2,639 research outputs found

    Measurement of branching fractions and direct CP asymmetries for B→Kπ and B→ππ decays at Belle II

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    We report measurements of the branching fractions and direct CP asymmetries of the decays B0→K+π−, B+→K+π0, B+→K0π+, and B0→K0π0, and use these for testing the standard model through an isospin-based sum rule. In addition, we measure the branching fraction and direct CP asymmetry of the decay B+→π+π0 and the branching fraction of the decay B0→π+π−. The data are collected with the Belle II detector from e+e− collisions at the Υ(4S) resonance produced by the SuperKEKB asymmetric-energy collider and contain 387×106 bottom-antibottom meson pairs. Signal yields are determined in two-dimensional fits to background-discriminating variables, and range from 500 to 3900 decays, depending on the channel. We obtain −0.03±0.13±0.04 for the sum rule in agreement with the standard model expectation of zero and with a precision comparable to the best existing determinations

    Measurement of the τ\tau-lepton mass with the Belle II experiment

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    We present a measurement of the τ\tau-lepton mass using a sample of about 175 million e+eτ+τe^+e^- \to \tau^+\tau^- events collected with the Belle II detector at the SuperKEKB e+ee^+e^- collider at a center-of-mass energy of 10.579GeV10.579\,\mathrm{Ge\kern -0.1em V}. This sample corresponds to an integrated luminosity of 190fb1190\,\mathrm{fb^{-1}}. We use the kinematic edge of the τ\tau pseudomass distribution in the decay τππ+πντ{\tau^-\to\pi^-\pi^+\pi^-\nu_\tau} and measure the τ\tau mass to be 1777.09±0.08±0.11MeV ⁣/c21777.09 \pm 0.08 \pm 0.11 \,\mathrm{Me\kern -0.1em V\!/c^2}, where the first uncertainty is statistical and the second systematic. This result is the most precise to date

    Precise measurement of the Ds+D^+_s lifetime at Belle II

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    7 pages, 4 figures, to be submitted to Physical Review LettersInternational audienceWe measure the lifetime of the Ds+D_s^+ meson using a data sample of 207 fb1^{-1} collected by the Belle II experiment running at the SuperKEKB asymmetric-energy e+ee^+ e^- collider. The lifetime is determined by fitting the decay-time distribution of a sample of 116×103116\times 10^3 Ds+ϕπ+D_s^+\rightarrow\phi\pi^+ decays. Our result is \tau^{}_{D^+_s} = (498.7\pm 1.7\,^{+1.1}_{-0.8}) fs, where the first uncertainty is statistical and the second is systematic. This result is significantly more precise than previous measurements

    New detection systems for an enhanced sensitivity in key stellar (n,γ) measurements

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    Neutron capture cross-section measurements are fundamental in the study of astrophysical phenomena, such as the slow neutron capture (s-) process of nucleosynthesis operating in red-giant and massive stars. However, neutron capture measurements via the time-of-flight (TOF) technique on key s-process nuclei are often challenging. Difficulties arise from the limited mass (∼mg) available and the high sample-related background in the case of the unstable s-process branching points. Measurements on neutron magic nuclei, that act as s-process bottlenecks, are affected by low (n,γ) cross sections and a dominant neutron scattering background. Overcoming these experimental challenges requires the combination of facilities with high instantaneous flux, such as n_TOFEAR2, with detection systems with an enhanced detection sensitivity and high counting rate capabilities. This contribution reviews some of the latest detector developments in detection systems for (n,γ) measurements at n_TOF, such as i-TED, an innovative detection system which exploits the Compton imaging technique to reduce the dominant neutron scattering background and s-TED, a highly segmented total energy detector intended for high flux facilities. The discussion will be illustrated with results of the first measurement of key the s-process branching-point reaction 79Se(n,γ).Title in Web of Science: New detection systems for an enhanced sensitivity in key stellar (n,gamma) measurements</p

    Collins and Sivers transverse-spin asymmetries in inclusive muoproduction of ρ0\rho^0 mesons

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    The production of vector mesons in deep inelastic scattering is an interesting yet scarsely explored channel to study the transverse spin structure of the nucleon and the related phenomena. The COMPASS collaboration has performed the first measurement of the Collins and Sivers asymmetries for inclusively produced ρ0\rho^0 mesons. The analysis is based on the data set collected in deep inelastic scattering in 20102010 using a 160GeV/c160\,\,\rm{GeV}/c μ+\mu^+ beam impinging on a transversely polarized NH3\rm{NH}_3 target. The ρ0\rho^{0} mesons are selected from oppositely charged hadron pairs, and the asymmetries are extracted as a function of the Bjorken-xx variable, the transverse momentum of the pair and the fraction of the energy zz carried by the pair. Indications for positive Collins and Sivers asymmetries are observed

    Templates of expected measurement uncertainties

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    The covariance committee of CSEWG (Cross Section Evaluation Working Group) established templates of expected measurement uncertainties for neutron-induced total, (n,γ), neutron-induced charged-particle, and (n,xn) reaction cross sections as well as prompt fission neutron spectra, average prompt and total fission neutron multiplicities, and fission yields. Templates provide a list of what uncertainty sources are expected for each measurement type and observable, and suggest typical ranges of these uncertainties and correlations based on a survey of experimental data, associated literature, and feedback from experimenters. Information needed to faithfully include the experimental data in the nuclear-data evaluation process is also provided. These templates could assist (a) experimenters and EXFOR compilers in delivering more complete uncertainties and measurement information relevant for evaluations of new experimental data, and (b) evaluators in achieving a more comprehensive uncertainty quantification for evaluation purposes. This effort might ultimately lead to more realistic evaluated covariances for nuclear-data applications. In this topical issue, we cover the templates coming out of this CSEWG effort–typically, one observable per paper. This paper here prefaces this topical issue by introducing the concept and mathematical framework of templates, discussing potential use cases, and giving an example of how they can be applied (estimating missing experimental uncertainties of 235U(n,f) average prompt fission neutron multiplicities), and their impact on nuclear-data evaluations

    Search for a long-lived spin-0 mediator in b→s transitions at the Belle II experiment

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    Additional spin-0 particles appear in many extensions of the standard model. We search for long-lived spin-0 particles S in B-meson decays mediated by a b→s quark transition in e+e− collisions at the Υ(4S) resonance at the Belle II experiment. Based on a sample corresponding to an integrated luminosity of 189  fb−1, we observe no evidence for signal. We set model-independent upper limits on the product of branching fractions B(B0→K∗(892)0(→K+π−)S)×B(S→x+x−) and B(B+→K+S)×B(S→x+x−), where x+x− indicates e+e−,μ+μ−,π+π−, or K+K−, as functions of S mass and lifetime at the level of 10−7

    High resolution

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    Neutron capture cross section measurements of isotopes close to s-process branching-points are of fundamental importance for the understanding of this nucleosynthesis mechanism through which about 50% of the elements heavier than iron are produced. We present in this contribution the results corresponding to the high resolution measurement, for first time ever, of the 80Se(n, γ) cross section, in which 98 resonances never measured before have been reported. As a consequence, ten times more precise values for the MACS have been obtained compared to previous accepted value adopted in the astrophysical KADoNiS data base

    Measurement of branching-fraction ratios and CPCP asymmetries in B±DCP±K±B^{\pm} \to D_{CP\pm}K^{\pm} decays at Belle and Belle II

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    We report results from a study of B±DK±B^\pm \rightarrow DK^\pm decays followed by DD decaying to CPCP~eigenstates, where DD indicates a D0D^0 or Dˉ0\bar{D}^{0} meson. These decays are sensitive to the Cabibbo-Kobayashi-Maskawa unitarity-triangle angle ϕ3\phi_{3}. The results are based on a combined analysis of the final data set of 772×106 BBˉ772 \times 10^6~B\bar{B} pairs collected by the Belle experiment and a data set of 198×106 BBˉ198 \times 10^6~B\bar{B} pairs collected by the Belle~II experiment, both in electron-positron collisions at the Υ(4S)\Upsilon(4S) resonance. We measure the CPCP asymmetries to be ACP+= (+12.5±5.8±1.4)%\mathcal{ A}_{CP +} =~(+12.5 \pm 5.8 \pm 1.4)\% and ACP= (16.7±5.7±0.6)%\mathcal{ A}_{CP -} =~(-16.7 \pm 5.7 \pm 0.6)\%, and the ratios of branching fractions to be RCP+= 1.164±0.081±0.036\mathcal{ R}_{CP+}=~1.164 \pm 0.081 \pm 0.036 and RCP= 1.151±0.074±0.019\mathcal{ R}_{CP-} =~1.151 \pm 0.074 \pm 0.019. The first contribution to the uncertainties is statistical, and the second is systematic. The asymmetries ACP+\mathcal{A}_{CP +} and ACP\mathcal{A}_{CP -} have similar magnitudes and opposite signs; their difference corresponds to 3.5~standard deviations. From these values we calculate 68.3% confidence intervals of (8.5<ϕ3<16.58.5^{\circ}<\phi_{3}<16.5^{\circ}) or (84.5<ϕ3<95.584.5^{\circ}<\phi_{3}<95.5^{\circ}) or (163.3<ϕ3<171.5163.3^{\circ}<\phi_{3}<171.5^{\circ}) and 0.321<rB<0.4650.321<r_{B}<0.465
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