Measurements of exclusive B_s^0 decays at the Y(5S) resonance

Several exclusive $B_s^0$ decays are studied using a 1.86 fb-1 data sample collected at the Y(5S) resonance with the Belle detector at the KEKB asymmetric energy e^+ e^- collider. In the $B_s^0 \to D_s^- \pi^+$ decay mode we find 10 $B_s^0$ candidates and measure the corresponding branching fraction. Combining the B_s^0 -> D_s^{(*)-} \pi^+, B_s^0 -> D_s^{(*)-} \rho^+, B_s^0 -> J/\psi \phi and B_s^0 -> J/\psi \eta decay modes, a significant $B_s^0$ signal is observed. The ratio \sigma (e^+ e^- -> B_s^* \bar{B}_s^*) / \sigma (e^+ e^- -> B_s^{(*)} \bar{B}_s^{(*)}) = (93^{+7}_{-9} \pm 1)% is obtained at the Y(5S) energy, indicating that $B_s^0$ meson production proceeds predominantly through the creation of $B^*_s \bar{B}^*_s$ pairs. The $B_s^0$ and $B_s^*$ meson masses are measured to be M(B_s^0)=(5370 \pm 1 \pm 3)MeV/c^2 and M(B_s^*)=(5418 \pm 1 \pm 3)MeV/c^2. Upper limits on the B_s^0 -> \gamma \gamma, B_s^0 -> \phi \gamma, B_s^0 -> K^+ K^- and B_s^0 -> D_s^{(*)+} D_s^{(*)-} branching fractions are also reported.Comment: 9 pages, 5 figures, published in Phys. Rev. D76, 012002 (2007

Suzaku Observations of Tycho's Supernova Remnant

Tycho's supernova remnant was observed by the XIS and HXD instruments onboard the Suzaku satellite on 2006 June 26-29 for 92 ks. The spectrum up to 30 keV was well fitted with a two-component model, consisting of a power-law with photon index of 2.7 and a thermal bremsstrahlung model with temperature of 4.7 keV. The former component can alternatively be modeled as synchrotron emission from a population of relativistic electrons with an estimated roll-off energy of around 1 keV. In the XIS spectra, in addition to the prominent Fe K_alpha line (6.445 keV), we observe for the first time significant K_alpha line emission from the trace species Cr and Mn at energies of 5.48 keV and 5.95 keV, respectively. Faint K_beta lines from Ca (4.56 keV) and Fe (7.11 keV) are also seen. The ionization states of Cr and Mn, based on their line centroids, are estimated to be similar to that of Fe K_alpha (Fe XV or XVI).textapplication/pdfjournal articl

Search for Electron Neutrino Appearance in a 250 km Long-Baseline Experiment

journal articl

Measurements of exclusive B^{0}_{s} decays at the γ(5S) resonance

Several exclusive B^{O}_{s} decays are studied using a 1.86 fb^{-1} data sample collected at the Υ(5S) resonance with the Belle detector at the KEKB asymmetric energy e^+e^- collider. In the B^{O}_{s}→D^{-}\{s}π^+ decay mode we find 10 B^{O}_{s} candidates and measure the corresponding branching fraction. Combining the B^{O}_{s}→ D^(*)-_s π^+, B^{O}_{s} → D^(*)-_sρ^+, B^{O}_{s}→ J/Ψφ, and B^{O}_{s}→ J/Ψη decay modes, a significant B^{O}_{S}signal is observed. The ratio σ(e^+e^- → B^{*}_{s}\bar{b}^{*}_{s})/σ(e^+e^- → B^{(*)}_S\bar{B}^{(*)}_s)=(93^{+7}_{-9}±1)% is obtained at the Υ(5S) energy, indicating that B^{O}_{s} meson production proceeds predominantly through the creation of B^{*}_{s}\bar{B}^{*}_S pairs. The B^{O}_{s} and B^{*}_{s} meson masses are measured to be M(B^{O}_{s})=(5370±1±3) MeV/c^2 and M(B^{*}_{s})=(5418±1±3) MeV/c^2. Upper limits on the B^{O}_{s} →γγ, B^{O}_{s} → φγ, B^{O}_{s} → K^+K^-, and B^{O}_{s} → D^{(*)}+_{s}D^{(*)}_s- branching fractions are also reported.journal articl

【活動報告 報告部(個人) ※希望者のみ掲載。五十音順。】新沼雅代

departmental bulletin pape

Proposal of stable method of block generation time considering the amount of mining power in bitcoin

近年，ビットコインは世界中で流通している．ビットコインには10分に1回ブロックを生成する仕組みがあるが，実際にはマイニングパワーの変化によりブロック生成時間が変化し，取引件数や取引完了時間の不安定さが懸念されている．本研究では，マイニングパワーの変化によりマイニングの難易度を調整し，ブロック生成時間の安定手法を提案する．その結果，マイニングパワーが大きく変化する場合に効果があると考える．In recent years, Bitcoin has been distributed all over the world. The Bitcoin blockchain has a mechanism to generate blocks once every 10 minutes, but in reality, the block generation time changes significantly due to changes in mining power. Therefore, there is concern that the number of transactions and transaction completion time will not be stable. In this research, we propose a method to stabilize the block generation time by adjusting the difficulty of mining by changing the mining power. As a result, we think that it is effective when the mining power changes significantly in an actual blockchain network.application/pdfdepartmental bulletin pape

研究速報 : バイアスされた交流電圧による真空中静電浮上

departmental bulletin pape