474 research outputs found

    First hint for CP violation in neutrino oscillations from upcoming superbeam and reactor experiments

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    We compare the physics potential of the upcoming neutrino oscillation experiments Daya Bay, Double Chooz, NOvA, RENO, and T2K based on their anticipated nominal luminosities and schedules. After discussing the sensitivity to theta_{13} and the leading atmospheric parameters, we demonstrate that leptonic CP violation will hardly be measurable without upgrades of the T2K and NOvA proton drivers, even if theta_{13} is large. In the presence of the proton drivers, the fast track to hints for CP violation requires communication between the T2K and NOvA collaborations in terms of a mutual synchronization of their neutrino-antineutrino run plans. Even in that case, upgrades will only discover CP violation in a relatively small part of the parameter space at the 3 sigma confidence level, while 90% confidence level hints will most likely be obtained. Therefore, we conclude that a new facility will be required if the goal is to obtain a significant result with high probability.Comment: 27 pages, 12 figure

    Inclusive Measure of |V_ub| with the Analytic Coupling Model

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    By analyzing B -> X_u l nu_l spectra with a model based on soft-gluon resummation and an analytic time-like QCD coupling, we obtain |V_ub| = (3.76 +-0.13 +- 0.22)*10^(-3), where the first and the second error refers to experimental and theoretical errors, respectively. The V_ub value is obtained from the available measured semileptonic branching fractions in limited regions of the phase-space. The distributions in the lepton energy E_l, the hadron invariant mass m_X, the light-cone momentum P_+ = E_X - p_X, together with the double distributions in (m_X,q^2) and (E_l,s_h^max), are used to select the phase-space regions. The q^2 is the dilepton squared momentum and s_h^max is the maximal m_X^2 at fixed q^2 and E_l. The V_ub value obtained is in complete agreement with the value coming from exclusive B decays and from an over-all fit to the Standard Model parameters. We show that the slight disagreement (up to +2 sigma) with respect to previous inclusive measurements is not related to different choices for the b (and c) masses but to a different modelling of the threshold (Sudakov) region.Comment: 19 pages, 2 figures, revised version accepted in Eur.Phys.J.

    Search for Bπ+B \to \pi \ell^+\ell^- Decays at Belle

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    We present a search for the B-> pi e^+ e^- and B-> pi \mu^+ \mu^- decays, with a data sample of 657 million BBbar pairs collected with the Belle detector at the KEKB e+ee^+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 -> \pi \ell^+\ell^-) < 6.2x10^-8 at the 90% confidence level.Comment: 8 pages, 3 figures, accepted by PRD(RC

    Measurement of D0 -> pilnu (Klnu) Form Factors and Absolute Branching Fractions

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    Using a 282 1/fb data sample collected by the Belle experiment at the KEKB e+e- collider, we study D0 decays to K-l+nu and pi-l+nu final states. The D0 flavor and momentum are tagged through a full reconstruction of the recoiling charm meson and additional mesons from fragmentation. The reconstruction method provides very good resolution in neutrino momentum and in q^2 = (p_l+p_nu)^2. Normalizing to the total number of D0 tags, we measure the absolute branching fractions to be B(D0 -> Klnu) =(3.45 +- 0.07stat +- 0.20syst)% and B(D0 -> pilnu) = (0.255 +- 0.019stat +- 0.016syst)% and the semi-leptonic form factors (within the modified pole model) f+^K(0) = 0.695 +- 0.007stat +- 0.022syst and f+^pi(0) = 0.624 +- 0.020stat +- 0.030syst.Comment: 9 pages, 2 figures, submitted to Phys. Rev. Let

    Measurement of B0π+ππ+πB^0\to\pi^+\pi^-\pi^+\pi^- Decays and Search for B0ρ0ρ0B^0\to\rho^0\rho^0

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    We report on a search for the decay B0ρ0ρ0B^0\to\rho^0\rho^0 and other charmless modes with a π+ππ+π\pi^+\pi^-\pi^+\pi^- final state, including B0ρ0π+πB^0\to\rho^0\pi^+\pi^-, non-resonant B04π±B^0\to 4\pi^{\pm}, B0ρ0f0(980)B^0\to\rho^0f_0(980), B0f0(980)f0(980)B^0\to f_0(980)f_0(980) and B0f0(980)π+πB^0\to f_0(980)\pi^+\pi^-. These results are obtained from a data sample containing 657 million BBB \overline B pairs collected with the Belle detector at the KEKB asymmetric-energy e+ee^+e^- collider. We set an upper limit on B(B0ρ0ρ0)\mathcal{B}(B^0\to\rho^0\rho^0) of 1.0×1061.0\times 10^{-6} at the 90% confidence level (C.L.). From our B0ρ0ρ0B^0\to\rho^0\rho^0 measurement and an isospin analysis, we determine the Cabibbo-Kobayashi-Maskawa phase ϕ2\phi_2 to be 91.7±14.991.7 \pm 14.9 degrees. We find excesses in B0ρ0π+πB^0\to \rho^0\pi^+\pi^- and non-resonant B04π±B^0\to 4\pi^{\pm} with 1.3σ\sigma and 2.5σ\sigma significance, respectively. The corresponding branching fractions are less than 12.0×10612.0 \times 10^{-6} and 19.3×10619.3 \times 10^{-6} at the 90% C.L. In addition, we set 90% C.L. upper limits as follows: B(B0ρ0f0(980))<0.3×106\mathcal{B}(B^0\to\rho^0f_0(980))< 0.3 \times 10^{-6}, B(B0f0(980)f0(980))<0.1×106\mathcal{B}(B^0\to f_0(980)f_0(980))< 0.1 \times 10^{-6}, and B(B0f0(980)π+π)<3.8×106\mathcal{B}(B^0\to f_0(980)\pi^+\pi^-)< 3.8 \times 10^{-6}.Comment: 6 pages, 2 figures. Submitted to PRD(RC

    Improved Measurements of Partial Rate Asymmetry in B -> h h Decays

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    We report improved measurements of the partial rate asymmetry (Acp) in B -> h h decays with 140fb^-1 of data collected with the Belle detector at the KEKB e+e- collider. Here h stands for a charged or neutral pion or kaon and in total five decay modes are included: K-+ pi+-, K0s pi-+, K-+ pi0, pi-+ pi0 and K0s pi0. The flavor of the last decay mode is determined from the accompanying B meson. Using a data sample 4.7 times larger than that of our previous measurement, we find Acp(K-+ pi+-) -0.088+-0.035+-0.013, 2.4 sigma from zero. Results for other decay modes are also presented.Comment: 9 pages, 1 figur

    Study of B0 -> rho+-pi-+ Time-dependent CP Violation at Belle

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    We present a time-dependent analysis of CP violation in B0 -> rho pi decays based on a 140 1/fb data sample collected at the Y(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e- collider. We fully reconstruct one neutral B meson in the rho+-pi-+ final state and identify the flavor of the accompanying B meson from its decay products. We obtain the charge asymmetry ACP = -0.16+-0.10(stat)+-0.02(syst). An unbinned maximum likelihood fit to the proper-time distributions yields C = 0.25+-0.17(stat)+0.02-0.06(syst), DC = 0.38+-0.18(stat)+0.02-0.04(syst), S = -0.28+-0.23(stat)+0.10-0.08(syst), and DS = -0.30+-0.24(stat)+-0.09(syst). The direct CP violation parameters for B -> rho+pi- and B -> rho-pi+ decays are A+- = -0.02+-0.16(stat)+0.05-0.02(syst) and A-+ = -0.53+-0.29(stat)+0.09-0.04(syst).Comment: 10 pages, 3 figures, submitted to Phys. Rev. Let

    Improved Evidence for Direct CP Violation in B0 --> pi+ pi- Decays and Model-Independent Constraints on phi_2

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    We present a new measurement of the time-dependent CP-violating parameters in B0 --> pi+ pi- decays with 275 x 10^6 BB-bar pairs collected with the Belle detector at the KEKB asymmetric-energy e+e- collider operating at the Upsilon(4S) resonance. We find 666 +/- 43 B0 --> pi+ pi- events and measure the CP-violating parameters: S_pipi = -0.67 +/- 0.16(stat) +/- 0.06(syst) and A_pipi = +0.56 +/- 0.12(stat) +/- 0.06(syst). We find evidence for large direct CP-violation with a significance greater than 4 standard deviations for any S_pipi value. Using isospin relations, we obtain 95.4% confidence intervals for the CKM angle phi_2 of 0 deg. < phi_2 < 19 deg. and 71 deg. < phi_2 < 180 deg.Comment: 10 pages, 4 figures, the title and abstract have been changed on May 13th, submitted to Phys. Rev. Lett., replaced on Apr. 30th to a paper draft that is submitted to PRL. Original comments: 13 pages, 6 figures, contributed to the 2005 Aspen Winter Conference on The Higest Energy Physics, Feb. 13-19, 2005, Aspen, Colorado, U.S.
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