Showing papers on "Pseudoscalar published in 1997"

Ground-state spectrum of light-quark mesons

Abstract: A confining, Goldstone theorem preserving, separable ansatz for the ladder kernel of the two-body Bethe-Salpeter equation is constructed from phenomenologically efficacious $u$, $d$, and $s$ dressed-quark propagators. The simplicity of the approach is its merit. It provides a good description of the ground-state flavor-octet pseudoscalar, vector, and axial-vector meson spectrum facilitates an exploration of the relative importance of various components of the two-body Bethe-Salpeter amplitudes, showing that subleading Dirac components are quantitatively important in the flavor-octet pseudoscalar meson channels, and allows a scrutiny of the domain of applicability of ladder truncation studies. A color-antitriplet diquark spectrum is obtained. The shortcomings of separable Ans\"atze and the ladder kernel are highlighted.

Separation of S-wave pseudoscalar and pseudovector amplitudes in π−P↑ → π+π−n reaction on polarized target

Abstract: A new analysis of S-wave production amplitudes for the reaction π−p↑ → π+π−n on a transversely polarized target is performed. It is based on the results obtained by the CERN-Cracow-Munich collaboration in the ππ energy range from 600 MeV to 1600 MeV at 17.2 GeV/c π− momentum. Energy-independent separation of the S-wave pseudoscalar amplitude (π exchange) from the pseudovector amplitude (a 1 exchange) is carried out using assumptions much weaker than those in all previous analyses. We show that, especially around 1000 MeV and around 1500 MeV, the a1 exchange amplitude cannot be neglected. The scalarisoscalar ππ phase shifts are calculated using fairly weak assumptions. Below the KK threshold we find two solutions for the π — π phase shifts, for which the phases increase slower with the effective π — π mass than the P-wave phases. Both solutions are consistent with a broad f 0(500) but only one is similar to the well-known “down” solution. We find also the third solution (with a somewhat puzzling behavior of inelasticity) which exhibits a narrow f 0(750) claimed by Svec. All the solutions undergo a rapid change at the KK threshold. Above 1420 MeV the phase shifts increase with energy faster than those obtained without the polarized-target data. This phase behavior as well as an increase of the modulus of the a1-exchange amplitude can be due to the presence of the f 0(1500).

The $\eta - \eta'$ Mixing Angle Revisited

Abstract: The value of the $\eta - \eta'$ mixing angle $\theta_P$ is phenomenologically deduced from a rather exhaustive and up-to-date analysis of data including strong decays of tensor and higher-spin mesons, electromagnetic decays of vector and pseudoscalar mesons, $J/\psi$ decays into a vector and a pseudoscalar meson, and other transitions. A value of $\theta_P$ between $-17^\circ$ and $-13^\circ$ is consistent with all the present experimental evidence and the average $\theta_P=-15.5^\circ\pm 1.3^\circ$ seems to be favoured.

Pion Eletromagnetic Current in the Ligth-Cone Formalism

Abstract: The electromagnetic form factor of the pion is calculated in a pseudoscalar field theoretical model which constituent quarks We extract the form factor using the "+" component of the electromagnetic current in the light-cone formalism For comparison, we also compute the form factor in the covariant framework and we obtain perfect agreement It is shown that the pair terms do not contribute in this pseudoscalar model This explains why a naive light-cone calculation, ie, omitting pair terms from the onset, also yields the same results

General second-rank correlation tensors for homogeneous magnetohydrodynamic turbulence

Abstract: The properties and structure of second-order ~Cartesian! correlation tensors are derived for the general case of two solenoidal random vector fields. The theory is intended to describe homogeneous magnetohydrodynamic turbulence, with no assumed rotational or reflectional symmetries. Each correlation tensor can be written in terms of four scalar generating functions and the relationship of these functions to the potentials that generate the poloidal and toroidal components of the underlying vector fields is derived. The physical nature of the scalar functions is investigated and their true or pseudoscalar character is ascertained. In our general discussion we clarify several misleading statements dating back to Robertson’s original paper in the field @Proc. Camb. Philos. Soc. 36, 209 ~1940!#. It is also shown that using the one-dimensional correlation function, it is possible to obtain spectral information on the induced electric field in directions perpendicular to the measurement direction. @S1063-651X~97!09208-8#

Unquenching the scalar glueball

Abstract: Computations in the quenched approximation on the lattice predict the lightest glueball to be a scalar in the 1.5−1.8 GeV region. Here we calculate the dynamical effect the coupling to two pseudoscalars has on the mass, width and decay pattern of such a scalar glueball. These hadronic interactions allow mixing with the qq scalar nonet, which is largely fixed by the well-established K ∗ 0 (1430). This non-perturbative mixing means that, if the pure gluestate has a width to two pseudoscalar channels of ∼ 100 MeV as predicted on the lattice, the resulting hadron has a width to these channels of only ∼ 30 MeV with a large �� component. Experimental results need to be reanalyzed in the light of these predictions to decide if either the f0(1500) or an f0(1710) coincides with this dressed glueball.

Techniques of amplitude analysis for two-pseudoscalar systems

Abstract: The analytical tools needed for an amplitude analysis of two-pseudoscalar systems are described in some detail. Analyses involving two identical spinless particles require a new type of polynomial; the general form of such a polynomial is given for the first time.

Nucleon self-energy in the relativistic Brueckner approach

Abstract: The formalism of the relativistic (or Dirac-) Brueckner approach in infinite nuclear matter is described. For the nucleon-nucleon interaction the one-boson exchange potentials Bonn $A,B,C$ and for comparison the Walecka model, are used. The $T$ matrix is determined from the Thompson equation and is projected onto five covariant amplitudes. By the restriction to positive energy states an ambiguity arises in the relativistic Brueckner approach which is discussed here in terms of the pseudoscalar and the pseudovector projection. The influence of the coupling of the nucleon via the $T$ matrix as an effective two-nucleon interaction to the nuclear medium is expressed by the self-energy. In particular we investigate the scalar and vector components of the self-energy for the different one-boson exchange potentials and discuss their density and momentum dependence. We estimate the uncertainty of the self-energy due to the pseudoscalar and the pseudovector choice. Usually the momentum dependence of the self-energy is thought to be weak, however, we find that this depends on the one-boson exchange potentials. For the Bonn potentials, in contrast to the $\ensuremath{\sigma}\ensuremath{\omega}$ potential, the momentum dependence is strikingly strong above as well as below the Fermi surface. We compare with the results of other groups and study the effects on the equation of state and the nucleon optical potential.

Higgs boson decay to top quarks at O({alpha}{sub s}{sup 2})

Abstract: Three-loop corrections to the scalar and pseudoscalar current correlator are calculated. By applying the large momentum, expansion mass terms up to order (m{sup 2}/q{sup 2}){sup 4} are evaluated analytically. As an application O({alpha}{sub s}{sup 2}) corrections to the decay of a scalar and pseudoscalar Higgs boson into top quarks are considered. It is shown that for a Higgs mass not far above the t{bar t} threshold these higher order mass corrections are necessary to get reliable results. {copyright} {ital 1997} {ital The American Physical Society}

Non-perturbative renormalization constants on the lattice from flavour non-singlet Ward identities

Abstract: By imposing axial and vector Ward identities for flavour-non-singlet currents, we estimate in the quenched approximation the non-perturbative values of combinations of improvement coefficients, which appear in the expansion around the massless case of the renormalization constants of axial, pseudoscalar, vector, scalar non-singlet currents and of the renormalized mass. These coefficients are relevant for the completion of the improvement programme to O(a) of such operators. The simulations are performed with a clover Wilson action non-perturbatively improved.

A Covariant OBE Model for $\eta$ Production in NN Collisions

Abstract: A relativistic covariant one boson exchange model, previously applied to describe elastic nucleon-nucleon scattering, is extended to study $\eta$ production in NN collisions. The transition amplitude for the elementary BN->$\eta$N process with B being the meson exchanged (B=$\pi$, $|sigma$,$\eta$, $\rho$, $\omega$ and $\delta$) are taken to be the sum of four terms corresponding to s and u-channels with a nucleon or a nucleon isobar N*(1535MeV) in the intermediate states. Taking the relative phases of the various exchange amplitudes to be +1, the model reproduces the cross sections for the $NN\to X\eta$ reactions in a consistent manner. In the limit where all $\eta$'s are produced via N^* excitations, interference terms between the overall contributions from the exchange of pseudoscalart and scalar mesons with that of vector mesons cancel out. Consequently, much of the ambiguities in the model predictions due to unknown relative phases of different vector pseudoscalar exchanges are strongly reduced.

Exclusive nonleptonic bottom to charm baryon decays including nonfactorizable contributions

Abstract: Exclusive nonleptonic decays of bottom baryons to charm baryons and pseudoscalar light mesons are analyzed within a relativistic three-quark model. We include factorizing as well as nonfactorizing contributions to the decay amplitudes. The total contribution of the nonfactorizing diagrams amount up to 30% of the factorizing contributions in amplitude. We present detailed predictions for rates and asymmetry parameters.

Spontaneous Generation of Pseudoscalar Mass in the U(3)xU(3) Linear Sigma Model

Abstract: A novel, nonperturbative, way to generate chiral symmetry breaking within the linear sigma model for 3 flavours is discussed. After spontaneous chiral symmetry breaking in the vacuum at the tree level the scalar nonet obtains mass, while the pseudoscalars are massless. Then, including quantum loops in a nonperturbative, self-consistent way chiral symmetry is broken by nonplanar graphs in a second step, and also the pseudoscalars become massive. By interpreting the basic symmetry to be a discrete permutation symmetry, in accord with superselection rules, no additional Goldstone bosons are expected.

Nonlinear approach to NN interactions using self-interacting meson fields

Abstract: Motivated by the success of models based on chiral symmetry in NN interactions, we investigate self-interacting scalar, pseudoscalar, and vector meson fields and their impact for NN forces. We parametrize the corresponding nonlinear field equations and get analytic wavelike solutions. A probability amplitude for the propagation of particle states is calculated and applied in the framework of a boson-exchange NN potential. Using a proper normalization of the meson fields makes all self-scattering amplitudes finite. The same normalization is able to substitute for the phenomenological form factors used in conventional boson-exchange potentials and thus yields a phenomenological understanding of this part of the NN interaction. We find an empirical scaling law which relates the meson self-interaction couplings to the pion mass and self-interaction coupling constant. Our model yields np phase shifts comparable to the Bonn B potential results and deuteron properties, in excellent agreement with experimental data. {copyright} {ital 1997} {ital The American Physical Society}

Branching Ratios and CP Asymmetries of B Decays to a Vector and a Pseudoscalar Meson

Abstract: We consider two body decays of B meson into a light vector (V) and a pseudoscalar (P) meson. The constraint obtained from the $B\to P P$ modes on the parameter space of the input parameters is imposed also on $B\to V P$ modes. In particular we constrain $\xi\equiv (1/N_c)$ for those modes from recently measured $B\to \omega K, \phi K$ and are able to get a satisfactory pictures for all modes where data exists. Modes that should be seen shortly and those with possibly large CP asymmetries are identified.

Topological Charge and the Spectrum of the Fermion Matrix in Lattice-QED_2

Abstract: We investigate the interplay between topological charge and the spectrum of the fermion matrix in lattice-QED_2 using analytic methods and Monte Carlo simulations with dynamical fermions. A new theorem on the spectral decomposition of the fermion matrix establishes that its real eigenvalues (and corresponding eigenvectors) play a role similar to the zero eigenvalues (zero modes) of the Dirac operator in continuous background fields. Using numerical techniques we concentrate on studying the real part of the spectrum. These results provide new insights into the behaviour of physical quantities as a function of the topological charge. In particular we discuss fermion determinant, effective action and pseudoscalar densities.

Beyond the Narrow Resonance Approximation: Decay Constant and Width of the First Pion-Excitation State

Abstract: We consider the first pion excitation as a sub-continuum resonance in the pseudoscalar channel, and we obtain parameters characterizing this resonance through a global fit of the Borel-parameter dependence of the field-theoretical pseudoscalar Laplace sum rule to its hadronic (pion + pion-excitation + QCD-continuum) content. Our analysis incorporates finite-width deviations from the narrow resonance approximation, instanton effects, and higher-loop perturbative contributions to the pseudoscalar correlator. We obtain the following values (uncertainties reflect 90% confidence levels): mass $M_\Pi = 1.15 \pm 0.28 GeV$, width $\Gamma_\Pi = < 0.48 GeV$, decay constant $r \equiv [F_\Pi M_\Pi^2 / f_\pi m_\pi^2]^2 = 4.7 \pm 2.8$.

The eta-prime meson with staggered fermions

Abstract: We have computed the eta-prime pseudoscalar octet mass splitting using staggered fermions on both dynamical and quenched gauge configurations. We have used Wuppertal smeared operators to reduce excited state contributions. We compare our results with the theoretical forms predicted by partially quenched chiral perturbation theory in the lowest order. Using lattice volumes of size 16^3 x 32 with a^{-1}=2GeV we obtain results consistent with the physical eta-prime mass. We also demonstrate that the flavor singlet piece of the eta-prime mass comes from zero modes of the Dirac operator.

Towards resolution of the scalar meson nonet enigma

Abstract: By the application of a linear mass spectrum to a composite system of both the pseudoscalar and scalar meson nonets, we find three relations for the masses of the scalar states which suggest the $$q\bar q$$ assignment for the scalar meson nonet a0(1320), K 0 * (1430), f0(1500), and f0 ′(980).

The Eta-prime Meson with Staggered Fermions

Abstract: We have computed the eta-prime pseudoscalar octet mass splitting using staggered fermions on both dynamical and quenched gauge configurations. We have used Wuppertal smeared operators to reduce excited state contributions. We compare our results with the theoretical forms predicted by partially quenched chiral perturbation theory in the lowest order. Using lattice volumes of size 16^3 x 32 with a^{-1}=2GeV we obtain results consistent with the physical eta-prime mass. We also demonstrate that the flavor singlet piece of the eta-prime mass comes from zero modes of the Dirac operator.

Strangeness in the nucleon and the ratio of proton-to-neutron neutrino-induced quasi—elastic yield

Abstract: The electroweak form factors of the nucleon as obtained within a three flavor pseudoscalar vector meson soliton model are employed to predict the ratio of the proton and neutron yields from 12C, which are induced by quasi—elastic neutrino reactions. These predictions are found to vary only moderately in the parameter space allowed by the model. The antineutrino flux of the up—coming experiment determining this ratio was previously overestimated. The corresponding correction is shown to have only a small effect on the predicted ratio. However, it is found that the experimental result for the ratio crucially depends on an accurate measurement of the energy of the knocked out nucleon.