We present a study of hadronic tau decays, especially decay into three-hadron final states with kaon(s), using more than 500fb^-1 of data collected with the Belle detector at the KEKB asymmetric-energy e+e- collider. We measure the branching ratios both inclusively and exclusively while considering the intermediated states of K(892)^*0. The following results are obtained: B(tau- -> K- pi+ pi- nu)=(3.25 +- 0.02 +0.16-0.15)x10^-3, B(tau- -> K- K+ pi- nu)=(1.53 +- 0.01 +- 0.06)x10^-3, B(tau- -> K- K+ K- nu)=(2.60 +- 0.23 +- 0.10)x10^-5 and B(tau- -> K^*(892)^0 K-nu)=(1.56 +- 0.02 +- 0.09)x10^-3. We also measure the mass and width of the K^*(892)^0 resonance as M_{K^*(892)^0} = 895.10 +- 0.27 +- 0.31 MeV/c^2 and Gamma_{K^*(892)^0} = 47.23 +- 0.49 +- 0.79 MeV, which are the first results obtained using tau decay.
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 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.
A review of recent results concerning decays of charmed mesons, charmed baryons and $τ$ leptons for the Belle and BaBar Experiments is given. The review was presented at the 43$^{rd}$ Rencontres de Moriond (QCD and High Energy Interactions), LaThuile, March 8-15, 2008.
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 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 present measurements of B+ -> Dbar*0 tau+ nu_tau and B+ -> Dbar^0 tau+ nu_tau decays in a data sample of 657 x 10^6 BBbar pairs collected with the Belle detector at the KEKB asymmetric-energy e+e- collider. We find 446^{+58}_{-56} events of the decay B+ -> Dbar*0 tau+ nu_tau with a significance of 8.1 standard deviations, and 146^{+42}_{-41} events of the decay B+ -> Dbar0 tau+ nu_tau with a significance of 3.5 standard deviations. The latter signal provides the first evidence for this decay mode. The measured branching fractions are B(B+ -> Dbar*0 tau+ nu_tau)=(2.12^{+0.28}_{-0.27} (stat) …
Two-body charmless hadronic decays of $B$ mesons are important for determining Standard Model parameters and for detecting the presence of new physics. We present recent results from the Belle experiment on the charmless hadronic decays $B\rightarrow ηπ^0$ and $B\rightarrow π^0 π^0$.
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 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 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 present a study of the decay tau- -> K_S pi- nu_tau using a 351 fb^-1 data sample collected with the Belle detector. The analysis is based on 53110 lepton-tagged signal events. The measured branching fraction B(tau- -> K_S pi- nu_tau)=(0.404 +- 0.002(stat.) +- 0.013(syst.))% is consistent with the world average value and has better accuracy. An analysis of the K_S pi- invariant mass spectrum reveals contributions from the K*(892)- as well as other states. For the first time the K*(892)- mass and width have been measured in tau decay: M(K*(892)-)=(895.47 +- 0.20(stat.) +- 0.44(syst.) +- 0.59…
We review recent results of the BABAR and BELLE Collaborations on the the alpha and gamma angles of the unitary triangle, on the B to K pi pi Dalitz-plot analyses, and on the searches for baryonic B decays and for B to DD decays.
We present a new measurement of the purely leptonic decay B- -> tau- nu_tau-bar with a semileptonic B tagging method, using a data sample containing 657*10^6 BB-bar pairs collected with the Belle detector at the KEKB asymmetric e+e- collider. A sample of BB-bar pairs are tagged by reconstructing one B meson decaying semileptonically. We detect the B- -> tau- nu_tau-bar candidate in the recoil. We obtain a signal with a significance of 3.8 standard deviations including systematics, and measure the branching fraction to be B(B- -> tau- nu_tau-bar) = 1.65+0.38-0.37(stat)+0.35-0.37(syst))*10^-4. T…
We report on measurements of branching fractions for several hadronic tau decays to final states with kaons, which can be used to determine the strange quark mass and the element |V_us| of the Cabibbo-Kobayashi-Maskawa quark-mixing matrix. The results are obtained from data collected with the BaBar and Belle detectors at the PEP-II and KEKB asymmetric-energy e+e- colliders at SLAC and KEK, respectively, both operating at center-of-mass energies near the Y(4S) resonance.
We report a measurement of the first and second moment of the hadronic mass distribution M_X in B -> X_c l nu decays for lepton threshold momenta ranging from 0.9 to 1.6 GeV/c in the center of mass frame. The measurement uses B Bbar events in which the hadronic decay of one B meson is fully reconstructed and a charged lepton from the decay of the other B meson is identified. These results are obtained from a 140 fb^-1 data sample collected near the Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric energy e^+ e^- collider.
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.
We present a measurement of the hadronic invariant mass squared (M^2_X) spectrum in charmed semileptonic B meson decays B --> X_c l nu based on 140 fb^-1 of Belle data collected near the Y(4S) resonance. We determine the first, the second central and the second non-central moments of this spectrum for lepton energy thresholds ranging between 0.7 and 1.9 GeV. Full correlations between these measurements are evaluated.
There are several exciting results for the hadronic B decays of Belle and BaBar recently. My report focuses on the ratios of branching fractions and $CP$ asymmetry for $B \to hh$ decays at Belle and BaBar where $h$ denotes $π$ or $K$. The observations of $B^+ \to K^+ \bar{K}{}^0$, $B^0 \to K^0 \bar{K}{}^0$ are published both by Belle and BaBar and shown here. We also report the observation of $B^+ \to ρ^+ K^0$ and search of $B^+ \to \bar{K}{}^{* 0} K^+$, $B^0 \to ρ^0 ρ^0$, $B^0 \to a_0^- π^+$ and $B^0 \to a_0^- K^+$ at BaBar. Finally, we will show the results of amplitude analysis of the decay…
We review recent experimental results on Bd and Bs mesons decays by the BaBar and Belle experiments. These include measurements of the color-suppressed decays B0bar to D(*)0h0, h0=pi0, eta, etaprime, omega, observation of the baryonic decay B0bar to Lambdac+ Lambdabar K-, measurements of the charmless decays B to eta h, h=K, pi, B to Kpi and observation of CP eigenstates in the Bs decays: B0s to J/psi f0(980), B0s to J/psi f0(1370) and B0s to J/psi eta. The theoretical implications of these results will be considered.
Belle II is an experiment designed to study billions of $τ$-lepton, $b$- and $c$-quark decays observed with low background in asymmetric-energy electron-positron collisions at the SuperKEKB $B$-factory. In March 2019, the newly completed Belle II started operating and collected its first physics data reaching 10 fb$^{-1}$ to date. We report the reconstruction of prominent signals from various hadronic $B$ decays including $B^{-}\to D^{(*)0}π^{-}$, $B^{0}\to D^{-}K^{+}$, and $B^{0}\to K^{+}π^{-}$ in the first data set corresponding to 5.15 fb$^{-1}$. These results show a remarkable level of ear…
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.
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 the recent results of a search for the decay B- --> tau- anti-nu_tau, observations of new resonances X, Y and Z, and the first results from Upsilon(5S) data collected with the Belle detector at KEKB e+e- collider.
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 $\tauTO \KKspizero ν_τ$.
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 report an observation of the decay B0 -> D*- tau+ nu and a search for the rare decays B -> h(*) nu nubar\ove, 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. We find a signal with a significance of 5.2 standard deviations on B0 -> D*- tau+ nu and measure the branching fraction to be 2.02 +0.40/-0.37 (stat.) +- 0.37 (syst.)%. No significant signal is observed for B -> h(*) nu nubar decays and we set upper limits on the branching fractions at 90% confidence level. The limits on B0 -> K*0 nu nuba…
Charmless hadronic $B$ decays are a good testing ground for the Standard Model (SM) of Particle Physics. The dominant amplitudes are CKM suppressed tree diagrams and/or $ b\to s$ or $b\to d$ loop ("penguin") diagrams. Non-SM particle could appear in the loop, and hence these decays are sensitive to search for New Physics (NP). Some of the recent measurements of two-body charmless hadronic $B$ decays from Belle and their prospects at Belle II are discussed.
We present the first evidence of the decay B- --> tau- nu_tau-bar using 414 fb^-1 of data collected at the Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e- collider. Events are tagged by fully reconstructing one of the B mesons in hadronic modes. We detect the signal with a significance of 4.2 standard deviations including systematics, and measure the branching fraction to be Br(B- --> tau- nu_tau-bar) = (1.06 +0.34-0.28(stat) +0.22-0.25(syst))*10^-4. We also report results based on 1.86 fb^-1 data collected by the Belle detector at the Upsilon(5S) resonance. Se…
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…
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.
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 presence of tau leptons in the final state is an important signature in many Higgs boson and SUSY searches. With the ATLAS detector, hadronically decaying tau leptons can be reconstructed in a wide range of transverse energies. The reconstruction algorithm for hadronically decaying tau leptons is explained and the performance of tau lepton identification is shown. Particularly important is the discrimination of hadronically decaying tau leptons against overwhelming backgrounds from QCD jets.
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.
Hadronically decaying tau leptons are of prime importance in numerous physics analyses in ATLAS. The spectrum of the possible applications of hadronically decaying tau leptons reaches from Standard Model measurements, including Higgs searches, to searches for physics beyond the Standard Model. The basic principles behind the sophisticated tau reconstruction and identification techniques, which are specifically designed to identify hadronically decaying taus and reject various background processes, are delineated here along with current data-driven estimates of their respective performance.
The Collins effect connects transverse quark spin with a measurable azimuthal dependence in the yield of hadronic fragments around the quark's momentum vector. Using two different reconstruction methods we observe statistically significant azimuthal asymmetries for charged pion pairs in e+e- annihilation at a center-of-mass energy of 10.52 GeV, which can be attributed to a transverse polarization of the primordial quarks. The measurement was performed using a sample of 79 million hadronic events collected with the Belle detector.
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.
Today the B-factories BaBar and Belle have accumulated largest samples of tau-tau events and are competing to be called tau-factories. Among the problems to be tested and measurements to be done by BaBar and Belle are check of CP and CPT invariance in tau decays, measurement of strange and non-strange spectral functions, extraction of mass of strange quark and |V_us|, searches for lepton flavor violation processes. In this paper, the latest results in tau physics by these two experiments and measurements to be done within next few years are reviewed.
We present a new measurement of the decay B- -> tau- nu_tau-bar with a semileptonic B tagging method, using a data sample containing 657*10^6 BB-bar pairs collected at the (4S) resonance with the Belle detector at the KEKB asymmetric e+e- collider. A sample of BB pairs are tagged by reconstructing one B meson decaying semileptonically. We detect the B- -> tau- nu_tau-bar candidate in the recoil. We obtain a signal with a signicance of 3.8 standard deviations including systematics, and measure the branching fraction to be B(B- -> tau- nu_tau-bar)=(1.65+0.38-0.37(stat)+0.35-0.37(syst))*10^4. Thi…
In this review recent studies on $CP$ violation and related hadronic $B$ decays by the Belle experiment, in particular measurements of CKM angles $ϕ_1$ and $ϕ_2$ are reported.
Selected results on hadronic decays of the tau lepton from the TAU98 Workshop are reviewed. A comprehensive picture emerges for strange particle branching fractions, and exploration of resonant substructure of both strange and non-strange decays is seen to have matured substantially.
The identification of hadronic tau lepton decays is an important requirement for the LHC physics program, both in terms of standard model measurements and the search for beyond-the-standard-model physics. The ATLAS and CMS algorithms for identification and energy calibration of hadronic tau lepton decays are conceptually different. They are described together with measurements of relevant performance figures.
A theoretical description of the differential decay spectrum for the decay tau- -> nu_tau K_S pi-, which is based on the contributing K pi vector and scalar form factors F_+^{K pi}(s) and F_0^{K pi}(s) being calculated in the framework of resonance chiral theory (R$χ$T), additionally imposing constraints from dispersion relations as well as short distance QCD, provides a good representation of a recent measurement of the spectrum by the Belle collaboration. Our fit allows to deduce the total branching fraction B[tau- -> nu_tau K_S pi-] = 0.427 +- 0.024 % by integrating the spectrum, as well as…
Since 1999, the B-factories collaborations BaBar and Belle have accumulated and studied large samples of tau lepton pairs. We summarize in the following the most interesting recent results.
I outline recent results using CLEO3 data involving the decay of the tau to three charged hadrons and a neutrino, as well as an investigation of the structure of the decay tau to KKpinu and the Wess-Zumino term in this decay.
New physics beyond the Standard Model could well preferentially show up at the LHC in final states with taus. The development of efficient and accurate reconstruction and identification of taus is therefore an important item in the CMS physics programme. The potentially superior performance of a particle-flow approach can help to achieve this goal with the CMS detector. Preliminary strategies are presented in this summary for the hadronic decays of the taus.
Results on a number of rare hadronic B decays are presented. A data sample of $29.1 {\rm fb}^{-1}$ accumulated using the Belle detector at the KEKB asymmetric $e^+e^-$ collider operating at the $Υ(4S)$ resonance is used.
This document presents a selection of QCD studies accessible to high-precision studies with hadronic final states in $e^+e^-$ collisions at Belle II. The exceptionally clean environment and the state-of-the-art capabilities of the Belle~II detector (including excellent particle identification and improved vertex reconstruction), coupled with an unprecedented data-set size, will make possible to carry out multiple valuable measurements of the strong interaction including hadronic contributions to the muon $(g-2)$ and the QCD coupling, as well as advanced studies of parton hadronization and dyna…
We present a measurement of the decay B- -> tau- nu_bar using a data sample containing 657 million BB_bar pairs collected at the Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e- collider. A sample of BB_bar pairs are tagged by reconstructing one B meson decaying semileptonically. We detect the B- -> tau- nu_bar candidate in the recoil. We obtain a signal with a significance of 3.6 standard deviations including systematic uncertainties, and measure the branching fraction to be Br(B- -> tau- nu_bar) = [1.54+0.38-0.37(stat)+0.29-0.31(syst)]*10^-4. This result confi…
We report on a search for CP violation in tau -> K^0_S pi nu_tau decays using a data sample of 699 fb^{-1} collected in the Belle experiment at the KEKB electron-positron asymmetric-energy collider. The CP asymmetry is measured in four bins of the invariant mass of the K^0_S pi system and found to be compatible with zero with a precision of O(10^{-3}) in each mass bin. Limits for the CP violation parameter Im(eta_S) are given at a 90 % confidence level. These limits are |Im(eta_S)|<0.026 or better, depending on the parameterization used to describe the hadronic form factors and improve upon pr…
We present a search for the decay B+ --> tau+ nu_tau using 467.8 x 10^6 B B-bar pairs collected at the Upsilon(4S) resonance with the BABAR detector at the SLAC PEP-II B-Factory. We select a sample of events with one completely reconstructed B- in an hadronic decay mode (B- --> D{(*)0}X- and B- --> J/psi X-). We examine the rest of the event to search for a B+ --> tau+ nu_tau decay. We identify the tau+ lepton in the following modes: tau+ --> e+ nu nu, tau+ --> mu+ nu nu, tau+ --> pi+ nu and tau+ --> rho nu. We find an excess of events with respect to expected background, which excludes the nu…
