1,845 research outputs found

    Top-quark electroweak couplings at the FCC-ee

    Full text link
    An optimal-observable analysis of the lepton angular and energy distributions from top-quark pair production with semi-leptonic decays in e+e- collisions is used to predict the potential sensitivity of the FCC-ee to the couplings of the top quark to the photon and the Z.Comment: 18 pages, 5 figures. To be published in JHEP (accepted for publication). Between version 2 and version 3, the suggestions of the JHEP referee were implemented both in the text (in Sections "Results and discussion" and "Summary and outlook") and in Figures 3 and

    Direct measurement of alpha_QED(mZ) at the FCC-ee

    Get PDF
    When the measurements from the FCC-ee become available, an improved determination of the standard-model "input" parameters will be needed to fully exploit the new precision data towards either constraining or fitting the parameters of beyond-the-standard-model theories. Among these input parameters is the electromagnetic coupling constant estimated at the Z mass scale, alpha_QED(mZ). The measurement of the muon forward-backward asymmetry at the FCC-ee, just below and just above the Z pole, can be used to make a direct determination of alpha_QED(mZ) with an accuracy deemed adequate for an optimal use of the FCC-ee precision data.Comment: Version 4: Corrigendum added (2 pages). Accepted for publication in JHE

    Closing the light sbottom mass window from a compilation of e+e- -> hadron data

    Get PDF
    The e+e- -> hadron cross section data from PEP, PETRA, TRISTAN, SLC and LEP, at centre-of-mass energies between 20 to 209 GeV, are analysed to search for the production of a pair of light sbottoms decaying hadronically via R-parity-violating couplings. This analysis allows the 95%C.L. exclusion of such a particle if its mass is below 7.5 GeV/c2. The light sbottom mass window is closed.Comment: 19 pages, 8 figures, 10 tables To be published in Physics Letters. This new version has been reshuffled with respect to the original version to include the suggestions from the Referees of Physics Letters. In particular, the e+e- -> hadron data compilation and combination method are now described in detail, to avoid references to unpublished material. A more realistic treatment of systematic uncertainties also improved the limit slightl

    The light gluino mass window revisited

    Get PDF
    The precise measurements of the ``electroweak observables'' performed at LEP and SLC are well consistent with the standard model predictions. Deviations from the standard model arising from vacuum polarization diagrams (also called ``weak loop corrections'') have been constrained in a model-independent manner with the epsilon formalism. Within the same formalism, additional deviations from new physics production processes can also be constrained, still in a model-independent way. For instance, a 95% C.L. limit of Delta Gamma_had} q qbar gluino gluino process, it allows an absolute lower limit to be set on the gluino mass, m_gluino > 6.3 GeV/c2 at 95% C.L., which definitely closes the so-called light gluino mass window. The precise measurements of the "electroweak observables" performed at LEP and SLC are well consistent with the standard model predictions. Deviations from the standard model arising from vacuum polarization diagrams (also called "weak loop corrections") have been constrained in a model-independent manner with the formalism. Within the same formalism, additional deviations from new physics production processes can also be constrained, still in a model-independent way. For instance, a 95% C.L. limit of had<3.9 MeV is set on the partial width of any purely hadronic exotic contribution to Z decays. When applied to the process, it allows an absolute lower limit to be set on the gluino mass, C.L., which definitely closes the so-called light gluino mass window

    Higgs Physics

    Get PDF
    The existence of the Higgs boson was postulated more than 50 years ago, without any indication of its mass. The quest that followed, with several generations of particle physics experiments, culminated with the recent discovery of a new particle with a mass of 125 GeV. At least another half-century will be needed to map the properties of this particle with sufficient precision to understand its deepest origin.L’existence du boson de Higgs a Ă©tĂ© postulĂ©e il y a plus de 50 ans sans indication d’un ordre de grandeur pour sa masse. La longue recherche qui s’en suivit, impliquant plusieurs gĂ©nĂ©rations d’expĂ©riences de physique des particules a Ă©tĂ© enfin couronnĂ©e par la dĂ©couverte rĂ©cente d’une nouvelle particule de masse de 125 GeV. Il s’en faudra sans doute de cinquante annĂ©es supplĂ©mentaires pour en dĂ©couvrir les propriĂ©tĂ©s avec une prĂ©cision suffisante pour comprendre la profonde origine physique de cette particule

    Prospective Studies for LEP3 with the CMS Detector

    Full text link
    On July 4, 2012, the discovery of a new boson, with mass around 125 GeV/c2 and with properties compatible with those of a standard-model Higgs boson, was announced at CERN. In this context, a high-luminosity electron-positron collider ring, operating in the LHC tunnel at a centre-of-mass energy of 240 GeV and called LEP3, becomes an attractive opportunity both from financial and scientific point of views. The performance and the suitability of the CMS detector are evaluated, with emphasis on an accurate measurement of the Higgs boson properties. The precision expected for the Higgs boson couplings is found to be significantly better than that predicted by Linear Collider studies.Comment: 25 pages, 13 figures, 3 tables, Submitted to the European Strategy Preparatory Group (contribution 171), Companion to arXiV:1208.0504. Version 2 contains several additional Higgs decay channels studied, and numbers for TLEP as well as for LEP

    Naturalness and Higgs Decays in the MSSM with a Singlet

    Get PDF
    The simplest extension of the supersymmetric standard model - the addition of one singlet superfield - can have a profound impact on the Higgs and its decays. We perform a general operator analysis of this scenario, focusing on the phenomenologically distinct scenarios that can arise, and not restricting the scope to the narrow framework of the NMSSM. We reexamine decays to four b quarks and four tau's, finding that they are still generally viable, but at the edge of LEP limits. We find a broad set of Higgs decay modes, some new, including those with four gluon final states, as well as more general six and eight parton final states. We find the phenomenology of these scenarios is dramatically impacted by operators typically ignored, specifically those arising from D-terms in the hidden sector, and those arising from weak-scale colored fields. In addition to sensitivity of m_Z, there are potential tunings of other aspects of the spectrum. In spite of this, these models can be very natural, with light stops and a Higgs as light as 82 GeV. These scenarios motivate further analyses of LEP data as well as studies of the detection capabilities of future colliders to the new decay channels presented.Comment: 3 figures, 1 appendix; version to appear in JHEP; typos fixed and additional references and acknowledgements adde

    Machine detector interface for the e+e−e^+e^- future circular collider

    Full text link
    The international Future Circular Collider (FCC) study aims at a design of pppp, e+e−e^+e^-, epep colliders to be built in a new 100 km tunnel in the Geneva region. The e+e−e^+e^- collider (FCC-ee) has a centre of mass energy range between 90 (Z-pole) and 375 GeV (tt_bar). To reach such unprecedented energies and luminosities, the design of the interaction region is crucial. The crab-waist collision scheme has been chosen for the design and it will be compatible with all beam energies. In this paper we will describe the machine detector interface layout including the solenoid compensation scheme. We will describe how this layout fulfills all the requirements set by the parameters table and by the physical constraints. We will summarize the studies of the impact of the synchrotron radiation, the analysis of trapped modes and of the backgrounds induced by single beam and luminosity effects giving an estimate of the losses in the interaction region and in the detector.Comment: 6 pages, 7 figures, 62th ICFA ABDW on High Luminosity Circular e+e−e^+e^- Colliders, eeFACT2018, Hong Kong, Chin

    Top-quark electroweak couplings at the FCC-ee

    Full text link
    • 

    corecore