Axial vector meson production

Recently available differential cross section and density matrix information on π^?p → B^?p at 4 GeV/c are successfully described in terms of t channel exchanges and s channel absorptive effects. The s channel helicity amplitude which is dominant at small |t| (zero net helicity flip ω exchange) is found to have a zero at ?t = 0.2 GeV². SU(3) and higher symmetries are used to predict cross sections for further axial vector meson production processes, in particular non-diffractive A₁ production. The importance of these processes with regard to Regge phenomenology and meson spectroscopy is emphasized.     

Asymptotic energy scale factors for pseudoscalar meson scattering and charmed meson couplings

Energy scale factors ν₀ for PP → PP scattering amplitudes are related via the absence of exotic resonances to ratios of tensor to vector coupling strengths. These same ratios are extracted from FESR's for non-exotic reactions. The scale factors obtained are all of the order of 1.0 GeV²or less, independent of quantum numbers. This contradicts the expectations of dual amplitudes in which ν₀ = 1/α′, and trajectory slopes are smaller for charmed mesons. Decay widths for tensor mesons are predicted. An observed SU(3) violation for the ratio $\text{A}{}_2\text{→}\text{K}\text{K}\text{/}\text{K}{}^7\text{→}\text{K}\text{π}$ is shown to be consistent with the FESR results. Charmed meson decays are predicted to be factors of 2–3 larger than those predicted by SU(4).     

Non-diffractive production of meson resonances

We study the peripheral cross sections of resonances that cannot be produced by π-exchange. In particular, we concentrate on the four meson nonets expected as L = 1 quark states (i.e., the J^P = 0⁺π_N(980); J^P = 1⁺ A₁, B; J^P = 2⁺ A₂). We use SU(3), Regge poles, factorization, exchange degeneracy, pole extrapolation, and the vector-meson-photon analogy. We predict the cross sections in both photoproduction and non-diffractive hadronic reactions. In passing, we discuss the large unnatural-parity (B, K?Q_B) exchange contributions and even the possibility of studying ππ → πω while avoiding the B production background.     

New form of vector meson dominance and the dependence on the vector meson mass squared

We propose a new form of VMD which relates the reactions πN → VN and γN → πN. Our form fits the experimental results within errors. As our restriction is strong enough, we can discuss the k_μ² dependence. Unexpectedly the k_μ² dependence is larger and this suggest the necessity of generalized vector dominance.     

Lifetime of f meson

The differential and total cross sections for the photoproduction of the f meson are calculated in terms of the width f→γγ.     

The QCD sum rule approach for the semileptonic decay of the D or B meson into a light meson and leptons

We use the method of QCD sum rules to treat the semileptonic weak decay of the D or B meson into a light meson and leptons. To obtain the transition form factors, we adopt the two-point Green’s function in the presence of an external vector or axial-vector field. We find that this method can be related approximately to the traditional three-point Green’s function in the heavy quark limit (m _Q → ∞). Unlike some existing QCD sum rule calculations, our results indicate that the form factors have simple dipole or monopole behavior. We obtain results on the various form factors of the semileptonic decay of D and B mesons into a light meson and investigate various decay processes such as B?⁰ → π ⁺ τ _^?ν?_τ and B?⁰ → ρ ⁺ τ^～ν?_τ. The method allows us to take into account nonperturbative strong interaction effects, thereby providing a more reliable determination of the Cabibbo-Kobayashi-Maskawa matrix elements from the experimental data.     

Generalized parton distributions from meson leptoproduction

Generalized parton distributions (GPDs) extracted from exclusive meson leptoproduction within the handbag approach are briefly reviewed. Only the GPD E is discussed in some detail. Applications of these GPDs to virtual Compton scattering (DVCS) and to Ji’s sum rule are also presented.     

Spin-parity analysis of the B meson

We have done a J^P analysis of the low-mass π⁺ω system, using the reaction π⁺p→π⁺ωp at 7.1 GeV/c.     

Strange meson enhancement in PbPb collisions

The NA44 Collaboration has measured yields and differential distributions of K⁺, K⁻, π⁺, π⁻ in transverse kinetic energy and rapidity, around the center-of-mass rapidity in 158 A GeV/c Pb+Pb collisions at the CERN SPS. A considerable enhancement of K⁺ production per π is observed, as compared to p+p collisions at this energy. To illustrate the importance of secondary hadron rescattering as an enhancement mechanism, we compare strangeness production at the SPS and AGS with predictions of the transport model RQMD.     

Penguin decays of B meson

The theory of loop induced rare B decays is reviewed. Both electromagnetic penguin processes and gluon mediated penguin processes are discussed. After consideringb→sy andb→se ⁺ e ^? decays, purely hadronic modes likeB→K? are estimated. Constraints on the Higgs sector of SUSY theory fromb→sy is discussed. CP violation in charged B Decays is reviewed.     

Hadronic gauge couplings in meson decays

The branching ratiosR(J→ππρ)≡Γ(J→ππρ)/Γ(J→ππ) for naturalJ ^P mesons have been evaluated under the assumption that theT(J→ππρ) amplitudes are generated by the gauge principle for ρ-mesons originally proposed by Sakurai in his approach to VMD. The ratios are predicted to increase withJ and are compatible with the present-day data. This suggests that the hadronic interactions of the photon proceed exclusively through its hadronic (VMD) component.     

Charmed meson decays and right-handed currents

In the presence of right-handed currents including $\text{(}\text{c}\text{s}\text{)}{}_{\mathrm{<mtext>R</mtext>}}$, it is emphasized that the dominant parity-violating (-conserving) Hamiltonian for nonleptonic decays of charmed hadrons transforms like $\text{45}\text{+}\text{45}{}^1\text{(}\text{20″ +}\text{84}\text{)}$ of SU(4), and leads to distinctive results especially in D⁺ → K_Sπ⁺, F⁺ → μ⁺ν_μ and D⁰ → K^?e⁺ν_e, etc.     

Secondary vacuum trajectories and scalar meson exchange

A new second vacuum trajectory passing throughf*(1515) and σ(548), α(t)=? 0.3+t, is proposed, which, together with α_p″(t=0)=? 0.5, overcomes the failure of Igi's original superconvergent πN sum rule and avoids the ghost-state of the conventionalP′-trajectory. The negative residue att=0 confirms the repulsive contribution of a vacuum pole component withJ=0 to the generalizeds-reaction potential, as postulated by Chew (1965). TheP- andP′-poles can build the non resonating background. The Gell-Mann nonsense mechanism at the negative integers with wrong signature explains the dips in the elastic π^± p-scattering att=?0.7, ?2.7 and ?4.5 (GeV/c)². σ(∞) for πN reactions turns out to be 24.3 mb, if α _p (t=0)=1, but the best fits to the total πN cross sections for pion momenta between 2 and 29 GeV/c yield α _p (t=0)=0.93.     

Majorana neutrinos in rare meson decays

The rare meson decays K ⁺ → π ^??⁺?′⁺ and D ⁺ → K ^??⁺?′⁺ (?, ?′ = e, μ), which are induced by Majorana neutrino exchange and which are accompanied by lepton-number nonconservation, are considered. The effects of the meson structure are taken into account on the basis of the Gaussian model for the respective Bethe-Salpeter amplitudes. It is shown that existing direct experimental constraints on the decay branching ratios are overly lenient and therefore give no way to set realistic limits on effective Majorana masses. On the basis of the constraints on the lepton-mixing parameters and neutrino masses from precision measurements of electroweak processes, neutrino-oscillation experiments, searches for neutrinoless double-beta decay of nuclei, and cosmological data, indirect constraints on the branching ratios for the decays in question are obtained and found to be much more stringent than the above direct constraints.     

Gluon exchange in meson spectroscopy

We discuss the spin structure ofN=L=0 andN=L=1 mesons in terms of the one-gluon exchange model with scalar confinement of quarks. SU(3)_flavour is broken by taking different masses for the quarks and the SU (3) breaking of the nonperturbed hamiltonian is shown to be very important in understanding the hyperfine splittings in the ground state mesons, including the charmed states. A fit to the experimental mass spectrum is performed for theN=L=0 andN=L=1 levels simultaneously. The spin-orbit splittings of the spectrum cannot be explained by the convential terms from gluon exchange and scalar confinement. We argue that additional terms, which break the ideal mixing pattern, have to be present. The inclusion of such a term gives a dramatic improvement in χ² and leads to an almost perfect fit to the data for masses and mixing angles.     

Determination of coupling constants from superconvergence sum rules in vector meson — Vector meson scattering

Dynamical relations between masses and coupling constants have been studied using the superconvergent sum rule technique in vector meson — vector meson scattering. Unessential complications due to the spin have been removed by defining a set of 25 KSF invariant amplitudes. Commonly accepted analyticity properties and asymptotics estimated arguing along the line of unitarity then lead to superconvergent sum rules for three amplitudes. Their saturation by one-intermediate-particle contributions in the processesωρ→ ωρ, ωB→ωB andωA ₁→ωA ₁ results in a system of nine coupled equations which have been approximately solved for coupling constants and aρ-ω-B- A ₁ mass sum rule.