On the B to D* tau nu Sensitivity to New Physics

B physics has played a prominent role in investigations of new physics effects at low-energies. Presently, the largest discrepancy between a standard model prediction and experimental measurements appears in the branching ratio of the charged current mediated B to tau nu decay, where the large tau mass lifts the helicity suppression arising in leptonic B decays. Less significant systematic deviations are also observed in the semileptonic B to D(*) tau nu rates. Due to the rich spin structure of the final state, the decay mode B to D* tau nu offers a number of tests of such possible standard model deviations. We investigate the most general set of lowest dimensional effective operators leading to helicity suppressed modifications of b to c (semi)leptonic transitions. We explore such contributions to the B to D* tau nu decay amplitudes by determining the differential decay rate, longitudinal D* polarization fraction, D* - tau opening angle asymmetry and the tau helicity asymmetry. We identify the size of possible new physics contributions constrained by the present B to D(*) tau nu rate measurements and find significant modifications are still possible in all of them. In particular, the opening angle asymmetry can be shifted by almost 30%, relative to the standard model prediction, while the tau helicity asymmetry can still deviate by as much as 80%.Comment: 10 pages, 4 figures; corrected several typos, added references, conclusions unchange

Observation of B+ -> Dbar*0 tau+ nu_tau and Evidence for B+ -> Dbar^0 tau+ nu_tau at Belle

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) +- 0.29 (syst)) % and B(B+ -> Dbar0 tau+ nu_tau)=(0.77 +- 0.22 (stat) +- 0.12 (syst)) %.Comment: 6 pages, 4 figures, submitted to Phys. Rev. Let

Measurement Of |V_ub| From Inclusive Charmless Semileptonic B Decays

We present the partial branching fraction for inclusive charmless semileptonic B decays and the corresponding value of the CKM matrix element |Vub|, using a multivariate analysis method to access ~90% of the B -> Xu l nu phase space. This approach dramatically reduces the theoretical uncertainties from the b-quark mass and non-perturbative QCD compared to all previous inclusive measurements. The results are based on a sample of 657 million B -Bbar pairs collected with the Belle detector. We find that Delta BR(B -> Xu l nu; p^*B_l>1.0 GeV/c=1.963 x (1 +/- 0.088(stat.) +/- 0.081(sys.)) x 10^-3. Corresponding values of |Vub| are extracted using several theoretical calculations.Comment: 9 pages, 1 figure, 2 tables. Published in PR

Evidence for B0→χc1π0B^0 \to \chi_{c1} \pi ^0 at Belle

We present a measurement of the branching fraction for the Cabibbo- and color-suppressed $B^0 \to \chi_{c1}\pi^0$ decay based on a data sample of $657\times 10^6$ $B\bar B$ events collected at the $\Upsilon(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. We observe a signal of $40\pm9$ events with a significance of $4.7\sigma$ including systematic uncertainties. The measured branching fraction is $\mathcal {B}(B^0 \to \chi_{c1} \pi^0) = (1.12\pm 0.25(\rm {stat.})\pm 0.12({\rm syst.}))\times 10^{-5}$.Comment: 5 pages, 5 figure

Search for leptonic decays of D0 mesons

We search for the flavor-changing neutral current decays D0\to mu+mu- and D0\to e+e-, and for the lepton-flavor violating decays D0\to e\pm mu\mp using 660 fb^-1 of data collected with the Belle detector at the KEKB asymmetric-energy e+e- collider. We find no evidence for any of these decays. We obtain significantly improved upper limits on the branching fractions: B(D0\to mu+mu-)<1.4x10-7, B(D0\to e+e-)<7.9x10-8, and B(D0\to e+mu-)+B(D0\to mu+e-)<2.6x10-7 at 90% confidence level.Comment: 6 pages, 3 figure

Measurement of Inclusive Radiative B-meson Decays with a Photon Energy Threshold of 1.7 GeV

Using 605/fb of data collected at the Upsilon(4S) resonance we present a measurement of the inclusive radiative B-meson decay channel, B to X_s gamma. For the lower photon energy thresholds of 1.7, 1.8, 1.9 and 2.0GeV, as defined in the rest frame of the B-meson, we measure the partial branching fraction and the mean and variance of the photon energy spectrum. At the 1.7GeV threshold we obtain the partial branching fraction BF(B to X_s gamma) = (3.45 +/- 0.15 +/- 0.40) x 10^-4, where the errors are statistical and systematic.Comment: 9 pages, 3 figures, 2 table

Observation of the ϕ(1680)\phi(1680) and the Y(2175) in e+e−→ϕπ+π−e^+ e^- \to \phi\pi^+\pi^-

The cross sections for $e^+ e^- \to \phi\pi^+\pi^-$ and e^+ e^- \to \phi \fzero are measured from threshold to $\sqrt{s}=3.0$ $\hbox{GeV}$ using initial state radiation. The analysis is based on a data sample of 673 fb$^{-1}$ collected on and below the $\Upsilon(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. First measurements are reported for the resonance parameters of the $\phi(1680)$ in the $\phi\pi^+\pi^-$ mode: $m=(1689\pm 7\pm 10)$ MeV/$c^2$ and $\Gamma=(211\pm 14\pm 19)$ MeV/$c^2$. A structure at $\sqrt{s}=2.1 \hbox{GeV}/c^2$, corresponding to the so called Y(2175), is observed; its mass and width are determined to be $2079\pm13^{+79}_{-28}$ MeV/$c^2$ and $192\pm23^{+25}_{-61} \hbox{MeV}/c^2$, respectively.Comment: 11 pages, 6 figures. Add one plot. Accepted by Phys.Rev.D(RC

Measurement of B0→π+π−π+π−B^0\to\pi^+\pi^-\pi^+\pi^- Decays and Search for B0→ρ0ρ0B^0\to\rho^0\rho^0

We report on a search for the decay $B^0\to\rho^0\rho^0$ and other charmless modes with a $\pi^+\pi^-\pi^+\pi^-$ final state, including $B^0\to\rho^0\pi^+\pi^-$, non-resonant $B^0\to 4\pi^{\pm}$, $B^0\to\rho^0f_0(980)$, $B^0\to f_0(980)f_0(980)$ and $B^0\to f_0(980)\pi^+\pi^-$. These results are obtained from a data sample containing 657 million $B \overline B$ pairs collected with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. We set an upper limit on $\mathcal{B}(B^0\to\rho^0\rho^0)$ of $1.0\times 10^{-6}$ at the 90% confidence level (C.L.). From our $B^0\to\rho^0\rho^0$ measurement and an isospin analysis, we determine the Cabibbo-Kobayashi-Maskawa phase $\phi_2$ to be $91.7 \pm 14.9$ degrees. We find excesses in $B^0\to \rho^0\pi^+\pi^-$ and non-resonant $B^0\to 4\pi^{\pm}$ with 1.3$\sigma$ and 2.5$\sigma$ significance, respectively. The corresponding branching fractions are less than $12.0 \times 10^{-6}$ and $19.3 \times 10^{-6}$ at the 90% C.L. In addition, we set 90% C.L. upper limits as follows: $\mathcal{B}(B^0\to\rho^0f_0(980))< 0.3 \times 10^{-6}$, $\mathcal{B}(B^0\to f_0(980)f_0(980))< 0.1 \times 10^{-6}$, and $\mathcal{B}(B^0\to f_0(980)\pi^+\pi^-)< 3.8 \times 10^{-6}$.Comment: 6 pages, 2 figures. Submitted to PRD(RC

Search for Lepton Flavor and Lepton Number Violating tau Decays into a Lepton and Two Charged Mesons

We search for lepton flavor and lepton number violating tau decays into a lepton (ell = electron or muon) and two charged mesons (h,h' = pi^\pm or K^\pm), tau- -> ell-h+h'- and tau- -> ell+h-h'-, using 671 fb^{-1} of data collected with the Belle detector at the KEKB asymmetric-energy e+e- collider. We obtain 90% C.L. upper limits on the branching fractions in the range (4.4-8.8)x10^{-8} for tau -> ehh', and (3.3-16)x10^{-8} for tau -> muhh' processes. These results improve upon previously published upper limits by factors between 1.6 to 8.8.Comment: 15 page, 7 figures, submitted to Phys. Lett.

Evidence of time-dependent CP violation in the decay B0 to D*+D*-

We report a measurement of the CP-odd fraction and the time-dependent CP violation in B0 to D*+D*- decays, using 657.10^6 BBbar events collected at the Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e- collider. We measure a CP-odd fraction of Rperp=0.125+/-0.043(stat)+/-0.023(syst). From the distributions of the proper-time intervals between a B0to D*+D*- decay and the other B meson in the event, we obtain evidence of CP violation with measured parameters AD*+D*-=0.15+/-0.13(stat)+/-0.04(syst) and SD*+D*-=-0.96+/-0.25(stat)-0.16+0.13(syst).Comment: Published in PR