We have searched for neutrinoless $τ$ lepton decays into $\ell$ and $V^0$, where $\ell$ stands for an electron or muon, and $V^0$ for a vector meson ($ϕ$, $ω$, $K^{*0}$, $\bar{K}^{*0}$ or $ρ^0$), using 543 fb$^{-1}$ of data collected with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. No excess of signal events over the expected background has been observed, and we set upper limits on the branching fractions in the range $(5.9-18) \times 10^{-8}$ at the 90% confidence level. These upper limits include the first results for the $\ell ω$ mode as well as new limits that are significantly more restrictive than our previous results for the $\ell ϕ$, $\ell K^{*0}$, $\ell \bar{K}^{*0}$ and $\ell ρ^0$ modes.
We have searched for the Lepton Flavor Violating decay $τ^- \to μ^- η$ using a data sample of 84.3 fb$^{-1}$ accumulated with the Belle detector at KEK. The $η$-meson was detected through the decay modes: $η\to γγ$ and $π^+π^-π^0$. No signal candidates are found, and we obtain an upper limit for the branching fraction ${\cal B}(τ^- \to μ^- η)<3.4\times 10^{-7}$ at the 90% confidence level.
We report the recent measurements of $B^0\to J/ψπ^0$ and other CP violation modes based on the data collected by the Belle experiment at the KEKB collider. The CP asymmetry parameters for the decay $B^0\to J/ψπ^0$ have previously been measured by BaBar and Belle experiments, but the results of mixing induced CP asymmetry $[S=-η_f\sin(2ϕ_1)]$ were not in good agreement with each other. Furthermore, the BaBar result lies outside the physically allowed region. Previous Belle measurements were based on $535\times10^6$ $B\bar{B}$ pairs. We updated the measurements using the final Belle data set of …
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 new measurements of CP-violation parameters in B0 --> phi K0, K+ K- Ks, f0(980) Ks, eta' Ks, omega Ks, Ks pi0, and K*0 gamma (K*0 --> Ks pi0) decays based on a sample of 275 x 10^6 BBbar pairs collected at the Upsilon(4S) resonance with the Belle detector at the KEKB energy-asymmetric e+e- collider. One neutral B meson is fully reconstructed in one of the specified decay channels, and the flavor of the accompanying B meson is identified from its decay products. CP-violation parameters for each of the decay modes are obtained from the asymmetries in the distributions of the proper-ti…
We have searched for neutrinoless $τ$ lepton decays into $\ell$ and $V^0$, where $\ell$ stands for an electron or muon, and $V^0$ for a vector meson ($ϕ$, $ω$, $K^{*0}$ or $\bar{K}^{*0}$), using 543 fb$^{-1}$ of data collected with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. No excess of signal events over the expected background is observed, and we set upper limits on the branching fractions in the range $(0.7 - 1.8) \times 10^{-7}$ at the 90% confidence level. These upper limits include the first results for $\ell ω$ as well as new limits that are $3.6 - 9.6$ times mo…
We present new measurements of CP-violation parameters in B0 -> KsKsKs and Ks pi0 gamma decays based on a sample of 275 x 10^6 BBbar pairs collected at the Upsilon(4S) resonance with the Belle detector at the KEKB energy-asymmetric e+e- collider. One neutral B meson is fully reconstructed in one of the specified decay channels, and the flavor of the accompanying B meson is identified from its decay products. CP-violation parameters are obtained from the asymmetries in the distributions of the proper-time intervals between the two B decays. We obtain S_{KsKsKs} = +1.26 +/- 0.68(stat) +/- 0.18(s…
I will review the latest developments in determining the CP-violating phases of the CKM matrix elements from measurements by the BaBar and BELLE experiments at the high-luminosity B factories (PEP-II and KEKB). The emphasis will be on the angle gamma/phi_3 of the Unitarity Triangle, which is the relative phase arg(-V_ud V_ub^*/V_cd V_cb^*), or the CP-violating phase of the b to u transition in the commonly used Wolfenstein convention.
We present a measurement of CP-violating asymmetries in B0 -> pi+pi- decays based on 41.8 fb-1 data sample collected at the Y(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e- collider. From the asymmetry in the distribution of the time intervals between the two B meson decay points, we obtain the CP-violating asymmetry parameters S_pipi = -1.21 + 0.38 - 0.27 (stat) + 0.16 - 0.13 (syst) and A_pipi = +0.94 + 0.25 - 0.31 (stat) +- 0.09 (syst).
Recently, it was pointed out that the electron and muon g-2 discrepancies can be explained simultaneously by a flavor-violating axion-like particle (ALP). We show that the parameter regions favored by the muon g-2 are already excluded by the muonium-antimuonium oscillation bound. In contrast, those for the electron g-2 can be consistent with this bound when the ALP is heavier than 1.5 GeV. We propose to search for a signature of the same-sign and same-flavor lepton pairs and the forward-backward muon asymmetry to test the model at the Belle II experiment.
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}).
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.
Evidence for the inclusive $B \to X_s \ell^+ \ell^-$ decay has been presented based on 41.8 fb-1 data sample collected at the Y(4S) resonance with the Belle detector at the KEKB asymmetric e+e- collider. A preliminary result for the branching fraction is B($B \to X_s \ell^+ \ell^-$) = (7.1 +- 1.6 (stat.) + 1.4 - 1.2(syst.)) \times 10^-6.
We discuss the latest results and future prospects of the Belle experiment on the electroweak and radiative processes b --> s ell+ ell-, b --> s gamma and b --> d gamma. In particular, the first measurement of the inclusive rate for B --> X(s) ell+ ell- provides a new constraint on the physics beyond the Standard Model. The yet to be measured decay B --> rho gamma is expected to provide a new constraint on the CKM matrix element |V(td)| in the near future.
We present a search for the B-> pi e^+ e^- and B-> pi μ^+ μ^- decays, with a data sample of 657 million BBbar pairs collected with the Belle detector at the KEKB $e^+e^-$ collider. Signal events are reconstructed from a charged or a neutral pion candidate and a pair of oppositely charged electrons or muons. No significant signal is observed and we set the upper limit on the isospin-averaged branching fraction BF(B -> π\ell^+\ell^-) < 6.2x10^-8 at the 90% confidence level.
Recent measurements of branching fractions and CP-violating partial-rate asymmetries for rare hadronic B-meson decays by the asymmetric-energy B-factory experiments, Belle and BaBar, are reviewed.
We report on the measurement of inclusive charmless semileptonic B decays $B \to X_{u} \ell ν$. The analysis makes use of hadronic tagging and is performed on the full data set of the Belle experiment comprising 772 million $B\bar{B}$ pairs. In the proceedings, the preliminary results of measurements of partial branching fractions and the CKM matrix element $|V_{ub}|$ are presented.
We report on preliminary measurements of branching fractions, charge-parity-violating asymmetries, and longitudinal polarization fractions in charmless bottom-meson decays from the Belle~II experiment. We use samples of electron-positron collisions collected in 2019 and 2020 at the $Υ(4S)$ resonance, corresponding to integrated luminosities of up to 62.8 ${\rm fb^{-1}}$. The results are compatible with known values, indicating good understanding of early detector performance.
We report on the results of penguin-mediated B decays at the Belle experiment. The analyses were based on approximately 32 million $B\bar{B}$ events collected at the $Υ(4S)$ resonance with the Belle detector at the KEKB $e^+e^-$ storage ring. The $b \to s γ$ transition was studied through exclusive decays: $B \to K^{*} γ$, $B^0 \to K_{2}^{*}(1430)^0 γ$, $B^+ \to K^+π^-π^- γ$, $B^+ \to K^{*0} π^+ γ$ and $B^+ \to K^+ρ^0 γ$. The $b \to s \ell^+ \ell^-$ transition was searched through both exclusive decays, $B \to K^{(*)} \ell^+ \ell^-$, and inclusive decay, $B \to X_{s} \ell^+ \ell^-$. We observe…
We have searched for the lepton-flavor-violating decay tau -> e gamma using a data sample of 86.7/fb collected with the Belle detector at the KEKB asymmetric e^+ e^- collider. No evidence for a signal is obtained, and we set an upper limit for the branching fraction Br(tau -> e gamma) < 3.9 x 10^-7 at the 90% C.L.
We update our search for the lepton flavor violating tau -> mu gamma and tau -> e gamma decays based on 535/fb of data accumulated at the Belle experiment. No signal is found and we set preliminary 90% confidence level upper limits: B(tau -> mu gamma) < 4.5x 10^-8 and B(tau -> e gamma) < 1.2x 10^-7.
We report a preliminary study of the branching fractions and $q^2$ distributions of exclusive charmless semileptonic B decays, using events tagged by fully reconstructing one of the $B$ mesons in a hadronic decay mode. These results are obtained from a data sample that contains 535 $\times 10^6\ B\bar{B}$ pairs, collected near the $Υ(4S)$ resonance with the Belle detector at the KEKB asymmetric energy $e^+ e^-$ collider.
The semileptonic $B$ meson decays of the type $B \to X_u \ell ν$ are important for measuring the magnitude of the CKM matrix element $V_{ub}$. Recent measurements of inclusive $B \to X_u e ν_e$ and hadronically tagged $B^0 \to π^- \ell^+ ν$ from the Belle II experiment are presented. The results are obtained using the data collected at Belle II between March 2019 and March 2020, with a total integrated luminosity of 37.8 ${\rm fb}^{-1}$. These preliminary measurements are used to validate the detector and reconstruction software performance. The measured preliminary branching fraction of $B^0 …
The Belle~II Collaboration presents four new analyses: The measurement of $V_{ub}$ from $B \to πe ν_e$ decays with a fit to the differential $q^2$ spectrum, the determination of $V_{cb}$ using a fit to the differential $w$ distribution from $B^0 \to D^{\ast -} \ell^+ ν_\ell$ decays, and the measurement of $q^2$ moments in inclusive $B \to X_c \ell ν_\ell$ decays. In all these analyses tag-side $B$ meson is reconstructed in a fully hadronic decay chain. The last result are branching fraction measurement of $B \to K^\ast \ell^+ \ell^-$ decays using an untagged approach.
We have performed a search for the lepton-flavor-violating decay tau -> mu gamma using a data sample of 86.3fb^{-1} accumulated by the Belle detector at KEK. No evidence for a signal is seen, and we set an upper limit for the branching fraction of B(tau -> mu gamma) < 3.1 x 10^{-7} at the 90% confidence level.
We are reporting on a search for flavour-changing neutral current decays $D^0 \to μ^+ μ^-$ and $D^0 \to e^+ e^-$, and for lepton-flavour violating decays $D^0 \to e^\pm μ^\mp$, the measurement of $D^+_{(s)} \to K_S^0 π^+$ and $D^+_{(s)}\to K_S^0 K^+$ branching fractions, and the search for CP violation in $D^+_{(s)} \to K_S^0 π^+$ and $D^+_{(s)} \to K_S^0 K^+$ decays. The analyses are based on 600 fb$^{-1}$ to 700 fb$^{-1}$ of data collected in $e^+e^-$ collisions at the centre-of-mass (CM) energy of the $Υ(4S)$ resonance and 60 MeV below by the Belle detector at the KEKB collider.
Radiative and electroweak penguin mediated decays of $B$ mesons are a great probe for physics beyond the Standard Model of particle physics. Furthermore, recently anomalies on exclusive $b \rightarrow s \ell^{+} \ell^{-}$ processes, which may imply lepton flavor universality violation, have been observed. Belle II experiment sheds light on the anomalies with the measurement of an inclusive analysis in this mode. Thanks to smaller hadronic uncertainties compared with exclusive modes, complementary information can be provided. Belle II is also a unique experiment to search for processes involvin…
We report on a search for the lepton flavor violating tau- -> mu- gamma and tau- -> e- gamma decays based on 535/fb of data accumulated at the Belle experiment. No signal is found and we set 90% confidence level upper limits on the branching ratios Br(tau- -> mu- gamma) < 4.5x10^-8 and Br(tau- -> e- gamma) < 1.2x10^-7.
$CP$ violation asymmetry is expected to be very small within the Standard Model. Observation of $CP$ violation in charm sector would hint towards New Physics. Time-reversal asymmetry is sensitive to $CPV$ via the $CPT$ Theorem, and is a clean and alternative way to search for CP violation in charm decays. This is achieved by the use of triple-product correlations in 4-body charm meson decays. The results from previous searches at BaBar and LHCb Collaborations and the latest results from Belle are reported. The most recent result from Belle performed in $D^{0} \to K^{+}K^{-}π^{+}π^{-}$ decays u…
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…
Rare and flavour-changing neutral current decays of the B meson are an important probe in the search for physics beyond the Standard Model. There have recently been several anomalies in rare B decays, and lepton-universality measurements, specifically involving the $b\to s\ell^+\ell^-$ quark transition. These results tend towards a non-Standard-Model interpretation. The Belle II experiment is a next-generation b physics experiment located at SuperKEKB, an upgraded B factory $e^+e^-$ collider, in Tsukuba, Japan. The first collisions are expected in early 2018 with full physics data expected in …
We report on the first measurements of branching fractions, CP-violating charge asymmetries, and longitudinal polarization fractions in charmless $B$ decays at the Belle II experiment. We use a sample of electron-positron collisions collected in 2019 and 2020 at the $Υ(4S)$ resonance that corresponds to 34.6 fb$^{-1}$ of integrated luminosity. The results are compatible with the known values, which indicates a good understanding of detector performance.
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…
The $b \rightarrow s γ$, $b \rightarrow d γ$ and $b \rightarrow s \ell^+ \ell^-$ processes are allowed at higher order via the electroweak loop or box diagrams in the Standard model. It is sensitive probe to search for new physics beyond the Standard model because new particles might enter in the loop. We present preliminary results of branching fraction of the $\bar{B} \rightarrow X_s γ$, $CP$ asymmetry in the $\bar{B} \rightarrow X_{s+d} γ$, and the forward-backward asymmetry in the $\bar{B} \rightarrow X_s \ell^+ \ell^-$. The results are based on a data sample containing $772 \times 10^6 B\…
The decays $\bar{B} \rightarrow D^{(*)} τ^- \barν_τ$ are good probes to new physics beyond the Standard Model. The ratios of branching fractions $R(D^{(*)}) \equiv \mathit{BF}(\bar{B} \rightarrow D^{(*)} τ^- \barν_τ) / \mathit{BF}(\bar{B} \rightarrow D^{(*)} \ell^- \barν_\ell)$ (where $\ell^- = e^-, μ^-$) measured by Belle, BaBar and LHCb show 3.9$σ$ deviation from the SM expectations as of 2015. In 2016, the Belle collaboration has shown two new measurements for the $\bar{B} \rightarrow D^{(*)} τ^- \barν_τ$ decay. These include the first application of the semileptonic tagging to the $R(D^*)$…
Both the B-factories BaBar and Belle have ended data-taking and have mostly completed the data analysis aimed at searching Lepton Flavor Violation in Tau decays. No evidence of LFV in tau decays has been found yet. We review in the following the experimental upper limits that have been set.
With the first data being recorded at Belle II, we are at the brink of a new era in quark flavour physics. The many exciting new opportunities for Belle~II include a full angular analysis of inclusive ${\bar B \to X_{s} \, \ell^+\ell^-}$ which has the potential to reveal new physics, in particular by its interplay with the exclusive $b \to s \ell^+\ell^-$ counterparts studied extensively at LHCb. In this paper, we present fully updated Standard Model predictions for all angular observables necessary for this endeavour. These predictions are tailored to Belle II and include an elaborate study o…
We present the results of a time-dependent Dalitz plot analysis of B0 -> pi+ pi- pi0 decays based on a 414fb^-1 data sample that contains 449MBB pairs collected on the Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric energy e+e- collider. The direct CP violating parameters of B0 -> rho+-pi-+ decay mode are measured to be A_rhopi^+- = +0.22 +- 0.08(stat.) +- 0.05(syst.) and A_rhopi^-+ = +0.08 +- 0.17(stat.) +- 0.12(syst.). We also measure the CP violating parameters of the decay mode B0 -> rho0pi0 as A_rho0pi0 = -0.45 +- 0.35(stat.) +- 0.32(syst.) and S_rho0pi0 = +0.15 +- 0.…
In this paper, we briefly review results on rare decays of $B$ mesons from the Belle experiment, based on 10.4 fb$^{-1}$ data collected on the $Υ$(4S) resonance. The topics include measurements of Cabibbo suppressed decays $B \to D^{(*)} K^{(*)}$, charmless two-body decays $B \to ππ$, $Kπ$, $KK$ and $B \to η^{'} h (h = K^+, π^+, K^0)$, and a search for flavor changing neutral current decays $B \to K^{(*)} \ell^{+} \ell^{-}$.
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 present the measurement of the first to fourth order moments of the four-momentum transfer squared, $q^{2}$, of inclusive $B \rightarrow X_{c} \ell ν$ decays using the full Belle data set consisting of $711~\rm fb^{-1}$ of integrated luminosity at the $Υ(4S)$ resonance for $\ell = e, μ$. The measured moments are crucial experimental inputs for a novel, data-driven approach to determine inclusive $|V_{cb}|$, which we implement in order to extract a preliminary value of $|V_{cb}| \times 10^{3} = 41.7 \pm 1.2$.
We present the recent measurements of the B0 -> eta' K0 and the B -> omega K decay modes based on the full data set of 772x10^6 BBbar pairs collected by the Belle detector at the KEKB e+e- collider. In the B0 -> eta' K^{0} mode, we obtain the CP-violating parameters A(eta'K0) = +0.03+/-0.05(stat)+/-0.04(syst), S(eta'K0) = +0.68+/-0.07(stat)+/-0.03(syst). This is the world's most precise result on the eta' K0 CP parameters. In B -> omega K decays, we measure the branching fractions B(B0 -> omega K0) = (4.5+/-0.4(stat)+/-0.3(syst))x10^-6, B(B- -> omega K-) = (6.8+/-0.4(stat)+/-0.4(syst))x10^-6, …
We present a search for lepton-flavor-violating tau decays into three leptons (electrons or muons) using 782 fb^-1 of data collected with the Belle detector at the KEKB asymmetric-energy e+e- collider. No evidence for these decays is observed and we set 90% confidence level upper limits on the branching fractions between 1.5 x 10^-8 and 2.7 x 10^-8.
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…
We search for lepton-flavor-violating tau decays into three leptons (electron or muon) using 535 fb-1 of data collected with the Belle detector at the KEKB asymmetric-energy e+e- collider. No evidence for these decays is observed, and we set 90% confidence level upper limits on the branching fractions of (2.0-4.1)x10^-8. These results improve upon our previously published upper limits by factors of 4.9 to 10.
We overview recent measurements in B -> rho rho decays which are based on data samples collected at the PEP-II and KEKB asymmetric-energy e+e- colliders with the BABAR and Belle detectors. Special emphasis is given to the determination of the CP-violating coefficients A and S from an analysis of B -> rho+ rho- decays. The values of A and S, branching fractions, and longitudinal polarization fractions of B -> rho rho decays are used to constrain the Cabibbo-Kobayashi-Maskawa phase alpha/phi2 using an isospin analysis; the solution consistent with the standard model is 71 deg. < alpha < 113 deg.…
We search for lepton-flavor-violating tau decays into three leptons (electron or muon) using 535 fb^{-1} of data collected with the Belle detector at the KEKB asymmetric-energy e+e- collider. No evidence for these decays is observed and we set 90% confidence level upper limits on the branching fractions between 2.0x10^{-8} and 4.1x10^{-8}. These results improve the best previously published upper limits by factors from 4.9 to 7.0.
