Study of hadronic event shape in flavour tagged events in e+e- annihilation at "Equation missing" = 197 GeV

Abstract

Results are presented from a study of the structure of hadronic events in high-energy e + e -interactions detected by the L3 detector at LEP. Various event shape distributions and their moments are measured at several energy points at and above the Z-boson mass. The event flavour is tagged by using the decay characteristics of b-hadrons. Measurements of distributions of event shape variables for all hadronic events, for light (u, d, s, c) and heavy (b) quark flavours are compared to several QCD models with improved leading log approximation: JETSET, HERWIG and ARIADNE. A good description of the data is provided by the models.PACS Codes: 12.38.Qk, 13.66.Bc IntroductionHadronic events produced in e + e -annihilation have been a powerful tool to test the predictions of Quantum Chromodynamics (QCD) [1][2][3][4][5]. Perturbative QCD successfully accounts for many aspects of the hadronic decays of the Z boson [6]. The primary quarks from Z-boson decays first radiate gluons, which in turn may split into quark or gluon pairs. The quark and gluons then fragment into observable hadrons. Perturbative QCD itself does not describe the fragmentation process. Instead several phenomenological models have been developed to describe fragmentation. These models provide a way to correct for the effects of fragmentation in the experimental data, which can then be compared with the perturbative QCD calculations directly.The event shape variables which characterize the global structure of hadronic events are among the simplest experimental measurements sensitive to the parameters of perturbative QCD and fragmentation models. This article reports on the measurement of event shapes for hadronic events collected at LEP by the L3 detector [7][8][9][10] at e + e -centre-of-mass energies  189 GeV.Similar analyses were reported by all LEP experiments [11][12][13][14][15].Heavy flavour production in e + e -annihilation can be studied by exploiting the characteristics of heavy flavour decays. In the present study, hadronic events are separated into heavy (b) and light (u, d, s, c) flavours, and event shape variables are separately measured for these final states. This allows to test the modelling of heavy flavour mass effects. Earlier and similar measurements, at lower centre-of-mass energies, are reported in References [11] and [16]. Global event shape variablesEvent shape variables, insensitive to soft and collinear radiation, are built from linear sums of measured particle momenta. They are sensitive to the amount of hard-gluon radiation. Six global event shape variables are measured here, using calorimetric and tracking information measured as described in References [7][8][9][10] and [11]. They are: thrust, scaled heavy jet mass, total and wide jet broadening, the C-parameter and the jet resolution parameter. These event-shape variables are defined below. ThrustThe global event-shape variable thrust, T, [17,18] is defined as where is the momentum vector of particle i. The thrust axis is the unit vector which maximizes the abov...

Study of hadronic event-shape variables in multijet final states in pp collisions at s = 7 $$ \sqrt{s} = 7 $$ TeV

“…Event-shape variables measure the properties of the energy flow in the final states of high energy particle collisions. Their simplicity combined with their sensitivity to many important signatures of quantum chromodynamics (QCD) [1,2] make them interesting observables extensively studied in hadronic final states of electron-positron (e + e − ) and deep inelastic scattering (DIS) collisions [3][4][5]. Such event-shape variables are theoretically defined in an infrared-and collinear-safe manner and can be computed using perturbative techniques.…”