Production representation of partial wave scattering amplitudes and the fo（600） particle

The establishlnent of production representation of partial wave scattering alnplitudes is reviewed in the context of quantum field theory. Its relation to the production representation, or Ning Hu representation in quantum mechanical scattering theory is pointed out. One of the most important application of the production representation is the physics of the fo（600） and K（700） scalar hadron resonances, on which we also give a brief review. It is emphasized that all evidences accunmlated so far are consistent with the picture that the fo（600） meson is the chiral partner of the Nambu Goldstone bosons in a linear realization of chiral symmetry.     

Photo- and electro-production of mesons on nucleons and nuclei

In these lectures I will show some results obtained with the chiral unitary approach applied to the photo- and electro-production of mesons. The results for the photo-production of ηπ⁰p and K⁰π⁰Σ⁺, together with related reactions will be shown, having with common denominator the excitation of the Δ(1700) resonance which is one of those dynamically generated in the chiral unitary approach. Then I will show the results obtained for the e⁺e⁻→?f₀(980) reaction which reproduce the bulk of the data except for a pronounced peak, giving support to a new mesonic resonance, X(2175). Results will also be shown for the electromagnetic form factors of the N^∗(1535) resonance, also dynamically generated in this approach. Finally, I will show some results on the photo-production of the ω in the nuclei, showing that present experimental results claiming a shift of the ω mass in the medium are tied to a particular choice of background and are not conclusive. On the other hand, the same experimental results show unambiguously a huge increase of the ω width in the nuclear medium.     

Phenomenology of neutral D-meson decays and double-flavour oscillations

Decays of neutral D-mesons are considered phenomenologically without invoking any particular models. Special attention is given to cascade decays with intermediate neutral kaons where coherent double-flavour oscillations (CDFO) become possible. We show necessity and unique possibilities of experiments on CDFO. They allow to relate with each other widths and masses of D-meson eigenstates, to separate interference effects due to D ⁰-ˉD ⁰ mixing and/or Cabibbo-favoured vs. doubly-suppressed transitions. Such experiments provide the only known ways to unambiguous model-independent measurements of all CP-violating parameters and of Cabibbo-doubly-suppressed amplitudes, where the New Physics may have more prominent manifestations. Similar experiments would be useful and interesting also for charged D-meson decays to neutral kaons. Received: 13 August 1998     

Glueball-Quarkonia Content of the f0(1370),f0(1500) and f0(1710)

Based on a 3 × 3 mass matrix describing the mixing of the scalar states f₀(1370),f₀(1500) and f₀(1710), the hadronic decays of the three states are investigated. Taking into account the two possible assumptions concerning the mass level order of the bare states |N> =|μμ+dd>/ √2 |S>= |ss> and |G> = |gg> in the scalar sector, M_G > M_S > M_N and M_G > M_N > M_S, the glueball-quarkonia content of the three states is obtained by solving the nonlinear equations. Some predictions about the hadronic and two-photon decays of the three states in two cases are presented. It is pointed out that the predictions about the two-photon decay width ratios for the three states can provide a stringent consistency check of the two assumptions.     

A calculation of the physical mass of sigma meson

We calculate the physical mass and the width of the sigma meson by considering that it couples in vacuum to two virtual pions. The mass is calculated by using the spectral function, and we find that it is about 600 MeV. In addition, we obtained 220 MeV as the value for the width of its spectral function. The value obtained for the mass is in good agreement with that reported in the Particle Data Book for the σ-meson, which is also named f ₀ (600). This result also shows that σ-meson can be considered as a two-pion resonance.      

In-medium properties of hadrons — Recent experimental results and perspectives

Recent experimental results on the modification of hadron properties in a nuclear medium are discussed. Experiments using hadron, heavy-ion and photon beams are described. Particular emphasis is given to the photonuclear production of light vector mesons and scalar mesons off nuclei. Recent results on the search for meson-nucleus bound states are presented. Perspectives for extending these studies to the charm sector are outlined     

D and D_s in mass loaded flux tube

Heavy-light hadrons are studied in a mass loaded flux tube model. The study indicates that the dynamics of mesons and baryons containing a c quark is described well by the mass loaded flux tube. The hypothesis of good diquark-antiquark degeneracy is found reasonable in heavy-light quark systems. The spectrum of charmed (D) and charmed strange (Ds) mesons is systematically computed. D and Ds in 1D multiplets are predicted to have lower masses in comparison with other theoretical predictions. The predicted masses of the 1(13D1) and the 3(13D3) Ds agree well with those of recently observed Ds1(2700)± and DsJ(2860), respectively.     

Investigation of in-medium ω photoproduction

Recent experimental results on the in-medium modification of the ω meson are discussed. The experiment described was performed at the ELSA accelerator facility in Bonn using the combined detector system of Crystal Barrel and TAPS. Theω-meson was identified via the reaction γ+A → ω +X → π⁰ γ +X     

Multichannel calculation of the very narrow D<Subscript>s0</Subscript><Superscript>*</Superscript>(2317) and the very broad D<Subscript>0</Subscript><Superscript>*</Superscript>(2300-2400)

The narrow D _s0 ^* (2317) and broad D ₀ ^* (2300-2400) charmed scalar mesons and their radial excitations are described in a coupled-channel quark model that also reproduces the properties of the light scalar nonet. All two-meson channels containing ground-state pseudoscalars and vectors are included. The parameters are chosen fixed at published values, except for the overall coupling constant λ, which is fine-tuned to reproduce the D _s0 ^* (2317) mass, and a damping constant α for subthreshold contributions. Variations of λ and D ₀ ^* (2300-2400) pole postions are studied for different α values. Calculated cross-sections for S-wave DK and Dπ scattering, as well as resonance pole positions, are given for the value of α that fits the light scalars. The thus predicted radially excited state D _s0 ^*′(2850), with a width of about 50MeV, seems to have been observed already.     

Hamiltonian Approach to Meson Structure in Extended Nambu-Jona-Lasinio Model

The Nambu-Jona-Lasinio model,is extended to inclusion of the nonlocal effective quark interaction with confinement. An effective Hamiltonian in the instantaneous approximation is used to study meson properties in the random phse approximation.     

New exotic charmonium states

In the last years many states in the charmonium mass region were discovery by BABAR, Belle and CDF collaborations. I discuss some of these discoveries, and how the QCD Sum Rule approach can be used to understand the structure of these states.     

D and D_s in mass loaded flux tube

Heavy-light hadrons are studied in a mass loaded flux tube model. The study indicates that the dynamics of mesons and baryons containing a c quark is described well by the mass loaded flux tube. The hypothesis of good diquark-antiquark degeneracy is found reasonable in heavy-light quark systems. The spectrum of charmed (D) and charmed strange (Ds) mesons is systematically computed. D and Ds in 1D multiplets are predicted to have lower masses in comparison with other theoretical predictions. The predicted ma...     

New exotic charmonium states

In the last years many states in the charmonium mass region were discovery by BABAR,Belle and CDF collaborations.I discuss some of these discoveries,and how the QCD Sum Rule approach can be used to understand the structure of these states.     

Dynamics of strong and radiative decays of Ds-mesons in the hadrogenesis conjecture

The positive parity scalar D*s0(2317) and axial-vector D*s1(2460) charmed strange mesons are generated by coupled-channel dynamics through the s-wave scattering of Goldstone bosons off the pseudoscalar and vector D(Ds)-meson ground states. The specific masses of these states are obtained as a consequence of the attraction arising from the Weinberg-Tomozawa interaction in the chiral Lagrangian. Chiral corrections to order Q2χ are calculated and found to be small. The D*s0(2317) and D*s1(2460) mesons decay either strongly into the isospin-violating π0Ds and π0D*s channels or electromagnetically. We show that the π0-η and (K0D+-K+D0) mixings act constructively to generate strong widths of the order of 140 keV and emphasize the sensitivity of this value to the KD component of the states. The one-loop contribution to the radiative decay amplitudes of scalar and axial-vector states is calculated using the electromagnetic Lagrangian to chiral order Q2χ. We show the importance of taking into account processes involving light vector mesons explicitly in the dynamics of electromagnetic decays. The radiative width are sensitive to both η Ds and KD components, hence providing information complementary to the strong widths on the positive parity Ds-meson structure.     

Kl4 decays

An effective theory of large-N_C QCD of pseudoscalar, vector, and axial-vector mesons has been used to study six K_l4 decay modes. It has been found that the matrix elements of the axial-vector current dominate the K_l4 decays. PCAC is satisfied. A relationship between three form factors of the axial-vector current has been predicted. Partial-wave analysis has been done. Non-zero phase shifts are originated in ρ→ππ. The decay rates are calculated in the chiral limit. In this study there is no adjustable parameter. Received: 17 October 2000 / Accepted: 20 February 2001     

KLOE results on scalar and pseudoscalar mesons

The data collected by the KLOE Collaboration at the Frascati φ-factory DAΦNE from 2001 to 2006 have been used for extensive studies in meson spectroscopy.The decays of the scalar mesons a0(980) and f0(980) into two pseudoscalar mesons have been exploited to measure the relevant parameters of those resonances.The radiative decays φ→ηγ and ηγ have been used for the determination of the pseudoscalar mixing angle and to search for a possible gluonium content in the η.The dynamics of the η→ 3π decay has been studied and the Dalitz Plot parameters have been measured.The large amount of η mesons produced allowed also to study interesting rare η decays.     

Spin and isospin effects in the NN → NKΛ reaction near threshold

The spin and isospin structure of the amplitudes and observables for K⁺Λ production in nucleon-nucleon collisions in the near-threshold region is analysed. Five experiments are required in order to isolate the amplitudes, up to an overall phase and two discrete ambiguities, in a model-independent way. It is shown that, with reasonable values for the relative strengths of the π and ρ terms in a meson-exchange model, one expects production on the neutron to be significantly stronger than that on the proton. Negative values of the spin-transfer coefficient D_NN are also predicted due to π-ρ interference.     

The Optical Analogue of CP-Violation

The peculiar features of the mixing in the neutral pseudoscalar mesons can be introduced by the analogy to the optical polarization. The time-reversed not-invariant processes and the related phenomenon of CP-nonconservation can be then joined to the dissipative effects which yield a not vanishing imaginary part in the relevant propagation of electromagnetic radiation in a medium. Thus, the propagation of the two transverse polarization states can reproduce the peculiar asymmetries which are so common in the realm of high energy particle physics.     

The puzzle of the D and D<Subscript>s</Subscript> mesons

We present a theoretical framework that accounts for the new D_J and D_sJ mesons measured in the open-charm sector. These resonances are properly described if considered as a mixture of conventional P-wave quark-antiquark states and four-quark components. The narrowest states are basically P-wave quark-antiquark mesons, while the dominantly four-quark states are shifted above the corresponding two-meson threshold. We study the electromagnetic decay widths as basic tools to scrutiny their nature.