Observation of the decay xi0 --> sigma+ mu- nu(mu)

The xi0 muon semileptonic decay has been observed for the first time with nine identified events using the KTeV beam line and detector at Fermilab. The decay is normalized to the xi0 beta decay mode and yields a value for the ratio of decay rates gamma(xi0 --> sigma+ mu- nu(mu))/gamma(xi0 --> sigma+ e- nu(e)) of [1.8(-0.5)(+0.7)(stat) +/- 0.2(syst)] x 10(-2). This is in agreement with the SU(3) flavor symmetric quark model.     

Experimental investigation of the two-photon widths of the chi(c0) and the chi(c2) mesons

Using 12.7 fb(-1) of data collected with the CLEO detector at CESR, we observed two-photon production of the cc states chi(c0) and chi(c2) in their decay to pi(+)pi(-)pi(+)pi(-). We measured gamma(gammagamma)(chi(c))xB(chi(c)-->pi(+)pi(-)pi(+)pi(-)) to be 75+/-13(stat)+/-8(syst) eV for the chi(c0) and 6.4+/-1.8(stat)+/-0.8(syst) eV for the chi(c2), implying gamma(gammagamma)(chi(c0)) = 3.76+/-0.65(stat)+/-0.41(syst)+/-1.69(br) keV and gamma(gammagamma)(chi(c2)) = 0.53+/-0.15(stat)+/-0.06(syst)+/-0.22(br) keV. Also, cancellation of dominant experimental and theoretical uncertainties permits a precise comparison of gamma(gammagamma)(chi(c0))/gamma(gammagamma)(chi(c2)), evaluated to be 7.4+/-2.4(stat)+/-0.5(syst)+/-0.9(br), with QCD-based predictions.     

Radiative B meson decays into kpigamma and kpipigamma final states

We report observations of radiative B meson decays into the K+pi(-)gamma and K+pi(-)pi(+)gamma final states. In the B0-->K+pi(-)gamma channel, we present evidence for decays via an intermediate tensor meson state with a branching fraction of B(B0-->K(*)(2)(1430)(0)gamma)=[1.3+/-0.5(stat)+/-0.1(syst)]x10(-5). We measure the branching fraction B(B+-->K+pi(-)pi(+)gamma)=[2.4+/-0.5(stat) +0.4-0.2(syst)]x10(-5), in which the B+-->K(*0)pi(+)gamma and B+-->K+rho(0)gamma channels dominate. The analysis is based on a data set of 29.4 fb(-1) recorded by the Belle experiment at the KEKB collider.     

Measurement of the time-dependent CP-violating asymmetry in B(0)-->K(0)(S)pi(0)gamma decays

We present a new measurement of CP-violation parameters in B(0)-->K(0)(S)pi(0)gamma decay based on a sample of 275 x 10(6) BB pairs collected at the Gamma(4S) resonance with the Belle detector at the KEKB energy-asymmetric e(+)e(-) collider. One of the B mesons is fully reconstructed in the B(0)-->K(0)(S)pi(0)gamma decay. The flavor of the accompanying B meson is identified from its decay products. CP-violation parameters are obtained from the asymmetry in the distribution of the proper time intervals between the two B decays. We obtain SK(0)(S)(pi(0)gamma) = -0.58(+0.46)(-0.38)(stat) +/- 0.11(syst) and AK(0)(S)(pi(0)gamma) = +0.03 +/- 0.34(stat) +/- 0.11(syst), for the K(0)(S)pi(0) invariant mass covering the full range up to 1.8 GeV/c2. We also measure the CP-violation parameters for the case B(0)-->K(*0)(-->K(0)(S)pi(0))gamma and obtain S(K(*0)gamma) = -0.79(+0.63)(-0.50)(stat) +/- 0.10(syst) for A(K(*0)gamma) fixed at 0.     

极性超晶格中电子—声子的相互作用

本文在Wendler、潘金声研究双层极性晶体时得出的声子振动极化场所满足的微分、积分方程及归一化条件的基础上,讨论周期性排列的层状极性晶体中声子振动极化场所满足的微分、积分方程,得到了SO声子的色散关系,SO声子和LO声子极化强度矢量.用声子产生、湮灭算符表出了声子振动能量及电子—声子的相互作用哈密顿量.     

Study of exclusive radiative B meson decays

We have studied exclusive, radiative B meson decays to charmless mesons in 9.7x10(6) B&Bmacr; decays accumulated with the CLEO detector. We measure B(B0-->K(*0)(892)gamma) = (4.55(+0.72)(-0. 68)+/-0.34)x10(-5) and B(B+-->K(*+)(892)gamma) = (3.76(+0.89)(-0. 83)+/-0.28)x10(-5). We have searched for CP asymmetry in B-->K(*)(892)gamma decays and measure A(CP) = +0.08+/-0.13+/-0.03. We report the first observation of B-->K(*)(2)(1430)gamma decays with a branching fraction of (1.66(+0.59)(-0.53)+/-0.13)x10(-5). No evidence for the decays B-->rhogamma and B0-->omegagamma is found and we limit B(B-->(rho/omega)gamma)/B(B-->K(*)(892)gamma)<0.32 at 90% C.L.     

Improved branching ratio measurement for the decay K(0)(L) --> &mgr;(+)&mgr;(-)

We report results from Experiment 871, performed at the BNL AGS, of a measurement of the branching ratio K(0)(L)-->&mgr;(+)&mgr;(-) with respect to the CP-violating mode K(0)(L)-->pi(+)pi(-). This experiment detected over 6200 candidate &mgr;(+)&mgr;(-) events, a factor of 6 more than that seen in all previous measurements combined. The resulting branching ratio gamma(K(0)(L)-->&mgr;(+)&mgr;(-))/gamma(K(0)(L)-->pi(+)pi(-)) = (3. 474+/-0.057)x10(-6) leads to a branching fraction B(K(0)(L)-->&mgr;(+)&mgr;(-)) = (7.18+/-0.17)x10(-9), which is consistent with the current world average, and reduces the uncertainty in this decay mode by a factor of 3.     

Deviations from linear theory for fluctuations below the supercritical primary bifurcation to electroconvection

Over two decades ago it was predicted that nonlinear interactions between thermally driven fluctuations in dissipative nonlinear nonequilibrium systems lead to deviations from mean-field theory. Here we report experimental observations of such deviations as a supercritical primary bifurcation is approached. We measured the mean-square director-angle fluctuations below the bifurcation to electroconvection of two different nematic liquid crystals. For epsilon(mf) identical withV2/V(2)(c,mf)-1 less, similar-0.1 ( V is the applied voltage) we find approximately |epsilon(mf)|(-gamma) with gamma given by linear theory (LT). Closer to the bifurcation there are deviations from LT with a smaller gamma and with V(2)(c)>V(2)(c,mf).     

Bounds on the CP asymmetry in like-sign dileptons from B(0)B*(0) meson decays

We have measured the charge asymmetry in like-sign dilepton yields from B(0)B*(0) meson decays using the CLEO detector at the Cornell Electron Storage Ring. We find a(0)(ll) identical with[N(l(+)l(+))-N(l(-)l(-))]/[N(l(+)l(+))+N(l(-)l(-))] = +0.013+/-0.050+/-0.005. We combine this result with a previous, independent measurement and obtain Re(epsilon(B))/(1+ the absolute value of epsilon(B)(2)) = +0.0035+/-0.0103+/-0.0015 (uncertainties are statistical and systematic, respectively) for the CP impurity parameter, epsilon(B).     

Observation of B(s)(0) → J/ψf(2)'(1525) in J/ψK+ K- final states

The decay B(s)(0) → J/ψK+ K- is investigated using 0.16 fb(-1) of data collected with the LHCb detector using 7 TeV pp collisions. Although the J/ψ? channel is well known, final states at higher K+ K- masses have not previously been studied. In the K+ K- mass spectrum we observe a significant signal in the f(2)'(1525) region as well as a nonresonant component. After subtracting the nonresonant component, we find B(B(s)(0) → J/ψf(2)'(1525))/B(B(s)(0) → J/ψ?) = (26.4 ± 2.7 ± 2.4)%.     

Measurements of the decay KL-->e+ e- gamma

The E799-II (KTeV) experiment at Fermilab has collected 83 262 K(L)-->e+ e- gamma(gamma) events above a background of 79 events. We measure a decay width, normalized to the K(L)-->pi0pi0pi(D)0 (pi0-->gammagamma, pi0-->gammagamma, pi(D0-->e+ e- gamma(gamma)) decay width, of Gamma(K(L)-->e+e-gamma(gamma))/Gamma(K(L)-->pi0pi0pi(D)0)=(1.3302+/-0.0046(stat)+/-0.0102(syst)) x 10(-3). We also measure parameters of two K(L)gamma*gamma form factor models. In the Bergstr?m-Massó-Singer parametrization, we find Calpha(K*)= -0.517 +/- 0.030(stat) +/- 0.022(syst). We separately fit for the first parameter of the D'Ambrosio-Isidori-Portolés model and find alpha(DIP)= -1.729 +/- 0.043(stat) +/- 0.028(syst).     

Extracting weak phase information from B-->V1V2 decays

We describe a new method for extracting weak, CP-violating &Dmacr;phase information, with no hadronic uncertainties, from an angular analysis of B-->V1V2 decays, where V1 and V2 are vector mesons. The quantity sin (2)(2beta+gamma) can be cleanly obtained from the study of decays such as B(0)(d)(t)-->D*+/-rho(-/+), D(*+/-)a(-/+)(1), D(;) *0K(;) (*0), etc. Similarly, one can use B(0)(s)(t)-->D(*+/-)(s)K*-/+ to extract sin (2)gamma. There are no penguin contributions to these decays. It is possible that sin (2)(2beta+gamma) will be the second function of CP phases, after sin2beta, to be measured at B factories.     

Rigorous analysis of singularities and absence of analytic continuation at first-order phase-transition points in lattice-spin models

We report about two new rigorous results on the nonanalytic properties of thermodynamic potentials at first-order phase transition. For lattice models (d>or=2) with arbitrary finite state space, finite-range interactions which have two ground states, we prove that the pressure has no analytic continuation at the first-order phase-transition point, under the only further assumptions that the Peierls condition is satisfied for the ground states and that the temperature is sufficiently low. For Ising models with Kac potentials J(gamma)(x)=gamma(d)phi(gammax), where 00) and analyticity in the mean field limit (gamma SE pointing arrow 0).     

Absolute Intensities Measurements in the nu(4) + nu(5) Band of (12)C(2)H(2): Analysis of Herman-Wallis Effects and Forbidden Transitions

We measured absolute line intensities in two bands of (12)C(2)H(2) near 7.5 μm, namely the nu(4) + nu(5)(Sigma(+)(u))-0(Sigma(+)(g)) and nu(4) + nu(5)(Delta(u))-0(Sigma(+)(g)) bands, using Fourier transform spectroscopy with an accuracy estimated to be better than 2%. Using theoretical predictions from Watson [J. K. G. Watson, J. Mol. Spectrosc. 188, 78 (1998)], the observation of the forbidden nu(4) + nu(5)(Delta(u))-0(Sigma(+)(g)) band and the Herman-Wallis behavior exhibited by its rotational lines were studied quantitatively in terms of two types of interactions affecting the levels involved by the band: l-type resonance and Coriolis interaction. In the case of the nu(4) + nu(5)(Sigma(+)(u))-0(Sigma(+)(g)) band, the influence of l-type resonance is also confirmed. We also attributed the intensity asymmetry observed between the R and P branches of that latter band to a Coriolis interaction with l = 1 levels. We did not observe the nu(4) + nu(5)(Sigma(-)(u))-0(Sigma(+)(g)) band, consisting only of a Q branch, in agreement with Watson's prediction. Copyright 2000 Academic Press.     

New magnetic field dependence of Landau levels in a graphenelike structure

We consider a tight-binding model on the honeycomb lattice in a magnetic field. For special values of the hopping integrals, the dispersion relation is linear in one direction and quadratic in the other. We find that, in this case, the energy of the Landau levels varies with the field B as epsilon(n)(B) ~ [(n+gamma)B](2/3). This result is obtained from the low-field study of the tight-binding spectrum on the honeycomb lattice in a magnetic field (Hofstadter spectrum) as well as from a calculation in the continuum approximation at low field. The latter links the new spectrum to the one of a modified quartic oscillator. The obtained value gamma=1/2 is found to result from the cancellation of a Berry phase.     

Observation of in-medium modifications of the omega meson

The photoproduction of omega mesons on nuclei has been investigated using the Crystal Barrel/TAPS experiment at the ELSA tagged photon facility in Bonn. The aim is to study possible in-medium modifications of the omega meson via the reaction gamma + A --> omega + X --> pi(0)gamma + X('). Results obtained for Nb are compared to a reference measurement on a LH2 target. While for recoiling, long-lived mesons (pi(0), eta, and eta;(')), which decay outside of the nucleus, a difference in the line shape for the two data samples is not observed, we find a significant enhancement towards lower masses for omega mesons produced on the Nb target. For momenta less than 500 MeV/c an in-medium omega meson mass of M(medium) = [722(+4)(-4)(stat)+35-5(syst)] MeV/c(2) has been deduced at an estimated average nuclear density of 0.6rho(0).     

Dynamics of fluctuations below a stationary bifurcation to electroconvection in the planar nematic liquid crystal N4

We fitted C(k,tau,epsilon) proportional to exp([-sigma(k,epsilon)tau] to time-correlation functions C(k,tau,epsilon) of structure factors S(k,t,epsilon) of shadowgraph images of fluctuations below a supercritical bifurcation at V(0)=V(c) to electroconvection of a planar nematic liquid crystal in the presence of a voltage V=sqrt[2]V(0)cos((2pift) [k=(p,q) is the wave vector and epsilon identical with V(2)(0)/V(2)(c)-1]. There were stationary oblique (normal) rolls at small (large) f. Fits of a modified Swift-Hohenberg form to sigma(k,epsilon) gave f-dependent critical behavior for the minimum decay rates sigma(0)(epsilon) and the correlation lengths xi(p,q)(epsilon).     

Measurement of B --> K*gamma branching fractions and charge asymmetries

The branching fractions of the exclusive decays B0-->K(*0)gamma and B+-->K(*+)gamma are measured from a sample of (22.74+/-0.36)x10(6) BB decays collected with the BABAR detector at the PEP-II asymmetric e(+)e(-) collider. We find B (B0-->K(*0)gamma) = [4.23+/-0.40(stat)+/-0.22(syst)]x10(-5), B(B+-->K(*+)gamma) = [3.83+/-0.62(stat)+/-0.22(syst)]x10(-5) and constrain the CP-violating charge asymmetry to be -0.170K(*)gamma)<0.082 at 90% C.L.     

Magnetoresistance anisotropy of a one-dimensional superconducting niobium strip

We investigated confinement effects on the resistive anisotropy of a superconducting niobium strip with a rectangular cross section. When its transverse dimensions are comparable to the superconducting coherence length, the angle dependent magnetoresistances at a fixed temperature can be scaled as R(theta,H) = R(H/Hctheta) where Hctheta =Hc0(cos2theta + gamma(-2)sin2theta)(-1/2) is the angular dependent critical field, gamma is the width to thickness ratio, and Hc0 is the critical field in the thickness direction at theta=0 degrees . The results can be understood in terms of the anisotropic diamagnetic energy for a given field in a one-dimensional superconductor.     

Hypernuclear fine structure in (16)(Lambda)O and the LambdaN tensor interaction

We have observed two gamma-ray transitions in (16)(Lambda)O from the 6.6 MeV excited 1(-)(2) state to both ground-state spin-doublet members (1(-)(1),0(-)) by the (K-,pi(-)gamma) reaction. We have obtained the ground-state doublet spacing to be 26.4+/-1.6(stat)+/-0.5(syst) keV and the excitation energy of the 1(-)(2) state to be 6561.7+/-1.1(stat)+/-1.7(syst) keV. The ground-state doublet spacing provides a small but nonzero strength of the tensor interaction between a Lambda and a nucleon. This is the first experimental result on the LambdaN tensor interaction.