Determination of the number of light neutrino species from single photon production at LEP

A determination of the number of light neutrino families performed by measuring the cross section of single photon production in \ee\ collision near the \Zo\ resonance is reported. From an integrated luminosity of $100~\mathrm{pb^{-1}}$, collected during the years 1991--94, we have observed 2091 single photon candidates with an energy above 1~\GeV\ in the polar angular region $45^\circ < \theta_\gamma < 135^\circ$. From a maximum likelihood fit to the single photon cross section, the \Zo\ decay width into invisible particles is measured to be \Ginv = 498 \pm 12 \mathrm{(stat)} \pm 12 \mathrm{(sys)~MeV}. Using the Standard Model couplings of neutrinos to the \Zo, the number of light neutrino species is determined to be $N_\nu = 2.98 \pm 0.07 (\mathrm{stat}) \pm 0.07 (\mathrm{sys}).

Angular multiplicity fluctuations in hadronic Z decays and comparison to QCD models and analytical calculations

Local multiplicity fluctuations in angular phase space intervals are studied using factorial moments measured in hadronic events at \sqrt{s}\simeq 91.2\GeV, which were collected by the L3 detector at LEP in 1994. Parton shower Monte Carlo programs agree well with the data. On the other hand, first-order QCD calculations in the Double Leading Log Approximation and the Modified Leading Log Approximation are found to deviate significantly from the data

Search for neutral B meson decays to two charged leptons

The decays $\mathrm{B_d^0,\,B_s^0 \rightarrow e^+e^-,\,\mu^+\mu^-,\, e^\pm\mu^\mp}$ are searched for in 3.5 million hadronic ${\mathrm{Z}}$ events, which constitute the full LEP I data sample collected by the L3 detector. No signals are observed, therefore upper limits at the 90\%(95\%) confidence levels are set on the following branching fractions: % \begin{center}% {\setlength{\tabcolsep}{2pt} \begin{tabular}{lccccclcccc}% % Br$({\mathrm{B_d^0 \rightarrow {\mathrm{e^+e^-}}}})$ & $<$ & $1.4(1.8)$ & $\times$ & $10^{-5}$; & \hspace*{5mm} & Br$({\mathrm{B_s^0 \rightarrow {\mathrm{e^+e^-}}}})$ & $<$ & $5.4(7.0)$ & $\times$ & $10^{-5}$; \\% Br$({\mathrm{B_d^0 \rightarrow \mu^+\mu^-}})$ & $<$ & $1.0(1.4)$ & $\times$ & $10^{-5}$; & \hspace*{5mm} & Br$({\mathrm{B_s^0 \rightarrow \mu^+\mu^-}})$ & $<$ & $3.8(5.1)$ & $\times$ & $10^{-5}$; \\% Br$({\mathrm{B_d^0 \rightarrow {\mathrm{e^\pm\mu^\mp}}}})$ & $<$ & $1.6(2.0)$ & $\times$ & $10^{-5}$; & \hspace*{5mm} & Br$({\mathrm{B_s^0 \rightarrow {\mathrm{e^\pm\mu^\mp}}}})$ & $<$ & $4.1(5.3)$ & $\times$ & $10^{-5}$. \\% % \end{tabular}% } \end{center}% % The results for ${\mathrm{B_s^0\rightarrow{\mathrm{e^+e^-}}}}$ and ${\mathrm{B_s^0 \rightarrow {\mathrm{e^\pm\mu^\mp}}}}$ are the first limits set on these decay modes

Measurement of η′(958)\eta '(958) formation in two-photon collisions at LEP1

The formation of the eta' in the reaction ee->ee eta'->ee pi pi gamma has been measured by the L3 detector at a centre-of-mass energy of 91 GeV. The radiative width of the eta' has been found to be 4.17 +/- 0.10(stat.) +/- 0.27(sys.) keV . The Q^2 dependence of the eta' formation cross section has been measured for Q^2 < 10 GeV^2 and the eta' electromagnetic transition form factor has been determined. The form factor can be parametrised by a pole form with Lambda = 0.900 +/- 0.046(stat) +/- 0.022(sys) GeV. It is also consistent with recent non-perturbative QCD calculations

Measurement of the inclusive charmless semileptonic branching fraction of beauty hadrons and a determination of |VubV_{ub}| at LEP

A measurement of the inclusive charmless semileptonic branching fraction of beauty hadrons, $\mathrm{b}\rightarrow\mathrm{X}_\mathrm{u }\ell\nu$, has been performed using almost two million hadronic Z decays collected by the L3 experiment at LEP, yielding the result: \begin{displaymath} \mathrm{Br}(\mathrm{b}\rightarrow\mathrm{X}_\mathr m{u}\ell\nu) = (3.3 \pm 1.0 \pm 1.7)\times 10^{-3}. \end{displaymath} The first uncertainty is statistical and the second is systematic. The modulus of the Cabibbo-Kobayashi-Maskawa matrix element $\mathrm{V_{ub}}$ extracted from this measurement is: \begin{displaymath} |\mathrm{V_{ub}}| = (6.0\, ^{+0.8}_{-1.0} \, ^{+1.4}_{-1.9} \pm 0.2)\times 10^{-3}, \end{displaymath} where the uncertainties are statistical, systematic and theoretical, respectively

Measurement of the effective weak mixing angle by jet-charge asymmetry in hadronic decays of the Z boson

The coupling of the Z boson to quarks is studied in a sample of about 3.5 million hadronic Z decays collected by the L3 experiment at LEP from 1991 to 1995. The forward-backward quark charge asymmet ry is measured by means of a jet charge technique. From the measured asymmetries, the effective weak mixing angle is determined to be \begin{center} $\STE = 0.2327 \pm 0.0012(\mbox{\emph{stat.}} ) \pm 0.0013(\mbox{\emph{syst.}}).