[en] Full text: We report the determination of the B⁰B⁰ mixing parameter Δm from the time evolution of dilepton yields in Y(4s) decays. Data was collected by the Belle detector at KEKB. The charge of a lepton from a semileptonic B meson decay uniquely defines its flavor at the time of decay. Employing this method of flavor tagging, the proper-time difference for same-sign (mixed) and opposite-sign (unmixed) dilepton events were simultaneously fitted to an expression containing Δm as a free parameter. Both muons and electrons were used in this analysis. The phenomenon of B⁰B⁰ mixing is a manifestation of higher-order box diagrams in the standard model, and its rate is regarded as a fundamental parameter of the B⁰ meson system. The observed value should be well described by the standard model and is proportional to |V*_t,_bV_td|² if the top-quark loop is the dominant contribution. B⁰B⁰ mixing is also a source of CP violation in B⁰ decays into CP eigenstates, and a precise determination of the mixing parameter Δm is necessary to make precise measurements of any CP asymmetries. In this study Δm is determined from the time evolution of same-sign and opposite-sign dilepton yields in Y(4s) decays created by the KEKB asymmetric electron positron colliding beam accelerator. KEKB employs an 8.0GeV electron beam and a 3.5GeV positron beam, resulting in a center of mass moving along the electron beam direction with a Lorentz boost of βγ=0.425. Consequently, the decay vertices of the two B mesons are typically separated by 200 mm, a distance large enough to be measured by the Silicon Vertex Detector of Belle

[en] Full text: The Australian Experimental High Energy Physics Group is heavily involved in the construction, operation and data analysis of the BELLE experiment now collecting data at KEK in Japan. The Standard Model of Particle Physics predicts that there will be sizable CP violating effects in some rare decays of B mesons. The primary aim of the BELLE experiment is to search for this CP violation in the B meson system. If we find such processes it will be only the second time such effects have been found in nature. In addition the richness of the predicted effects in the B meson system enable stringent tests of the Standard Model in this to-now un-explored region. To do this the BELLE experiment exploits the high luminosity KEKB accelerator in Japan. This collides 8.0GeV e^- with 3.5GeV e⁺ particles at luminosities above 2.0xl0³³cm²sec^-1. The interaction point of the accelerator is surrounded by the sophisticated BELLE detector which employs state of the hardware to perform vetexing, tracking, momentum and energy measurements along with particle identification for all long lived charged and neutral particles (except neutrinos). This presentation will introduce the main features of the BELLE experiment along with initial results for CP violation, B mixing and rare B decays

[en] Full text: The Standard Model of particle physics explains mixing between quark flavours in charged current weak interaction via the Cabibbo Kobayashi Maskawa Matrix V_CKM. The Standard Model of Particle Physics predicts that CP violation will occur if this matrix contains complex elements. Conservation of probability requires that this matrix be unitary. This in turn requires that V_udV_ub + V_cdV_cb + V_tdV_tb^* =0. When this relation is shown on a complex plane it forms the so-called Unitarity triangle and CP violation results if the angles of the triangle are non zero. The decay B→ππ is expected to exhibit CP-violation. More-over within the Standard Model the size of the effect is sensitive to the second angle of the CKM matrix φ₂ This talk will present the current status of BELLE's measurements of B→ππ and our plans for obtaining φ₂

[en] We present an improved measurement of CP-violating asymmetries in B⁰→π⁺π^- decays based on a 78 fb^-1 data sample collected at the Υ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e⁺e^- collider. We reconstruct one neutral B meson as a B⁰→π⁺π^- CP eigenstate and identify the flavor of the accompanying B meson from inclusive properties of its decay products. We apply an unbinned maximum likelihood fit to the distribution of the time intervals between the two B meson decay points. The fit yields the CP-violating asymmetry amplitudes A_ππ=+0.77 ±0.27(stat) ±0.08(syst) and S_ππ=-1.23±0.41(stat) _-0.07^+0.08(syst), where the statistical uncertainties are determined from the Monte Carlo pseudoexperiments. We obtain confidence intervals for CP-violating asymmetry parameters A_ππ and S_ππ based on a frequentist approach. We rule out the CP-conserving case, A_ππ=S_ππ=0, at the 99.93% confidence level. We discuss how these results constrain the value of the Cabibbo-Kobayashi-Maskawa (CKM) angle φ₂

[en] We report the first observation of the B→D-barD_sJ(2317) and B→D-barD_sJ(2457) decays based on 123.8x10⁶ BB-bar events collected with the Belle detector at KEKB. We observe the D_sJ(2317) decay to D_sπ⁰ and the D_sJ(2457) decay to the D_s^*π⁰ and D_sγ final states. We also set 90% C.L. upper limits for the decays D_sJ(2317)→D_s^*γ, D_sJ(2457)→D_s^*γ, D_sJ(2457)→D_sπ⁰, and D_sJ(2457)→D_sπ⁺π^-

[en] We report the observation of an isotriplet of excited charmed baryons, decaying into Λ_c⁺π^-, Λ_c⁺π⁰, and Λ_c⁺π⁺. We measure the mass differences M(Λ_c⁺π)-M(Λ_c⁺) and widths to be 515.4_-3.1-6.0^+3.2+2.1 MeV/c², 61_-13-13⁺¹⁸⁺²² MeV for the neutral state; 505.4_-4.6-2.0^+5.8+12.4 MeV/c², 62_-23-38⁺³⁷⁺⁵² MeV for the charged state; and 514.5_-3.1-4.9^+3.4+2.8 MeV/c², 75_-13-11⁺¹⁸⁺¹² MeV for the doubly charged state, where the uncertainties are statistical and systematic, respectively. These results are obtained from a 281 fb^-1 data sample collected with the Belle detector near the Υ(4S) resonance, at the KEKB asymmetric energy e⁺e^- collider

[en] We report improved measurements of branching fractions for charmless hadronic two-body B meson decays containing an ω meson in the final state. The results are based on a data sample of 78 fb^-1 collected on the Υ(4S) resonance by the Belle detector. We measure the branching fractions B(B⁺→ωK⁺)=(6.5_-1.2^+1.3±0.6)x10^-6 and B(B⁺→ωπ⁺)=(5.7_-1.3^+1.4±0.6)x10^-6. We give 90% confidence upper limits for B(B⁰→ωK⁰)<7.6x10^-6 and B(B⁰→ωπ⁰)<1.9x10^-6. We also obtain the partial rate asymmetries A_CP=0.06_-0.18^+0.21±0.01 for B^±→ωK^± and A_CP=0.50_-0.20^+0.23±0.02 for B^±→ωπ^±

[en] We present the first evidence of the decay B⁰→ρ⁰π⁰, using 140 fb^-1 of data collected at the Υ(4S) resonance with the Belle detector at the KEKB asymmetric e⁺e^- collider. We detect 15.1±4.8 signal events with a significance of 3.5 standard deviations and measure the branching fraction to be B(B⁰→ρ⁰π⁰)=(5.1±1.6(stat)±0.9(syst))x10^-6

[en] We report first measurements of e⁺e^-→D⁽*⁾⁺D⁽*^)- processes far above threshold. The cross sections for e⁺e^-→D_T*⁺D_L*^- and e⁺e^-→D⁺D_T*^- at √(s)≅10.6 GeV/c² are measured to be 0.55±0.03±0.05 and 0.62±0.03±0.06 pb, respectively. We set upper limits on the cross sections for e⁺e^-→D_T*⁺D_T*^-, e⁺e^-→D_L*⁺D_L*^-, e⁺e^-→D⁺D_L*^-, and e⁺e^-→D⁺D^- processes. The analysis is based on 88.9 fb^-1 of data collected by the Belle experiment at the KEKB e⁺e^- asymmetric collider

[en] We report a search for CP-violating asymmetry in B⁰→D*^±D^± decays. The analysis employs two methods of B⁰ reconstruction: full and partial. In the full reconstruction method all daughter particles of the B⁰ are required to be detected; the partial reconstruction technique requires a fully reconstructed D^- and only a slow pion from the D*⁺→D⁰π_slow⁺ decay. From a fit to the distribution of the time interval corresponding to the distance between two B meson decay points we calculate the CP-violating parameters and find the significance of nonzero CP asymmetry to be 2.7 standard deviations