QCD calculation of theB→π,K form factors

We calculate the form factors for the heavy-to-light transitionsB,K by means of QCD sum rules using andK light-cone wave functions. Higher twist contributions as well as gluonic corrections are taken into account. The sensitivity to the shape of the leading-twist wave functions and effects ofSU (3)-breaking are discussed. The results are compared with quark model predictions and with the results from QCD sum rules for three-point correlators.Work supported by the German Federal Ministry for Research and Technology under contract No. 05 6MU93P     

Chiral anomaly in Kγ → Kπ reactions

Implications of the chiral anomaly for the cross sections of the reactions K ⁺γ → K ⁺π⁰, K ⁰γ → K ⁰π⁰, K ⁺γ → K ⁰π⁺, and K ⁰γ → K ⁺π^? are investigated. Near the threshold, the contribution of the chiral anomaly dominates the cross sections for the first and the second reaction. These cross sections are compared with the cross sections for the third and the fourth reaction, which receive no contribution from the chiral anomaly. Prospects for an experimental study of the KKπγ vertex in the Coulomb production of π mesons by a K-meson beam are discussed.     

TheΛ b →Λ c decay form factors

The recently measured cross-sections for diffractive dissociation of nuclei in high-energy proton nucleus (pA) collisions show a strikingA ^1/3 dependence on the target massA. Such a dependence emerges from an optical model which incorporates a simple mechanism to produce the absorption fluctuations required for inelastic diffraction. The observed momentum transfer (t) dependence of the differential cross-section, dσ/dt∝ exp(?B|t|), is described in terms of a correlation length \(R_F = \sqrt {2B} \) of the absorption fluctuations which turns out to be of the size of a nucleon. The excitation massM dependence, dσ/dM ²∝M ^?2, is explained by a bremsstrahlung mechanism.     

Inelastic final-state interactions in B → VV →π K processes

We study the final-state interactions in B →π K decays through B → VV →π K processes where the inelastic rescattering occurs via single pion exchange. The next-to-leading order low-energy effective Hamiltonian and Bauer-Stech-Wirbel (BSW) model are used to evaluate the weak transition matrix elements and final-state interactions. We found that the final-state interaction effects in B →ρ K^*→π K processes are significant. The Fleischer-Mannel relation for the Cabibbo-Kobayashi-Maskawa (CKM) angle γ can be significantly modified. Received: 13 August 1998     

Implications of unitarity and analyticity for the Dπ form factors

We consider the vector and scalar form factors of the charm-changing current responsible for the semileptonic decay D → πlν. Using as input dispersion relations and unitarity for the moments of suitable heavy-light correlators evaluated with Operator Product Expansions, including O(α _s ²) terms in perturbative QCD, we constrain the shape parameters of the form factors and find exclusion regions for zeros on the real axis and in the complex plane. For the scalar form factor, a low-energy theorem and phase information on the unitarity cut are also implemented to further constrain the shape parameters. We finally propose new analytic expressions for the Dπ form factors, derive constraints on the relevant coefficients from unitarity and analyticity, and briefly discuss the usefulness of the new parametrizations for describing semileptonic data.     

The form factors of the decays π− → e−¯veγ and K− → e−¯veγ

In the special type of the quark model we obtain the ratio=h _A/h_V of the axial (h_A) and vector (h_V) form factors for the decays ^– e^– ¯v_e and K^– e^–¯v_e different from unity. The low-energy theorem, relating the electric polarizability of the charged pion with the ratio, is analyzed. It is shown that < 1 corresponds to , calculated by accounting the contribution of the scalar meson(700) into the amplitude of the Compton effect on the pion. In the absence of the(700) contribution we have=1.Dedicated to Academician Václav Votruba on the occasion of his eightieth birthday.     

Electromagnetic N-Δ transition form factors in a covariant quark-diquark model

The electromagnetic N-Δ transition form factors are calculated in the framework of a formally covariant constituent diquark model. As a spin- $tfrac {3}{2}$ particle the Δ is assumed to be a bound state of a quark and an axial-vector diquark. The wave function is obtained from a diquark-quark Salpeter equation with an instantaneous quark exchange potential. The three transition form factors are calculated for momentum transfers squared from the pseudothreshold (M_Δ ?M _N )² up to ?2 (GeV/c)². The magnetic form factor is in qualitative agreement with experiment. We find very interesting results for the ratios E2/M1 and C2/M1.     

Strong nucleon and Δ-isobar form factors in the quark-confinement model

The nucleon and the -isobar are investigated as three-quark systems in the quark-confinement model (QCM). This model is based on two hypotheses. First, quark confinement is accomplished through averaging over some vacuum gluon fields which are assumed to provide the confinement of any colour states. Second, hadrons are treated as collective colourless excitations of quark-gluon interactions.The QCM is applied to low-energy baryon physics. The nucleon magnetic moments and electromagnetic radii, the ratioG _A /G _V , and the decay width for p are calculated. The behaviour of the electromagnetic and strong mesonnucleon (meson-isobar) form factors is determined for space-like momentum transfers. The results are compared with experimental data for the electromagnetic form factors and phenomenological strong form factors as used in the Bonn potential.     

Study of the B_c→B_sπ decay with the perturbative QCD approach

The Bc→Bsπ decay is studied with the perturbative QCD approach. Three types of wave functions for Bsmeson are considered.The transition form factor FBc→Bs0(0) and the branching ratio Br(Bc→Bsπ)aresensitivetothemodelofthe Bsmeson wave functions.With appropriate inputs, our estimate on Br(Bc→Bsπ) is comparable with the recent LHCb measurement. A clear signal of Bc→Bsπ decay should be easily observed at the Large Hadron Collider.     

Generalized baryon form factors and proton structure functions in the Sakai–Sugimoto model

We investigate the production of positive parity baryon resonances in proton electromagnetic scattering within the Sakai–Sugimoto model. The latter is a string model for the non-perturbative regime of large _Nc$N_c$ QCD. Using holographic techniques we calculate the generalized Dirac and Pauli form factors that describe resonance production. We use these results to estimate the contribution of resonance production to the proton structure functions. Interestingly, we find an approximate Callan–Gross relation for the structure functions in a regime of intermediate values of the Bjorken variable.     

Spectroscopic factors of resonance states with the Gamow shell model

We provide an investigation of the spectroscopic factor of resonance states in A=5-8 nuclei, utilizing the Gamow shell model(GSM). Within the GSM, the configuration mixing is taken into account exactly with the shell model framework, and the continuum coupling is addressed via the complex-energy Berggren ensemble, which treats bound, resonance, and non-resonant continuum single-particle states on an equal footing. As a result, both the configuration mixing and continuum coupling are meticulously...     

Measurements of the γγ＊ → π^0 and γγ＊ → ηc transition form factors at BABAR

We present measurements of the γγ＊ → π^0 transition form factor for the momentum transfer range Q^2=4-40 GeV^2 and the γγ＊ → ηc transition form factor for the range Q^2=2-50 GeV^2. The current status of measurements of the meson-photon transition form factors for the η and η＇ mesons is discussed. The results of the measurement of the ηc mass, total and two-photon widths are also presented.     

The process\bar p p→e − e + with polarized initial particles and proton form factors in time-like region

The process pe ^– e ⁺ is considered in the general case of polarized initial particles. A relation between the difference of the phases of the electromagnetic form factorsG _M andG _E in the time-like region and measurable asymmetries is derived. It is shown that the moduli of the form factors can be determined from measurements of the total unpolarized cross section and of the integral asymmetry for longitudinally polarized (or, transversely polarized) andp. The behaviour of the proton form factors at highq ² in the time-like region is also discussed. From the Phragmén-Lindelöf's theorem it follows that the asymptotical behaviour of the form factors in the space-like and time-like regions must be the same. An analysis of experimental data in both regions based on perturbative QCD is presented.