6,193 research outputs found

    Electroweak measurements from the Tevatron

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    I review the status of electroweak measurements including W and Z bosons produced at the Tevatron. I describe measurements of the W-boson mass, the W production charge asymmetry, diboson production and limits on anomalous trilinear gauge couplings. These analyses use integrated luminosities ranging from 200 pb−1 to 3.6 fb−1 of data collected by the CDF and DØ Run-II detectors at the Fermilab Tevatron

    Implications of gauge-mediated supersymmetry breaking with vector-like quarks and a ~125 GeV Higgs boson

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    We investigate the implications of models that achieve a Standard Model-like Higgs boson of mass near 125 GeV by introducing additional TeV-scale supermultiplets in the vector-like 10+\bar{10} representation of SU(5), within the context of gauge-mediated supersymmetry breaking. We study the resulting mass spectrum of superpartners, comparing and contrasting to the usual gauge-mediated and CMSSM scenarios, and discuss implications for LHC supersymmetry searches. This approach implies that exotic vector-like fermions t'_{1,2}, b',and \tau' should be within the reach of the LHC. We discuss the masses, the couplings to electroweak bosons, and the decay branching ratios of the exotic fermions, with and without various unification assumptions for the mass and mixing parameters. We comment on LHC prospects for discovery of the exotic fermion states, both for decays that are prompt and non-prompt on detector-crossing time scales.Comment: 32 pages. v2: references added, figure caption 5.3 correcte

    Search for Light Gluinos via the Spontaneous Appearance of pi+pi- Pairs with an 800 GeV/c Proton Beam at Fermilab

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    We searched for the appearance of pi+pi- pairs with invariant mass greater than 648 MeV in a neutral beam. Such an observation could signify the decay of a long-lived light neutral particle. We find no evidence for this decay. Our null result severely constrains the existence of an R0 hadron, which is the lightest bound state of a gluon and a light gluino, and thereby also the possibility of a light gluino. Depending on the photino mass, we exclude the R0 in the mass and lifetime ranges of 1.2 -- 4.6 GeV and 2E-10 -- 7E-4 seconds, respectively. (To Appear in Phys. Rev. Lett.)Comment: Documentstyle aps,epsfig,prl (revtex), 6 pages, 7 figure

    Measurements of the rare decay K_{L} -> e^{+} e^{-} e^{+} e^{-}

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    We observe 441 K_{L} -> e^{+} e^{-} e^{+} e^{-} candidate events with a background of 4.2 events and measure B(K_{L} -> e^{+} e^{-} e^{+} e^{-}) = (3.72 \pm 0.18(stat) \pm 0.23(syst)) \times 10^{-8} in the KTeV/E799II experiment at Fermilab. Using the distribution of the angle between the planes of the e^{+} e^{-} pairs, we measure the CP parameters beta_{CP} = -0.23 \pm 0.09(stat) \pm 0.02(syst) and gamma_{CP} = -0.09 \pm 0.09(stat) \pm 0.02(syst). We also present the first detailed study of the e^{+} e^{-} invariant mass spectrum in this decay mode.Comment: 14 pages, 4 figure

    First Observation of the decay KL -> pi0 e e gamma

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    We report on the first observation of the decay KL -> pi0 ee gamma by the KTeV E799 experiment at Fermilab. Based upon a sample of 48 events with an estimated background of 3.6 +/- 1.1 events, we measure the KL -> pi0 ee gamma branching ratio to be (2.34 +/- 0.35 +/- 0.13)x10^{-8}. Our data agree with recent O(p^6) calculations in chiral perturbation theory that include contributions from vector meson exchange through the parameter a_V. A fit was made to the KL -> pi0 ee gamma data for a_V with the result -0.67 +/- 0.21 +/- 0.12, which is consistent with previous results from KTeV.Comment: Submitted to Physical Review Letters, 5 pages, 5 figure

    Search for the Decay K_L -> pi^0 nu nubar using pi^0 -> e^+ e^- gamma

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    We report on a search for the decay K_L -> pi^0 nu nubar, carried out as a part of E799-II, a rare K_L decay experiment at Fermilab. Within the Standard Model, the K_L -> pi^0 nu nubar decay is dominated by direct CP violating processes, and thus an observation of the decay implies confirmation of direct CP violation. Due to theoretically clean calculations, a measurement of B(K_L -> pi^0 nu nubar) is one of the best ways to determine the CKM parameter eta. No events were observed, and we set an upper limit B(K_L -> pi^0 nu nubar) < 5.9 times 10^-7 at the 90% confidence level.Comment: 5 pages, 4 figure

    Observation of the Decay KLμ+μγγK_L\to \mu^+\mu^- \gamma \gamma

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    We have observed the decay KLμ+μγγK_L\to \mu^+\mu^- \gamma \gamma at the KTeV experiment at Fermilab. This decay presents a formidable background to the search for new physics in KLπ0μ+μK_L\to\pi^0\mu^+\mu^-. The 1997 data yielded a sample of 4 signal events, with an expected background of 0.155 ±\pm 0.081 events. The branching ratio is B(KLμ+μγγ{\mathcal B}(K_L\to \mu^+\mu^- \gamma \gamma) =(10.45.9+7.5(stat)±0.7(sys))×109 = (10.4^{+7.5}_{-5.9} {\rm (stat)} \pm 0.7 {\rm (sys)})\times 10^{-9} with mγγ1MeV/c2m_{\gamma\gamma} \geq 1 {\rm MeV/c}^2, consistent with a QED calculation which predicts (9.1±0.8)×109(9.1\pm 0.8)\times 10^{-9}.Comment: See also the paper "Search for the Decay KLπ0μ+μK_L \to \pi^0 \mu^+ \mu^-", also by the KTeV collaboratio

    Search for the K(L) --> PI0 PI0 E+ E- Decay in the KTeV Experiment

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    The recent discovery of a large CP violating asymmetry in K(L) --> PI+ PI- E+ E- mode has prompted us to seach for the associated K(L) --> PI0 PI0 E+ E- decay mode in the KTeV-E799 experiment at Fermilab. In 2.7E+11 K(L) decays, one candidate event has been observed with an expected background of 0.3 event, resulting in an upper limit for the K(L) --> PI0 PI0 E+ E- branching ratio of 6.6E-09 at the 90% confidence level.Comment: To be published in Phys. Rev. Let

    A Measurement of the KL Charge Asymmetry

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    We present a measurement of the charge asymmetry δL\delta_L in the mode KLπ±eνK_L \to \pi^{\pm}e^{\mp}\nu based on 298 million analyzed decays. We measure a value of δL=(3322±58(stat)±47(sys))106\delta_L = (3322 \pm 58(stat) \pm 47(sys))\cdot 10^{-6}, in good agreement with previous measurements and 2.4 times more precise than the current best published result. The result is used to place more stringent limits on CPT and ΔS=ΔQ\Delta S = \Delta Q violation in the neutral kaon system.Comment: Submitted to Physical Review Letters, Dec 31, 2001. 4 pages, 4 figure

    A New Measurement of the Radiative Ke3 Branching Ratio and Photon Spectrum

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    We present a preliminary report on a new measurement of the radiative neutral Ke3 branching ratio and the first study of the photon spectrum in this decay. We find BR(Ke3g, E*_g>30 GeV, Th*_eg>20 deg)/BR(Ke3) = 0.911+-0.009(stat)+0.021-0.010(syst)%. Our measurement of the spectrum is consistent with inner bremsstrahlung only as the source of photons at the 2 sigma level.Comment: 5 pages, 4 figures, proceedings paper from Meson 2000, Cracow, Poland, May 200
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