0000000000170687
AUTHOR
Wang B
First Measurement of the Absolute Branching Fraction of Λ→pμ−ν¯μ
The absolute branching fraction of Λ→pμ−ν¯μ is reported for the first time based on an e+e− annihilation sample of 10×109 J/ψ events collected with the BESIII detector at s=3.097 GeV. The branching fraction is determined to be B(Λ→pμ−ν¯μ)=[1.48±0.21(stat)±0.08(syst)]×10−4, which is improved by about 30% in precision over the previous indirect measurements. Combining this result with the world average of B(Λ→pe−ν¯e), we obtain the ratio {[Γ(Λ→pμ−ν¯μ)]/[Γ(Λ→pe−ν¯e)]} to be 0.178±0.028, which agrees with the standard model prediction assuming lepton flavor universality. The asymmetry of the branching fractions of Λ→pμ−ν¯μ and Λ¯→p¯μ+νμ is also determined, and no evidence for CP violation is fo…
Distance decay 2.0 – a global synthesis of taxonomic and functional turnover in ecological communities
AbstractUnderstanding the variation in community composition and species abundances, i.e., β-diversity, is at the heart of community ecology. A common approach to examine β-diversity is to evaluate directional turnover in community composition by measuring the decay in the similarity among pairs of communities along spatial or environmental distances. We provide the first global synthesis of taxonomic and functional distance decay along spatial and environmental distance by analysing 149 datasets comprising different types of organisms and environments. We modelled an exponential distance decay for each dataset using generalized linear models and extracted r2 and slope to analyse the streng…
Complete Measurement of the Λ Electromagnetic Form Factors.
The exclusive process e+e−→ΛΛ¯, with Λ→pπ− and Λ¯→p¯π+, has been studied at s=2.396 GeV for measurement of the timelike Λ electric and magnetic form factors, GE and GM. A data sample, corresponding to an integrated luminosity of 66.9 pb−1, was collected with the BESIII detector for this purpose. A multidimensional analysis with a complete decomposition of the spin structure of the reaction enables a determination of the modulus of the ratio R=|GE/GM| and, for the first time for any baryon, the relative phase ΔΦ=ΦE−ΦM. The resulting values are R=0.96±0.14(stat)±0.02(syst) and ΔΦ=37°±12°(stat)±6°(syst), respectively. These are obtained using the recently established and most precise value of …
The ARGO-YBJ Experiment Progresses and Future Extension
Gamma ray source detection above 30 TeV is an encouraging approach for finding galactic cosmic ray origins. All sky survey for gamma ray sources using wide field of view detector is essential for population accumulation for various types of sources above 100 GeV. To target the goals, the ARGO-YBJ experiment has been established. Significant progresses have been made in the experiment. A large air shower detector array in an area of 1 km2 is proposed to boost the sensitivity. Hybrid detections with multi-techniques will allow a good discrimination between different types of primary particles, including photons and protons, thus enable an energy spectrum measurement for individual species. F…
Background radioactivity in the scaler mode technique of the Argo-YBJ detector
""ARGO-YBJ is an extensive air shower detector located at the Yangbajing Cosmic Ray Laboratory (4300 ma.s.l., 606 g cm^−2 atmospheric depth, Tibet, China).. It is made by a single layer of Resistive Plate Chambers. (RPCs, total surface ~ 6700 m^2) grouped into 153 units. called “clusters”. The low energy threshold of the experiment is obtained using the ”scaler operation mode”, counting all the particles hitting the detector without reconstruction of the shower size and arrival direction. For each cluster the signals generated by these particles are put in coincidence in a narrow time window (150 ns) and read by four independent. scaler channels, giving the counting rates of channel. >= 1, …
Evidence for the direct two-photon transition from ψ(3686) to J/ψ.
The two-photon transition ψ(3686)→γγJ/ψ is studied in a sample of 1.06×10(8) ψ(3686) decays collected by the BESIII detector. The branching fraction is measured to be (3.1±0.6(stat)(-1.0)(+0.8)(syst))×10(-4) using J/ψ→e(+)e(-) and J/ψ→μ(+)μ(-) decays, and its upper limit is estimated to be 4.5×10(-4) at the 90% confidence level. This work represents the first measurement of a two-photon transition among charmonium states. The orientation of the ψ(3686) decay plane and the J/ψ polarization in this decay are also studied. In addition, the product branching fractions of sequential E1 transitions ψ(3686)→γχ(cJ) and χ(cJ)→γJ/ψ(J=0,1,2) are reported.
Gamma ray sources observation with the ARGO-YBJ detector
In this paper we report on the observations of TeV gamma ray sources performed by the air shower de- tector ARGO-YBJ. The objects studied in this work are the blazar Markarian 421 and the extended galactic source MGROJ1908+06, monitored during 2 years of operation. Mrk421 has been detected by ARGO-YBJ with a statisti- cal significance of 11 standard deviations. The observed TeV emission was highly variable, showing large enhance- ments of the flux during active periods. The study of the spectral behaviour during flares revealed a positive correla- tion of the hardness with the flux, as already reported in the past by the Whipple telescope, suggesting that this is a long term property of the…