arXiv subjects
Publications and source records attributed to T. Kawasaki.
We report the results of the first search for the decay $B_s^0\rightarrowπ^0π^0$ using $121.4\ \rm fb^{-1}$ of data collected at the $Υ(5\rm S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. We observe no signal and set a 90\% confidence level upper limit of $7.7\times 10^{-6}$ on the $B_s^0\rightarrowπ^0π^0$ decay branching fraction.
We present a measurement of the differential shapes of exclusive $B\to D^* \ell \barν_\ell$ ($B = B^-, \bar{B}^0 $ and $\ell = e, μ$) decays with hadronic tag-side reconstruction for the full Belle data set of $711\,\mathrm{fb}^{-1}$ integrated luminosity. We extract the Caprini-Lellouch-Neubert (CLN) and Boyd-Grinstein-Lebed (BGL) form factor parameters and use an external input for the absolute branching fractions to determine the Cabibbo-Kobayashi-Maskawa matrix element and find $|V_{cb}|_\mathrm{CLN} = (40.1\pm0.9)\times 10^{-3}$ and $|V_{cb}|_\mathrm{BGL} = (40.6\pm 0.9)\times 10^{-3}$ with the zero-recoil lattice QCD point $\mathcal{F}(1) = 0.906 \pm 0.013$. We also perform a study of the impact of preliminary beyond zero-recoil lattice QCD calculations on the $|V_{cb}|$ determinations. Additionally, we present the lepton flavor universality ratio $R_{eμ} = \mathcal{B}(B \to D^* e \barν_e) / \mathcal{B}(B \to D^* μ\barν_μ) = 0.990 \pm 0.021 \pm 0.023$, the electron and muon forward-backward asymmetry and their difference $ΔA_{FB}=0.022\pm0.026\pm 0.007$, and the electron and muon $D^*$ longitudinal polarization fraction and their difference $ΔF_L^{D^*} = 0.034 \pm 0.024 \pm 0.007$. The uncertainties quoted correspond to the statistical and systematic uncertainties, respectively.
We search for the tree-diagram dominated process $B^+ \rightarrow p \overline{n} π^0$, using a data sample of $772 \times 10^6~B\overline B$ pairs collected at the $Υ(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+ e^-$ collider. This is the first search with the Belle detector for a decay mode including an anti-neutron. No significant signal is observed and an $90\%$ credible upper limit on the branching fraction is set at $6.1\times10^{-6}$.
We present a study of a singly Cabibbo-suppressed decay $Λ_c^+\to{}pK_S^0K_S^0$ and a Cabibbo-favored decay $Λ_c^+\to{}pK_S^0η$ based on 980 $\rm fb^{-1}$ of data collected by the Belle detector, operating at the KEKB energy-asymmetric $e^+e^-$ collider. We measure their branching fractions relative to $Λ_c^+\to{}pK_S^0$: $\mathcal{B}(Λ_c^+\to{}pK_S^0K_S^0)/\mathcal{B}(Λ_c^+\to{}pK_S^0)={(1.48 \pm 0.08 \pm 0.04)\times 10^{-2}}$ and $\mathcal{B}(Λ_c^+\to{}pK_S^0η)/\mathcal{B}(Λ_c^+\to{}pK_S^0)={(2.73\pm 0.06\pm 0.13)\times 10^{-1}}$. Combining with the world average $\mathcal{B}(Λ_c^+\to{}pK_S^0)$, we have the absolute branching fractions: $\mathcal{B}(Λ_c^+\to{}pK_S^0K_S^0) = {(2.35\pm 0.12\pm 0.07 \pm 0.12 )\times 10^{-4}}$ and $\mathcal{B}(Λ_c^+\to{}pK_S^0η) = {(4.35\pm 0.10\pm 0.20 \pm 0.22 )\times 10^{-3}}$. The first and second uncertainties are statistical and systematic, respectively, while the third ones arise from the uncertainty on $\mathcal{B}(Λ_c^+\to{}pK_S^0)$. The mode $Λ_c^+\to{}pK_S^0K_S^0$ is observed for the first time and has a statistical significance of $>\!10σ$. The branching fraction of $Λ_c^+\to{}pK_S^0η$ has been measured with a threefold improvement in precision over previous results and is found to be consistent with the world average.
We present measurements of the branching fractions for the singly Cabibbo-suppressed decays $D^+\to K^{+}K^{-}π^{+}π^{0}$ and $D_s^{+}\to K^{+}π^{-}π^{+}π^{0}$, and the doubly Cabibbo-suppressed decay $D^{+}\to K^{+}π^{-}π^{+}π^{0}$, based on 980 ${\rm fb}^{-1}$ of data recorded by the Belle experiment at the KEKB $e^{+}e^{-}$ collider. We measure these modes relative to the Cabibbo-favored modes $D^{+}\to K^{-}π^{+}π^{+}π^{0}$ and $D_s^{+}\to K^{+}K^{-}π^{+}π^{0}$. Our results for the ratios of branching fractions are $B(D^{+}\to K^{+}K^{-}π^{+}π^{0})/B(D^{+}\to K^{-}π^{+}π^{+}π^{0}) = (11.32 \pm 0.13 \pm 0.26)\%$, $B(D^{+}\to K^{+}π^{-}π^{+}π^{0})/B(D^{+}\to K^{-}π^{+}π^{+}π^{0}) = (1.68 \pm 0.11\pm 0.03)\%$, and $B(D_s^{+}\to K^{+}π^{-}π^{+}π^{0})/B(D_s^{+}\to K^{+}K^{-}π^{+}π^{0}) = (17.13 \pm 0.62 \pm 0.51)\%$, where the uncertainties are statistical and systematic, respectively. The second value corresponds to $(5.83\pm 0.42)\times\tan^4θ_C$, where $θ_C$ is the Cabibbo angle; this value is larger than other measured ratios of branching fractions for a doubly Cabibbo-suppressed charm decay to a Cabibbo-favored decay. Multiplying these results by world average values for $B(D^{+}\to K^{-}π^{+}π^{+}π^{0})$ and $B(D_s^{+}\to K^{+}K^{-}π^{+}π^{0})$ yields $B(D^{+}\to K^{+}K^{-}π^{+}π^{0})= (7.08\pm 0.08\pm 0.16\pm 0.20)\times10^{-3}$, $B(D^{+}\to K^{+}π^{-}π^{+}π^{0})= (1.05\pm 0.07\pm 0.02\pm 0.03)\times10^{-3}$, and $B(D_s^{+}\to K^{+}π^{-}π^{+}π^{0}) = (9.44\pm 0.34\pm 0.28\pm 0.32)\times10^{-3}$, where the third uncertainty is due to the branching fraction of the normalization mode. The first two results are consistent with, but more precise than, the current world averages. The last result is the first measurement of this branching fraction.
We report measurements of the ratios of branching fractions for $B \to \bar{D}^{(*)}π\ell^+ν_\ell$ and $B \to \bar{D}^{(*)}π^+π^-\ell^+ν_\ell$ relative to $B \to \bar{D}^*\ell^+ν_\ell$ decays with $\ell = e, μ$. These results are obtained from a data sample that contains $772 \times 10^6 B\bar{B}$ pairs collected near the $Υ(4S)$ resonance with the Belle detector at the KEKB asymmetric energy $e^+e^-$ collider. Fully reconstructing both $B$ mesons in the event, we obtain \begin{align*} \frac{B(B^0 \to \bar{D}^0π^-\ell^+ν_\ell)}{B(B^0 \to D^{*-}\ell^+ν_\ell)} &= (7.24\pm0.36\pm0.12)\%\ ,\\ \frac{B(B^+ \to D^-π^+\ell^+ν_\ell)}{B(B^+ \to \bar{D}^{*0}\ell^+ν_\ell)} &= (6.78\pm0.24\pm0.15)\%\ ,\\ \frac{B(B^0 \to \bar{D}^{*0}π^-\ell^+ν_\ell)}{B(B^0 \to D^{*-}\ell^+ν_\ell)} &= (11.10\pm0.48\pm0.20)\%\ ,\\ \frac{B(B^+ \to D^{*-}π^+\ell^+ν_\ell)}{B(B^+ \to \bar{D}^{*0}\ell^+ν_\ell)} &= (9.50\pm0.33\pm0.27)\%\ ,\\ \frac{B(B^0 \to D^-π^+π^-\ell^+ν_\ell)}{B(B^0 \to D^{*-}\ell^+ν_\ell)} &= (2.91\pm0.37\pm0.25)\%\ ,\\ \frac{B(B^+ \to \bar{D}^0π^+π^-\ell^+ν_\ell)}{B(B^+ \to \bar{D}^{*0}\ell^+ν_\ell)} &= (3.10\pm0.26\pm0.21)\%\ ,\\ \frac{B(B^0 \to D^{*-}π^+π^-\ell^+ν_\ell)}{B(B^0 \to D^{*-}\ell^+ν_\ell)} &= (1.03\pm0.43\pm0.18)\%\ ,\\ \frac{B(B^+ \to \bar{D}^{*0}π^+π^-\ell^+ν_\ell)}{B(B^+ \to \bar{D}^{*0}\ell^+ν_\ell)} &= (1.25\pm0.27\pm0.15)\%\ , \end{align*} where the uncertainties are statistical and systematic, respectively. The invariant mass spectra of the $Dπ$, $D^*π$, and $Dππ$ systems are studied. Branching fraction products are extracted, among them the first observations of $B(B^0 \to D_1^-\ell^+ν_\ell) \times B(D_1^- \to D^-π^+π^-) = (0.102\pm0.013\pm0.009)\%$ and $B(B^+ \to \bar{D}_1^0\ell^+ν_\ell) \times B(\bar{D}_1^0 \to \bar{D}^0π^+π^-) = (0.105\pm0.011\pm0.008)\%$.
Using $(771.6 \pm 10.6) \times 10^6$ $B\bar{B}$ meson pairs recorded by the Belle experiment at the KEKB $e^+ e^-$ collider, we report the branching fractions $\mathcal{B}(\bar{B}^0 \to D^{*+} π^-) = (2.62 \pm 0.02 \pm 0.09)\times 10^{-3}$ and $\mathcal{B}(\bar{B}^0 \to D^{*+} K^-) = (2.22 \pm 0.06 \pm 0.08)\times 10^{-4}$; the quoted uncertainties are statistical and systematic, respectively. A measurement of the ratio of these branching fractions is also presented, $\mathcal{R}_{K/π}=\mathcal{B}(\bar{B} \to D^{*+}K^-) /\mathcal{B}( \bar{B} \to D^{*+}π^-) = (8.41 \pm 0.24 \pm 0.13)\times 10^{-2}$, where systematic uncertainties due to the $D^{*+}$ meson reconstruction cancel out. Furthermore, we report a new QCD factorization test based on the measured ratios for $\bar{B} \to D^{*+}h^-$ and $\bar{B} \to D^{*+}\ell^-ν$ decays at squared momentum transfer values equivalent to the mass of the $h = π$ or $K$ hadron. The parameters $|a_1(h)|$ are measured to be $|a_1(π)|= 0.884 \pm 0.004 \pm 0.003 \pm 0.016$ and $|a_1(K)|=0.913 \pm 0.019 \pm 0.008 \pm 0.013$, where the last uncertainties account for all external inputs. These values are approximately $15\%$ lower than those expected from theoretical predictions. Subsequently, flavor $SU(3)$ symmetry is tested by measuring the ratios for pions and kaons, $|a_1(K)|^2/ |a_1(π)|^2=1.066 \pm 0.042 \pm 0.018 \pm 0.023$, as well as for different particle species. The ratio is consistent with unity and therefore no evidence for $SU(3)$ symmetry breaking effects is found at the $5\%$ precision level.
We present the study of $\bar{B}^{0} \to Σ_{c}(2455)^{0,++} π^{\pm} \bar{p}$ decays based on $772\times 10^{6}$ $B\bar{B}$ events collected with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. The $Σ_{c}(2455)^{0,++} $ candidates are reconstructed via their decay to $Λ_{c}^{+} π^{\mp}$ and $Λ_{c}^{+}$ decays to $pK^{-}π^{+},~pK_{S}^{0},$ and $Λπ^{+}$ final states. The corresponding branching fractions are measured to be ${\cal B}(\bar{B}^{0} \to Σ_{c}(2455)^{0} π^{+} \bar{p}) = (1.09 \pm 0.06 \pm 0.07)\times10^{-4}$ and ${\cal B}(\bar{B}^{0} \to Σ_{c}(2455)^{++} π^{-} \bar{p}) = (1.84\pm 0.11 \pm 0.12)\times 10^{-4}$, which are consistent with the world average values with improved precision. A new structure is found in the $M_{Σ_{c}(2455)^{0,++}π^{\pm}}$ spectrum with a significance of $4.2σ$ including systematic uncertainty. The structure is possibly an excited $Λ_{c}^{+}$ and is tentatively named $Λ_{c}(2910)^{+}$. Its mass and width are measured to be $(2913.8 \pm 5.6 \pm 3.8)$ MeV/$c^{2}$ and $(51.8\pm20.0 \pm 18.8)$ MeV, respectively. The products of branching fractions for the $Λ_{c}(2910)^{+}$ are measured to be ${\cal B}(\bar{B}^{0} \to Λ_{c}(2910)^{+}\bar{p})\times{\cal B}(Λ_{c}(2910)^{+} \to Σ_{c}(2455)^{0}π^{+}) = (9.5 \pm 3.6 \pm 1.6)\times 10^{-6}$ and ${\cal B}(\bar{B}^{0} \to Λ_{c} (2910)^{+}\bar{p})\times {\cal B}(Λ_{c}(2910)^{+} \to Σ_{c}(2455)^{++}π^{-}) = (1.24 \pm 0.35 \pm 0.10)\times 10^{-5}$. Here, the first and second uncertainties are statistical and systematic, respectively.
KAGRA, the underground and cryogenic gravitational-wave detector, was operated for its solo observation from February 25th to March 10th, 2020, and its first joint observation with the GEO 600 detector from April 7th -- 21st, 2020 (O3GK). This study presents an overview of the input optics systems of the KAGRA detector, which consist of various optical systems, such as a laser source, its intensity and frequency stabilization systems, modulators, a Faraday isolator, mode-matching telescopes, and a high-power beam dump. These optics were successfully delivered to the KAGRA interferometer and operated stably during the observations. The laser frequency noise was observed to limit the detector sensitivity above a few kHz, whereas the laser intensity did not significantly limit the detector sensitivity.
The branching fractions of the decays $B^{+} \to η\ell^{+} ν_{\ell}$ and $B^{+} \to η^{\prime} \ell^{+} ν_{\ell}$ are measured, where $\ell$ is either an electron or a muon, using a data sample of $711\,{\rm fb}^{-1}$ containing $772 \times 10^6 B\bar{B}$ pairs collected at the $Υ(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+ e^-$ collider. To reduce the dependence of the result on the form factor model, the measurement is performed over the entire $q^2$ range. The resulting branching fractions are ${\cal B}(B^{+} \rightarrow η\ell^{+} ν_{\ell}) = (2.83 \pm 0.55_{\rm (stat.)} \pm 0.34_{\rm (syst.)}) \times 10^{-5}$ and ${\cal B}(B^{+} \rightarrow η' \ell^{+} ν_{\ell}) = (2.79 \pm 1.29_{\rm (stat.)} \pm 0.30_{\rm (syst.)}) \times 10^{-5}$.
We search for a new gauge boson $Z'$ that couples only to heavy leptons and their corresponding neutrinos in the process $e^{+} e^{-} \rightarrow Z'(\rightarrow μ^{+}μ^{-}) μ^{+}μ^{-}$, using a 643 fb$^{-1}$ data sample collected by the Belle experiment at or near the $Υ(1S,2S,3S,4S,5S)$ resonances at the KEKB collider. For the first time, effects due to initial state radiation are used in estimating the detection efficiency. No signal is observed in the mass range of 0.212 \ -- 10 GeV/${\it c}^2$ and we set an upper limit on the coupling strengh, $g'$, constraining $Z'$ as a possible contributor to the anomalous magnetic dipole moment of muon.
DaRveX stands for "Decay at Rest $ν_e$-Pb cross (X) section measurement". So far, there has not been good target to detect low energy $ν_e$. Lead is expected to be an excellent $ν_e$ target because the cross section is expected to be very large and the delayed coincidence technique can be used using final state neutron(s). However, the cross section have not been measured yet. If it is measured, it opens a new window to the future neutrino research field, such as low energy $ν_e$ oscillation measurements, flavor specific detection of the supernova explosion $ν_e$ and understanding of $ν_e$-nucleus interactions. This report explains a conceptual design of DaRveX experiment, which measures cross section of $ν_e$+Pb charged current interaction, $ν_e$(E~30MeV)+Pb $\to$ $e^-$+$xn$+Bi; ($x$=1 or 2), using $ν_e$ from $μ^+$ decay at rest at J-PARC MLF. The energy and direction of the final state $e^-$ will be measured by using 1-ton scale lead-scintillator sandwich detector. With two years of data taking, the cross section is expected to be measured with 20% of precision.
We present the first observation of the $Ω_{c}^{0} \to Ω^{-} μ^{+} ν_μ$ decay and present measurements of the branching fraction ratios of the $Ω_{c}^{0} \to Ω^{-} \ell^{+} ν_{\ell}$ decays compared to the reference mode $Ω_{c}^{0} \to Ω^{-} π^+$, ($\ell = e$ or $μ$). This analysis is based on 89.5 fb$^{-1}$, 711 fb$^{-1}$, and 121.1 fb$^{-1}$ data samples collected with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider at the center-of-mass energies of 10.52 GeV, 10.58 GeV, and 10.86 GeV, respectively. The $Ω_{c}^{0}$ signal yields are extracted by fitting $M_{Ω^{-} \ell^{+}}$ and $M_{Ω^{-}π^+}$ spectra. The branching fraction ratios ${\cal B}(Ω_{c}^{0} \to Ω^{-} e^{+} ν_{e})/{\cal B}(Ω_{c}^{0} \to Ω^{-} π^+)$ and ${\cal B}(Ω_{c}^{0} \to Ω^{-} μ^{+} ν_μ)/{\cal B}(Ω_{c}^{0} \to Ω^{-} π^+)$ are measured to be $1.98 \pm0.13~({\rm stat.}) \pm 0.08~({\rm syst.})$ and $ 1.94 \pm 0.18~({\rm stat.}) \pm 0.10~({\rm syst.})$, respectively. The ratio of ${\cal B}(Ω_{c}^{0} \to Ω^{-} e^{+} ν_{e})/{\cal B}(Ω_{c}^{0} \to Ω^{-} μ^{+} ν_μ)$ is measured to be $1.02 \pm 0.10~({\rm stat.}) \pm 0.02~({\rm syst.})$, which is consistent with the expectation of lepton flavor universality.
We present a search for the charged lepton-flavor-violating decays $Υ(1S)\rightarrow\ell\ell^\prime$ and radiative charged lepton-flavour-violating decays $Υ(1S)\rightarrowγ\ell\ell^\prime$ [$\ell,\ell^\prime = e, μ, τ$] using the 158 million $Υ(2S)$ sample collected by the Belle detector at the KEKB collider. This search uses $Υ(1S)$ mesons produced in $π^+π^-Υ(1S)$ transitions. We do not find any significant signal, so we provide upper limits on the branching fractions at the 90% confidence level.
We report a measurement of the electric dipole moment of the $τ$ lepton ($d_τ$) using an 833~fb$^{-1}$ data sample collected near the $Υ(4S)$ resonance, with the Belle detector at the KEKB asymmetric-energy $e^+ e^-$ collider. Using an optimal observable method, we obtain the real and imaginary parts of $d_τ$ as ${\rm Re}(d_τ) = ( -0.62 \pm 0.63 ) \times 10^{-17} ~e{\rm cm}$ and ${\rm Im}(d_τ) = ( -0.40 \pm 0.32 ) \times 10^{-17} ~e{\rm cm}$, respectively. These results are consistent with null electric dipole moment at the present level of experimental sensitivity and improve the sensitivity by about a factor of three.
We measure the branching fractions and $CP$ asymmetries for the decays $B^{0}\to \bar{D}^{0}π^{0}$ and $B^{+}\to \bar{D}^{0}π^{+}$, using a data sample of $772\times 10^{6}$ $B\bar{B}$ pairs collected at the $Υ(4S)$ resonance with the Belle detector at the KEKB $e^{+}e^{-}$ collider. The branching fractions obtained and direct $CP$ asymmetries are $\mathcal{B}(B^{0}\to \bar{D}^{0}π^{0}) = [2.70 \pm 0.06~ \text{(stat.)} \pm 0.10~ \text{(syst.)}] \times 10^{-4}$, $\mathcal{B}(B^{+}\to \bar{D}^{0}π^{+}) = [4.53 \pm 0.02~ \text{(stat.)} \pm 0.15~ \text{(syst.)}] \times 10^{-3}$, $ {\cal A}_{CP}(B^{0}\to \bar{D}^{0}π^{0}) = [+0.42 \pm 2.05~ \text{(stat.)} \pm 1.22~ \text{(syst.)}]\%$, and $ {\cal A}_{CP}(B^{+}\to \bar{D}^{0}π^{+}) = [+0.19 \pm 0.36~ \text{(stat.)} \pm 0.57~ \text{(syst.)}]\%$. The measurements of $\mathcal{B}$ are the most precise to date and are in good agreement with previous results, as is the measurement of ${\cal A}_{CP}(B^{+}\to \bar{D}^{0}π^{+})$. The measurement of ${\cal A}_{CP}$ for $B^{0}\to \bar{D}^{0}π^{0}$ is the first for this mode, and the value is consistent with Standard Model expectations.
JSNS$^2$ (J-PARC Sterile Neutrino Search at J-PARC Spallation Neutron Source) is an experiment that is searching for sterile neutrinos via the observation of $\barν_μ \to \barν_{e}$ appearance oscillations using muon decay-at-rest neutrinos. Before dedicated data taking in the first-half of 2021, we performed a commissioning run for 10 days in June 2020. Using the data obtained in this commissioning run, in this paper, we present an estimate of the correlated background which imitates the $\barν_{e}$ signal in a sterile neutrino search. In addition, in order to demonstrate future prospects of the JSNS$^2$ experiment, possible pulse shape discrimination improvements towards reducing cosmic ray induced fast neutron background are described.
We report the first search for the penguin-dominated process $B^0 \rightarrow K_S^0 K_S^0 γ$ using the full data sample of $772\times 10^6$ $B\bar{B}$ pairs collected with the Belle detector at the KEKB asymmetric-energy $e^+ e^-$ collider. We do not observe any statistically significant signal yield in the $K_S^0$-pair invariant mass range 1 GeV/$c^2 < M_{K_S^0 K_S^0} < $ 3 GeV/$c^2$, and set the following upper limits at 90% confidence level: $\mathcal{B}(B^0 \to K_S^0 K_S^0 γ) < 5.8\times10^{-7}$, $\mathcal{B}(B^0 \to f_2 γ)\times \mathcal{B}(f_2 (1270) \to K_S^0 K_S^0 ) < 3.1\times10^{-7}$, and $\mathcal{B}(B^0 \to f_2^{\prime} γ)\times \mathcal{B}(f_2^{\prime} (1525) \to K_S^0 K_S^0 ) < 2.1\times10^{-7}$. Further, 90% confidence upper limits have also been set in the range of [0.7-2.9]$\times10^{-7}$ on the $B^0 \rightarrow K_S^0 K_S^0 γ$ branching fraction in bins of $M_{K_S^0 K_S^0}$.