Search Results (447 total)

Using a 492  fb^-1 data sample collected near the Υ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e⁺e^- collider, we observe the decay B⁰→pp̅ K^*0 with a branching fraction of (1.18_-0.25^+0.29(stat)±0.11(syst))×10^-6. We study the decay dynamics of B⁰→pp̅ K^*0 and compare with B⁺→pp̅ K^*+. The K^*0 meson is found to be almost 100% polarized (with a fraction of (101±13±3)% in the helicity zero state), while the K^*+ meson has a (32±17±9)% fraction in the helicity zero state. The direct CP asymmetries for B⁰→pp̅ K^*0 and B⁺→pp̅ K^*+ are measured to be -0.08±0.20±0.02 and -0.01±0.19±0.02, respectively. In addition, we report improved measurements of the branching fractions B(B⁺→pp̅ K^*+)=(3.38_-0.60^+0.73±0.39)×10^-6 and B(B⁰→pp̅ K⁰)=(2.51_-0.29^+0.35±0.21)×10^-6, which supersede our previous measurements.

³P₂ superfluidity of neutrons in neutron star matter is investigated using several potential models and the separation method. As a first step, the dependence of the pure ³P₂ energy gap on the projection M of total momentum J is analyzed. The energy gap functions for pure ³P₂ pairing are treated as vectors indexed by M, and it is shown that the magnitudes of these vectors at Fermi surface are close to each other, whereas their components are different. On the basis of these works, the influence of hyperons on the energy gap for ³P₂ neutron pairing, with and without coupling to the ³F₂ state, at Fermi surface in neutron star matter is studied. The results show that in the OPEG case hyperons increase the energy gap when the baryon number density is in the range of 0.2 fm^-3<n_B<0.33 fm^-3 and reduce it when n_B>0.33 fm^-3, and in the Argonne υ18 case hyperons increase the energy gap in the whole range where the ³P₂ superfluidity exists. The energy gaps are zero in two types of neutron star matter for the Bonn potential.

We present a measurement of the branching fraction B(D_s⁺→μ⁺ν_μ) using a 548  fb^-1 data sample collected by the Belle experiment at the KEKB e⁺e^- collider. The D_s momentum is determined by reconstruction of the system recoiling against DKγX in events of the type e⁺e^-→D_s^*DKX, D_s^*→D_sγ, where X represents additional pions or photons from fragmentation. This full-reconstruction method provides high resolution in the neutrino momentum and thus good background separation, equivalent to that achieved by experiments at the tau-charm factories. We obtain the branching fraction B(D_s⁺→μ⁺ν_μ)=[6.44±0.76(stat)±0.57(syst)]×10^-3, implying a D_s decay constant of f_Ds=[275±16(stat)±12(syst)]  MeV.

A search for mixing in the neutral D meson system has been performed using semileptonic D⁰→K^(*)-e⁺ν and D⁰→K^(*)-μ⁺ν decays. Neutral D mesons from D^*+→D⁰π_s⁺ decays are used and the flavor at production is tagged by the charge of the slow pion. The measurement is performed using 492  fb^-1 of data recorded by the Belle detector. From the yield of right-sign and wrong-sign decays arising from nonmixed and mixed events, respectively, we measure the ratio of the time-integrated mixing rate to the unmixed rate to be R_M=(1.3±2.2±2.0)×10^-4. This corresponds to an upper limit of R_M<6.1×10^-4 at the 90% C.L.

We report simulated infrared (IR) spectra of deuterated water and ice using Car–Parrinello molecular dynamics with maximally localized Wannier functions. Experimental features are accurately reproduced within the harmonic approximation. By decomposing the line shapes in terms of intramolecular and intermolecular dipole correlation functions, we find that short-range intermolecular dynamic charge fluctuations associated to hydrogen bonds are prominent over the entire spectral range. Our analysis reveals the origin of several spectral features and identifies network bending modes in the far IR range.

We report a study of the processes e⁺e^-→J/ψD^(*)D̅ ^(*). In J/ψD^*D̅ ^* we observe a significant enhancement in the D^*D̅ ^* invariant mass spectrum, which we interpret as a new charmoniumlike state and denote X(4160). The X(4160) parameters are M=(4156_-20⁺²⁵±15)  MeV/c² and Γ=(139_-61⁺¹¹¹±21)  MeV. We also report a new measurement of the X(3940) mass and width: M=(3942_-6⁺⁷±6)  MeV/c² and Γ=(37_-15⁺²⁶±8)  MeV. The analysis is based on a 693  fb^-1 data sample recorded near the Υ(4S) resonance by the Belle detector at the KEKB asymmetric-energy collider.

We report improved measurements of time-dependent CP violation parameters for B⁰(B̅ ⁰)→ψ(2S)K_S⁰. This analysis is based on a data sample of 657×10⁶ BB̅ pairs collected at the Υ(4S) resonance with the Belle detector at the KEKB energy-asymmetric e⁺e^- collider. We fully reconstruct one neutral B meson in the ψ(2S)K_S⁰ CP-eigenstate decay channel, and the flavor of the accompanying B meson is identified to be either B⁰ or B̅ ⁰ from its decay products. CP violation parameters are obtained from the asymmetries in the distributions of the proper-time intervals between the two B decays: S_ψ(2S)KS⁰=+0.72±0.09(stat)±0.03(syst), A_ψ(2S)KS⁰=+0.04±0.07(stat)±0.05(syst). These results are in agreement with results from measurements of B⁰→J/ψK⁰.

We report a study of semileptonic B decays to P-wave D^** mesons. Semileptonic decay to a D₂^* meson is observed for the first time and its product branching ratio is measured to be B(B⁺→D̅ ₂^*0ℓ⁺ν)×B(D̅ ₂^*0→D^-π⁺)=0.22±0.03(stat.)±0.04(syst.)%. The result is obtained using fully reconstructed B tags from a data sample that contains 657×10⁶BB̅ pairs collected at the Υ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e⁺e^- collider.

We report an improved measurement of the B⁺→D⁺D̅ ⁰ and B⁰→D⁰D̅ ⁰ decays based on 657×10⁶ BB̅ events collected with the Belle detector at KEKB. We measure the branching fraction and charge asymmetry for the B⁺→D⁺D̅ ⁰ decay: B(B⁺→D⁺D̅ ⁰)=(3.85±0.31±0.38)×10^-4 and A_CP(B⁺→D⁺D̅ ⁰)=0.00±0.08±0.02, where the first error is statistical and the second is systematic. We also set the upper limit for the B⁰→D⁰D̅ ⁰ decay: B(B⁰→D⁰D̅ ⁰)<0.43×10^-4 at 90% CL.

A distinct peak is observed in the π^±ψ^′ invariant mass distribution near 4.43 GeV in B→Kπ^±ψ^′ decays. A fit using a Breit-Wigner resonance shape yields a peak mass and width of M=4433±4(stat)±2(syst)  MeV and Γ=45_-13⁺¹⁸(stat)_-13⁺³⁰(syst)  MeV. The product branching fraction is determined to be B(B⁰→K^∓Z^±(4430))×B(Z^±(4430)→π^±ψ^′)=(4.1±1.0(stat)±1.4(syst))×10^-5, where Z^±(4430) is used to denote the observed structure. The statistical significance of the observed peak is 6.5σ. These results are obtained from a 605  fb^-1 data sample that contains 657×10⁶ BB̅ pairs collected near the Υ(4S) resonance with the Belle detector at the KEKB asymmetric energy e⁺e^- collider.

We consider a defect in a strongly correlated host metal and discuss, within a slave-boson mean field formalism for the t-t^′-J model, the formation of an induced paramagnetic moment which is extended over nearby sites. We study in particular an impurity in a metallic band, suitable for modeling the optimally doped cuprates, in a regime where the impurity moment is paramagnetic. The form of the local susceptibility as a function of temperature and doping is found to agree well with recent NMR experiments, without including screening processes leading to the Kondo effect.

We present the results of a time-dependent Dalitz plot analysis of B⁰→π⁺π^-π⁰ decays based on a 414  fb^-1 data sample that contains 449×10⁶BB̅ pairs. The data were collected on the Υ(4S) resonance with the Belle detector at the KEKB asymmetric energy e⁺e^- collider. Combining our analysis with information on charged B decay modes, we perform a full Dalitz and isospin analysis and obtain a constraint on the quark mixing angle ϕ₂, 68°<ϕ₂<95° at the 68.3% confidence level for the ϕ₂ solution consistent with the standard model. A large standard-model–disfavored region also remains. The branching fractions for the decay processes B⁰→ρ^±(770)π^∓ and B⁰→ρ⁰(770)π⁰ are measured to be (22.6±1.1[stat]±4.4[syst])×10^-6 and (3.0±0.5[stat]±0.7[syst])×10^-6, respectively. These are the first branching fraction measurements of the process B⁰→ρ(770)π with the lowest resonance ρ(770) explicitly separated from the radial excitations.

We report a measurement of the CP-violating parameters in B⁰→K_S⁰K_S⁰ decays based on a data sample of 657×10⁶ BB̅ pairs collected at the Υ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e⁺e^- collider. In this Letter, one neutral B meson is fully reconstructed in the B⁰→K_S⁰K_S⁰ decay mode, and the flavor of the accompanying B meson is identified by its decay products. The CP-violating parameters are measured from the asymmetry in the distributions of the proper-time interval between the two B decays: S_KS⁰KS⁰=-0.38_-0.77^+0.69(stat)±0.09(syst) and A_KS⁰KS⁰=-0.38±0.38(stat)±0.05(syst).

We search for the radiative penguin decays B_s⁰→ϕγ and B_s⁰→γγ in a 23.6  fb^-1 data sample collected at the Υ(5S) resonance with the Belle detector at the KEKB e⁺e^- asymmetric-energy collider. We observe for the first time a radiative penguin decay of the B_s⁰ meson in the B_s⁰→ϕγ mode and we measure B(B_s⁰→ϕγ)=(57_-15⁺¹⁸(stat)_-11⁺¹²(syst))×10^-6. No significant B_s⁰→γγ signal is observed and we set a 90% confidence level upper limit of B(B_s⁰→γγ)<8.7×10^-6.

We report the first observation of e⁺e^-→Υ(1S)π⁺π^-, Υ(2S)π⁺π^-, and first evidence for e⁺e^-→Υ(3S)π⁺π^-, Υ(1S)K⁺K^-, near the peak of the Υ(5S) resonance at sqrt[s]∼10.87  GeV. The results are based on a data sample of 21.7  fb^-1 collected with the Belle detector at the KEKB e⁺e^- collider. Attributing the signals to the Υ(5S) resonance, the partial widths Γ(Υ(5S)→Υ(1S)π⁺π^-)=0.59±0.04(stat)±0.09(syst)  MeV and Γ(Υ(5S)→Υ(2S)π⁺π^-)=0.85±0.07(stat)±0.16(syst)  MeV are obtained from the observed cross sections. These values exceed by more than 2 orders of magnitude the previously measured partial widths for dipion transitions between lower Υ resonances.

The fabrication of epitaxial graphene (EG) on SiC substrate by annealing has attracted a lot of interest as it may speed up the application of graphene for future electronic devices. The interaction of EG and the SiC substrate is critical to its electronic and physical properties. In this work, the Raman spectroscopy was used to study the structure of EG and its interaction with SiC substrate. All the Raman bands of EG blueshift from that of bulk graphite and graphene made by micromechanical cleavage, which was attributed to the compressive strain induced by the substrate. A model containing 13×13 honeycomb lattice cells of graphene on carbon nanomesh was constructed to explain the origin of strain. The lattice mismatch between graphene layer and substrate causes the compressive stress of 2.27  GPa on graphene. We also demonstrate that the electronic structures of EG grown on Si- and C-terminated SiC substrates are quite different. Our experimental results shed light on the interaction between graphene and SiC substrate, which are critical to the future applications of EG.

We report the observation of a new D_sJ meson produced in B⁺→D̅ ⁰D_sJ→D̅ ⁰D⁰K⁺. This state has a mass of M=2708±9_-10⁺¹¹  MeV/c², a width Γ=108±23_-31⁺³⁶  MeV/c² and a 1^- spin-parity. The statistical significance of this observation is 8.4σ. The results are based on an analysis of 449×10⁶ BB̅ events collected at the Υ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e⁺e^- collider.

We search for the doubly charmed baryonic decay B̅ ⁰→Λ_c⁺Λ̅ _c^-, in a data sample of 520×10⁶ BB̅ events accumulated at the Υ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e⁺e^- collider. We find no significant signal and set an upper limit of B(B̅ ⁰→Λ_c⁺Λ̅ _c^-)<6.2×10^-5 at 90% confidence level. The result is significantly below a naive extrapolation from B(B^-→Ξ_c⁰Λ̅ _c^-) assuming a simple Cabibbo-suppression factor of |V_cd/V_cs|². The small branching fraction may be attributed to a suppression due to the large momentum of the baryonic decay products, which has been observed in other charmed baryonic two-body B decays.

We have experimentally demonstrated a decoy-state quantum key distribution scheme (QKD) with a heralded single-photon source based on parametric down-conversion. We used a one-way Bennett-Brassard 1984 protocol with a four states and one-detector phase-coding scheme, which is immune to recently proposed time-shift attacks, photon-number splitting attacks, and can also be proven to be secure against Trojan horse attacks and any other standard individual or coherent attacks. In principle, the setup can tolerate the highest losses or it can give the highest secure key generation rate under fixed losses compared with other practical schemes. This makes it a quite promising candidate for future quantum key distribution systems.

Spin Hall effect (SHE) is studied with first-principles relativistic band calculations for platinum, which is one of the most important materials for metallic SHE and spintronics. We find that intrinsic spin Hall conductivity (SHC) is as large as ∼2000(ℏ/e)(Ω cm)^-1 at low temperature and decreases down to ∼200(ℏ/e)(Ω cm)^-1 at room temperature. It is due to the resonant contribution from the spin-orbit splitting of the doubly degenerated d bands at high-symmetry L and X points near the Fermi level. By modeling these near degeneracies by an effective Hamiltonian, we show that SHC has a peak near the Fermi energy and that the vertex correction due to impurity scattering vanishes. We therefore argue that the large SHE observed experimentally in platinum is of intrinsic nature.

Using 462  fb^-1 of e⁺e^- annihilation data recorded by the Belle detector, we report the first observation of the decay D_s1(2536)⁺→D⁺π^-K⁺. The ratio of branching fractions B(D_s1(2536)⁺→D⁺π^-K⁺) / B(D_s1(2536)⁺→D^*+K⁰) is measured to be (3.27±0.18±0.37)%. We also study the angular distributions in the D_s1(2536)⁺→D^*+K_S⁰ decay and measure the ratio of D- and S-wave amplitudes. The S-wave dominates, with a partial width of Γ_S/Γ_total=0.72±0.05±0.01.

We report measurements of the exclusive cross section for e⁺e^-→D⁰D^-π⁺ over the center-of-mass energy range 4.0 GeV to 5.0 GeV with initial-state radiation and the first observation of the decay ψ(4415)→D⁰D^-π⁺. From a study of the resonant substructure in ψ(4415) decay we conclude that the ψ(4415)→D⁰D^-π⁺ decay is dominated by ψ(4415)→DD̅ ₂^*(2460). We obtain B(ψ(4415)→D⁰D^-π_nonresonant⁺)/B(ψ(4415)→DD̅ ₂^*(2460)→D⁰D^-π⁺)<0.22 at 90% C.L. The analysis is based on a data sample collected with the Belle detector with an integrated luminosity of 673  fb^-1.

Magneto-optical spectroscopy in combination with tunable laser spectroscopy is employed to study optical spin injection from a diluted magnetic semiconductor (DMS) ZnMnSe into nonmagnetic CdSe quantum dots (QDs). Observation of a DMS feature in the excitation spectra of the QD photoluminescence polarization provides clear evidence for optical spin-injection from the DMS to the QDs. By means of a rate equation analysis, the injected spin polarization is deduced to be about 32% at 5  T, decreasing from 100% before the injection. The observed spin loss is shown to occur during the spin injection process including crossing the heterointerfaces and energy relaxation within the QDs.

We report the first measurement of CP-violation parameters in B⁰→ρ⁰γ decays based on a data sample of 657×10⁶BB̅ pairs collected with the Belle detector at the KEKB asymmetric-energy e⁺e^- collider. We obtain the time-dependent and direct CP-violating parameters, S_ρ⁰γ=-0.83±0.65(stat)±0.18(syst) and A_ρ⁰γ=-0.44±0.49(stat)±0.14(syst), respectively.

The process e⁺e^-→K⁺K^-J/ψ is observed for the first time via initial-state radiation. The cross section of e⁺e^-→K⁺K^-J/ψ for center-of-mass energies between threshold and 6.0 GeV is measured using 673  fb^-1 of data collected with the Belle detector on and off the Υ(4S) resonance. No significant signal for Y(4260)→K⁺K^-J/ψ is observed, and we determine B(Y(4260)→K⁺K^-J/ψ)Γ(Y(4260)→e⁺e^-)<1.2  eV/c² at a 90% confidence level. We also find evidence for e⁺e^-→K_S⁰K_S⁰J/ψ in the same data sample.