10,370 research outputs found
Optimization of multivariate analysis for IACT stereoscopic systems
Multivariate methods have been recently introduced and successfully applied
for the discrimination of signal from background in the selection of genuine
very-high energy gamma-ray events with the H.E.S.S. Imaging Atmospheric
Cerenkov Telescope. The complementary performance of three independent
reconstruction methods developed for the H.E.S.S. data analysis, namely Hillas,
model and 3D-model suggests the optimization of their combination through the
application of a resulting efficient multivariate estimator. In this work the
boosted decision tree method is proposed leading to a significant increase in
the signal over background ratio compared to the standard approaches. The
improved sensitivity is also demonstrated through a comparative analysis of a
set of benchmark astrophysical sources.Comment: 10 pages, 8 figures, 3 tables, accepted for publication in
Astroparticle Physic
Limits on τ lepton-flavor violating decays into three charged leptons
A search for the neutrinoless, lepton-flavor violating decay of the τ lepton into three charged leptons has been performed using an integrated luminosity of 468 fb^(-1) collected with the BABAR detector at the PEP-II collider. In all six decay modes considered, the numbers of events found in data are compatible with the background expectations. Upper limits on the branching fractions are set in the range (1.8–3.3)×10^(-8) at 90% confidence level
Measurement of the γγ^*→η_c transition form factor
We study the reaction e^+e^-→e^+e^-η_c, η_c→K_SK^±π^∓ and obtain η_c mass and width values 2982.2±0.4±1.6 MeV/c^2 and 31.7±1.2±0.8 MeV, respectively. We find Γ(η_c→γγ)B(ηc→KK π)=0.374±0.009±0.031 keV, and measure the γγ^*→η_c transition form factor in the momentum transfer range from 2 to 50 GeV^2. The analysis is based on 469 fb^(-1) of integrated luminosity collected at PEP-II with the BABAR detector at e^+e^- center-of-mass energies near 10.6 GeV
Measurement of the semileptonic branching fraction of the B_s meson
We report a measurement of the inclusive semileptonic branching fraction of the B_s meson using data collected with the BABAR detector in the center-of-mass energy region above the Υ(4S) resonance. We use the inclusive yield of ϕ mesons and the ϕ yield in association with a high-momentum lepton to perform a simultaneous measurement of the semileptonic branching fraction and the production rate of B_s mesons relative to all B mesons as a function of center-of-mass energy. The inclusive semileptonic branching fraction of the B_s meson is determined to be B(B_s→ℓνX)=9.5_(-2.0)^(+2.5)(stat)_(-1.9)^(+1.1)(syst)%, where ℓ indicates the average of e and μ
B^0 meson decays to ρ^0K^(*0), f_0K^(*0), and ρ^-K^(*+), including higher K^* resonances
We present branching fraction measurements for the decays B^0→ρ^0K^(*0), B^0→f_0K^(*0), and B^0→ρ^-K^(*+), where K^* is an S-wave (Kπ)_0^* or a K^*(892) meson; we also measure B^0→f_0K_2^*(1430)^0. For the K^*(892) channels, we report measurements of longitudinal polarization fractions (for ρ final states) and direct CP violation asymmetries. These results are obtained from a sample of (471.0±2.8)×10^6 BB̅ pairs collected with the BABAR detector at the PEP-II asymmetric-energy e^+e^- collider at the SLAC National Accelerator Laboratory. We observe ρ^0K^*(892)^0, ρ^0(Kπ)_0^(*0), f_0K^*(892)^0, and ρ^-K^*(892)^+ with greater than 5σ significance, including systematics. We report first evidence for f_0(Kπ)_0^(*0) and f_0K_2^*(1430)^0, and place an upper limit on ρ^-(Kπ)_0^(*+). Our results in the K^*(892) channels are consistent with no direct CP violation
Study of Y(3S,2S) → ηY(1S) and Y(3S,2S) → π^+π^-Y(1S) hadronic transitions
We study the Υ(3S,2S)→ηΥ(1S) and Υ(3S,2S)→π^+π^-Υ(1S) transitions with 122×10^6Υ(3S) and 100×10^6Υ(2S) mesons collected by the BABAR detector at the PEP-II asymmetric-energy e^+e^- collider. We measure B[Υ(2S)→ηΥ(1S)]=(2.39±0.31(stat.)±0.14(syst.))×10^(-4) and Γ[Υ(2S)→ηΥ(1S)]/Γ[Υ(2S)→π^+π^-Υ(1S)]=(1.35±0.17(stat.)±0.08(syst.))×10^(-3). We find no evidence for Υ(3S)→ηΥ(1S) and obtain B[Υ(3S)→ηΥ(1S)]<1.0×10^(-4) and Γ[Υ(3S)→ηΥ(1S)]/ Γ[Υ(3S)→π^+π^-Υ(1S)]<2.3×10^(-3) as upper limits at the 90% confidence level. We also provide improved measurements of the Υ(2S)-Υ(1S) and Υ(3S)-Υ(1S) mass differences, 562.170±0.007(stat.)±0.088(syst.) MeV/c^2 and 893.813±0.015(stat.)±0.107(syst.) MeV/c^2, respectively
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