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.
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 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 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 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 s…
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.
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…
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 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.
The $B$-factories provide rich opportunities to search for new phenomena, in $B$, charm, and tau decays. Presented here is a selection of recent results from Belle and Babar.
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 study of B+- to J/psi eta K+- decays at Belle. In this analysis we search for X(3872) as well as other narrow resonances in the J/psi eta final state.
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 …
The expected sensitivity of Belle is reported for the Dark Photon, A, and Dark Higgs, h' searches, for mass ranges, respectively of 0.27 < m_A < 3 GeV/c^2 and 0.54 < m_h' < 10 GeV/c^2. The Dark Photon and Dark Higgs will be searched for in the Higgs-strahlung channels: e^+e^- -> Ah', with h' -> AA and A -> l^+l^- (with l = e or mu). Results will be unblinded soon.
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.
Recent results on the search for new physics at BaBar and Belle B-factories are presented. The search for a light Higgs boson produced in the decay of different Y resonances is shown. In addition, recent measurements aimed to discover invisible final states produced by new physics mechanisms beyond the standard model are presented.
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.
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 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 measurements and searches for resonant $B^{\pm} \to K^{\pm} h \to K^{\pm} γγ$ decays where $h$ is a $η,η^{\prime},η_{c},η_{c}(2S),χ_{c0},χ_{c2},J/ψ$ meson or the X(3872) particle.
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\…
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.
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.
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 $R(D^*)$…
We report an improved measurement of D0-D0bar mixing and a search for CP violation in D0 decays to CP-even final states K+K- and pi+pi-. The measurement is based on the final Belle data sample of 976/fb. The results are y_CP=(1.11 +- 0.22 +- 0.09)% and A_Gamma=(-0.03 +- 0.20 +- 0.07)%, where the first uncertainty is statistical and the second is systematic.
We report the first measurement of the forward-backward asymmetry and the ratios of Wilson coefficients A_9/A_7 and A_10/A_7 in B to K*l+l-, obtained using 386M BBbar pairs that were collected at the Y(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+ e- collider. We also summarise the results obtained by Belle in searches for purely leptonic B decays, with emphasis on their impact on models of physics beyond the Standard Model.
We present a search for the decay B -> tau nu in a 140 fb^-1 data sample collected at the Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric B factory. Combinatorial and continuum backgrounds are suppressed by selecting a sample of events with one fully reconstructed B. The decay products of the other side B in the event are analyzed to search for a B -> tau nu decay. We find no significant evidence for a signal and set a 90% confidence level upper limit of Br(B -> tau nu) < 2.9 * 10^-4. All results are preliminary.
We report on a new search for two-body baryonic decays of the B meson. Improved sensitivity compared to previous Belle results is obtained from 414 fb^-1 of data that corresponds to 449 million B B-bar pairs, which were taken on the Upsilon(4S) resonance and collected with the Belle detector at the KEKB e^+e^- collider. No significant signals are observed and we set the 90% confidence level upper limits: Br(B^0-> p pbar) <1.1X10^-7, Br(B^0-> Lambda Lambda-bar) < 3.2X10^-7 and Br(B^+-> p Lambda-bar) < 3.2X10^-7.
We search for the radiative penguin decays B_s to phi gamma and B_s to gamma gamma in a 23.6 fb-1 data sample collected at the Upsilon(5S) resonance with the Belle detector at the KEKB e+e- asymmetric-energy collider. We observe for the first time a radiative penguin decay of the B_s meson in the B_s to phi gamma mode. No significant B_s to gamma gamma signal is observed.
We reconstruct B0bar --> Ds-D+ decays using a sample of 449 x 10^6 BBbar pairs recorded by the Belle experiment, and measure the branching fraction to be Br(B0bar --> Ds-D+)=[7.5 +- 0.2(stat) +- 0.8(syst) +- 0.8(Br's)] x 10^(-3). A search for the related decay B0bar --> Ds+Ds- is also performed. Since we observe no statistically significant signal an upper limit on the branching fraction is set at 3.6 x 10^(-5) (90% C.L.).
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 on a search for the exclusive two-body charmless hadronic B meson decays B-> eta' rho, B-> eta' K*, B-> eta' phi, B-> eta' omega and B->eta' eta('). The results are obtained from a data sample containing 535 x 10^6 BBbar pairs that were collected at the Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+ e- collider. We find no significant signals and report upper limits in the range 0.5-6.5 x 10^{-6} for all of the above decays.
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 $|V_{cb}| \times 10^{3} = 41.7 \pm 1.2$.
Using kaon secondary interactions in the material of the Belle detector, we search for both inclusive and exclusive production of the Theta(1540)+. We set an upper limit of 2.5% at the 90% C.L. on the ratio of the Theta(1540)+ to Lambda(1520) inclusive production cross sections. We also search for the Theta(1540)+ as an intermediate resonance in the charge exchange reaction K+ n -> p Ks. An upper limit of Gamma(Theta+)<0.64MeV at the 90% C.L. at m(Theta+)=1.539MeV is set. These results are obtained from a 397/fb data sample collected with the Belle detector near the Upsilon(4S) resonance, at t…
We search for the strange pentaquark $Θ^+$ using kaon interactions in the material of the Belle detector. No signal is observed in the $p K_S$ final state, while in the $p K^-$ final state we observe $\sim 1.6 \cdot 10^4$ $Λ(1520) \to p K^-$ decays. We set an upper limit on the ratio of $Θ^+$ to $Λ(1520)$ yields $σ(Θ^+) / σ(Λ(1520)) < 2%$ at 90% CL assuming that the $Θ^+$ is narrow. We also report on searches for strange and charmed pentaquarks in B meson decays. These results are obtained from a 155$fb^{-1}$ data sample collected with the Belle detector near the $Υ(4S)$ resonance, at the KEKB…
The HyperCP experiment reported the observation of three events for the $Σ^+ \rightarrow p μ^+μ^-$ decay. The dimuon masses of the observed events are clustered within the detector resolution of 1 MeV/$c^2$. These decays might be interpreted as a two-body decay, $Σ^+ \rightarrow pX^0$, $X^0 \rightarrow μ^+μ^-$, where $X^0$ is a new particle with mass (214.3 $\pm$ 0.5) MeV/$c^2$. We report on a search for the $X^0$ particle in $\bzkx$ and $\bzrhox$ decays using 656 million $B$ meson pairs collected with the Belle detector at the KEKB asymmetric energy $e^+e^-$ collider.
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 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 report the results of a search for the decay B^0 -> e^+ e^-, mu^+ mu^- and e^{+-} mu^{-+} based on an analysis of 78 fb^{-1} of data collected by the Belle detector at KEKB. No candidate events have been found. Upper limits on the branching fractions are calculated at the 90% confidence level: B(B^0 -> e^+ e^-) < 1.9 x 10^{-7}, B(B^0 -> mu^+ mu^-) < 1.6 x 10^{-7}, and B(B^0 -> e^{+-} mu^{-+})< 1.7 x 10^{-7}. A limit on the Pati-Salam leptoquark mass M_{LQ}> 46 TeV/c^2 is obtained at the 90% confidence level.
A search for mixing in the neutral D meson system was performed using semileptonic D^0 -> K- e+ nu decays. The flavor of neutral D mesons at production was tagged by the charge of the slow pion from the decay D*+ -> D^0 π+. The measurement was performed using 140 fb^-1 of data recorded by the Belle detector. The yield of right and wrong sign decays arising from un-mixed and mixed events, respectively, was determined by a fit to kinematic observables. From the number of signal events we derive an upper limit for the time-integrated mixing rate r_D < 1.4 x 10^-3 at 90% C.L.
We reconstruct B0bar -> D_s^-D^+ decays using a sample of 275 million BBbar pairs recorded by the Belle experiment, and we measure the branching fraction to be [7.42 +- 0.23(stat) +- 1.36(syst)] x 10^(-3). We also search for the related decay B0bar -> D_s^+D_s^-. We observe no statistically significant signal and set an upper limit on the branching fraction of 2.0 x 10^(-4) at 90% C.L.
Using the large data sample accumulated by the Belle experiment at KEKB asymmetry energy $e^+e^-$ Collider, we report the preliminary measurements of the branching fractions of the radiative decays $D^0 \rightarrow Vγ$, where $V$ = $ϕ,\bar{K^*}^0, ρ^0$. This is the first observation of the decay $D^0 \rightarrow ρ^0γ$ and also present the preliminary results of the first measurement of $CP$ asymmetry in these decays. We present the preliminary result of the $CP$ asymmetry of the $D^0 \rightarrow K^0_S K^0_S$ decay, which is consistent with no $CP$ violation and improves the uncertainty with re…
The Belle II experiment at the SuperKEKB asymmetric $e^+e^-$ collider at KEK, Tsukuba, Japan, is recording data since 2018. The expected high luminosity of $\mathcal{L}=8\cdot 10^{35}~$cm$^{-2}$s$^{-1}$ enables searches for yet unobserved exotic hadronic states in B meson decays. We describe the search for a partner state of the $X(3872)$ at the $D^{*}\bar{D}^{*0}$ threshold. The reconstruction of charmed mesons is tested with experimental data corresponding to an integrated luminosity of $504~$pb$^{-1}$ collected at the energy in the center of mass of $Υ(4S)$ in 2018, and $2.62~$fb$^{-1}$ in …
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 search for the rare decays B -> h(*) nu nubar, where h(*) stands for a light meson. A data sample of 535 million BBbar pairs collected with the Belle detector at the KEKB e+e- collider is used. Signal candidates are required to have an accompanying B meson fully reconstructed in a hadronic mode and signal-side particles consistent with a single h(*) meson. No significant signal is observed and we set upper limits on the branching fractions at 90% confidence level. The limits on B0 -> K*0 nu nubar and B+ -> K+ nu nubar decays are more stringent than the previous constraints, while …
We present a search for the decays B -> tau nu and B -> K nu nubar in a 253 fb^-1 data sample collected at the Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric energy B factory. Combinatorial and continuum backgrounds are suppressed by selecting a sample of events with one fully reconstructed B. The decay products of the B on the other side of the event are analyzed to search for B -> tau nu and B -> K nu nubar decays. We find no significant evidence for a signal and set 90% confidence level upper limits of B(B -> tau nu) < 1.8*10^-4 and B(B -> K nu nubar) < 3.6*10^-5.
