We report a measurement of the electric dipole moment of the $tau$ lepton ($d_tau$) using an 833 fb$^{-1}$ data sample collected near the $Upsilon(4S)$ resonance, with the Belle detector at the KEKB asymmetric-energy $e^+ e^-$ collider. Using an opti
mal observable method, we obtain the real and imaginary parts of $d_tau$ as ${rm Re}(d_tau) = ( -0.62 pm 0.63 ) times 10^{-17} ~e{rm cm}$ and ${rm Im}(d_tau) = ( -0.40 pm 0.32 ) times 10^{-17} ~e{rm cm}$, respectively. These results are consistent with no electric dipole moment at the present level of experimental sensitivity and improve the sensitivity by about a factor of three.
We report results from a study of hadronic transitions of the $chi_{bJ}(nP)$ states of bottomonium at Belle. The $P$-wave states are reconstructed in transitions to the $Upsilon(1S)$ with the emission of an $omega$ meson. The transitions of the $n=2$
triplet states provide a unique laboratory in which to study nonrelativistic quantum chromodynamics, as the kinematic threshold for production of an $omega$ and $Upsilon(1S)$ lies between the $J=0$ and $J=1$ states. A search for the $chi_{bJ}(3P)$ states is also reported.
We report a measurement of the $D^0$ and $D^+$ lifetimes using $D^0to K^-pi^+$ and $D^+to K^-pi^+pi^+$ decays reconstructed in $e^+e^-to cbar{c}$ data recorded by the Belle II experiment at the SuperKEKB asymmetric-energy $e^+e^-$ collider. The data
correspond to an integrated luminosity of $72,{rm fb}^{-1}$. The results, $tau(D^0) = 410.5pm1.1,{rm(stat)}pm0.8,{rm(syst.)},{rm fs}$ and $tau(D^+) = 1030.4pm4.7,{rm(stat)}pm3.1,{rm(syst.)},{rm fs}$, are the most precise to date and are consistent with previous determinations.
We report the first reconstruction of the $B^{0} to pi^{0} pi^{0}$ decay mode at Belle II using samples of 2019 and 2020 data that correspond to 62.8 fb$^{-1}$ of integrated luminosity. We find $14.0^{+6.8}_{-5.6}$ signal decays, corresponding to a s
ignificance of 3.4 standard deviations and determine a branching ratio of $mathcal{B}(B^{0} rightarrow pi^{0} pi^{0}) = [0.98^{+0.48}_{-0.39} pm 0.27] times 10^{-6}$. The results agree with previous determinations and contribute important information to an early assessment of detector performance and Belle IIs potential for future determinations of $alpha/phi_2$ using $B rightarrow pi pi$ modes.
We present preliminary results on the reconstruction of the $B^0to Jmskip 1mu / psimskip 2mu K^0_{scriptscriptstyle L}$ decay, where $Jmskip 1mu / psimskip 2mutomu^+mu^-$ or $e^+e^-$. Using a dataset corresponding to a luminosity of $62.8pm0.6mbox{fb
}^{-1}$ collected by the Belle II experiment at the SuperKEKB asymmetric energy $e^+e^-$ collider, we measure a total of $267pm21$ candidates with $Jmskip 1mu / psimskip 2mutomu^+mu^-$ and $226pm20$ with with $Jmskip 1mu / psimskip 2muto e^+e^-$. The quoted errors are statistical only.
We report the results of the first search for the decay $B_s^0 rightarrow eta^prime eta$ using $121.4~textrm{fb}^{-1}$ of data collected at the $Upsilon(5S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. We observ
e no significant signal and set a 90% confidence-level upper limit of %$7.1 times 10^{-5}$ $6.5 times 10^{-5}$ on the branching fraction of this decay.
For the first time we search for the $eta_{c2}(1D)$ in $e^+e^-togammaeta_{c2}(1D)$ at $sqrt{s}$ = 10.52, 10.58, and 10.867 GeV with data samples of 89.5 fb$^{-1}$, 711 fb$^{-1}$, and 121.4 fb$^{-1}$, respectively, accumulated with the Belle detector
at the KEKB asymmetric energy electron-positron collider. No significant $eta_{c2}(1D)$ signal is observed in the mass range between 3.8 and 3.88 GeV/$c^2$. The upper limit at 90% confidence level on the product of the Born cross section for $e^+e^- to gammaeta_{c2}(1D)$ and branching fraction for $eta_{c2}(1D)to gamma h_c(1P)$ is determined to be $sigma(e^+e^- to gammaeta_{c2}(1D)){cal B}(eta_{c2}(1D)to gamma h_c(1P))$ $<$ 4.9 fb at $sqrt{s}$ near 10.6 GeV.
We report updated measurements of branching fractions ($mathcal{B}$) and CP-violating charge asymmetries ($mathcal{A_{rm CP}}$) for charmless $B$ decays at Belle II, which operates on or near the $Upsilon$(4S) resonance at the SuperKEKB asymmetric en
ergy $e^{+}e^{-}$ collider. We use samples of 2019 and 2020 data corresponding to 62.8 fb$^{-1}$ of integrated luminosity. The samples are analysed using two-dimensional fits in $Delta E$ and $M_{it bc}$ to determine signal yields of approximately 568, 103, and 115 decays for the channels $B^0 to K^+pi^-$, $B^+ to K_{rm S}^0pi^+$, and $B^0 to pi^+pi^-$, respectively. Signal yields are corrected for efficiencies determined from simulation and control data samples to obtain branching fractions and CP-violating asymmetries for flavour-specific channels. The results are compatible with known determinations and contribute important information to an early assessment of Belle II detector performance.
We present the first measurement of the time-integrated mixing probability $chi_d$ using Belle II data collected at a center-of-mass (CM) energy of 10.58 GeV, corresponding to the mass of the $Upsilon$(4S) resonance, with an integrated luminosity of
$34.6 {rm fb}^{-1}$ at the SuperKEKB $e^+ e^-$ collider. We reconstruct pairs of B mesons both of which decay to semileptonic final states. Using a novel methodology, we measure $chi_d = 0.187 pm 0.010 text{ (stat.)} pm 0.019 text{ (syst.)}$, which is compatible with existing indirect and direct determinations.
We report measurements of branching fractions ($mathcal B$) and direct ${it CP}$-violating asymmetries ($mathcal A_{it CP}$) for the decays $B^+to K^+pi^0$ and $B^+ to pi^+pi^0$ reconstructed with the Belle II detector in a sample of asymmetric-energ
y electron-positron collisions at the $Upsilon(4S)$ resonance corresponding to 62.8 $text{fb}^{-1}$ of integrated luminosity. The results are $mathcal{B}(B^+ to K^+pi^0) = [11.9 ^{+1.1}_{-1.0} (rm stat)pm 1.6(rm syst)]times 10^{-6}$, $mathcal{B}(B^+ to pi^+pi^0) = [5.5 ^{+1.0}_{-0.9} (rm stat)pm 0.7(rm syst)]times 10^{-6}$, $mathcal A_{it CP}(B^+ to K^+pi^0) = -0.09 pm 0.09 (rm stat)pm 0.03(rm syst)$, and $mathcal A_{it CP}(B^+ to pi^+pi^0) = -0.04 pm 0.17 (rm stat)pm 0.06(rm syst)$. The results are consistent with previous measurements and show a detector performance comparable with early Belle performance.
