Search for Charginos with a Small Mass Difference with the Lightest Supersymmetric Particle at \sqrt{s} = 189 GeV

A search for charginos nearly mass-degenerate with the lightest supersymmetric particle is performed using the 176 pb^-1 of data collected at 189 GeV in 1998 with the L3 detector. Mass differences between the chargino and the lightest supersymmetric particle below 4 GeV are considered. The presence of a high transverse momentum photon is required to single out the signal from the photon-photon interaction background. No evidence for charginos is found and upper limits on the cross section for chargino pair production are set. For the first time, in the case of heavy scalar leptons, chargino mass limits are obtained for any \tilde{\chi}^{+-}_1 - \tilde{\chi}^0_1 mass difference

Search for Low Scale Gravity Effects in e+e- Collisions at LEP

Recent theories propose that quantum gravity effects may be observable at LEP energies via gravitons that couple to Standard Model particles and propagate into extra spatial dimensions. The associated production of a graviton and a photon is searched for as well as the effects of virtual graviton exchange in the processes: e+e- -> gamma gamma, ZZ, WW, mu mu, tau tau, qq and ee No evidence for this new interaction is found in the data sample collected by the L3 detector at LEP at centre-of-mass energies up to 183 GeV. Limits close to 1 TeV on the scale of this new scenario of quantum gravity are set

Measurement of the Average Lifetime of b-Hadrons in Z Decays

We present a measurement of the average b-hadron lifetime ${\rm \tau_b}$ at the $\mathrm{e^+e^-} \,$ collider LEP. Using hadronic Z decays collected in the period from 1991 to 1994, two independent analyses have been performed. In the first one, the b-decay position is reconstructed as a secondary vertex of hadronic b-decay particles. The second analysis is an updated measurement of ${\rm \tau_b}$ using the impact parameter of leptons with high momentum and high transverse momentum. The combined result is \begin{center} ${\rm \tau_b= [ 1549 \pm 9 \, (stat) \, \pm 15 \, (syst) ] \; fs \,}$ . \end{center} In addition, we measure the average charged b-decay multiplicity ${\rm \langle n_{\rm b}} \rangle$ and the normalized average b-energy ${\rm \langle x_E \rangle_{\rm b}}$ at LEP to be \begin{center} ${\rm \langle n_{\rm b} \rangle = 4.90 \pm 0.04 \ (stat) \pm 0.11 \, (syst)}$ , \end{center} \begin{center} ${\rm \langle x_E \rangle_{\rm b} = 0.709 \pm 0.004 \, (stat + syst).}$ \end{center

Single and multi-photon events with missing energy in e(+)e(-) collisions at 161 GeV <root s < 172 GeV

Contains fulltext : 26276.pdf (publisher's version ) (Open Access

Measurement of inclusive omega and eta' production in hadronic Z decays

Contains fulltext : 26257.pdf (publisher's version ) (Open Access

Principles for supporting school drug education.

Children and young people often find visitors to school a useful and informative part of their learning, but for visits to be successful there needs to be a shared understanding about the nature and content of the sessions. This paper is intended to set out principles that visitors and schools can consider applying to ensure better outcomes from using external support in a school's delivery of drug education

Measurement of the e+e--> Z -> bb̅ forward-backward asymmetry and the B-0B̅0 mixing parameter using prompt leptons

The time-integrated $\mathrm{B}^{0}\bar{\mathrm{B}}^{0}$ mixing parameter and the forward-backward charge asymmetry in the process $\mathrm{e}^{+}\mathrm{e}^{-} \rightarrow \mathrm{b}\bar{\mathrm{b}}$ are measured in hadronic \Z events containing prompt muons or electrons, collected by the L3 experiment in the years 1990 to 1995. The total sample of 3.3 million hadronic $\mathrm{Z}$ events with a mean centre-of-mass energy of 91.26 GeV yields: \begin{eqnarray*} \mbox{$A_{\mathrm{FB}}^{\mathrm{b} }$} & = & 0.0960 \pm 0.0066(stat.) \pm 0.0033(sys.) \,, \\ %corel-6 \mbox{$\chi_{\mathrm{b}}$} & = & 0.1192 \pm 0.0068(stat.) \pm 0.0051(sys.) \,. % \end{eqnarray*} %%% %%% %%% %%% This asymmetry measurement together with measurements at energies away from the $\mathrm{Z}$ pole energy yield a pole asymmetry and corresponding effective electroweak mixing angle of: \begin{eqnarray*} \mbox{$A_{\mathrm{FB}}^{0,\mathrm{b}}$} & = & 0.1015 \pm 0.0064(stat.) \pm 0.0035(sys.) \,, \\ %corel-6.nb \mbox{$\sin^{2}\bar{\theta}_{\mathrm{W}}$} & = & 0.2318 \pm 0.0013 \, .\\ %sin2tw-3.nb \end{eqnarray*

Measurement of the e+e−→Zγγe^+ e^- \to Z\gamma\gamma cross section and determination of quartic gauge boson couplings at LEP

A first measurement of the cross section of the process$\rm e^+e^-\rightarrow Z\gamma\gamma$ is reported using a total integrated luminosity of 231\,pb$^{-1}$collected with the L3 detector at centre-of-mass energiesof 182.7\,GeV and 188.7\,GeV. By selectinghadronic events with two isolated photonsthe $\rm e^+e^-\rightarrow Z\gamma\gamma$cross section is measured to be$0.49^{+0.20}_{-0.17}\pm0.04\,{\mathrm{pb}}$ at 182.7\,GeV and $0.47 \pm 0.10\pm0.04\,{\mathrm{pb}}$ at 188.7\,GeV. Themeasurements are consistent with Standard Model expectations.Limits on Quartic Gauge Boson Couplings $a_0/\Lambda^2$ and $a_c/\Lambda^2$ of-0.009\, GeV$^{-2}$ $ Z gamma gamma is reported using a total integrated luminosity of 231 pb^-1 collected with the L3 detector at centre-of-mass energies of 182.7 GeV and 188.7 GeV. By selecting hadronic events with two isolated photons the e+e- -> Z gamma gamma cross section is measured to be 0.49 +0.20 -0.17 +/- 0.04 pb at 182.7 GeV and 0.47 +/- 0.10 +/- 0.04 pb at 188.7 GeV. The measurements are consistent with Standard Model expectations. Limits on Quartic Gauge Boson Couplings a_0/Lambda^2 and a_c/Lambda^2 of -0.009 GeV^-2 &lt; a_0/Lambda^2 &lt; 0.008 GeV^-2 and -0.007 GeV^-2 &lt; a_c/Lambda^2 &lt; 0.013 GeV^-2 are derived at 95% confidence level

Measurements of the bb‾b\overline{b} production cross section and forward- backward asymmetry at centre-of-mass energies above the Z pole at LEP

The measurements of R_{b} = \sigma(e^+e^-} \to b\overline{b})/\sigma( e^+e^-} \to{m q\overline{q}) and of the b quarkforward--backward charge asymmetry,A_fb}^{b}, at centre--of--mass energies above the Z pole are described. The measurement of $R_{b}$ is performed at $\sqrt{s}$ between 130 and 189 GeV using a b--tagging method thatexploits the relatively large decay length ofb--hadrons. The measurement of $A_{fb}^{b}$ is performedusing the large statistics event sample collected at $\sqrt{s}$=189 GeV with a lepton--tag analysis based on the selection of prompt muons and electrons. The results at $\sqrt{s}$=189 GeV are: $R_{b} = 0.163 pm 0.013 (stat.) pm 0.005 (syst.)$, $A_{fb}^{b} = 0.61 pm 0.18 (stat.) pm 0.09 (syst.).$The measurements of Rb = sigma(e+e- -> bb~)/sigma(e+e- -> qq~) and of the b quark forward-backward charge asymmetry, A^b_fb, at centre-of-mass energies above the Z pole are described. The measurement of Rb is performed at \root{s} between 130 and 189 GeV using a b-tagging method that exploits the relatively large decay length of b-hadrons. The measurement of A^b_fb is performed using the large statistics event sample collected at \root{s}=189 GeV with a lepton-tag analysis based on the selection of prompt muons and electrons. The results at \root{s}=189 GeV are: Rb = 0.163 +/- 0.013 (stat.) +/- 0.005 (syst.), A^b_fb = 0.61 +/- 0.18 (stat.) +/- 0.09 (syst.).The measurements of R b =σ( e + e − → b b ̄ )/σ( e + e − → q q ̄ ) and of the b quark forward–backward charge asymmetry, A fb b , at centre-of-mass energies above the Z pole are described. The measurement of R b is performed at s between 130 and 189 GeV using a b-tagging method that exploits the relatively large decay length of b-hadrons. The measurement of A fb b is performed using the large statistics event sample collected at s =189 GeV with a lepton-tag analysis based on the selection of prompt muons and electrons. The results at s =189 GeV are R b =0.163±0.013 (stat.) ±0.005 (syst.) , A fb b =0.61±0.18 (stat.) ±0.09 (syst.)