6 research outputs found
MEASUREMENT OF THE GAMMA(B-B-OVER-BAR)/GAMMA(HAD) BRANCHING RATIO OF THE Z BY DOUBLE HEMISPHERE TAGGING
No full textTwo measurements of Gamma(b () over bar b)/Gamma(had) is found to be 0.2209 +/- 0.0041 (stat.) +/- 0.0042(syst.) +/- 0.0018 (Gamma(c () over bar b)/Gamma(had) are presented. Both measurements use 250000 Z decays taken with the DELPHI detector in 1991 and rely mainly on the precision of the microvertex detector. One tagging method is as simple as possible so that background rates can be reliably predicted by simulation. The other one uses a more involved tagging technique and reduces the dependence on simulation as much as possible. Combining both results, Gamma(b () over bar c))
PRODUCTION CHARACTERISTICS OF K-0 AND LIGHT MESON RESONANCES IN HADRONIC DECAYS OF THE Z(0)
No full textAn analysis of inclusive production of KO and the meson resonances K*(+/-)(892), rho(0)(770), f(0)(975) and f(2)(1270) in hadronic decays of the Z(0) is presented, based on about 973,000 multihadronic events collected by the DELPHI detector at LEP during 1991 and 1992. Overall multiplicities have been determined as 1.962 +/- 0.060 K-0 mesons, 0.712 +/- 0.067 K*(+/-)(892) and 1.21 +/- 0.15 rho(0)(770) per hadronic Z(0) decay. The average multiplicities of f(0)(975) for scaled momentum, x(p) = p/p(beam), in the range 0.05 less than or equal to x(p) less than or equal to 0.6 and of f(2)(1270) for 0.05 less than or equal to x(p) less than or equal to 1.0 are 0.098 +/- 0.016 and 0.170 +/- 0.043 respectively. The f(0)(975) and rho(0)(770) x(p)-spectra have p similar shapes. The f(2)(1270)/rho(0)(770) ratio increases with x(p). The average multiplicities and the differential cross sections are compared with the JETSET Parton Shower model. The model with default parameters fails to reproduce the experimental K-0 momentum spectrum at low momentum, describes the K*(+/-)(892) and rho(0)(770) x(p)-spectrum shapes, but significantly overestimates their production rates
Measurement of the forward-backward asymmetry of e(+)e(-)-]Z-]B(B)over-bar using prompt leptons and a lifetime tag
No full textThe forward-backward asymmetry of the process e(+)e(-) --> Z --> b () over bar b) = 0.107 +/- 0.011(stat. + syst. + mixing).
With the semileptonic sample, the forward-backward asymmetry of the process e(+)e(-) --> Z --> c () over bar c) = 0.083 +/- 0.022(stat.) +/- 0.016(syst.).
The effective value of the Weinberg mixing angle derived from these measurements was
sin(2) theta(eff)(lep) = 0.2294 +/- 0.0021
Observation of orbitally excited B mesons
No full textExperimental evidence for the existence of orbitally excited B meson states is presented in an analysis of the Bπ and B*π distribution of Q = m(B**) - m(B(*)) - m(π) using Z0 decay data taken with the DELPHI detector at LEP. The mean Q-value of the decays B** → B(*)π is measured to be 284 ± 5 (stat.) ± 15 (syst.) MeV/c2, and the Gaussian width of the signal is 79 ± 5 (stat.) ± 8 (syst.) MeV/c2. This signal can be described as a single resonance of mass m = 5732 ± 5 (stat.) ± 20 (syst.) MeV/c2 and full width Γ = 145 ± 28 MeV/c2. The observed shape is also consistent with the production of several broad and narrow states as predicted by the quark model and partly observed in the D-meson sector. The production rate of B** per b-jet is found to be 0.27 ± 0.02 (stat.) ± 0.06 (syst.).0info:eu-repo/semantics/publishe
A Study of radiative muon pair events at Z0 energies and limits on an additional Z-prime gauge boson
No full textAn analysis is reported on the channel e+e-→μ+μ- (nγ), n=1,2..., using data taken with the DELPHI detector at LEP from 1990 to 1992. Differential cross sections of the radiative photons as a function of photon energy and of the angle between the photon and the muon are presented. No significant deviations from expectations are observed. The data are also used to extract the muon-pair cross section and asymmetry below the Z0 peak by using those events with relatively hard initial state radiative photon(s). The measured cross section and asymmetry show no significant deviation from the Standard Model expectations. These results together with the DELPHI cross section and asymmetry measurements at the LEP energies from the 1990 to 1992 running periods are used to determine limits on the Z0-Z′ gauge boson mixing angle θZ′ and on the Z′ mass. There is no indication of the existence of a Z′; the limits obtained on the mixing angle substantially improve upon existing limits. The 95% confidence level allowed ranges of θZ′ in various models are: {Mathematical expression} © 1995 Springer-Verlag
OBSERVATION OF ORBITALLY EXCITED B-MESONS
No full textExperimental evidence for the existence of orbitally excited B meson states is presented in an analysis of the B pi and B*pi distribution of Q = m(B**) - m(B(*)) - m(pi) using Z(0) decay data taken with the DELPHI detector at LEP. The mean Q-value of the decays B** –> B(*)pi is measured to be 284 +/-5 (stat.) +/- 15 (syst.) MeV/c(2), and the Gaussian width of the signal is 79 +/- 5 (stat.) +/- 8 (syst) MeV/c(2). This signal can be described as a single resonance of mass m = 5732+/-5 (stat.) +/- 20(syst.) MeV/c(2) and full width Gamma = 145 +/- 28 MeV/c(2). The observed shape is also consistent with the production of several broad and narrow states as predicted by the quark model and partly observed in the D-meson sector. The production rate of B** per b-jet is found to be 0.27 +/- 0.02(stat.) +/- 0.06 (syst.)
