arXiv subjects

T. Iijima

Publications and source records attributed to T. Iijima.

At least 109 records · Page 6Linked to original sources

arXiv2018

Observation of $Ξ_{c}(2930)^0$ and updated measurement of $B^{-} \to K^{-} Λ_{c}^{+} \barΛ_{c}^{-}$ at Belle

We report the first observation of the $Ξ_{c}(2930)^0$ charmed-strange baryon with a significance greater than 5$σ$. The $Ξ_{c}(2930)^0$ is found in its decay to $K^- Λ_{c}^+$ in $B^{-} \to K^{-} Λ_{c}^{+} \barΛ_{c}^{-}$ decays. The measured mass and width are $[2928.9 \pm 3.0(\rm stat.)^{+0.9}_{-12.0}(\rm syst.)]$ MeV/$c^{2}$ and $[19.5 \pm 8.4(\rm stat.) ^{+5.9}_{-7.9}(\rm syst.)]$ MeV, respectively, and the product branching fraction is ${\cal B}(B^{-} \to Ξ_{c}(2930)^0 \barΛ_{c}^{-}) {\cal B}(Ξ_{c}(2930)^0 \to K^- Λ_{c}^{+})=[1.73 \pm 0.45(\rm stat.) \pm 0.21(\rm syst.)]\times 10^{-4}$. We also measure ${\cal B}(B^{-} \to K^{-} Λ_{c}^{+} \barΛ_{c}^{-}) = [4.80 \pm 0.43(\rm stat.) \pm 0.60(\rm syst.)] \times 10^{-4}$ with improved precision, and search for the charmonium-like state $Y(4660)$ and its spin partner, $Y_η$, in the $Λ_{c}^{+}\barΛ_{c}^{-}$ invariant mass spectrum. No clear signals of the $Y(4660)$ nor its spin partner are observed and the 90\% credibility level (C.L.) upper limits on their production rates are determined. These measurements are obtained from a sample of $(772\pm11)\times 10^{6} B\bar{B}$ pairs collected at the $Υ(4S)$ resonance by the Belle detector at the KEKB asymmetric energy electron-positron collider.

hep-ex↗

arXiv2018

Observation of Transverse $Λ/\barΛ$ Hyperon Polarization in $e^+e^-$ Annihilation at Belle

We report the first observation of the spontaneous polarization of $Λ$ and $\barΛ$ hyperons transverse to the production plane in $e^+e^-$ annihilation, which is attributed to the effect arising from a polarizing fragmentation function. For inclusive $Λ/\barΛ$ production, we also report results with subtracted feed-down contributions from $Σ^0$ and charm. This measurement uses a dataset of 800.4 fb$^{-1}$ collected by the Belle experiment at or near a center-of-mass energy of 10.58 GeV. We observe a significant polarization that rises with the fractional energy carried by the $Λ/\barΛ$ hyperon.

hep-ex↗

arXiv2018

Search for $Υ(1S,2S) \to Z^{+}_{c}Z^{(\prime) -}_{c}$ and $e^{+}e^{-} \to Z^{+}_{c}Z^{(\prime) -}_{c}$ at $\sqrt{s}$ = 10.52, 10.58, and 10.867 GeV

The first search for $Z_{c}$ pair production in $Υ(1S)$ and $Υ(2S)$ decays and in $e^{+}e^{-}$ annihilation at $\sqrt{s}$ = 10.52, 10.58, and 10.867 GeV is conducted using data collected with the Belle detector at the KEKB asymmetric energy electron-positron collider. No significant signals are observed in any of the studied modes, and the 90\% credibility level upper limits on their product branching fractions in $Υ(1S)$ and $Υ(2S)$ decays (${\cal B}(Υ(1S,2S)\to Z^{+}_{c}Z^{(\prime) -}_{c})\times{\cal B}(Z^{+}_{c}\toπ^{+}+c\bar c)$ ($c\bar c=J/ψ$, $χ_{c1}(1P)$, $ψ(2S)$)) and the product of Born cross section and branching fraction for $e^{+}e^{-} \to Z^{+}_{c}Z^{(\prime) -}_{c}$ ($σ(e^+e^- \to Z^{+}_{c}Z^{(\prime) -}_{c})\times {\cal B}(Z^{+}_{c} \to π^+ +c\bar c)$) at $\sqrt{s}$ = 10.52, 10.58, and 10.867 GeV are determined. Here, $Z_{c}$ refers to the $Z_{c}(3900)$ and $Z_{c}(4200)$ observed in the $πJ/ψ$ final state, the $Z_{c1}(4050)$ and $Z_{c2}(4250)$ in the $πχ_{c1}(1P)$ state, and the $Z_{c}(4050)$ and $Z_{c}(4430)$ in the $πψ(2S)$ state.

hep-ex↗

arXiv2018

Measurements of the absolute branching fractions of $B^{+} \to X_{c\bar{c}} K^{+}$ and $B^{+} \to \bar{D}^{(\ast) 0} π^{+} $ at Belle

We present the measurement of the absolute branching fractions of $B^{+} \to X_{c\bar{c}} K^{+}$ and $B^{+} \to \bar{D}^{(\ast) 0} π^{+} $ decays, using a data sample of $772\times10^{6}$ $B\bar{B}$ pairs collected at the $Υ(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^{+}e^{-}$ collider. Here, $X_{c\bar{c}}$ denotes $η_{c}$, $J/ψ$, $χ_{c0}$, $χ_{c1}$, $η_{c}(2S)$, $ψ(2S)$, $ψ(3770)$, $X(3872)$, and $X(3915)$. We do not observe significant signals for $X(3872)$ nor $X(3915)$, and set the 90$\%$ confidence level upper limits: ${\cal B}(B^{+} \to X(3872) K^{+} )<2.7 \times 10^{-4}$ and ${\cal B}(B^{+} \to X(3915) K^{+} )<2.9 \times 10^{-4}$. These represent the most stringent upper limit for ${\cal B}(B^{+} \to X(3872) K^{+} )$ to date and the first measurement for ${\cal B}(B^{+} \to X(3915) K^{+} )$. The measured branching fractions for $η_{c}$ and $η_{c}(2S)$ are the most precise to date: ${\cal B}(B^{+} \to η_{c} K^{+} )=(12.3\pm0.8\pm0.7) \times 10^{-4}$ and ${\cal B}(B^{+} \to η_{c}(2S)K^{+}) =(4.9\pm1.1\pm0.3) \times 10^{-4}$ , where the first and second uncertainties are statistical and systematic, respectively.

hep-ex↗

arXiv2018

Measurement of Time-dependent $CP$ Asymmetries in $B^{0}\to K_S^0 ηγ$ Decays

We report a measurement of time-dependent $CP$ violation parameters in ${B^0 \to K_S^0 ηγ}$ decays. The study is based on a data sample, containing ${772 \times 10^6 B\bar{B}}$ pairs, that was collected at the $Υ(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+ e^-$ collider. We obtain the $CP$ violation parameters of ${{\cal S} = -1.32 \pm 0.77 {\rm (stat.)} \pm 0.36{\rm (syst.)}}$ and ${{\cal A} = -0.48 \pm 0.41 {\rm (stat.)} \pm 0.07{\rm (syst.)}}$ for the invariant mass of the $K_S^0 η$ system up to 2.1 GeV/$c^2$.

hep-ex↗

arXiv2018

Physics Potentials with the Second Hyper-Kamiokande Detector in Korea

Hyper-Kamiokande consists of two identical water-Cherenkov detectors of total 520~kt with the first one in Japan at 295~km from the J-PARC neutrino beam with 2.5$^{\textrm{o}}$ Off-Axis Angles (OAAs), and the second one possibly in Korea in a later stage. Having the second detector in Korea would benefit almost all areas of neutrino oscillation physics mainly due to longer baselines. There are several candidate sites in Korea with baselines of 1,000$\sim$1,300~km and OAAs of 1$^{\textrm{o}}$$\sim$3$^{\textrm{o}}$. We conducted sensitivity studies on neutrino oscillation physics for a second detector, either in Japan (JD $\times$ 2) or Korea (JD + KD) and compared the results with a single detector in Japan. Leptonic CP violation sensitivity is improved especially when the CP is non-maximally violated. The larger matter effect at Korean candidate sites significantly enhances sensitivities to non-standard interactions of neutrinos and mass ordering determination. Current studies indicate the best sensitivity is obtained at Mt. Bisul (1,088~km baseline, $1.3^\circ$ OAA). Thanks to a larger (1,000~m) overburden than the first detector site, clear improvements to sensitivities for solar and supernova relic neutrino searches are expected.

hep-ex↗

arXiv2018

First muon acceleration using a radio frequency accelerator

Muons have been accelerated by using a radio frequency accelerator for the first time. Negative muonium atoms (Mu$^-$), which are bound states of positive muons ($μ^+$) and two electrons, are generated from $μ^+$'s through the electron capture process in an aluminum degrader. The generated Mu$^-$'s are initially electrostatically accelerated and injected into a radio frequency quadrupole linac (RFQ). In the RFQ, the Mu$^-$'s are accelerated to 89 keV. The accelerated Mu$^-$'s are identified by momentum measurement and time of flight. This compact muon linac opens the door to various muon accelerator applications including particle physics measurements and the construction of a transmission muon microscope.

physics.acc-ph↗

arXiv2018

Production cross sections of hyperons and charmed baryons from $e^+e^-$ annihilation near $\sqrt{s} = 10.52$~GeV

We measure the inclusive production cross sections of hyperons and charmed baryons from $e^+e^-$ annihilation using a 800 fb$^{-1}$ data sample taken near the $Υ(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+ e^-$ collider. The feed-down contributions from heavy particles are subtracted using our data, and the direct production cross sections are presented for the first time. The production cross sections divided by the number of spin states for $S=-1$ hyperons follow an exponential function with a single slope parameter except for the $Σ(1385)^+$ resonance. Suppression for $Σ(1385)^+$ and $Ξ(1530)^0$ hyperons is observed. Among the production cross sections of charmed baryons, a factor of three difference for $Λ_c^+$ states over $Σ_c$ states is observed. This observation suggests a diquark structure for these baryons.

hep-ex↗

arXiv2018

Measurement of Branching Fractions of Hadronic Decays of the $Ω_c^0$ Baryon

Using a data sample of 980 ${\rm fb}^{-1}$ of $e^+e^-$ annihilation data taken with the Belle detector operating at the KEKB asymmetric-energy $e^+e^-$ collider, we report the results of a study of the decays of the $Ω_c^0$ charmed baryon into hadronic final states. We report the most precise measurements to date of the relative branching fractions of the $Ω_c^0$ into $Ω^-π^+π^0$, $Ω^-π^+π^-π^+$, $Ξ^-K^-π^+π^+$, and $Ξ^0K^-π^+$, as well as the first measurements of the branching fractions of the $Ω_c^0$ into $Ξ^-\bar{K}^0π^+$, $Ξ^0\bar{K}^0$, and $Λ\bar{K}^0\bar{K}^0$, all with respect to the $Ω^-π^+$ decay. In addition, we investigate the resonant substructure of these modes. Finally, we present a limit on the branching fraction for the decay $Ω_c^0\toΣ^+K^-K^-π^+$.

hep-ex↗

arXiv2018

Measurement of the $τ$ lepton polarization and $R(D^)$ in the decay $\bar{B} \rightarrow D^ τ^- \barν_τ$ with one-prong hadronic $τ$ decays at Belle

With the full data sample of $772 \times 10^6$ $B{\bar B}$ pairs recorded by the Belle detector at the KEKB electron-positron collider, the decay $\bar{B} \rightarrow D^* τ^- \barν_τ$ is studied with the hadronic $τ$ decays $τ^- \rightarrow π^- ν_τ$ and $τ^- \rightarrow ρ^- ν_τ$. The $τ$ polarization $P_τ(D^*)$ in two-body hadronic $τ$ decays is measured, as well as the ratio of the branching fractions $R(D^{*}) = \mathcal{B}(\bar {B} \rightarrow D^* τ^- \barν_τ) / \mathcal{B}(\bar{B} \rightarrow D^* \ell^- \barν_\ell)$, where $\ell^-$ denotes an electron or a muon. Our results, $P_τ(D^*) = -0.38 \pm 0.51 {\rm (stat)} ^{+0.21}_{-0.16} {\rm (syst)}$ and $R(D^*) = 0.270 \pm 0.035{\rm (stat)} ^{+0.028}_{-0.025}{\rm (syst)}$, are consistent with the theoretical predictions of the Standard Model. The polarization values of $P_τ(D^*) > +0.5$ are excluded at the 90\% confidence level.

hep-ex↗

arXiv2017

Measurement of the branching fraction and $CP$ asymmetry in $B^{0} \to π^{0}π^{0}$ decays, and an improved constraint on $ϕ_{2}$

We measure the branching fraction and $CP$ violation asymmetry in the decay $B^{0}\to π^{0}π^{0}$, using a data sample of $752\times 10^{6}$ $B\bar{B}$ pairs collected at the $Υ(4S)$ resonance with the Belle detector at the KEKB $e^{+}e^{-}$ collider. The obtained branching fraction and direct $CP$ asymmetry are $ \mathcal{B}(B\to π^{0}π^{0}) = [1.31 \pm 0.19~ \text{(stat.)} \pm 0.19~ \text{(syst.)}] \times 10^{-6}$ and $ A_{CP} = +0.14 \pm 0.36~ \text{(stat.)} \pm 0.10~ \text{(syst.)}, $ respectively. The signal significance, including the systematic uncertainty, is 6.4 standard deviations. We combine these results with Belle's earlier measurements of $B^{0}\to π^{+} π^{-}$ and $B^{\pm} \to π^{\pm} π^{0}$ to exclude the $CP$-violating parameter $ϕ_{2}$ from the range $15.5^{\circ} < ϕ_{2} < 75.0^{\circ}$ at 95\% confidence level.

hep-ex↗

arXiv2017

Search for $B^{-}\toμ^{-}\barν_μ$ Decays at the Belle Experiment

We report the result of a search for the decay $B^{-}\toμ^{-}\barν_μ$. 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 ${\cal B}(B^{-}\toμ^{-}\barν_μ) =(6.46 \pm 2.22 \pm 1.60 )\times10^{-7}$ or a frequentist 90% confidence level interval on the $B^{-}\toμ^{-}\barν_μ$ branching fraction of $[2.9, 10.7]\times 10^{-7}$. This result is obtained from a $711\ \text{fb}^{-1}$ 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.

hep-ex↗

arXiv2017

Study of $K^0_S$ pair production in single-tag two-photon collisions

We report a measurement of the cross section for $K^0_S$ pair production in single-tag two-photon collisions, $γ^* γ\to K^0_S K^0_S$, for $Q^2$ up to 30 GeV$^2$, where $Q^2$ is the negative of the invariant mass squared of the tagged photon. The measurement covers the kinematic range 1.0 GeV < W < 2.6 GeV and $|\cos θ^*| < 1.0$ for the total energy and kaon scattering angle, respectively, in the $γ^* γ$ center-of-mass system. These results are based on a data sample of 759 fb$^{-1}$ collected with the Belle detector at the KEKB asymmetric-energy $e^+ e^-$ collider. For the first time, the transition form factor of the $f_2'(1525)$ meson is measured separately for the helicity-0, -1, and -2 components and also compared with theoretical calculations. Finally, the partial decay widths of the $χ_{c0}$ and $χ_{c2}$ mesons are measured as a function of $Q^2$.

hep-ex↗

arXiv2017

Search for light tetraquark states in $Υ(1S)$ and $Υ(2S)$ decays

We search for the $J^{PC}=0^{--}$ and $1^{+-}$ light tetraquark states with masses up to 2.46~GeV/$c^2$ in $Υ(1S)$ and $Υ(2S)$ decays with data samples of $(102\pm 2)$ million and $(158\pm 4)$ million events, respectively, collected with the Belle detector. No significant signals are observed in any of the studied production modes, and 90\% credibility level (C.L.) upper limits on their branching fractions in $Υ(1S)$ and $Υ(2S)$ decays are obtained. The inclusive branching fractions of the $Υ(1S)$ and $Υ(2S)$ decays into final states with $f_1(1285)$ are measured to be ${\cal B}(Υ(1S)\to f_1(1285)+anything)=(46\pm28({\rm stat.})\pm13({\rm syst.}))\times 10^{-4}$ and ${\cal B}(Υ(2S)\to f_1(1285)+anything)=(22\pm15({\rm stat.})\pm6.3({\rm syst.}))\times 10^{-4}$. The measured $χ_{b2} \to J/ψ+ anything$ branching fraction is measured to be $(1.50\pm0.34({\rm stat.})\pm0.22({\rm syst.}))\times 10^{-3}$, and 90\% C.L. upper limits for the $χ_{b0,b1} \to J/ψ+ anything$ branching fractions are found to be $2.3\times 10^{-3}$ and $1.1\times 10^{-3}$, respectively. For ${\cal B}(χ_{b1} \to ω+ anything)$, the branching fraction is measured to be $(4.9\pm1.3({\rm stat.})\pm0.6({\rm syst.}))\times 10^{-2}$. %($<3.68\times 10^{-2}$ at 90\% C.L.). All results reported here are the first measurements for these modes.

hep-ex↗

arXiv2017

Measurement of the Decays $\boldsymbol{B\toη\ellν_\ell}$ and $\boldsymbol{B\toη^\prime\ellν_\ell}$ in Fully Reconstructed Events at Belle

We report branching fraction measurements of the decays $B^+\toη\ell^+ν_\ell$ and $B^+\toη^\prime\ell^+ν_\ell$ based on 711~fb$^{-1}$ of data collected near the $Υ(4S)$ resonance with the Belle experiment at the KEKB asymmetric-energy $e^+e^-$ collider. This data sample contains 772 million $B\bar B$~events. One of the two $B$~mesons is fully reconstructed in a hadronic decay mode. Among the remaining ("signal-$B$") daughters, we search for the $η$~meson in two decay channels, $η\toγγ$ and $η\toπ^+π^-π^0$, and reconstruct the $η^{\prime}$~meson in $η^\prime\toηπ^+π^-$ with subsequent decay of the $η$ into $γγ$. Combining the two $η$ modes and using an extended maximum likelihood, the $B^+\toη\ell^+ν_\ell$ branching fraction is measured to be $(4.2\pm 1.1 (\rm stat.)\pm 0.3 (\rm syst.))\times 10^{-5}$. For $B^+\toη^\prime\ell^+ν_\ell$, we observe no significant signal and set an upper limit of $0.72\times 10^{-4}$ at 90\% confidence level.

hep-ex↗

arXiv2017

Search for $\boldsymbol{B\to hν\barν}$ decays with semileptonic tagging at Belle

We present the results of a search for the rare decays $B\to hν\overlineν$, where $h$ stands for $K^+,\:K^0_{\mathrm{S}},\:K^{\ast +},\:K^{\ast 0},\:π^+,\:π^0,\:ρ^+$ and $ρ^{0}$. The results are obtained with $772\times10^{6}$ $B\overline{B}$ pairs collected with the Belle detector at the KEKB $e^+ e^-$ collider. We reconstruct one $B$ meson in a semileptonic decay and require a single $h$ meson but nothing else on the signal side. We observe no significant signal and set upper limits on the branching fractions. The limits set on the $B\to K^0_{\mathrm{S}}ν\overlineν$, $B^0\to K^{*0}ν\overlineν$, $B\to π^+ν\overlineν$, $B^0\toπ^0ν\overlineν$, $B^+\toρ^+ν\overlineν$, and $B^0\toρ^0ν\overlineν$ channels are the world's most stringent.

hep-ex↗

arXiv2017

Search for $CP$ Violation and Measurement of the Branching Fraction in the Decay $D^{0} \to K^0_S K^0_S$

We report a study of the decay $D^0 \to K^0_S K^0_S$ using 921~fb$^{-1}$ of data collected at or near the $Υ(4S)$ and $Υ(5S)$ resonances with the Belle detector at the KEKB asymmetric energy $e^+e^-$ collider. The measured time-integrated $CP$ asymmetry is $ A_{CP}(D^0 \to K^0_S K^0_S) = (-0.02 \pm 1.53 \pm 0.02 \pm 0.17) \%$, and the branching fraction is $\mathcal{B} (D^{0}\rightarrow K_{S}^{0}K_{S}^{0})$ = (1.321 $\pm$ 0.023 $\pm$ 0.036 $\pm$ 0.044) $\times$ 10$^{-4}$, where the first uncertainty is statistical, the second is systematic, and the third is due to the normalization mode ($D^0 \to K_S^0 π^0$). These results are significantly more precise than previous measurements available for this mode. The $A_{CP}$ measurement is consistent with the standard model expectation.

hep-ex↗

arXiv2017

Evidence for Isospin Violation and Measurement of $CP$ Asymmetries in $B \to K^{\ast}(892) γ$

We report the first evidence for isospin violation in $B \to K^* γ$ and the first measurement of difference of $CP$ asymmetries between $B^+ \to K^{*+} γ$ and $B^0 \to K^{*0} γ$. This analysis is based on the data sample containing $772 \times 10^6 B\bar{B}$ pairs that was collected with the Belle detector at the KEKB energy-asymmetric $e^+ e^-$ collider. We find evidence for the isospin violation with a significance of 3.1$σ$, $Δ_{0+} = (+6.2 \pm 1.5 ({\rm stat.}) \pm 0.6 ({\rm syst.}) \pm 1.2 (f_{+-}/f_{00}))$\%, where the third uncertainty is due to the uncertainty on the fraction of $B^+B^-$ to $B^0\bar{B}^0$ production in $Υ(4S)$ decays. The measured value is consistent with predictions of the SM. The result for the difference of $CP$ asymmetries is $ΔA_{CP} = (+2.4 \pm 2.8({\rm stat.}) \pm 0.5({\rm syst.}))$\%, consistent with zero. The measured branching fractions and $CP$ asymmetries for charged and neutral $B$ meson decays are the most precise to date. We also calculate the ratio of branching fractions of $B^0 \to K^{*0} γ$ to $B_s^0 \to ϕγ$.

hep-ex↗