418 research outputs found

    Search for black holes and sphalerons in high-multiplicity final states in proton-proton collisions at s=13 \sqrt{s}=13 TeV

    Get PDF
    A search in energetic, high-multiplicity final states for evidence of physics beyond the standard model, such as black holes, string balls, and electroweak sphalerons, is presented. The data sample corresponds to an integrated luminosity of 35.9 fb−1 collected with the CMS experiment at the LHC in proton-proton collisions at a center-of-mass energy of 13 TeV in 2016. Standard model backgrounds, dominated by multijet production, are determined from control regions in data without any reliance on simulation. No evidence for excesses above the predicted background is observed. Model-independent 95% confidence level upper limits on the cross section of beyond the standard model signals in these final states are set and further interpreted in terms of limits on semiclassical black hole, string ball, and sphaleron production. In the context of models with large extra dimensions, semiclassical black holes with minimum masses as high as 10.1 TeV and string balls with masses as high as 9.5 TeV are excluded by this search. Results of the first dedicated search for electroweak sphalerons are presented. An upper limit of 0.021 is set at 95% confidence level on the fraction of all quark-quark interactions above the nominal threshold energy of 9 TeV resulting in the sphaleron transition

    Extraction and validation of a new set of CMS pythia8 tunes from underlying-event measurements

    Get PDF

    Measurement of t ̄t normalised multi-differential cross sections inpp collisions at√s=13 TeV, and simultaneous determination ofthe strong coupling strength, top quark pole mass, and parton distribution functions

    Get PDF
    Normalised multi-differential cross sections for top quark pair (tt̄) production are measured in proton-proton collisions at a centre-of-mass energy of 13 TeV using events containing two oppositely charged leptons. The analysed data were recorded with the CMS detector in 2016 and correspond to an integrated luminosity of 35.9fb⁻¹. The double-differential tt̄ cross section is measured as a function of the kinematic properties of the top quark and of the tt̄ system at parton level in the full phase space. A triple-differential measurement is performed as a function of the invariant mass and rapidity of the tt̄ system and the multiplicity of additional jets at particle level. The data are compared to predictions of Monte Carlo event generators that complement next-to-leading-order (NLO) quantum chromodynamics (QCD) calculations with parton showers. Together with a fixed-order NLO QCD calculation, the triple-differential measurement is used to extract values of the strong coupling strength αS and the top quark pole mass (m_(pole_t) using several sets of parton distribution functions (PDFs). The measurement of m_(pole)_t exploits the sensitivity of the tt̄ invariant mass distribution to m_(pole)_t near the production threshold. Furthermore, a simultaneous fit of the PDFs, α_S, and m_(pole)_t is performed at NLO, demonstrating that the new data have significant impact on the gluon PDF, and at the same time allow an accurate determination of α_S and m_(pole)_t. The values α_S(m_Z) = 0.1135+0.0021−0.0017 and m_(pole)_t = 170.5±0.8GeV are extracted, which account for experimental and theoretical uncertainties, the latter being estimated from NLO scale variations. Possible effects from Coulomb and soft-gluon resummation near the tt̄ production threshold are neglected in these parameter extractions. A rough estimate of these effects indicates an expected correction of m_(pole)_t of the order of +1 GeV, which can be regarded as additional theoretical uncertainty in the current m_(pole)_t extraction

    Search for a heavy pseudoscalar boson decaying to a Z and a Higgs boson at s=13TeV\sqrt{s}=13\,\text {Te}\text {V}

    Get PDF
    corecore