6,868 research outputs found

    Multiplicities, fluctuations and correlations

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    The recent results on hadron multiplicities in heavy and light quark fragmentation, multiplicity local fluctuations and multiparticle correlations submitted to the Conference are reviewed.Comment: 5 pages, 4 eps figs. Talk given at the 31st International Conference on High Energy Physics (ICHEP02), Amsterdam, The Netherlands, 24-31 July 2002. To appear in the Proceeding

    Running of the QED coupling in small-angle Bhabha scattering at LEP

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    Using the OPAL detector at LEP, the running of the effective QED coupling alpha(t) is measured for space-like momentum transfer, 2 \leq -t \leq 6 GeV^2, from the angular distribution of small-angle Bhabha scattering. This is currently the most significant direct observation of the running of the QED coupling in a single experiment and the first clear evidence of the hadronic contribution to the running in the space-like region. Our result is in good agreement with standard evaluations of alpha(t), based on data in the time-like region.Comment: Talks given at the 19th Rencontres De Physique De La Vallee D'Aoste (27.2-5.3.05), La Thuile, Italy and at the 40th Rencontres De Moriond On Electroweak Interactions And Unified Theories (5.3-12.3.05), La Thuile, Italy. Added 1 figure and related text wrt vers.

    The CMS muon system in Run2: preparation, status and first results

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    The CMS muon system has played a key role for many physics results obtained from the LHC Run-1 data. During the Long Shutdown (2013-2014) significant upgrades have been carried out on the muon detectors and on the L1 muon trigger. In parallel the algorithms for muon reconstruction and identification have been improved for both the High-Level Trigger and the offline reconstruction. Results of studies performed on data and Monte Carlo simulations will be presented, with focus on the improvements aiming to ensure an excellent performance in conditions of multiplicity of pileup events and bunch spacing expected during the high-luminosity phase of Run-2. The early muon performance results from LHC Run-2 will be shown.Comment: 8 pages, 13 figures, to be published in the proceedings of EPS-HEP 201

    Fermion pair production at LEP2 and interpretations

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    Preliminary results on e+e−→ffˉe^+ e^- \to f \bar{f}, f=e,ÎŒ,τ,qf=e, \mu, \tau, q, including all LEP2 data are discussed. Good agreement is found with the Standard Model up to the highest energies. Limits on possible new physics are extracted.Comment: 8 pages, 4 figures, to appear in the Proceedings of the New Trends in High-Energy Physics, Yalta, Ukraine, September 22 - 29, 200

    A Framework to Simultaneously Explain Tiny Neutrino Mass and Huge Missing Mass Problem of the Universe

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    Recently a minimalistic scenario has been developed to explain dark matter and tiny but nonzero neutrino masses. In this scenario, a new scalar called SLIM plays the role of the dark matter. Neutrinos achieve Majorana mass through a one-loop diagram. This scenario can be realized for both real and complex SLIM. Simultaneously explaining the neutrino mass and dark matter abundance constrains the scenario. In particular for real SLIM, an upper bound of a few MeV on the masses of the new particles and a lower bound on their coupling are obtained which make the scenario testable. The low energy scenario can be embedded within various SU(2)×U(1)SU(2)\times U(1) symmetric models. I shall briefly review the scenario and a specific model that embeds the scenario, with special emphasis on the effects in the charged Kaon decay which might be observable at the KLOE and NA62 experiments.Comment: 7 pages, 1 figur

    Quark mixing and CP violation - the CKM matrix

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    I present the status of the elements and parameters of the Cabibbo-Kobayashi-Maskawa (CKM) matrix and summarise the related theoretical progress since "Lepton-Photon 2003". One finds |V_{us}| = 0.2227 +/- 0.0017 from K and tau decays and |V_{cb}| = (41.6 +/- 0.5) * 10^{-3} from inclusive semileptonic B decays. The unitarity triangle can now be determined from tree-level quantities alone and the result agrees well with the global fit including flavour-changing neutral current (FCNC) processes, which are sensitive to new physics. From the global fit one finds the three CKM angles theta_{12}=12.9 +/- 0.1 degrees, theta_{23}= 2.38 +/- 0.03 degrees and theta_{13}= 0.223 +/- 0.007 degrees in the standard PDG convention. The CP phase equals delta_{13} = gamma = (58.8 +5.3/-5.8) degrees at 1 sigma CL and gamma=(58.8 +11.2/-15.4) degrees at 2 sigma CL. A major progress are first results from fully unquenched lattice QCD computations for the hadronic quantities entering the UT fit. I further present the calculation of three-loop QCD corrections to the charm contribution in K+ -> pi+ nu nu-bar decays, which removes the last relevant theoretical uncertainty from the K -> pi nu nu-bar system. Finally I discuss mixing-induced CP asymmetries in b -> s q-bar q penguin decays, whose naive average is below its Standard Model value by 3 sigma.Comment: 14 pages, 12 figures, plenary talk at "Lepton-Photon 2005

    Does the hard pomeron obey Regge factorisation?

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    While data for the proton structure function demand the presence of a hard-pomeron contribution even at quite small Q^2, previous fits to the pp and p\bar p total cross sections have found that in these there is little or no room for such a contribution. We re-analyse the data and show that itmay indeed be present and that, further, it probably obeys Regge factorisation: sigma^{gamma p}(s,Q_1^2)sigma^{gamma p}(s,Q_2^2)= sigma^{pp}(s)sigma^{gamma gamma}(s,Q_1^2,Q_2^2) for all values of Q_1^2 and Q_2^2.Comment: 11 pages, 10 figure