49 research outputs found

    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

    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

    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 KL→π±e∓νK_L \to \pi^{\pm}e^{\mp}\nu based on 298 million analyzed decays. We measure a value of δL=(3322±58(stat)±47(sys))⋅10−6\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

    Observation of the Decay KL→μ+μ−γγK_L\to \mu^+\mu^- \gamma \gamma

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    We have observed the decay KL→μ+μ−γγK_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 KL→π0μ+μ−K_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(KL→μ+μ−γγ{\mathcal B}(K_L\to \mu^+\mu^- \gamma \gamma) =(10.4−5.9+7.5(stat)±0.7(sys))×10−9 = (10.4^{+7.5}_{-5.9} {\rm (stat)} \pm 0.7 {\rm (sys)})\times 10^{-9} with mγγ≥1MeV/c2m_{\gamma\gamma} \geq 1 {\rm MeV/c}^2, consistent with a QED calculation which predicts (9.1±0.8)×10−9(9.1\pm 0.8)\times 10^{-9}.Comment: See also the paper "Search for the Decay KL→π0μ+μ−K_L \to \pi^0 \mu^+ \mu^-", also by the KTeV collaboratio

    Search for the Decay Kl -> pi0 e+ e-

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    We report on a search for the decay Kl -> pi0 e+ e- carried out by the KTeV/E799 experiment at Fermilab. This decay is expected to have a significant CP violating contribution and the measurement of its branching ratio could support the CKM mechanism for CP violation or could point to new physics. Two events were observed in the 1997 data with an expected background of 1.06 +-0.41 events, and we set an upper limit Br(Kl -> pi0 e+ e-) < 5.1 x 10^-10 at the 90% confidence level.Comment: 13 pages, 2 figure

    Search for the Decay KL→π0μ+μ−K_L \to \pi^0 \mu^+ \mu^-

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    We report on a search for the decay \klpimumu carried out as a part of the KTeV experiment at Fermilab. This decay is expected to have a significant CPCP violating contribution and a direct measurement will either support the CKM mechanism for CP violation or point to new physics. Two events were observed in the 1997 data with an expected background of 0.87±0.150.87 \pm 0.15 events, and we set an upper limit \BR{\klpimumu} <3.8×10−10 <3.8 \times 10^{-10} at the 90% confidence level.Comment: See also "Observation of the Decay KL→μ+μ−γγK_L\to \mu^+\mu^- \gamma \gamma", also by the KTeV collaboratio

    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

    Measurement of the branching ratio of pi^0 -> e^+e^- using K_L -> 3 pi^0 decays in flight

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    The branching ratio of the rare decay pi^0 -> e^+e^- has been measured in E799-II, a rare kaon decay experiment using the KTeV detector at Fermilab. The pi^0's were produced in fully-reconstructed K_L -> 3 pi^0 decays in flight. We observed 275 candidate pi^0 -> e^+e^- events, with an expected background of 21.4 +- 6.2 events which includes the contribution from Dalitz decays. We measured BR(pi^0 -> e^+e^-, x>0.95) = (6.09 +- 0.40 +- 0.24) times 10^{-8}, where the first error is statistical and the second systematic. This result is the first significant observation of the excess rate for this decay above the unitarity lower bound.Comment: New version shortened to PRL length limit. 5 pages, 4 figures. Published in Phys. Rev. Let

    A Measurement of the Branching Ratio of KL→e+e−γγK_L \to e^+e^-\gamma\gamma

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    We report on a study of the decay KL→e+e−γγK_L \to e^+e^-\gamma\gamma carried out as a part of the KTeV/E799 experiment at Fermilab. The 1997 data yielded a sample of 1543 events, including an expected background of 56±856 \pm 8 events. An effective form factor was determined from the observed distribution of the e+e−e^+e^- invariant mass. Using this form factor in the calculation of the detector acceptance, the branching ratio was measured to be B(KL→e+e−γγ,Eγ∗>5MeV)=(5.84±0.15 (stat)±0.32 (sys))×10−7{\mathcal B}(K_L \to e^+ e^- \gamma \gamma, E^*_\gamma > 5 {MeV}) = (5.84 \pm 0.15 {\rm ~(stat)} \pm 0.32 {\rm ~(sys)})\times 10^{-7}.Comment: 5 pages, 4 figure

    Measurement of the Decay KL -> Pi0 Gamma Gamma

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    We report on a new measurement of the decay KL -> pi0 gamma gamma by the KTeV experiment at Fermilab. We determine the KL -> pi0 gamma gamma branching ratio to be (1.68 +/- 0.07 +/- 0.08)x10**-6. Our data shows the first evidence for a low-mass gamma gamma signal as predicted by recent O(p**6) chiral perturbation calculations that include vector meson exchange contributions. From our data, we extract a value for the effective vector coupling aV = -0.72 +/- 0.05 +/- 0.06.Comment: 5 pages, 4 figure
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