“…This appendix contains some further comparisons of the sector shower with LEP distributions, as follows: the C event-shape variable (figure 21), and the Wide and Total Jet broadening parameters (figures 22 and 23, respectively), defined as in [52], to which we compare. We also compare the production rates of selected identified baryon and meson species, normalized to the average charged-particle multiplicity, to our own average over the various identified-particle measurements performed at LEP [55,56] (figure 24).…”