We report a study of $τ$ lepton decays involving $\Ks$ with a 669 fb$^{-1}$ data sample accumulated with the Belle detector at the KEKB asymmetric-energy $e^{+}e^{-}$ collider. The branching fractions have been measured for the $\tauTO \piKs ν_τ$, $\KKs ν_τ$, $\piKspizero ν_τ$, $\KKspizero ν_τ$, $\piKsKs ν_τ$ and $\piKsKspizero ν_τ$ decays. We also provide the unfolded mass spectra for $\tauTO \piKspizero ν_τ$ and $\tauTO \KKspizero ν_τ$.
Belle II has a broad $τ$ physics program, in particular in searches for lepton flavour and lepton number violations. Belle II profits from the relatively large $τ$-pair production rate in the low background environment of $e^+e^-$ -collisions at 10.58 GeV. Up to mid-2021 Belle II collected a sample corresponding to $214~\text{fb}^{-1}$ of data. We present a first measurement of the $τ$ mass, the prospects for the $τ$-lifetime measurement, and review the overall $τ$ lepton physics program of Belle II.
The Belle II experiment is an upgrade of the Belle detector and will operate at the SuperKEKB energy-asymmetric $e^+e^-$ collider. The accelerator has already successfully completed the first phase of commissioning and first electron positron-collisions in Belle II were observed in April 2018. The design luminosity of SuperKEKB is 8x10$^{35}$ cm$^{-2}$s$^{-1}$ and the Belle II experiment aims to record 50 ab$^{-1}$ of data. Belle II has a broad program of $τ$ physics, in particular, precision measurements of Standard Model parameters and searches of lepton flavor and lepton number violations, …
The Belle II experiment is a substantial upgrade of the Belle detector and will operate at the SuperKEKB energy-asymmetric $e^+e^-$ collider. The design luminosity of the machine is 8$\times10^{35}$ cm$^{-2}$s$^{-1}$ and the Belle II experiment aims to record 50 ab$^{-1}$ of data, a factor of 50 more than its predecessor. From February to July 2018, the machine has completed a commissioning run and main operation of SuperKEKB has started in March 2019. Belle II has a broad $τ$ physics program, in particular in searches for lepton flavor and lepton number violations (LFV and LNV), benefiting fr…
We measure the branching fraction for the Singly Cabibbo-suppressed decay $D^0\rightarrow K^0_S\,K^0_S\,π^+π^-$, and we search for $CP$ violation via a measurement of the $CP$ asymmetry $A^{}_{CP}$ and also the $T$-odd triple-product asymmetry $a_{CP}^{T}$. The later two measurements are complementary. We use 922~fb$^{-1}$ of data recorded by the Belle experiment, which ran at the KEKB asymmetric-energy $e^+ e^-$ collider. The branching fraction is measured relative to the Cabibbo-favored normalization channel $D^0\rightarrow K^0_S\,π^+π^-$. Singly Cabibbo-suppressed charm decays are expected …
We present a study of Michel parameters in leptonic $τ$ decays using experimental information collected at the Belle detector. Michel parameters are extracted in the unbinned maximum likelihood fit of the $(τ^\mp\to\ell^\mpνν,τ^\pm\toπ^\pmπ^0ν)$ events in the full nine-dimensional phase space. We exploit the spin-spin correlation of tau leptons to extract $ξ_ρξ$ and $ξ_ρξδ$ in addition to the $ρ$ and $η$ parameters.
Semileptonic decays of $B$ mesons that proceed via $b\rightarrow u$ and $b\rightarrow c$ transitions, as well as rare leptonic $B$ decays, are fertile grounds for probing new physics beyond the Standard Model. The Belle II experiment presents as an excellent opportunity to study such decays, and since beginning operation in 2019, Belle II has already recorded half of the data collected by its predecessor and reached an instantaneous luminosity greater than $4\times 10^{34}$ cm$^{-2}$s$^{-1}$. Belle II expects to explore flavour physics with $B$ and charmed mesons with unprecedented precision, …
Beyond the Standard Model at Belle: B to K*l+l- and search for leptonic B decays
本文报道了在KEKB非对称能量e ~+ e ~-对撞机上用Belle探测器在Y（~ 4S）共振条件下收集的386 M BBbar电子对，首次测量了B与K ~*l+l ~-的前后向非对称性和Wilson系数A_9/A_7和A_10/A_7的比值。我们还总结了贝尔在寻找纯轻子B衰变，重点是它们的影响超出了标准模型的物理模型所获得的结果。
The paper discusses new method for electron/pion and muon/pion separation in the Belle II detector at transverse momenta below 0.7 $\mathrm{GeV}/c$, which is essential for efficient measurements of semi-leptonic decays of $B$ mesons with tau lepton in the final state. The method is based on the analysis of patterns in the electromagnetic calorimeter by using a Convolutional Neural Network (CNN).
We report a measurement of the branching fraction of inclusive semileptonic $B$ meson decays $B\to X_c\ellν\ell$ in $Υ(4S)\to B\bar B$~data recorded by the Belle II experiment at the SuperKEKB asymmetric-energy $e^+e^-$ collider and corresponding to 62.8 fb$^{-1}$ of integrated luminosity. Only a charged lepton (electon or muon) is reconstructed and the signal yield is determined from a fit to the lepton momentum distribution in the center-of-mass frame of the colliding beams. Averaging the result in the electron and muon channels, we find ${\cal B}(B\to X_c\ellν_\ell) = (9.75\pm 0.03(\text{st…
We report a measurement of the branching fraction of the semileptonic decay B- -> D0 l- nubar_l (and its charge conjugate) using 62.8/fb of Upsilon(4S) -> B Bbar data recorded by the Belle II experiment at the SuperKEKB asymmetric-energy e+ e- collider. The neutral charm meson is searched for in the decay mode D0 -> K- pi+ and combined with a properly charged identified lepton (electron or muon) to reconstruct this decay. No reconstruction of the second B meson in the Upsilon(4S) event is performed. We obtain Br( B- -> D0 l- nubar_l ) = (2.29 +/- 0.05(stat) +/- 0.08(syst))%, in agreement with …
We report results of a search for tau lepton decays strongly suppressed in the Standard Model based on the world-largest data sample accumulated with the Belle detector at the KEKB asymmetric-energy e+e- collider. The decays include: lepton flavor and lepton number violating tau decays into a lepton (e or mu) and two charged mesons (K or pi) as well as lepton and baryon number violating tau decays into a Lambda and a charged meson (K or pi). The sensitivity to the branching fractions is significantly improved compared to our previous results and reaches O(10^{-8}).
Hadronic $B$ decays without a charm quark constitute a powerful probe to search for physics beyond the standard model as well as to provide constraints on $CP$ violation parameters. We report final measurements from Belle of the branching fractions and $CP$ asymmetries for the decays $B^{0} \rightarrow π^{0} π^{0}$ and $B^{\pm} \rightarrow K^{+} K^{-} π^{\pm}$. The $B^{0} \rightarrow π^{0} π^{0}$ measurements enable us to improve constraints on the angle $ϕ_{2}$ of the CKM unitarity triangle. For $B^{\pm} \rightarrow K^{+} K^{-} π^{\pm}$ we measure $CP$ asymmetry as a function of the invariant…
The Belle II experiment at the SuperKEKB energy-asymmetric $e^+e^-$ collider is a substantial upgrade of the B factory facility at the Japanese KEK laboratory. The design luminosity of the machine is $8\times10^{35}\, \mathrm{cm}^{-2}\mathrm{s}^{-1}$ and the Belle II experiment aims to record $50\, \mathrm{ab}^{-1}$ of data, a factor of 50 more than its predecessor. From February to July 2018, SuperKEKB has completed a commissioning run, achieved a peak luminosity of $5.5 \times 10^{33}\, \mathrm{cm}^{-2}\mathrm{s}^{-1}$, and Belle II recorded a data sample of about $0.5\, \mathrm{fb}^{-1}$. I…
We report on the recent results of searches for lepton-flavor-violating tau decays as well as lepton-number-violating B decays with the world-highest data samples accumulated at the Belle.
We present recent results for radiative and electroweak penguin decays of $B$ me son at Belle. Measurements of differential branching fraction, isospin asymmetr y, $K^*$ polarization, and forward-backward asymmetry as functions of $q^2$ for $B \to K^{(*)}ll$ decays are reported. For the results of the radiative process, we report measurements of branching fractions for inclusive $B\to X_s γ$ and the exclusive $B\to K η' γ$ modes.
It is experimentally observed that ratios of branching fractions for semitauonic and semileptonic $B$ decays, known as the $R(D^{(*)})$, are higher than Standard Model (SM) predictions. The $B \to \bar{D}^{(*)} τ^{+} ν_τ$ decays, except for the branching fractions, offer also other observables, in particular, angular observables may determine spin structure of a potential New Physics (NP) providing some clues to explain the $R(D^{(*)})$ puzzle. In this review, polarization measurements in $B \to \bar{D}^{*} τ^{+} ν_τ$ decays at Belle are presented and prospects for measurements of characterist…
Using the full Belle Upsilon(5S) data sample of 121 fb^-1we have measured exclusive branching fractions for the decays B_s^0 -> D_s^(*)+D_s^(*)-. Assuming these decay modes saturate decays to CP-even final states, the branching fraction determines the relative width difference between the CP-odd and -even eigenstates of the B_s.
The Belle Collaboration presented three recent Belle analyses: The search for $B\rightarrow lνγ$ ($l = e, μ$) with improved hadronic tagging, the search for $B\rightarrow μν_μ$ with inclusive tagging and the test of lepton universality in $B\rightarrow K^*ll$ ($l = e, μ$) decays.
We review measurements of semileptonic and leptonic charm meson decays performed by the Belle experiment, and we use these results to estimate the sensitivity of the follow-on Belle II experiment to these decays.
We present preliminary absolute branching fraction measurements of leptonic $D_s^+$ decays to $μ^+ν_μ$ and $τ^+ν_τ$, and of hadronic $D_s^+$ decays to $K^-K^+π^+$, $\bar{K}{}^0K^+$ and $ηπ^+$. The results are obtained from a large data sample collected near the $Υ(4S)$ and $Υ(5S)$ resonances with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. We obtain the the branching fractions ${\cal B}(D_s^+\toμ^+ν_μ)=(0.528\pm0.028\pm0.019)%$ and ${\cal B}(D_s^+\toτ^+ν_τ)=(5.70\pm0.21{}^{+0.31}_{-0.30})%$ which are combined to determine the $D_s$ decay constant $\fds=(255.0\pm4.2\pm5.…
We report the recent results of a search for lepton-flavor-violating tau decays and a search for CP violation in tau to nu Ks pi using a large data sample accumulated with the Belle detector at the KEKB asymmetric-energy e^+e^- collider. The sensitivity to these modes is significantly improved compared to previous experiments.
We report on the first Belle II measurements of branching fractions and CP-violating charge asymmetries in charmless $B$ decays. We use 34.6 fb$^{-1}$ from electron-positron collisions collected in 2019 and 2020 at the $Υ(4S)$ resonance. The results are compatible with known values and show performance already comparable with Belle.
This proceeding summarizes the recent measurements of semileptonic $b\to u$ decays from the Belle experiment. These analyses use the full data set collected at the $Υ(4S)$ resonance at KEKB accelerator complex with a center-of-mass energy of $\sqrt{s} = 10.58$ GeV, which contains an integrated luminosity of 711 fb$^{-1}$ and corresponds to 772 million $Υ(4S) \to B\bar{B}$ events. In the sector of inclusive decay, the partial branching fraction of $B \to X_{u} \ell ν$ decays and the CKM matrix element $|V_{ub}|$ are measured with hadronic tagging. The first measurement of differential branching…
Searches for lepton flavor violation in tau decays are unambiguous signatures of new physics. The branching ratios of tau leptons at the level of 10^-10 - 10^-9 can be probed with 50 ab^-1 of electron-positron annihilation data being collected by the Belle II experiment at the world's highest luminosity accelerator, the SuperKEKB, located at the High Energy Accelerator Research Organization, KEK, in Tsukuba, Japan. Searches with such expected sensitivity will either discover new physics or strongly constrain several new physics models.
Measurements of $\boldsymbol{B\rightarrow Kπ}$ and $\boldsymbol{B\rightarrow ππ}$ Branching Fractions and $\boldsymbol{\mathcal{A}_{CP}}$ Asymmetries at Belle II
Belle II 测量了多种 $B\to K\pi$ 和 $B\to\pi\pi$ 衰变的分支比及直接 CP 不对称性，通过同位旋求和规则检验标准模型，并测量了 CKM 角 $\phi_2$ 相关的衰变，结果与标准模型预期一致。
We search for the singly Cabibbo-suppressed decay $D^+ \to K^- K^0_s π^+ π^+ π^0$ using the full data set of 988 fb$^{-1}$ recorded by the Belle experiment at the KEKB $e^+e^-$ collider. We measure the branching fraction for this decay to be $\left({6.4^{+3.9}_{-3.8}}\right)\times10^{-5}$ with an upper limit at 95% credibility of $1.4\times10^{-4}$. We also measure the sum of the branching fractions for $D^+ \to \bar{K}^* ηπ^+$ and $D^+ \to \bar{K}^* ωπ^+$ to be $\left({6.0^{+6.3}_{-5.8}}\right) \times {10^{-5}}$ with an upper limit at 95% credibility of $1.8\times10^{-4}$.
We present measurements of the first to fourth moments of the lepton mass squared $q^2$ of \mbox{$B \to X_c \, \ell\, \bar ν_{\ell}$} decays for $\ell = e, μ$ and with $X_c$ a hadronic system containing a charm quark. These results use a sample of electron-positron collisions at the $Υ(4S)$ resonance corresponding to $62.8 \, \mathrm{fb}^{-1}$ of integrated luminosity and collected by the Belle II experiment in 2019 and 2020. To identify the $X_c$ system and reconstruct $q^2$, one of the $B$ mesons from an $Υ(4S) \to B \kern 0.18em\overline{\kern -0.18em B}$ decay is fully reconstructed in a h…
Semileptonic decays of $B$ mesons to the tau lepton, despite of experimental difficulties, are of great importance. In particular they are sensitive probes of models with extended Higgs sectors. The results of studies of semitauonic B decays at Belle are presented.
We report the recent results related to $π-K$ interactions based on the data collected by the Belle experiment at the KEKB collider. This includes the branching fraction and $CP$ asymmetry measurements of $B^+\to K^+K^-π^+$ decay, search for the $Λ_c^+\toϕpπ^0$, $Λ_c^+\to P_s^+π^0$ decays, branching fraction measurement of $Λ_c^+\to K^-π^+pπ^0$, first observation of doubly Cabibbo-suppressed decay $Λ_c^+\to K^+π^-p$, and the measurement of CKM angle $ϕ_3$ ($γ$) with a model-independent Dalitz plot analysis of $B^{\pm}\to DK^{\pm},D\to K_S^0π^+π^-$ decay.
We report the measurements of the leptonic decays B->lnu obtained at the Belle experiment. The results are consistent with the Standard Model expectations, and provide stringent constraints on new physics models including charged Higgs bosons. We also report an outlook of the measurements of B->lnu for the Belle II experiment.
We present the selected recent charm results at Belle: (1) the $CP$ asymmetries and branching fractions for the decays of charm mesons, i.e. $D^{0}\toπ^{+}π^{-}η,\,K^{+}K^{-}η$ and $D^{0}\toϕη$; $D_{s}^{+}\to K^{+}π^{0},\,K^{+}η$ and $D_{s}^{+}\toπ^{+}π^{0},\,π^{+}η$. (2) the branching fractions for the decays of charmed baryons, i.e. $Λ_{c}^{+}\to pπ^{0},\,pη$; $Λ_{c}^{+}\toΛπ^{+}η,\,Σ^0π^{+}η$ and intermediate processes $Λ_{c}^{+}\toΛ(1670)π^{+},\,ηΣ(1385)^+$; $Ξ_c^0\toΛ\bar{K}^{*0},\,Σ^0\bar{K}^{*0}$ and $Σ^+K^{*-}$. (3) properties of excited charmed baryons, i.e. search for electromagnetic…
