Kinetic exchange at low charge transfer energies

Specific features of kinetic exchange at low charge transfer energies are analysed. It is shown that the exchange may be of ferromagnetic type. The examples of Cu2+-Mn2+ and Ni2+-Mn2+ doping pairs in perovskite-type crystals are considered. The theoretical predictions agree with the experimental data

Limits on τ lepton-flavor violating decays into three charged leptons

A search for the neutrinoless, lepton-flavor violating decay of the τ lepton into three charged leptons has been performed using an integrated luminosity of 468  fb^(-1) collected with the BABAR detector at the PEP-II collider. In all six decay modes considered, the numbers of events found in data are compatible with the background expectations. Upper limits on the branching fractions are set in the range (1.8–3.3)×10^(-8) at 90% confidence level

Measurement of CP observables in B^± → D_(CP)K^± decays and constraints on the CKM angle γ

Using the entire sample of 467×10^6 Υ(4S)→BB[overbar] decays collected with the BABAR detector at the PEP-II asymmetric-energy B factory at the SLAC National Accelerator Laboratory, we perform an analysis of B^± → DK^± decays, using decay modes in which the neutral D meson decays to either CP-eigenstates or non-CP-eigenstates. We measure the partial decay rate charge asymmetries for CP-even and CP-odd D final states to be A_(CP+) = 0.25±0.06±0.02 and A_(CP-) = -0.09±0.07±0.02, respectively, where the first error is the statistical and the second is the systematic uncertainty. The parameter A_(CP+) is different from zero with a significance of 3.6 standard deviations, constituting evidence for direct CP violation. We also measure the ratios of the charged-averaged B partial decay rates in CP and non-CP decays, R_(CP+) = 1.18±0.09±0.05 and R_(CP-) = 1.07±0.08±0.04. We infer frequentist confidence intervals for the angle γ of the unitarity triangle, for the strong phase difference δ_B, and for the amplitude ratio r_B, which are related to the B^- → DK^- decay amplitude by r_(B)e^(i(δB-γ)) = A(B^- → D[overbar]^(0)K^-)/A(B^- → D^(0)K^-). Including statistical and systematic uncertainties, we obtain 0.24 < r_B < 0.45 (0.06 < r_B <0.51) and, modulo 180°, 11.3° < γ < 22.7° or 80.8° < γ <99.2° or 157.3° <γ < 168.7° (7.0°<γ<173.0°) at the 68% (95%) confidence level

Study of B → Xγ decays and determination of |V_(td)/V_(ts)|

Using a sample of 471×10^6 BB̅[overbar] events collected with the BABAR detector, we study the sum of seven exclusive final states B→X_(s(d))γ, where X_(s(d)) is a strange (nonstrange) hadronic system with a mass of up to 2.0  GeV/c^2. After correcting for unobserved decay modes, we obtain a branching fraction for b→dγ of (9.2±2.0(stat)±2.3(syst))×10^(-6) in this mass range, and a branching fraction for b→sγ of (23.0±0.8(stat)±3.0(syst))×10^(-5) in the same mass range. We find B[script](b→dγ)/B[script](b→sγ)=0.040±0.009(stat)±0.010(syst), from which we determine |V_(td)/V_(ts)|=0.199±0.022(stat)±0.024(syst)±0.002(th)

Measurement of the B → D̅ ^((*))D^((*))K branching fractions

We present a measurement of the branching fractions of the 22 decay channels of the B^0 and B+ mesons to D̅ ^((*))D^((*))K, where the D^((*)) and D̅ ^((*)) mesons are fully reconstructed. Summing the 10 neutral modes and the 12 charged modes, the branching fractions are found to be B(B^0→D̅6((*))D^((*))K)=(3.68 ± 0.10 ± 0.24)% and B(B^+→D̅ ^((*))D^((*))K)=(4.05 ± 0.11 ± 0.28)%, where the first uncertainties are statistical and the second systematic. The results are based on 429  fb^(-1) of data containing 471 × 10^6BB̅ pairs collected at the Υ(4S) resonance with the BABAR detector at the SLAC National Accelerator Laboratory

Measurement of partial branching fractions of inclusive charmless B meson decays to K^+, K^0, and π^+

We present measurements of partial branching fractions of B → K^+X, B → K^0X, and B → π^+X, where X denotes any accessible final state above the endpoint for B decays to charmed mesons, specifically for momenta of the candidate hadron greater than 2.34 (2.36) GeV for kaons (pions) in the B rest frame. These measurements are sensitive to potential new-physics particles which could enter the b → s(d) loop transitions. The analysis is performed on a data sample consisting of 383 × 10^6B B̅ pairs collected with the BABAR detector at the PEP-II e^+e^- asymmetric energy collider. We observe the inclusive B→π+X process, and we set upper limits for B → K^+X and B → K^0X. Our results for these inclusive branching fractions are consistent with those of known exclusive modes, and exclude large enhancements due to sources of new physics

Search for Production of Invisible Final States in Single-Photon Decays of Y(1S)

We search for single-photon decays of the Υ(1S) resonance, Υ → γ + invisible, where the invisible state is either a particle of definite mass, such as a light Higgs boson A^0, or a pair of dark matter particles, χχ̅ . Both A^0 and χ are assumed to have zero spin. We tag Υ(1S) decays with a dipion transition Υ(2S)→π^+π^-Υ(1S) and look for events with a single energetic photon and significant missing energy. We find no evidence for such processes in the mass range m_(A^0 ≤ 9.2  GeV and m_χ ≤ 4.5  GeV in the sample of 98×10^6 Υ(2S) decays collected with the BABAR detector and set stringent limits on new physics models that contain light dark matter states

Measurements of branching fractions, polarizations, and direct CP-violation asymmetries in B^+ → ρ^0K^(*+) and B^+ → f_0 (980)K^(*+) decays

We present measurements of the branching fractions, longitudinal polarization, and direct CP-violation asymmetries for the decays B^+→ρ^0K^(*+) and B^+→f_0(980)K^(*+) with a sample of (467±5)×10^6BB̅ pairs collected with the BABAR detector at the PEP-II asymmetric-energy e+e- collider at the SLAC National Accelerator Laboratory. We observe B+→ρ0K*+ with a significance of 5.3σ and measure the branching fraction B(B^+→ρ^0K^(*+))=(4.6±1.0±0.4)×10^(-6), the longitudinal polarization f_L=0.78±0.12±0.03, and the CP-violation asymmetry A_(CP)=0.31±0.13±0.03. We observe B^+→f_0(980)K^(*+) and measure the branching fraction B(B^+→f_0(980)K^(*+))×B(f_0(980)→π^+π^-)=(4.2±0.6±0.3)×10^(-6) and the CP-violation asymmetry A_(CP)=-0.15±0.12±0.03. The first uncertainty quoted is statistical and the second is systematic