Exclusive semileptonic heavy meson decays including lepton mass effects

We discuss the exclusive semi-leptonic (s.l.) bottom meson decaysB→D(D ^*)+l+v where we include non-zero lepton mass effects in the kinematics and dynamics. We develop the general formalism for the non-zero lepton mass case. We then look at how rates, spectra and angular correlations are affected by non-zero lepton masses in the context of a specific spectator quark model. Numerical results are presented for s.l. decays involving thee-, μ- and τ-leptons. We also discuss the s.l. decaysB→π(ρ),D→K(K ^*) and the free quark decay model.     

Long distance effects inb→s exclusive decays

We estimate long distance corrections to radiativeB →K ^*γ and to non leptonicB→Kπ,B→K ^*π,B→Kσ,B→K ^*σ,B→KΦ andB→K ^*Φ decays generated by the ( \(\overline b\) c) ( \(\overline c\) s) part of the non leptonic weak Hamiltonian. While vanishing in the vacuum saturation approximation, these corrections are finite if one includes single particle charmed states between the currents in the Hamiltonian. We find small effects in radiative decays, but significant contributions to several non leptonic processes.     

Formfactor effects in exclusiveD andB decays

Recent experimental results on the semileptonicD→K ^* transition seem to be in conflict with quark model expectations. Motivated by this finding we reinvestigate the predictions for exclusiveD andB decays in the relativistic quark model approach. Some of the invariant formfactors relevant for the transition matrix elementsD→K ^* andB→D ^* depend strongly on an explicit quarkmass-dependent integral over the meson wave functions. The dependence of decay rates and spectra in semi-leptonicD andB transitions on this integral is analysed and discussed in detail. Furthermore, we discuss how the predictions of the relativistic quark model for semi-leptonicD andB decays can be tested through measurements of the polarization of the produced vector mesonK ^* andD ^*, respectively. Some remarks on exclusive nonleptonic two-body decays of the heavy mesons are also presented. Finally the theoretical uncertainties for the determination of the K-M matrix element |V _ub | from exclusive semi-leptonic decays are discussed.     

Weak radiative decays of baryons

Using recent experimental baryon weak radiative decay data for the fiveB→B′γ decays, we employ the pole model self-consistently to extract the reduced matrix elements 〈B′|H _w|B〉. The resulting pattern is compatible with weak pion decaysB→B′π and also with the quark model.     

A determination of the CKM-matrix element ratio |V ts |/|V cb | from the rareB-decaysB→K *+γ andB→X s +γ

Implications of the recent CLEO observation [1] of the rare decay modeB→K ^*+γ having a combined branching ratio BR(B→K ^*+γ)=(4.5±1.5±0.9)×10^?5 and an improved upper limit on the inclusive branching ratio BR(B→X _s +γ)<5.4×10^?4 (95% C.L.) [2] are discussed in the context of the Standard Model (SM). Using the unitarity of the CKM-matrix and taking into account QCD radiative corrections in the decay rate and the inclusive photon energy spectrum we obtain an improved upper limit on the inclusive branching ratio BR(B→X _s +γ)<4.8×10^?4 (95% C.L.). This can be used to constrain possible non-SM contributions to the inclusive branching ratio, giving BR(B→X _s +γ) (non-SM)<3.0×10^?4 form _t >-108 GeV. Within the SM, we show that the resulting experimental upper limit can be interpreted as a corresponding limit on the CKM-matrix element ratio yielding |V _ts |/|V _cb |<1.67, with the top quark mass assumed to weigh less than 200 GeV. We calculate the relative exclusive to inclusive branching ratioR(K ^*/X _s )≡Γ(B→K ^*+γ)/Γ(B→X _s +γ), based on the inclusive hadronic invariant mass distribution inB→X _s +γ. Estimating theK ^*-contribution from this distribution in the threshold region (m _K +m _π)≤m _{X s} ≤0.97 GeV and using experimental measurements from the semileptonicD-decaysD→K+π+?v _? in the same mass interval, we obtainR(K ^*/X _s )=0.13±0.03. This enables us to put a lower bound on the ratio |V _ts |/|V _cb | from the 95% C.L. lower limit on the branching ratio BR(B→K ^*+γ)>1.6×10^?5 [1,2]. Combining the exclusive and inclusive decay rates, we determine 0.50≤|V _ts |/|V _cb |≤1.67 (at 95% C.L.).     

Winkelverteilungen elastisch an Edelgas-Atomstrahlen gestreuter Elektronen; Spinpolarisation eines an Argon gestreuten 40 eV-Elektronenstrahls

Various non-leptonic decay modes of baryons are calculated in a simple quark model. Form factors for various matrix elements are taken both from experiment and the quark model. Additionally theK→2π andK→3π decay modes are computed in the same model. The theory has theΔ I=1/2 rule and static SU⁶ built-in. A relation between the∑ ⁺→N ⁺ π ⁺ decay, not calculable in the model, and theK→3π decay is given via an effective six quark interaction. Agreement with experiment is order of magnitude for the baryonic decays and worse for theK decays.     

Quark model analysis of semileptonicD decays intoK andK *

We derive the form factors governing the decaysD→Kev andD→K ^* ev in the framework of a relativistic constituent quark model. Our results agree with the recently measured form factors and the data for rates at the level of the present experimental uncertainty.     

Determining theCP-violating phase γ

The weak phase γ is conventionally probed by theB _s→ρ ⁰ mode. The predicted rate is tiny. Even if aB _s→ρ ⁰ K _s rate difference could be established, it would not be clear that sin 2γ had been measured, because amplitudes with other weak phases may contribute significantly. Non-CP eigenstates, such asB _s →D _s ^± K ^?, have a two-fold advantage overB _s→ρ ⁰ K _s. Their rates are orders of magnitude above that forB _s→ρ ⁰ K _s, and they probe theCP-violating phase γ, without any contamination from other weak phases. Detailed time-dependent studies of non-CP eigenstates remove possible final-state phases and extract the weak phase γ.     

Weak radiative hyperon decays in the pole model

We compute the parity conserving and parity violating amplitudes of the weak radiative hyperon decays in a pole model which includes negative parity intermediate states. The matrix elements are determined from experimentally known quantities and also evaluated in a nonrelativistic quark model. We find good numerical agreement with the data for the decay Σ⁺→P+γ and obtain predictions for the other decays where experimental information has been scarce up to now.     

K→ππγ and chiral perturbation theory

Weak radiative decaysK _L,S →π⁺π^?γ andK ⁺→π⁺π⁰γ are reexamined. The electromagnetic form factors and long-distance contributions to the direct photon emission are evaluated using the higher order effective chiral Lagrangian. We find that (1) the naive soft-pion theorem cannot be applied to the magnetic-type transition amplitude, (2) the shortdistance contribution toK _L →π⁺π^?γ is comparable to or even bigger than the long-distance one, (3) the ΔI=1/2 enhancement persists in the decayK ⁺→π⁺π⁰γ, (4) to the order of 1/Λ _χ ² (Λ _χ being the chiral-symmetry breaking scale) the direct photon emission amplitude does not receive a contribution from penguin operators, and (5) the 1/N _c expansion improves the discrepancy between theory and experiment.     

Quark loop model of radiative meson decays

Radiative meson decays are computed from quark loop anomalies, taking into account the SU(3) splitting of the quark masses. Predicted rates for ?→ηγ,K ^*→Kγ, and η→ππγ are brought into satisfactory agreement with experiment. Formulas are given for the radiative decay rates of charmed las are given for the radiative decay rates of charmed mesons, and a mechanism suggested for suppression of the radiative decays of mesons containing a charmed quark.     

Rare kaon decaysK L(S) 0 →π0ℓ+ℓ− in the quark confinement model

K _L(S) ⁰ →π⁰?⁺?^?. The rare decaysK _L(S) ⁰ →π⁰?⁺?^?(?=e or μ) are investigated in the Quark Confinement Model (QCM), a relativistic quark model, based on some assumptions about hadronization and quark confinement. Using the effective electroweak Lagrangian (with QCD corrections), proposed by Gilman and Wise, the matrix elements of kaon transitions to a pion and lepton pair are calculated. The obtained results for the decay widths are in agreement with the experimental data for upper limits on branching ratios and the theoretical predictions calculated by effective chiral Lagrangian method.     

On semileptonicB-decays into longitudinally polarized ρ-mesons

The heavy quark limit can not be taken directly for the decayB→ρev if the ρ meson is longitudinally polarized. We employ some recent ideas of a special realization of chiral symmetry to relate the above process to the decayB→πev in the heavy quark limit, which corresponds to the chiral limit in this so called vector realization of chiral symmetry.     

Regularisation of theP→γγ vertex in the vector meson dominance model

The problem of the PCAC anomaly in the decaysP→γγ (P≡ pseudoscalar meson) is essentially one of regularisation. The constraints deriving there-from, together with similar ones from gauge invariance, typical of a spin 1/2 field theory, are used to define a vector meson dominance approximation for the corresponding amplitudes. The approximation is in this sense dual to the quark model and does indeed reconstruct the high energy quark model behaviour of the amplitudes in the Bjorken-Johnson-Low (BJL) limit. There are interesting new relations for vector meson (V) coupling constants in the decaysV→Pγ and for the PCAC anomaly itself.     

Contribution of the triangle graphs to the neutron electric dipole moment

In the Kobayashi-Maskawa model we compute a new contribution to the neutron electric dipole moment induced byCP violating flavour-changing transitions of the typess→d+gluon+γ through heavy quark loops. This contribution, essentially given by the triangle anomaly graph, is by itself gauge invariant. We obtain from this mechanismD _n /e=3.10^?32 cm, one order of magnitude below our previous estimate from usual penguin diagram contributions.     

The reactionsK − p→π ∓ Σ(1385)± at 8.25 GeV/c

The reactionsK ^? p→π ^? Σ(1385)^± are studied at an incident laboratory momentum of 8.25 GeV/c using data from a high statistics (?180 events/μb) bubble chamber experiment. In the case of the reactionK ^? p→π ^? Σ(1385)⁺ an amplitude analysis is performed and the complete Σ(1385)⁺ spin density matrix is extracted as a function oft′. The results are compared with the predictions of the additive quark model. In the case of the reactionK ^? p→π ⁺ Σ(1385)^? the cross-sections for forward and backward production are determined.     

Hyperon structure and projectile fragmentation

We investigate the hadron productions in hyperon proton collisions in terms of the quark-diquark cascade model with diffractive component. We compare our predicted spectra Ξ^?→Ξ^? X and Ξ^?→Ω^? X with the experimental data. The distribution functions of constituents in incident hadrons and the momentum sharing functions of cascade processes are characterized by the intercepts of Regge trajectories, revealing the difference betweens quark and non-strange quark.     

Test of QCD indū→W − γg,the radiation amplitude zero and the magnetic moment of theW boson

We have calculated the differential cross-section for the processdū→W ^? γg (Jet). It is found that, although the radiation amplitude zero, which occurs for the lowest-order processdū→W ^?γ, is spoiled, there remains a very large dip. Hence, both processes can be used to measure the magnetic moment of theW boson and the value of the quark charges. The presence of a dip is a test of the gauge theoretical value for the magnetic moment of theW bosong=K+1=2, and the angle at which the dip occurs is a measure of the quark charges.     

Determination of the internal structure of valons

We determine the internal structure functions of the valons introduced by Hwa and coworkers, using low-p _t data and Regge model constraints. Our calibration reaction is the fragmentation processp→π^? observed in 70 GeV/cK ⁺ p interactions. The fitted valon structure parameters are used to make successful predictions for various other fragmentation processes (p→π⁺ andp→K ⁺). A comparison with experimental data of the DISvW ₂ (x)-values implied by this same fit, indicates that soft processes probe the nucleon typically at aQ ²-value of ～1 GeV². This finding supports the hypothesis that soft hadronic reactions are useful (and often unique) tools to learn about hadron quark structure.     

Study of Strangeness Photoproduction on the Neutron in the Threshold Region

Photoproduction of the neutral kaon on the deuteron has been investigated at the Research Center for Electron Photon Science, Tohoku University. We constructed the Neutral Kaon Spectrometer-2 for the detection of charged particles from the decay of the neutral kaon and the hyperon. We obtained a momentum distribution of K ⁰ with the inclusive measurement. It was consistent with the previous measurement. The total cross section of γ + d → K ⁰ + Λ + p was estimated from the measured integral cross section of γ + d → Λ + X. The total cross section with respect to the photon energy was compared with the theoretical calculations. It favored the Saclay-Lyon A model calculation with the ratio of the neutral to charged coupling constants of the axial-vector meson, K ₁, as ~ ?1.5. The energy dependence and the magnitude of the total cross section were similar to the total cross section of γ + p → K ⁺ Λ.