Type

Database

Creator

Date

Thumbnail

Search results

131 records were found.

Measurement of the chemical and isotopic composition of cosmic rays is essential for the precise understanding of their propagation in the galaxy. While the model parameters are mainly determined using the B/C ratio, the study of extended sets of ratios can provide stronger constraints on the propagation models. In this paper, the relative abundances of light-nuclei lithium, beryllium, boron, and carbon are presented. The secondary-to-primary ratios Li/C, Be/C, and B/C have been measured in the kinetic energy range 0.35-45 GeV nucleon[superscript –1]. The isotopic ratio [superscript 7]Li/[superscript 6]Li is also determined in the magnetic rigidity interval 2.5-6.3 GV. The secondary-to-secondary ratios Li/Be, Li/B, and Be/B are also reported. These measurements are based on the data collected by the Alpha Magnetic Spectrometer AMS-01 d...
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.
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 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}
We report on the observation of single W boson production in a data sample collected by the L3 detector at LEP2. The signal consists of large missing energy final states with a single energetic lepton or two hadronic jets. The cross-section is measured to be $0.61^{+0.43}_{-0.33} \pm 0.05 \; \rm{pb}$ at the centre of mass energy $\sqrt{s}=172 \GeV{}$, consistent with the Standard Model expectation. From this measurement the following limits on the anomalous $\gamma$WW gauge couplings are derived at 95\% CL: $\rm -3.6 \Delta \kappa_\gamma 1.5$ and $\rm -3.6 \lambda_\gamma 3.6$.
An analysis of single and multi-photon events with missing energy is performed using data collected with the L3 detector at LEP at centre-of-mass energies around 183\gev, for a total of 55.3 pb$^{-1}$ of integrated luminosity. The results obtained are in good agreement with the Standard Model prediction and are used to derive the value for the $\epem\ra\nnbar\gamma(\gamma)$ cross section as well as upper limits on cross sections of new physics processes. Several interpretations in supersymmetric models providing new limits on the masses of the lightest neutralino and of the gravitino are presented.
New measurements at a centre-of-mass energy of 183 GeV of the hadronic photon structure function F2(x) in the Q2 interval, 9 GeV2 Q2 30 GeV2, are presented. The data, collected in 1997, with the L3 detector, correspond to an integrated luminosity of 51.9 pb-1. Combining with the data taken at centre-of-mass energies of 91 GeV, the evolution of F2 with Q2 is measured in the Q2 range from 1.2 GeV2 to 30 GeV2. F2 shows a linear growth with ln(Q2); the value of the slope (alpha-1)dF2(Q2)/dln(Q2) is measured in two x bins from 0.01 to 0.2 and is higher than predictions.
The tau lepton lifetime is measured with the L3 detector at LEP using the complete data taken at centre-of-mass energies around the Z pole resulting in $\tau_{\tau}\,=\,293.2\,\pm\,2.0~\mbox{(stat)}\,\pm\, 1.5~\mbox{(syst)}$ fs. The comparison of this result with the muon lifetime supports lepton universality of the weak charged current at the level of six per mille. Assuming lepton universality, the value of the strong coupling constant, $\alpha_s$ is found to be $\alpha_s(m_{\tau}^2)$ = 0.319 $\pm$ 0.015~\mbox{(exp)} $\pm$ 0.014~\mbox{(theory)}.
Want to know more?If you want to know more about this cutting edge product, or schedule a demonstration on your own organisation, please feel free to contact us or read the available documentation at http://www.keep.pt/produtos/retrievo/?lang=en