Limits on the production of scalar leptoquarks from Z (0) decays at LEP

A search has been made for pairs and for single production of scalar leptoquarks of the first and second generations using a data sample of 392000 Z0 decays from the DELPHI detector at LEP 1. No signal was found and limits on the leptoquark mass, production cross section and branching ratio were set. A mass limit at 95% confidence level of 45.5 GeV/c2 was obtained for leptoquark pair production. The search for the production of a single leptoquark probed the mass region above this limit and its results exclude first and second generation leptoquarks D0 with masses below 65 GeV/c2 and 73 GeV/c2 respectively, at 95% confidence level, assuming that the D0lq Yukawa coupling alpha(lambda) is equal to the electromagnetic one. An upper limit is also given on the coupling alpha(lambda) as a function of the leptoquark mass m(D0)

Measurement of the average lifetime of B hadrons

The average lifetime of B hadrons produced in hadronic Z0 decays has been measured with the DELPHI detector at LEP. The measurement is based on the analysis of the impact parameter distributions of high pt muons and hadrons. The resulting mean B lifetimes are τB=(1.30±0.10±0.08)ps and τB=(1.27±0.04±0.12)ps respectively, giving a combined value of τB=(1.28±0.10)ps. The hadronic sample was also used to measure the partial Z0 width Mathematical expression and gave a value of 0.222-0.031+0.033±0.017. © 1992 Springer-Verlag

A measurement of B meson production and lifetime using Dl- events in Z0 decays

A study of B meson decays into DlX final states is presented. In these events, neutral and charged D mesons originate predominantly from B+ and B0 decays, respectively. The dilution of this correlation due to D** production has been taken into account. From 263 700 hadronic Z0 decays collected in 1991 with the DELPHI detector at the LEP collider, 92 D0→K-π+, 35 D+→K-π+π+ and 61 D*0→D0π+ followed by D0→K-π+ or D0→K-π+π+π -, are found with an associated lepton of the same charge as the kaon. From the D0l- and D*+l-, the probability fd that a b quark hadronizes into a B- (or {Mathematical expression}) meson is found to be 0.44 ±0.08±0.09, corresponding to a total (Bs+Λb) hadronization fraction of 0.12-0.12+0.24. By reconstructing the energy of each B meson, the b quark fragmentation is directly measured for the first time. The mean value of the B meson energy fraction is: {Mathematical expression} Reconstructing D-lepton vertices, the following B lifetimes are measured: {Mathematical expression} and an average τ(B)=1.23-0.13+0.14(stat.)±0.15(syst.) ps is found. Allowing for decays into {Mathematical expression}, the B+ and B0 lifetimes are: {Mathematical expression} © 1993 Springer-Verlag