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OPERA is a neutrino oscillation experiment designed to perform a nu_tau appearance search at long distance in the future CNGS beam from CERN to Gran Sasso. It is based on the nuclear emulsion technique to distinguish among the neutrino interaction products the track of a tau produced by a nu_tau and its decay tracks. The OPERA detector is presently under construction in the Gran Sasso underground laboratory, 730 km from CERN, and will receive its first neutrinos in 2006. The experimental technique is reviewed and the development of the project described. Foreseen performances in measuring nu_tau appearance and also in searching for nu_e appearance are discussed.
We present the results of a search for nu_mu → nu_e oscillations in the NOMAD experiment at Cern. The experiment looked for the appearance of nu_e in a predominantly nu_mu wide-band neutrino beam at the CERN SPS. No evidence for oscillations was found. The 90% confidence limits obtained are Delta m^2 < 0.4 eV^2 for maximal mixing and sin^2(2theta) < 1.4 X 10^-3 for large Delta m^2. This result excludes the LSND allowed region of oscillation parameters with Delta m^2 >~ 10 eV^2.
One-prong $\tau$ decays into final states involving kaons are studied with about 161k $\tau^+\tau^-$ events collected by the ALEPH detector from 1991 to 1995. Charged kaons are identified by dE/dx measurement, while $K^0_L$'s are detected through their interaction in calorimeters. Branching ratios are measured for the inclusive mode, $B(\tau^-\rightarrow K^-X\nu_\tau)=(1.52 \pm 0.04\pm0.04)\%$, where $X$ can be any system of neutral particles, and for the exclusive modes \begin{center} \begin{tabular}{rcl} $B(\tau^-\to K^-\nu_\tau)$ &=& $(6.96\pm0.25\pm0.14)\times 10^{-3}$,\\ $B(\tau^-\to K^-\pi^0\nu_\tau)$ &=& $(4.44\pm0.26\pm0.24)\times 10^{-3}$,\\ $B(\tau^-\to K^-\pi^0\pi^0\nu_\tau)$ &=& $(0.56\pm0.20\pm0.15)\times 10^{-3}$,\\ $B(\tau^-\to K^-\pi^0\pi^0\pi^0\nu_\tau)$ &=& $(0.37\pm0.21\pm0.11)\times 10^{-3}$,\\ $B(\tau^-\to K^-K^{0}...
From a sample of about 160k $\mbox{Z}\!\!\to\!\!\tau^+\tau^-$ candidates collected with the ALEPH detector at LEP between 1991 and 1995, $\tau$ lepton decays involving $K^0_S\!\to\!\pi^+\pi^-$ are studied. The $K^0_SK^0_L$ associated production in $\tau$ decays is also investigated. The branching ratios are measured for the inclusive decay $B(\tau^-\!\!\to\!\!K^0_SX^-\nu_\tau)=(9.70\!\pm\!0.58\!\pm\!0.62)\ times10^{-3}$ , where $X^-$ can be anything, and for the exclusive decays \begin{center} \begin{tabular}{rcl} $B(\tau^-\!\!\to\!\!\overline{K}^0\pi^-\nu_\tau)$&=&$(8.55\!\pm\!1. 17\! \pm\!0.66)\times10^{-3}$,\\ $B(\tau^-\!\!\to\!\!\overline{K}^0\pi ^-\pi^0\nu_\tau)$&=&$(2.94\!\pm\! 0.73\!\pm\!0.37)\times10^{-3}$, \\ $B(\tau^-\!\!\to\!\!\overline{K} ^0K^-\nu_\tau)$&=&$(1.58\!\pm\!0.42\!\pm\! 0.17)\times10^{-3}$, \\ $B(\tau^-\!\!\to\!\...
A study of neutral-current four-fermion processes is performed, using data collected by the L3 detector at LEP during high-energy runs at centre-of-mass energies 130 - 136, 161 and 170 - 172 GeV, with integrated luminosities of 4.9, 10.7 and 10.1 pb$^{-1}$, respectively. The total cross sections for the final states $ \ell\ell \ell^\prime \ell^\prime $ and $\rm \ell\ell qq $ ($\ell$,~$\ell^\prime $ = e, $\mu$ or $\tau$) are measured and found to be in agreement with the Standard Model prediction.
Bose-Einstein correlations in W-pair decays are studied using data collected by the ALEPH detector at LEP at e+e- centre-of-mass energies from 183 to 209 GeV. The analysis is based on the comparison of WW-->qqqq events to ``mixed'' events constructed with the hadronic part of WW-->qqlnu events. The data are in agreement with the hypothesis that Bose-Einstein correlations are present only for pions from the same W decay. The JETSET model with Bose-Einstein correlations between pions from different W bosons is disfavoured.
We present a study of the inclusive $\omega$ and $\eta^{\prime}$ production based on 3.1 million hadronic Z decays recorded with the L3 detector at LEP during 1991--1994. The production rates per hadronic Z decay have been measured to be $1.17 \pm 0.17 $ $\omega$ mesons and $0.25 \pm 0.04 $ $\eta^{\prime}$ mesons. The production rates and the differential cross sections have been compared with predictions of the JETSET and the HERWIG Monte Carlo models. We have observed that the differential cross sections can be described by an analytical quantum chromodynamics calculation. \end{document}
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....
The measurements of hadron and lepton--pair production cross sections and lepton--pair forward--backward asymmetries performed with the L3 detector at centre--of--mass energies between 130 GeV and 172 GeV are used to search for new physics phenomena. New physics effects involving four fermion vertices -- contact interactions -- are looked for in all channels. For hadron production the exchange of virtual leptoquarks and scalar quarks is studied. No evidence for deviations from the Standard Model expectations is found. Lower limits on the scale $\Lambda$ of contact interactions in the range 1.2 -- 7.1 TeV are obtained at the 95\% confidence level for various models. Upper limits on the coupling strengths of leptoquarks and scalar quarks are derived.
The reaction $\mathrm{e}^{+} \mathrm{e}^{-} \rightarrow \mathrm{e}^{+} \mathrm{e}^{-} \gamma ^{*} \gamma ^{*} \rightarrow \mathrm{e}^{+} \mathrm{e}^{-} $ {\sl hadrons} is analysed using data collected by the L3 detector during the LEP runs at $\sqrt {s}$ = 130-140 GeV and $\sqrt {s}$ = 161 GeV. The cross sections $\sigma(\mathrm{e}^{+} \mathrm{e}^{-} \rightarrow \mathrm{e}^{+} \mathrm{e}^{-} $ {\sl hadrons}) and $\sigma (\gamma\gamma \rightarrow $ {\sl hadrons}) are measured in the interval 5 $\leq W_{\gamma\gamma} \leq$ 75 GeV. The energy dependence of the $\sigma (\gamma\gamma \rightarrow $ {\sl hadrons}) cross section is consistent with the universal Regge behaviour of total hadronic cross sections. %\end{abstract}
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