1769931
Soft pion emission in semileptonic B-meson decays.
An analysis of semileptonic decays of B mesons with the emission of a single soft pion is presented in the framework of the heavy-quark limit using an effective Lagrangian which implements chiral and heavy-quark symmetries. The analysis is performed at leading order of the chiral and inverse heavy mass expansions. In addition to the ground state heavy mesons some of their resonances are included. The estimates of the various coupling constants and form factors needed in the analysis are obtained using a chiral quark model. As the main result, a clear indication is found that the 0{sup +} and 1{sup +} resonances substantially affect the decay mode with a D{sup *} in the final state, and a less dramatic effect is also noticed in the D mode. An analysis of the decay spectrum in the D{sup *}-{pi}{sup 2} invariant mass is carried out, showing the main effects of including the resonances. The obtained rates show promising prospects for studies of soft pion emission in semileptonic B-meson decays in a B-meson factory where, module experimental cuts, about 10{sup 5} such decays in the D meson mode and 10{sup 4} in the D{sup *} mode could be observed per year.
120605148
Partial-wave analysis of lepton-pair annihilation into two photons
The partial-wave (Jp) composition of the process l+l− → γγ is analyzed in lowest order quantum electrodynamics. The results for low-momentum leptons are as expected, the partial wave with Jp = 0− being dominant. At high energies, the partial wave with Jp = 2+ has the largest single partial cross section. At all energies, it is found that lepton pairs in the triplet state give rise exclusively to positive-parity final states, whereas pairs in the singlet state give rise to negative-parity final states.Some features of the differential cross section are also explained in terms of the spin state of the annihilating lepton pair. Possible implications for e+e− → γγ → hadrons and hadrons are briefly discussed.
123512923
Sequential fragmentation and rate oscillations in exclusive decays
Abstract We consider the decay of heavy quarkonia into two light mesons, and assume that quark-antiquark pairs are created sequentially when the final state is formed. We find quantum oscillations in the decay rate as a function of total energy. These oscillations can explain the energy dependence observed in the πϱ and K ∗ K channels at the J ψ and ψ ′ and predict the behaviour at the heavier Ψ family. In the mechanism we discuss, a given final state is produced only in a narrow range of the possible distances between the initial light quark and light antiquark.
117025439
On the Monopole Model of Form Factors for Heavy Meson Decays
A pole model for the form factors describing heavy to light meson transitions is constructed, and the results compared with the predictions of the heavy quark effective theory (HQET). While most of the HQET-predicted relationships among form factors hold at the maximum value of q{sup 2}, many are violated, suggesting that the simplest version of the pole model of meson form factors should be used with caution, especially when combined with HQET.
125011745
Heavy quark effective theory
After a brief introduction, the results of application of the heavy quark effective theory to semileptonic decays of beta mesons are discussed. A nearly-model-independent extraction of {vert_bar}V{sub cb}{vert_bar} from data is described. Application of the effective theory to inclusive semileptonic decays of heavy mesons, in semileptonic decays of heavy baryons, and to the nonleptonic decays of hadrons are outlined. The authors conclude by mentioning other areas of research in this very active field.
119191937
Photoproduction of meson pairs: First measurement of the polarization observable I**s
Abstract The polarization observable I s , a feature exclusive to the acoplanar kinematics of multi-meson final states produced via linearly polarized photons, has been measured for the first time. Results for the reaction γ → p → p π 0 η are presented for incoming photon energies between 970 MeV and 1650 MeV along with the beam asymmetry I c . The comparably large asymmetries demonstrate a high sensitivity of I s to the dynamics of the reaction. The sensitivity of these new polarization observables to the contributing partial waves is demonstrated by fits using the Bonn–Gatchina partial wave analysis.
7361514
Continuum Study of Deconfinement at Finite Temperature.
Deconfinement and chiral symmetry restoration are explored in a confining, renormalizable, Dyson-Schwinger equation model of two-flavor QCD.An order parameter for deconfinement is introduced and used to establish that, in the chiral limit, deconfinement and chiral symmetry restoration are coincident at {ital T}{sub {ital c}}{approx_equal}150 MeV. The transitions are second order and each has the same critical exponent: {beta}{approx_equal}0.3. The deconfinement transition exhibits sensitivity to the current-quark mass. {ital f}{sub {pi}} and {ital m}{sub {pi}} change by less than 10{percent} for {ital T}{lt}0.7{ital T}{sub {ital c}}; however, as {ital T}{r_arrow}{ital T}{sub {ital c}}, thermal fluctuations cause the pion bound state contribution to the four-point quark-antiquark correlation function to disappear. {copyright} {ital 1996 The American Physical Society.}
26570396
Measurement of the inclusive semielectronic D0 branching fraction.
7502410
Model gluon propagator and pion and rho -meson observables.
A one parameter, model confined-gluon propagator is employed in a phenomenological application of the Dyson-Schwinger and Bethe-Salpeter equations to the calculation of a range of \ensuremath{\pi}- and \ensuremath{\rho}-meson observables. Good agreement is obtained with the data. The calculated quark propagator does not have a singularity on the real-${\mathit{p}}^{2}$ axis. A mass formula for the pion, involving only the vacuum, dressed quark propagator, is presented and shown to provide an accurate estimate of the mass obtained via a direct solution of the Bethe-Salpeter equation. \textcopyright{} 1996 The American Physical Society.
11657024
Critical coupling for dynamical chiral-symmetry breaking.
We study chiral-symmetry breaking in a model of quantum chromodynamics (QCD). In our study we make a critical analysis of an approximation that is often used in QCD and other theories to simplify the Schwinger-Dyson equation for the fermion self-energy. Solving the Schwinger-Dyson equation numerically, without employing the approximation, we find that chiral symmetry is restored when the running coupling constant at zero momentum transfer falls below 0.890.
32389654
Dynamical chiral symmetry breaking and confinement with an infrared-vanishing gluon propagator?
We have studied a model Dyson-Schwinger equation for the quark propagator, constructed using an Ansatz for the gluon propagator of the form D(q) {approximately} q{sup 2}/[(q{sup 2}){sup 2} + b{sup 4}] and two Ansatze for the quark-gluon vertex: the minimal Ball-Chiu and the modified form suggested by Curtis and Pennington. The aim was to determine whether such a form of the gluon propagator, which was suggested by a number of authors and which recent lattice simulations of QCD suggest may be plausible, can support dynamical chiral symmetry breaking and ensure quark confinement. The form of the gluon propagator at small space-like momenta is crucial to the nature of the strong interaction spectrum but is presently unknown and information gathered in such studies is invaluable in supporting or invalidating given hypotheses. It was found that there is a critical value of b = b{sub c} such that the model does not support dynamical chiral symmetry breaking for b > b{sub c}. Further, it was shown that this form of gluon propagator cannot confine quarks. As a consequence this form represents a physically unreasonable model. In addition, these results formed the basis for an invited presentation at a workshop on quantum infraredmore » physics and will be published in the proceedings.« less