1,732 research outputs found

    Bench test results on a new technique for far-infrared polarimetry

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    The results of bench tests performed on a new method of combined interferometry/polarimetry for the magnetic-field reconstruction of tokamak plasmas is presented. In particular, the sensitivity obtained in the polarimetric measurement shows the feasibility of Faraday rotation determination approaching a precision of ±0.2°. The method is based on an optically pumped far-infrared laser with a rotating polarization where both the interferometric and polarimetric information is determined from phase measurements. Specific sources that introduce disturbances in the optical arrangement and that can limit the attainment of the polarimetric precision, mentioned above, are discussed

    Bench Test Results on a new Technique for Far InfraRed Polarimetry

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    The results of bench tests performed on a new method of combined interferometry/polarimetry for the magnetic-field reconstruction of tokamak plasmas is presented. In particular, the sensitivity obtained in the polarimetric measurement shows the feasibility of Faraday rotation determination approaching a precision of ±0.2°. The method is based on an optically pumped far-infrared laser with a rotating polarization where both the interferometric and polarimetric information is determined from phase measurements. Specific sources that introduce disturbances in the optical arrangement and that can limit the attainment of the polarimetric precision, mentioned above, are discussed

    Measurement of the mass and lifetime of the Ωb−\Omega_b^- baryon

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    A proton-proton collision data sample, corresponding to an integrated luminosity of 3 fb−1^{-1} collected by LHCb at s=7\sqrt{s}=7 and 8 TeV, is used to reconstruct 63±963\pm9 Ωb−→Ωc0π−\Omega_b^-\to\Omega_c^0\pi^-, Ωc0→pK−K−π+\Omega_c^0\to pK^-K^-\pi^+ decays. Using the Ξb−→Ξc0π−\Xi_b^-\to\Xi_c^0\pi^-, Ξc0→pK−K−π+\Xi_c^0\to pK^-K^-\pi^+ decay mode for calibration, the lifetime ratio and absolute lifetime of the Ωb−\Omega_b^- baryon are measured to be \begin{align*} \frac{\tau_{\Omega_b^-}}{\tau_{\Xi_b^-}} &= 1.11\pm0.16\pm0.03, \\ \tau_{\Omega_b^-} &= 1.78\pm0.26\pm0.05\pm0.06~{\rm ps}, \end{align*} where the uncertainties are statistical, systematic and from the calibration mode (for τΩb−\tau_{\Omega_b^-} only). A measurement is also made of the mass difference, mΩb−−mΞb−m_{\Omega_b^-}-m_{\Xi_b^-}, and the corresponding Ωb−\Omega_b^- mass, which yields \begin{align*} m_{\Omega_b^-}-m_{\Xi_b^-} &= 247.4\pm3.2\pm0.5~{\rm MeV}/c^2, \\ m_{\Omega_b^-} &= 6045.1\pm3.2\pm 0.5\pm0.6~{\rm MeV}/c^2. \end{align*} These results are consistent with previous measurements.Comment: 11 pages, 5 figures, All figures and tables, along with any supplementary material and additional information, are available at https://lhcbproject.web.cern.ch/lhcbproject/Publications/LHCbProjectPublic/LHCb-PAPER-2016-008.htm

    Measurement of the Bs0→J/ψηB_{s}^{0} \rightarrow J/\psi \eta lifetime

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    Using a data set corresponding to an integrated luminosity of 3fb−13 fb^{-1}, collected by the LHCb experiment in pppp collisions at centre-of-mass energies of 7 and 8 TeV, the effective lifetime in the Bs0→J/ψηB^0_s \rightarrow J/\psi \eta decay mode, τeff\tau_{\textrm{eff}}, is measured to be τeff=1.479±0.034 (stat)±0.011 (syst)\tau_{\textrm{eff}} = 1.479 \pm 0.034~\textrm{(stat)} \pm 0.011 ~\textrm{(syst)} ps. Assuming CPCP conservation, τeff\tau_{\textrm{eff}} corresponds to the lifetime of the light Bs0B_s^0 mass eigenstate. This is the first measurement of the effective lifetime in this decay mode.Comment: All figures and tables, along with any supplementary material and additional information, are available at https://lhcbproject.web.cern.ch/lhcbproject/Publications/LHCbProjectPublic/LHCb-PAPER-2016-017.htm

    Constraints on the unitarity triangle angle Îł\gamma from Dalitz plot analysis of B0→DK+π−B^0 \to D K^+ \pi^- decays

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    The first study is presented of CP violation with an amplitude analysis of the Dalitz plot of B0→DK+π−B^0 \to D K^+ \pi^- decays, with D→K+π−D \to K^+ \pi^-, K+K−K^+ K^- and π+π−\pi^+ \pi^-. The analysis is based on a data sample corresponding to 3.0 fb−13.0\,{\rm fb}^{-1} of pppp collisions collected with the LHCb detector. No significant CP violation effect is seen, and constraints are placed on the angle Îł\gamma of the unitarity triangle formed from elements of the Cabibbo-Kobayashi-Maskawa quark mixing matrix. Hadronic parameters associated with the B0→DK∗(892)0B^0 \to D K^*(892)^0 decay are determined for the first time. These measurements can be used to improve the sensitivity to Îł\gamma of existing and future studies of the B0→DK∗(892)0B^0 \to D K^*(892)^0 decay.Comment: All figures and tables, along with any supplementary material and additional information, are available at https://lhcbproject.web.cern.ch/lhcbproject/Publications/LHCbProjectPublic/LHCb-PAPER-2015-059.html; updated to correct figure 9 (numerical results unchanged

    Observation of the Bs0→J/ψϕϕB_s^0 \rightarrow J/\psi \phi \phi decay

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    The Bs0→J/ψϕϕB_s^0 \rightarrow J/\psi \phi \phi decay is observed in pppp collision data corresponding to an integrated luminosity of 3 fb−1^{-1} recorded by the LHCb detector at centre-of-mass energies of 7 TeV and 8 TeV. This is the first observation of this decay channel, with a statistical significance of 15 standard deviations. The mass of the Bs0B_s^0 meson is measured to be 5367.08 ± 0.38 ± 0.155367.08\,\pm \,0.38\,\pm\, 0.15 MeV/c2^2. The branching fraction ratio B(Bs0→J/ψϕϕ)/B(Bs0→J/ψϕ)\mathcal{B}(B_s^0 \rightarrow J/\psi \phi \phi)/\mathcal{B}(B_s^0 \rightarrow J/\psi \phi) is measured to be 0.0115\,\pm\, 0.0012\, ^{+0.0005}_{-0.0009}. In both cases, the first uncertainty is statistical and the second is systematic. No evidence for non-resonant Bs0→J/ψϕK+K−B_s^0 \rightarrow J/\psi \phi K^+ K^- or Bs0→J/ψK+K−K+K−B_s^0 \rightarrow J/\psi K^+ K^- K^+ K^- decays is found.Comment: All figures and tables, along with any supplementary material and additional information, are available at https://lhcbproject.web.cern.ch/lhcbproject/Publications/LHCbProjectPublic/LHCb-PAPER-2015-033.htm

    A new algorithm for identifying the flavour of Bs0B_s^0 mesons at LHCb

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    A new algorithm for the determination of the initial flavour of Bs0B_s^0 mesons is presented. The algorithm is based on two neural networks and exploits the bb hadron production mechanism at a hadron collider. The first network is trained to select charged kaons produced in association with the Bs0B_s^0 meson. The second network combines the kaon charges to assign the Bs0B_s^0 flavour and estimates the probability of a wrong assignment. The algorithm is calibrated using data corresponding to an integrated luminosity of 3 fb−1^{-1} collected by the LHCb experiment in proton-proton collisions at 7 and 8 TeV centre-of-mass energies. The calibration is performed in two ways: by resolving the Bs0B_s^0-Bˉs0\bar{B}_s^0 flavour oscillations in Bs0→Ds−π+B_s^0 \to D_s^- \pi^+ decays, and by analysing flavour-specific Bs2∗(5840)0→B+K−B_{s 2}^{*}(5840)^0 \to B^+ K^- decays. The tagging power measured in Bs0→Ds−π+B_s^0 \to D_s^- \pi^+ decays is found to be (1.80±0.19(stat)±0.18(syst))(1.80 \pm 0.19({\rm stat}) \pm 0.18({\rm syst}))\%, which is an improvement of about 50\% compared to a similar algorithm previously used in the LHCb experiment.Comment: All figures and tables, along with any supplementary material and additional information, are available at https://lhcbproject.web.cern.ch/lhcbproject/Publications/LHCbProjectPublic/LHCb-PAPER-2015-056.htm

    Bose-Einstein correlations of same-sign charged pions in the forward region in pp collisions at √s=7 TeV

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    Bose-Einstein correlations of same-sign charged pions, produced in protonproton collisions at a 7 TeV centre-of-mass energy, are studied using a data sample collected by the LHCb experiment. The signature for Bose-Einstein correlations is observed in the form of an enhancement of pairs of like-sign charged pions with small four-momentum difference squared. The charged-particle multiplicity dependence of the Bose-Einstein correlation parameters describing the correlation strength and the size of the emitting source is investigated, determining both the correlation radius and the chaoticity parameter. The measured correlation radius is found to increase as a function of increasing charged-particle multiplicity, while the chaoticity parameter is seen to decreas
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