SCADRON70: Workshop on Scalar Mesons and Related Topics Honoring Michael Scadron's 70th Birthday
1030(2008); http://dx.doi.org/10.1063/1.2973538View Description Hide Description
The formulae needed to parametrise σ, κ, and are reviewed. For σ and κ, the Adler zero due to Chiral Symmetry Breaking plays a crucial role. The and are locked to the threshold by a cusp mechanism which leads to a sharp peak in attraction at the threshold. This mechanism may play a wider role. A novel suggestion is that the confinement potential involves a cooperative effect between QCD effects (coloured quarks and gluons) and conventional meson exchanges.
1030(2008); http://dx.doi.org/10.1063/1.2973488View Description Hide Description
Relativistic theories of nuclear matter are discussed in a new pespective. First the chiral character of the scalar nuclear field is introduced in the framework of the linear sigma model. With the assumption that the nucleon mass originates in part from the coupling to the quark condensate it is possible to relate the optical potential for the propagation of the scalar field to the QCD scalar susceptibility of the nucleon, on which indications exist from the lattice evolution of the nucleon mass with the quark mass. Constraining the parameters of the nuclear scalar potential by the lattice expansion parameters a successful description of the nuclear saturation properties can be reached.
1030(2008); http://dx.doi.org/10.1063/1.2973506View Description Hide Description
A model‐independent chiral soft‐pion theorem (SPT) shields the now observed scalar‐meson ground‐state isoscalar and isospinor resonances from detection in and processes. Moreover, for pseudoscalar‐to‐vector‐vector (PVV) decays, quark loops only are required.
1030(2008); http://dx.doi.org/10.1063/1.2973542View Description Hide Description
The light scalar mesons are being investigated at COSY‐Jülich by detecting the strong decays into and as well as radiative decays into vector mesons. Selected results are discussed with emphasis on recent measurements at the ANKE and WASA spectrometers.
1030(2008); http://dx.doi.org/10.1063/1.2973552View Description Hide Description
The first part of this report reviews recent developments at the interface between lattice work on QCD with light dynamical quarks, effective field theory and low energy precision experiments. Then I discuss how dispersion theory can be used to analyze the low energy structure of the scattering amplitude in a model independent manner. This leads to an exact formula for the mass and width of the lowest few resonances, in terms of observable quantities. As an application, I consider the pole position of the σ, paying particular to error propagation in the numerical analysis. The report is based on work done in collaboration with Irinel Caprini and Gilberto Colangelo .
1030(2008); http://dx.doi.org/10.1063/1.2973554View Description Hide Description
Interpretation of D‐meson decay‐dynamics has revealed itself to be strongly dependent on our understanding of the light‐meson sector. The interplay becomes particularly evident in Dalitz plot analyses to study physics within and beyond the Standard Model. Experience and results from FOCUS are presented and discussed. A brief update of the pentaquark search in the experiment is also reported.
1030(2008); http://dx.doi.org/10.1063/1.2973556View Description Hide Description
The scalar mesons of mass below 1 GeV have been studied with the KLOE detector at the Frascati φ‐factory DAΦNE, through the radiative decays of the The has been studied in the decays and looking also for a possible signal of the while for the the decay has been exploited. The branching ratios of these decays have been measured, and the relevant parameters of the scalar mesons have been extracted from the fit of the invariant mass distributions of the pseudoscalar mesons in the final states. Moreover an upper limit for the branching ratio of has been obtained.
1030(2008); http://dx.doi.org/10.1063/1.2973557View Description Hide Description
Old and new ideas regarding Higgs physics are reviewed. We first summarize the quadratic divergence/hierarchy problem which strongly suggests that the SM Higgs sector will be supplemented by new physics at high scales. We next consider means for delaying the hierarchy problem of the SM Higgs sector to unexpectedly high scales. We then outline the properties of the most ideal Higgs boson. The main advantages of a supersymmetric solution to the high scale problems are summarized and the reasons for preferring the next‐to‐minimal supersymmetric model over the minimal supersymmetric model in order to achieve an ideal Higgs are emphasized. This leads us to the strongly motivated scenario in which there is a Higgs h with SM‐like couplings and that decays via with where is preferred, implying The means for detecting an signal are then discussed.
1030(2008); http://dx.doi.org/10.1063/1.2973484View Description Hide Description
We discuss a possible interpretation of the and mesons as hadronic molecules—a bound state of K and mesons. Using a phenomenological Lagrangian approach we calculate the strong and as well as the electromagnetic and decays. The covariant and gauge invariant model, which also allows for finite size effects of the hadronic molecule, delivers results in good agreement with available data and results of other theoretical approaches.
1030(2008); http://dx.doi.org/10.1063/1.2973485View Description Hide Description
A consistent description of the invariant mass distribution in the decay and the in is suggested. A search for the consequences of the flavor symmetry for the scalar mesons can be based on such an analysis. In order to accurately treat the pseudoscalar meson dynamics, which is very important for the scalar meson decays, we employ Resonance Chiral Theory.
1030(2008); http://dx.doi.org/10.1063/1.2973486View Description Hide Description
It is shown that the scalar mesons σ, and as t‐channel exchanges quantitatively solve the problem of diamagnetism and give an explanation of the large missing part of the electric polarizability α showing up when only the pion cloud is taken into account. The electric polarizability of the proton confirms a two‐photon width of the σ meson of
1030(2008); http://dx.doi.org/10.1063/1.2973487View Description Hide Description
Alpha‐alpha scattering is discussed in terms of a chiral two pion exchange potential (TPE) which turns out to be attractive and singular at the origin, hence demanding renormalization. When is treated as a resonance state a model independent correlation between the Q‐factor and lifetime for the decay into two alpha particles arises. For a wide range of parameters compatible with potential model analyses of low energy scattering it is found in fairly good agreement with the experimental value The remaining discrepancy as well as the phase shift up to could be accommodated by the leading nuclear peripheral contributions due to the and continuum.
Screening in the bremsstrahlung reactions and determination of the magnetic moment of the Δ resonance1030(2008); http://dx.doi.org/10.1063/1.2973489View Description Hide Description
The new form of current conservation is used for the analytical determination of the dipole magnetic moments of the Δ resonances in the pion‐nucleon bremsstrahlung reaction . This current conservation condition presents a modified Ward‐Takahashi identity for the on shell bremsstrahlung amplitude. According to this identity the internal and external particle radiation parts of the bremsstrahlung amplitude have an opposite sign i.e. they contain terms which cancel each other. Therefore a screening of the internal and external particle radiation in the bremsstrahlung is generated. In particular it is shown, that the internal double A exchange diagram with the vertex cancel with the appropriate longitudinal part of the external particle radiation diagrams. This enables to obtain a model independent estimation of the dipole magnetic moment of and resonances through the anomalous magnetic moment of the proton as and in agreement with the values obtained from the fit of the experimental cross section of the reaction.
Considering pions and nucleons as bound (cluster) states of quarks in the usual quantum field theory [5,6,7,8] a generalization of the suggested approach is suggested . The resulting equations for the external and internal particle radiation amplitudes of the bremsstrahlung reaction have the same form as in formulation without quark degrees of freedom . Therefore the model independent estimation of the dipole magnetic moment of and resonances and in the usual local quantum field theory is preserved in the general quantum field formulation with the quark degrees of freedom.
1030(2008); http://dx.doi.org/10.1063/1.2973490View Description Hide Description
We report on a dispersion relation for the S‐wave in isospin I emphasizing the low energy region. The signal that emerges in is also discussed. Our results could be used to distinguish between different isoscalar S‐wave parameterizations. We also calculate the width of the σ resonance to and obtain the value Finally, we elaborate on the size of the coupling to and show that its smallness compared to the one is not related to the OZI rule.