781 research outputs found

    Lepton flavour violation in future linear colliders in the long-lived stau NLSP scenario

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    We analyze the prospects of observing lepton flavour violation in future e-e- and e+e- linear colliders in scenarios where the gravitino is the lightest supersymmetric particle, and the stau is the next-to-lightest supersymmetric particle. The signals consist of multilepton final states with two heavily ionizing charged tracks produced by the long-lived staus. The Standard Model backgrounds are very small and the supersymmetric backgrounds can be kept well under control by the use of suitable kinematical cuts. We discuss in particular the potential of the projected International Linear Collider to discover lepton flavour violation in this class of scenarios, and we compare the estimated sensitivity with the constraints stemming from the non-observation of rare decays.Comment: 30 pages, 12 figures. Discussion extended to include the efficiency of identifying long-lived staus, references added. To appear in JHE

    Combined CDF and D0 Upper Limits on Standard Model Higgs-Boson Production with 2.1 - 5.4 fb-1 of Data

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    We combine results from CDF and D0 on direct searches for a standard model (SM) Higgs boson (H) in ppbar collisions at the Fermilab Tevatron at sqrt(s)=1.96 TeV. Compared to the previous Tevatron Higgs search combination more data have been added and some previously used channels have been reanalyzed to gain sensitivity. We use the latest parton distribution functions and gg->H theoretical cross sections when comparing our limits to the SM predictions. With 2.0-4.8 fb-1 of data analyzed at CDF, and 2.1-5.4 fb-1 at D0, the 95% C.L. upper limits on Higgs boson production are a factor of 2.70 (0.94) times the SM cross section for a Higgs boson mass of m_H=115 (165) GeV/c^2. The corresponding median upper limits expected in the absence of Higgs boson production are 1.78 (0.89). The mass range excluded at 95% C.L. for a SM Higgs is 163<m_H<166 GeV/c^2, with an expected exclusion of 159<m_H<168 GeV/c^2.Comment: 30 pages, five figures. Results prepared for the HCP 2009 conference, November 16-20, in Evian, Franc

    Probing Lepton Flavor Violation Signal Induced by R-violating Minimal Supersymmetric Standard Model at a Linear Collider

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    The lepton-flavor violation (LFV) effect at an e+ee^+e^- linear collider (LC), in the frame of R-parity violating minimal supersymmetric standard model is studied. We take the R-parity violating processes e+eeμ±e^+e^-\to e^{\mp}\mu^{\pm} as signal, and define the summation of the two processes as ``experiment'' observable. We find that the cross-section summation can reach O\cal{O}(101)fb(10^1)fb in the parameter space without sneutrino resonance effect(smν~\sqrt{s} \sim m_{\tilde{\nu}}). The summation treatment manifests uniform differential distribution on cosθ\cos\theta, where θ\theta denotes the polar angles of both outgoing e+/ee^+/e^- respectively to incoming electron beam in two signal processes. The uniform feature together with eμe\mu collinearity would help to reduce the SM background dramatically. Consequently we conclude that at a 500GeV500 GeV LC with 480fb1480 fb^{-1} annual luminosity, it's either possible to detect the distinctive R-violating LFV eμe\mu signal, or exclude sneutrino to mν~>1.1TeVm_{\tilde{\nu}}>1.1 TeV at 95% CL in the machine's biennial runtime interval.Comment: 14 pages, 9 figure

    Analysis strategy for the SM Higgs boson search in the four-lepton final state in CMS

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    The current status of the searches for the SM Higgs boson in the HH\rightarrowZZ()ZZ^{(*)}\rightarrow44\ell decay channel with the CMS experiment is presented. The selection cuts for suppressing the backgrounds while keeping very high signal efficiencies are described, along with the data-driven algorithms implemented to estimate the background yields and the systematic uncertainties. With an integrated luminosity of 1.66fb11.66 \mathrm{fb}^{-1}, upper limits at 95% CL on the SM-like Higgs cross section ×\times branching ratio exclude cross sections from about one to two times the expected value from the Standard Model in the range 150<mH<420GeV150 < m_{H} < 420 \mathrm{GeV}. No evidence for the existence of the SM Higgs boson has been found so far.Comment: "Presented at the 2011 Hadron Collider Physics symposium (HCP-2011), Paris, France, November 14-18 2011, 3 pages, 5 figures.