522 research outputs found

    Conceptual design report for the LUXE experiment

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    This Conceptual Design Report describes LUXE (Laser Und XFEL Experiment), an experimental campaign that aims to combine the high-quality and high-energy electron beam of the European XFEL with a powerful laser to explore the uncharted terrain of quantum electrodynamics characterised by both high energy and high intensity. We will reach this hitherto inaccessible regime of quantum physics by analysing high-energy electron-photon and photon-photon interactions in the extreme environment provided by an intense laser focus. The physics background and its relevance are presented in the science case which in turn leads to, and justifies, the ensuing plan for all aspects of the experiment: Our choice of experimental parameters allows (i) field strengths to be probed where the coupling to charges becomes non-perturbative and (ii) a precision to be achieved that permits a detailed comparison of the measured data with calculations. In addition, the high photon flux predicted will enable a sensitive search for new physics beyond the Standard Model. The initial phase of the experiment will employ an existing 40 TW laser, whereas the second phase will utilise an upgraded laser power of 350 TW. All expectations regarding the performance of the experimental set-up as well as the expected physics results are based on detailed numerical simulations throughout

    Measurement of the cross-section ratio σψ(2S)/σJ/ψ(1S)\sigma_{\psi(2S )}/\sigma_{J/\psi(1S )} in exclusive photoproduction at HERA

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    The exclusive photoproduction reactions γpJ/ψ(1S)p\gamma p \to J/\psi(1S) p and γpψ(2S)p\gamma p \to \psi(2S) p have been measured at an epep centre-of-mass energy of 318 GeV with the ZEUS detector at HERA using an integrated luminosity of 373 pb1^{-1}. The measurement was made in the kinematic range 30<W<18030 < W < 180 GeV, Q2<1Q^2 < 1 GeV2^2 and t<1|t| < 1 GeV2^2, where WW is the photon--proton centre-of-mass energy, Q2Q^2 is the photon virtuality and tt is the squared four-momentum transfer at the proton vertex. The decay channels used were J/ψ(1S)μ+μJ/\psi(1S) \to \mu^+ \mu^-, ψ(2S)μ+μ\psi(2S) \to \mu^+ \mu^- and ψ(2S)J/ψ(1S)π+π\psi(2S) \to J/\psi(1S) \pi^+ \pi^- with subsequent decay J/ψ(1S)μ+μJ/\psi(1S) \to \mu^+ \mu^-. The ratio of the production cross sections, R=σψ(2S)/σJ/ψ(1S)R = \sigma_{\psi(2S)} / \sigma_{J/\psi(1S)}, has been measured as a function of WW and t|t| and compared to previous data in photoproduction and deep inelastic scattering and with predictions of QCD-inspired models of exclusive vector-meson production, which are in reasonable agreement with the data.Comment: 31 pages, 9 figures. Updated according to comments from journal referee including a new table. Added full collaboration author lis

    Search for high-mass exclusive γγ → WW and γγ → ZZ production in proton-proton collisions at s \sqrt{s} = 13 TeV

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    Search for pair-produced vector-like leptons in final states with third-generation leptons and at least three b quark jets in proton-proton collisions at √s = 13 TeV