A search for charginos nearly mass degenerate with the lightest neutralino is performed with the data collected by the ALEPH detector at LEP, at centre-of-mass energies between 189 and 209 GeV, ...corresponding to an integrated luminosity of 628 pb−1. The analysis is based on the detection of isolated and energetic initial state radiation photons, produced in association with chargino pairs whose decay products have little visible energy. The number of candidate events observed is in agreement with that expected from Standard Model background sources. These results are combined with those of other direct searches for charginos, and a lower limit of 88 GeV/c2 at 95% confidence level is derived for the chargino mass in the case of heavy sfermions, irrespective of the chargino-neutralino mass difference.
The prompt production of charmonium $\chi_{c}$ and $J/\psi$ states is studied in proton-proton collisions at a centre-of-mass energy of $\sqrt{s}=7$ TeV at the Large Hadron Collider. The $\chi_{c}$ ...and $J/\psi$ mesons are identified through their decays $\chi_{c}\rightarrow J/\psi \gamma$ and $J/\psi\rightarrow \mu^+\mu^-$ using 36 pb$^{-1}$ of data collected by the LHCb detector in 2010. The ratio of the prompt production cross-sections for $\chi_{c}$ and $J/\psi$, $\sigma (\chi_{c}\rightarrow J/\psi \gamma)/ \sigma (J/\psi)$, is determined as a function of the $J/\psi$ transverse momentum in the range $2 < p_{\mathrm T}^{J/\psi} < 15$ GeV/$c$. The results are in excellent agreement with next-to-leading order non-relativistic expectations and show a significant discrepancy compared with the colour singlet model prediction at leading order, especially in the low $p_{\mathrm T}^{J/\psi}$ region.
Measurements of inclusive $W$ and $Z$ boson production cross-sections in $pp$ collisions at $\sqrt{s}=7$ TeV using final states containing muons are presented. The data sample corresponds to an ...integrated luminosity of 37 pb$^{-1}$ collected with the LHCb detector. The $W$ and $Z$ bosons are reconstructed from muons with a transverse momentum above 20 GeV$/c$ and pseudorapidity between 2.0 and 4.5, and, in the case of the $Z$ cross-section, a dimuon invariant mass between 60 and 120 GeV$/c^2$. The cross-sections are measured to be {$831\pm9\pm27\pm 29$ pb} for $W^+$, {$656\pm8\pm19\pm 23$ pb} for $W^-$ and {$76.7\pm1.7\pm3.3\pm2.7$ pb} for $Z$, where the first uncertainty is statistical, the second is systematic and the third is due to the luminosity. Differential cross-sections, $W$ and $Z$ cross-section ratios and the lepton charge asymmetry are also measured in the same kinematic region. The ratios are determined to be $\sigma_{W^+\rightarrow\mu^+\nu} / \sigma_{W^-\rightarrow\mu^-\bar{\nu}}= ${$1.27\pm0.02\pm0.01$}, and $\sigma_{W^+\rightarrow\mu^+\nu} + \sigma_{W^-\rightarrow\mu^-\bar{\nu}})/\sigma_{Z\rightarrow\mu\mu}= ${$19.4\pm0.5\pm0.9$}. The results are in general agreement with theoretical predictions, performed at next-to-next-to-leading order in QCD using recently calculated parton distribution functions.
The charged-particle production ratios $\bar{p}/p$, $K^-/K^+$, $\pi^-/\pi^+$, $(p + \bar{p})/(\pi^+ + \pi^-)$, $(K^+ + K^-)/(\pi^+ + \pi^-)$ and $(p + \bar{p})/(K^+ + K^-)$ are measured with the LHCb ...detector using $0.3\,{\rm nb^{-1}}$ of $pp$ collisions delivered by the LHC at $\sqrt{s} = 0.9$ TeV and $1.8\,{\rm nb^{-1}}$ at $\sqrt{s} = 7$ TeV. The measurements are performed as a function of transverse momentum $p_{\rm T}$ and pseudorapidity $\eta$. The production ratios are compared to the predictions of several Monte Carlo generator settings, none of which are able to describe adequately all observables. The ratio $\bar{p}/p$ is also considered as a function of rapidity loss, $\Delta y \equiv y_{\rm beam} - y$, and is used to constrain models of baryon transport.
We study the upscaling of a system of many interacting particles through a heterogenous thin elongated obstacle as modeled via a two-dimensional diffusion problem with a one-directional nonlinear ...convective drift. Assuming that the obstacle can be described well by a thin composite strip with periodically placed microstructures, we aim at deriving the upscaled model equations as well as the effective transport coefficients for suitable scalings in terms of both the inherent thickness at the strip and the typical length scales of the microscopic heterogeneities. Aiming at computable scenarios, we consider that the heterogeneity of the strip is made of an array of periodically arranged impenetrable solid rectangles and identify two scaling regimes what concerns the small asymptotics parameter for the upscaling procedure: the characteristic size of the microstructure is either significantly smaller than the thickness of the thin obstacle or it is of the same order of magnitude. We scale up the diffusion–polynomial drift model and list computable formulas for the effective diffusion and drift tensorial coefficients for both scaling regimes. Our upscaling procedure combines ideas of two-scale asymptotics homogenization with dimension reduction arguments. Consequences of these results for the construction of more general transmission boundary conditions are discussed. We illustrate numerically the concentration profile of the chemical species passing through the upscaled strip in the finite thickness regime and point out that trapping of concentration inside the strip is likely to occur in at least two conceptually different transport situations: (i) full diffusion/dispersion matrix and nonlinear horizontal drift, and (ii) diagonal diffusion matrix and oblique nonlinear drift.
The quantum numbers of the X(3872) meson are determined to be J(PC)=1(++) based on angular correlations in B(+)→X(3872)K(+) decays, where X(3872)→π(+)π(-)J/ψ and J/ψ→μ(+)μ(-). The data correspond to ...1.0 fb(-1) of pp collisions collected by the LHCb detector. The only alternative assignment allowed by previous measurements J(PC)=2(-+) is rejected with a confidence level equivalent to more than 8 Gaussian standard deviations using a likelihood-ratio test in the full angular phase space. This result favors exotic explanations of the X(3872) state.
A search for selectron, smuon and stau pair production is performed with the data collected by the ALEPH detector at LEP at centre-of-mass energies up to 209 GeV. The numbers of candidate events are ...consistent with the background predicted by the Standard Model. Final mass limits from ALEPH are reported.
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