We report the first observation of the double strange baryon Ξ(1620)0 in its decay to Ξ−π+ via Ξ+c → Ξ−π+π+ decays based on a 980 fb−1 data sample collected with the Belle detector at the KEKB ...asymmetric-energy e+e− collider. The mass and width are measured to be 1610.4 ± 6.0(stat)+6.1−4.2(syst) MeV /c2 and 59.9 ± 4.8(stat)+2.8−7.1(syst) MeV, respectively. We obtain 4.0σ evidence of the Ξ(1690)0 with the same data sample. These results shed light on the structure of hyperon resonances with strangeness S = −2
We report the results of a search for the rare, purely leptonic decay B−→μ−ν¯μ performed with a 711 fb−1 data sample that contains 772×106 BB¯ pairs, collected near the ϒ(4S) resonance with the ...Belle detector at the KEKB asymmetric-energy e+e− collider. The signal events are selected based on the presence of a high momentum muon and the topology of the rest of the event showing properties of a generic B-meson decay, as well as the missing energy and momentum being consistent with the hypothesis of a neutrino from the signal decay. We find a 2.4 standard deviation excess above background including systematic uncertainties, which corresponds to a branching fraction of B(B−→μ−ν¯μ)=(6.46±2.22±1.60)×10−7 or a frequentist 90% confidence level interval on the B−→μ−ν¯μ branching fraction of 2.9,10.7×10−7.
We report on a measurement of the cosmic ray energy spectrum by the Telescope Array Low-Energy Extension (TALE) air fluorescence detector (FD). The TALE air FD is also sensitive to the Cherenkov ...light produced by shower particles. Low-energy cosmic rays, in the PeV energy range, are detectable by TALE as Cherenkov events. Using these events, we measure the energy spectrum from a low energy of ∼2 PeV to an energy greater than 100 PeV. Above 100 PeV, TALE can detect cosmic rays using air fluorescence. This allows for the extension of the measurement to energies greater than a few EeV. In this paper, we describe the detector, explain the technique, and present results from a measurement of the spectrum using ∼1000 hr of observation. The observed spectrum shows a clear steepening near 1017.1 eV, along with an ankle-like structure at 1016.2 eV. These features present important constraints on the origin of galactic cosmic rays and on propagation models. The feature at 1017.1 eV may also mark the end of the galactic cosmic ray flux and the start of the transition to extragalactic sources.
Cosmic rays are energetic charged particles from extraterrestrial sources, with the highest-energy events thought to come from extragalactic sources. Their arrival is infrequent, so detection ...requires instruments with large collecting areas. In this work, we report the detection of an extremely energetic particle recorded by the surface detector array of the Telescope Array experiment. We calculate the particle’s energy as
244
±
29
stat
.
−
76
+
51
syst
.
exa–electron volts
(~40 joules). Its arrival direction points back to a void in the large-scale structure of the Universe. Possible explanations include a large deflection by the foreground magnetic field, an unidentified source in the local extragalactic neighborhood, or an incomplete knowledge of particle physics.
Editor’s summary
Cosmic rays are charged particles from space. At low energies, they mostly originate from the Sun, whereas at high energies, they are expected to be emitted by nearby active galaxies. The Telescope Array Collaboration now reports the detection of a cosmic ray event with an energy of about 240 exa–electron volts, more than a million times higher than that achieved by artificial particle accelerators. Such high-energy particles should experience only small deflections by foreground magnetic fields, but tracing back the arrival direction shows no obvious source galaxy. The authors suggest that the foreground magnetic fields might be stronger than expected, or there could be unknown particle physics at high energies. —Keith T. Smith
Detection of a highly energetic cosmic ray is traced back to its arrival direction, but no source galaxy is evident.
Observation of ϒ(4S)→η^{'}ϒ(1S) Al Said, S; Asner, D M; Ayad, R ...
Physical review letters,
2018-Aug-10, Letnik:
121, Številka:
6
Journal Article
Recenzirano
Odprti dostop
We report the first observation of the hadronic transition ϒ(4S)→η^{'}ϒ(1S), using 496 fb^{-1} data collected at the ϒ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e^{+}e^{-} ...collider. We reconstruct the η^{'} meson through its decays to ρ^{0}γ and to π^{+}π^{-}η, with η→γγ. We measure B(ϒ(4S)→η^{'}ϒ(1S))=3.43±0.88(stat)±0.21(syst)×10^{-5}, with a significance of 5.7σ.
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