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Strong model independent upper bounds on Br(K{sub s} →?° e?) may be inferred from recent experimental limits on Br(K{sub L} →?° e?) and Br(K →?+e+?−). From this result, upper bounds for Br(K{sub s} → e?) may be obtained for a broad class of models. Models outside of this class seem unlikely.
A search for the lepton flavor violating decays?− → l− K{sub S}° (l = e or?) has been performed using a data sample corresponding to an integrated luminosity of 469 fb−1, collected with the BABAR detector at the SLAC PEP-II ee− asymmetric energy collider. No statistically significant signal has been observed in either channel and the estimated upper limits on branching fractions are?(?− → e− K{sub S}°)
We present the search for the lepton flavour violating decay [tau] → lK°{sub s} with the BaBar experiment data. This process and many other lepton flavour violating [tau] decays, like [tau] → [mu][gamma] and [tau] → lll, are one of the most promising channel to search for evidence of new physics. According to the Standard Model and the neutrino mixing parameters, branching fractions are estimated well below 10−14, but many models of new physics allow for branching fractions values close to the present experimental sensitivity. This analysis is based on a data sample of 469fb−1 collected by BABAR detector at the PEP-II storage ring from 1999 to 2007, equivalent to 431 millions of [tau] pairs. the BABAR experiment, initially designed for studying CP violation in B mesons, has demonstrated to be one of the most suitable environments for studying [tau] decays. The tracking system, the calorimeter and the particle identification of BABAR, together with the knowledge of the [tau] initial energy, allow an extremely powerful rejection of background events that, for this analysis, is better than 10−9. Being [tau] → lK°{sub s} a decay mode without neutrinos, the signal [tau] decay can be fully reconstructed. Kinematical constraints are used in a fit that provides a decay tree reconstruction with a high resolution. For this analysis MC simulated events play a decisive role for estimating the signal efficiency and study the residual background. High statistics MC sample are produced simulating detector conditions for different periods of data collection, in order to reduce any discrepancies with the data. When discrepancies can not be removed, we perform studies to compute a correction factor or an estimation of systematic errors that need to be included in the final measurement. A significant improvement of the current result can be reached only with a higher statistics and, therefore, with a new collider providing a luminosity from 10 to 100 times more than PEP-II. A new detector, with improved performance and able to collect data in a high background environment, is also requested to fully exploit the capability of such amount of data. In fact, only keeping the efficiency and the background as similar as possible to present ones, we will be able to scale almost linearly the estimated upper limit according to the luminosity. The strong potential of improvement for the search of lepton flavour violation [tau] decays makes the building of such a machine highly desirable.
A search for lepton flavor violating decays of the [tau] lepton to a lighter mass lepton and a pseudoscalar meson has been performed using 339 fb−1 of ee− annihilation data collected at a center-of-mass energy near 10.58GeV by the BABAR detector at the SLAC PEP-II storage ring. No evidence of signal has been found, and upper limits on the branching fractions are set at 10−7 level.
We present the most recent searches for lepton-flavor-violating (LFV)? decays in BABAR. We find no evidence of? decaying to three charged leptons or to a charged lepton and a neutral meson (K{sub S}°,?,?, K*°, {bar K}*°), and set upper limits on the corresponding branching fractions (BF) between 1.8 and 19 x 10−8 at 90% confidence level (CL).
A search for lepton flavor violating decays of a [tau] to a lighter-mass charged lepton and an [omega] vector meson is performed using 384.1 fb−1 of ee− annihilation data collected with the BABAR detector at the Stanford Linear Accelerator Center PEP-II storage ring. No signal is found, and the upper limits on the branching ratios are determined to be [beta]([tau]{sup {+-}} 2!e{sup {+-}}[omega])
Searches for lepton-flavor-violating decays of a? lepton to a lighter mass lepton and a photon have been performed with the entire dataset of (963 ± 7) x 106? decays collected by the BABAR detector near the?(4S),?(3S) and?(2S) resonances. The searches yield no evidence of signals and they set upper limits on the branching fractions of?(?{sup {+-}} → e{sup {+-}}?)
Searches for lepton-flavor-violating decays of a [tau] lepton to a lighter mass lepton and a photon have been performed with the entire dataset of (963 ± 7) x 106 [tau] decays collected by the BABAR detector near the [Upsilon](4S), [Upsilon](3S) and [Upsilon](2S) resonances. The searches yield no evidence of signals and they set upper limits on the branching fractions of [Beta]([tau]{sup {+-}} 2!e{sup {+-}}[gamma])
Charged lepton-flavor violating processes are extremely rare in the Standard Model, but they are predicted to occur in several beyond-the-Standard Model theories, including Supersymmetry or models with leptoquarks or compositeness. We present a search for such processes in a sample of 117 x 106 [Upsilon](3S) decays recorded with the BABAR detector. We place upper limits on the branching fractions BF([Upsilon](3S) 2!e{sup {+-}}[tau]{sup {-+}})