Experimental results on QCD and jets at LEP and SLC

A selection of results from e"+e"- annihilations at c.m. energies around the Z"0 resonance, testing the predictions of perturbative Quantum Chromodynamics, is presented. Measurements of the strong coupling strength, #alpha#_s, are updated and reviewed, and a world compilation of #alpha#_s determinations is given. Determinations of the QCD gauge group constants from 4- as well as from 2- and 3-jet events are summarised. Model independent studies of the properties of identified quark and gluon jets and results of sub-jet mutliplicities of 2-and 3-jet events are presented. The first comparison of the structure of jets from e"+e"- annihilation and from p anti p collisions is discussed. (orig.)Available from TIB Hannover: RN 6945(1994,29) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Measurement of the strong coupling constant #alpha#_s from jet rates in deep inelastic scattering

Based on R_2_+_1(Q"2), the rate of (2+1)-jet events as defined by a modified JADE algorithm, the strong coupling constant #alpha#_s is measured as a function of the momentum transfer Q"2 in the range 10<Q"2<4000 GeV"2, using data from deep inelastic electron proton scattering at the HERA collider. The result is consistent with the running of #alpha#_s according to the QCD prediction of the renormalization group equation. The extrapolation of the measured values to the mass of the Z leads to #alpha#_s(M_z"2)=0.121#+-#0.015. This preliminary result shows the sensitivity to #alpha#_s using jets in deep inelastic scattering. The method developed in this thesis will provide a precise measurement of #alpha#_s in future. (orig.)Available from TIB Hannover: RN 6945(1994,21) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Beauty production at the CERN proton antiproton collider: a test of QCD

This thesis is devoted to a study of beauty production at the CERN p anti p collider through the detection of b quark semileptonic decays in the UA1 detector, focusing on the results from dimuon events. The combination of the mixing measurement obtained from the inclusive dimuon sample with our earlier measurements yields an improved value for the B"0 anti B"0-mixing parameter #chi#=0.153#+-#0.021_s_t_a_t#+-#0.019_s_y_s. The measured b anti b angular and momentum correlations agree with the fully differential O(#alpha#_8"3) QCD calculation of Mangano, Nason, and Ridolfi. The splitting of the dimuon sample into four p_T_#mu# bins and the separation of the errors into p_T dependent and p_T independent parts yields an improved measurement of the shape of the inclusive beauty cross-section. Using the shape of this prediction to extrapolate to p_T = 0 and to all rapidities, an improved measurement of the total b anti b cross-section at the Sp anti pS collider #sigma#_t_o_t(p anti p#->#b anti bX) = 19.7#+-#4.3_e_x_p_-_6_._5_t_h"+"1"0"."4#mu#b is obtained. The measured inclusive b cross-section from dimuon events is separated into cross-sections for (quasi-) 2-body and 3-body final states. While the O(#alpha#_s"3) QCD prediction for the 2-body cross-section has a reduced dependence on the QCD renormalization and factorization scales, the ratio of the 2- and 3-body cross-sections is independent of the proton structure functions. Also, the predicted cross-sections for 2-body and 3-body final states are proportional to powers of the strong coupling constant, #alpha#_s"2 and #alpha#_s"3 respectively. These features are used to measure the strong coupling constant by varying the theoretical QCD parameters and determining the best fit to the data. Three slightly different methods yield the results #alpha#_s(20 GeV)=0.136_-_0_._0_2_4"+"0"."0"2"5 ren./fact. scale varied externally, #alpha#_s(20 GeV)=0.138_-_0_._0_1_8"+"0"."0"2"3 ren.fact. scale fitted from data, and #alpha#_s(20 GeV)=0.138_-_0_._0_1_9"+"0"."0"2"8 (quasi-)2-body final states only. (orig./HSI)Available from TIB Hannover: RN 6945(1992,31) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

First results from the H1 experiment at DESY

First results from the H1 experiment are reviewed. They include a measurement of the total photoproduction cross section at high enegies, studies of jets in photoproduction and deep inelastic scattering events, a first measurement of the proton structure function at very small values of the Bjorken x variable and a search for new particles at HERA. (orig.)Available from TIB Hannover: RN 6945(1993,24) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

QCD tests at e"+e"- colliders

A short review of the history and a 'slide-show' of QCD tests in e"+e"-annihilation is given. The world summary of measurements of #alpha#_s is updated. (orig.)Available from TIB Hannover: RN 6945(1997,37) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Experimental tests of asymptotic freedom

Measurements which probe the energy dependence of #alpha#_s, the coupling strength of the strong interaction, are reviewed. Jet counting in e"+e"-annihilation, combining results obtained in the centre of mass energy range from 22 to 133 GeV, provides direct evidence for an asymptotically free coupling, without the need to determine explicit values of #alpha#_s. Recent results from jet production in e p and in p p collisions, obtained in single experiments spanning large ranges of momentum transfer, Q"2, are in good agreement with the running of #alpha#_s as predicted by QCD. Mass spectra of hadronic decays of #tau#-leptons are analysed to probe the running #alpha#_s in the very low energy domain, 0.7 GeV"2 < Q"2 < M"2_#tau#. An update of the world summary of measurements of #alpha#_s(Q"2) consistently proves the energy dependence of #alpha#_s and results in a combined average of #alpha#_s(M_Z_"0=0.118#+-#0.006). (orig.)Available from TIB Hannover: RN 6945(1996,30) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Genaue Bestimmung der Masse und der Linienbreite des Z"0 sowie der Anzahl der leichten Neutrinos

SIGLEAvailable from TIB Hannover: RN6945(1991,13) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

B-production and the evidence for Bo- anti (Bo) mixing at the CERN p anti p collider

Invited talk at the 21. Rencontre de Moriond, 'perspectives in electroweak interactions and unified theories', Les Arcs, March 9-16, 1986SIGLETIB Hannover: RN 6945(1986,12) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Winkelverteilungen und Asymmetrien in der e+e- Annihilation in 3-Jet Ereignisse

SIGLETIB Hannover: RN 6945(1985,22) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Lattice Higgs models

Review talk given at the Workshop on lattice gauge theory, Wuppertal, November 1985SIGLETIB Hannover: RN 6945(1985,25) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman