2,318 research outputs found
Preliminary results of measurements by automated probes Vega 1 and 2 or particle concentration in clouds of Venus at heights 47-63 KM
Results of the preliminary processing of the Vega 1 and 2 descender data on the cloud layer structure of the Venusian atmosphere are discussed. A photoelectric counter for aerosol particles is described together with its optical and pneumatic circuits and operation algorithm. Vertical profiles of concentrations of particles with a diameter of 0.4 microns agree quantitatively with the Pioneer-Venus and Venera 9 and 10 data. Concentrations of these particles are: in the B layer, up to 190/cu cm; in the C layer, up to 10/cu cm; and in the D layer, up to 130/cu cm. Layers have sharp boundaries with a significant vertical heterogeneity of the aerosol concentration field inside them
Evidence for B- -> Ds+ K- l- nubar and search for B- -> Ds*+ K- l- nubar
We report measurements of the decays B- -> Ds(*)+ K- l- nubar in a data
sample containing 657x10^6 BBbar pairs collected with the Belle detector at the
KEKB asymmetric-energy e+e- collider. We observe a signal with a significance
of 6 sigma for the combined Ds and Ds* modes and find the first evidence of the
B- -> Ds+ K- l- nubar decay with a significance of 3.4 sigma. We measure the
following branching fractions: BF(B- -> Ds+ K- l nubar) = (0.30 +/- 0.09(stat)
+0.11 -0.08(syst)) x 10^-3 and BF(B- -> Ds*+ K- l- nubar) = (0.59 +/-
0.12(stat) +/- 0.15(syst)) x 10^-3 and set an upper limit BF(B- -> Ds*+ K- l-
nubar) < 0.56 x 10^-3 at the 90% confidence level. We also present the first
measurement of the Ds+K- invariant mass distribution in these decays, which is
dominated by a prominent peak around 2.6 GeV/c^2.Comment: Submitted to Phys. Rev.
CsI(Tl) Pulse Shape Discrimination with the Belle II Electromagnetic Calorimeter as a Novel Method to Improve Particle Identification at Electron-Positron Colliders
This paper describes the implementation and performance of CsI(Tl) pulse
shape discrimination for the Belle II electromagnetic calorimeter, representing
the first application of CsI(Tl) pulse shape discrimination for particle
identification at an electron-positron collider. The pulse shape
characterization algorithms applied by the Belle II calorimeter are described.
Control samples of , , , and are
used to demonstrate the significant insight into the secondary particle
composition of calorimeter clusters that is provided by CsI(Tl) pulse shape
discrimination. Comparisons with simulation are presented and provide further
validation for newly developed CsI(Tl) scintillation response simulation
techniques, which when incorporated with GEANT4 simulations allow the particle
dependent scintillation response of CsI(Tl) to be modelled. Comparisons between
data and simulation also demonstrate that pulse shape discrimination can be a
new tool to identify sources of improvement in the simulation of hadronic
interactions in materials. The efficiency and photon-as-hadron
fake-rate of a multivariate classifier that is trained to use pulse shape
discrimination is presented and comparisons are made to a shower-shape based
approach. CsI(Tl) pulse shape discrimination is shown to reduce the
photon-as-hadron fake-rate by over a factor of 3 at photon energies of 0.2 GeV
and over a factor 10 at photon energies of 1 GeV
Search for Lepton Flavor and Lepton Number Violating tau Decays into a Lepton and Two Charged Mesons
We search for lepton flavor and lepton number violating tau decays into a
lepton (ell = electron or muon) and two charged mesons (h,h' = pi^\pm or
K^\pm), tau- -> ell-h+h'- and tau- -> ell+h-h'-, using 671 fb^{-1} of data
collected with the Belle detector at the KEKB asymmetric-energy e+e- collider.
We obtain 90% C.L. upper limits on the branching fractions in the range
(4.4-8.8)x10^{-8} for tau -> ehh', and (3.3-16)x10^{-8} for tau -> muhh'
processes. These results improve upon previously published upper limits by
factors between 1.6 to 8.8.Comment: 15 page, 7 figures, submitted to Phys. Lett.
Study of the decays B->D_s1(2536)+ anti-D(*)
We report a study of the decays B -> D_s1(2536)+ anti-D(*), where anti-D(*)
is anti-D0, D- or D*-, using a sample of 657 x 10^6 B anti-B pairs collected at
the Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric-energy
e+e- collider. The branching fractions of the decays B+ -> D_s1(2536)+ anti-D0,
B0 -> D_s1(2536)+ D- and B0 -> D_s1(2536)+ D*- multiplied by that of
D_s1(2536)+ -> (D*0K+ + D*+K0) are found to be (3.97+-0.85+-0.56) x 10^-4,
(2.75+-0.62+-0.36) x 10^-4 and (5.01+-1.21+-0.70) x 10^-4, respectively.Comment: 6 pages, 2 figues, submitted to PRD (RC
Search for lepton-flavor-violating decays at Belle
We have searched for neutrinoless lepton decays into and ,
where stands for an electron or muon, and for a vector meson
(, , , or ), using 543 fb
of data collected with the Belle detector at the KEKB asymmetric-energy
collider. No excess of signal events over the expected background has
been observed, and we set upper limits on the branching fractions in the range
at the 90% confidence level. These upper limits
include the first results for the mode as well as new limits that
are significantly more restrictive than our previous results for the , , and modes.Comment: 7 pages, 16 figure
Energy scan of the cross sections and evidence for decays into charged bottomonium-like states
Using data collected with the Belle detector at the KEKB asymmetric-energy
collider, we measure the energy dependence of the cross sections from thresholds up to GeV.
We find clear and peaks with little or no
continuum contribution. We study the resonant substructure of the
transitions and find evidence that they
proceed entirely via the intermediate isovector states and
. The relative fraction of these states is loosely constrained by
the current data: the hypothesis that only is produced is excluded
at the level of 3.3 standard deviations, while the hypothesis that only
is produced is not excluded at a significant level.Comment: 8 pages, 4 figures, submitted to Physical Review Letter
First study of \eta_c, \eta(1760) and X(1835) production via \eta'\pi^+\pi^- final states in two-photon collisions
The invariant mass spectrum of the \eta' \pi^+ \pi^- final state produced in
two-photon collisions is obtained using a 673 fb^{-1} data sample collected in
the vicinity of the \Upsilon(4S) resonance with the Belle detector at the KEKB
asymmetric-energy e^+e^- collider. We observe a clear signal of the \eta_c and
measure its mass and width to be M(\eta_c)=(2982.7 +- 1.8(stat) +- 2.2(syst) +-
0.3(model)) MeV/c^2 and \Gamma(\eta_c) = (37.8^{+5.8}_{-5.3}(stat) +- 2.8(syst)
+- 1.4(model)) MeV/c^2. The third error is an uncertainty due to possible
interference between the \eta_c and a non-resonant component. We also report
the first evidence for \eta(1760) decay to \eta' \pi^+ \pi^-; we find two
solutions for its parameters, depending on the inclusion or not of the X(1835),
whose existence is of marginal significance in our data. From a fit to the mass
spectrum using coherent X(1835) and \eta(1760) resonant amplitudes, we set a
90% confidence level upper limit on the product \Gamma_{\gamma\gamma} \BR
(\eta' \pi^+ \pi^-) for the X(1835).Comment: 13 pages, 7 figures, submitted to PR
Search for decays to invisible final states at Belle
We report the result from the first search for decays to invisible
final states. The analysis is performed on a data sample of 924
collected at and near the and resonances with the
Belle detector at the KEKB asymmetric-energy collider. The
absolute branching fraction is determined using an inclusive sample,
obtained by fully reconstructing the rest of the particle system including the
other charmed particle. No significant signal yield is observed and an upper
limit of is set on the branching fraction of to
invisible final states at 90\% confidence level.Comment: 17 pages, 4 figures, submitted to PRD(RC
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