arXiv subjects

Amir H. Fariborz

Publications and source records attributed to Amir H. Fariborz.

59 records · Page 4Linked to original sources

arXiv1999

Chiral Lagrangian treatment of pi eta scattering

We study pi eta scattering in a model which starts from the tree diagrams of a non-linear chiral Lagrangian including appropriate resonances. Previously, models of this type were applied to pi pi and pi K scattering and were seen to require the existence of light scalar sigma(560) and kappa(900) mesons and to be consistent with the f0(980). The present calculation extends this to include the a0(980), thereby completing a possible nonet of light scalars, all ``seen'' in the same manner. We note that, at the initial level, the pi eta channel is considerably cleaner than the pi pi and pi K channels for the study of light scalars. This is because the large competing effects of vector meson exchange and ``current-algebra'' contact terms are absent. The simplicity of this channel enables us to demonstrate the closeness of our exactly crossing symmetric amplitude to a related exactly unitary amplitude. The calculation is also extended to higher energies in order to let us discuss the role played by the a0(1450) resonance.

hep-ph↗

arXiv1999

Lowest-Lying Scalar Mesons and a Possible Probe of Their Quark Substructure

In this talk, an overview of the status of the light scalar mesons in the context of the non linear chiral Lagrangian of references [1-3] is presented. The evidence for the existence of a scalar nonet below 1 GeV is reviewed, and it is shown that by introducing a scalar nonet an indirect way of probing the quark substructure of these scalars through the scalar mixing angle can be obtained. It is then reviewed that consistency of this non-linear chiral Lagrangian framework with the experimental data on pi pi and pi K scattering, as well as the decay eta' to eta pi pi, results in a range for the mixing angle which indicates that the quark substructure of these light scalars are closer to a four quark picture.

hep-ph↗

arXiv1999

Mechanism for a next-to-lowest lying scalar meson nonet

Recent work suggests the existence of a non-conventional lowest-lying scalar nonet containing the a0(980). Then the a0(1450) and also the K0*(1430) are likely candidates to belong to a conventional p-wave $q \bar q$ nonet. However a comparison of their properties with those expected on this basis reveals a number of puzzling features. It is pointed out that these puzzles can be resolved in a natural and robust way by assuming a ``bare'' conventional p-wave scalar $q \bar q$ nonet to mix with a lighter four quark $qq \bar q \bar q$ scalar nonet to form new ``physical'' states. The essential mechanism is driven by the fact that the isospinor is lighter than the isovector in the unmixed $qq \bar q \bar q$ multiplet.

hep-ph↗

arXiv1999

eta' to eta pi pi Decay as a Probe of a Possible Lowest-Lying Scalar Nonet

We study the eta' to eta pi pi decay within an effective chiral Lagrangian approach in which the lowest lying scalar meson candidates sigma(560) and kappa(900) together with the f0(980) and a0(980) are combined into a possible nonet. We show that there exists a unique choice of the free parameters of this model which, in addition to fitting the pi pi and pi K scattering amplitudes, well describes the experimental measurements for the partial decay width of eta' to eta pi pi and the energy dependence of this decay. As a by-product, we estimate the a0(980) width to be 70 MeV, in agreement with a new experimental analysis.

hep-ph↗

arXiv1998

Putative Light Scalar Nonet

We investigate the "family" relationship of a possible scalar nonet composed of the a_0(980), the f_0(980) and the σand κtype states found in recent treatments of ππand πK scattering. We work in the effective Lagrangian framework, starting from terms which yield "ideal mixing" according to Okubo's original formulation. It is noted that there is another solution corresponding to dual ideal mixing which agrees with Jaffe's picture of scalars as qq\bar q \bar q states rather than as q\bar q states. At the Lagrangian level there is no difference in the formulation of the two cases (other than the numerical values of the coefficients). In order to agree with experiment, additional mass and coupling terms which break ideal mixing are included. The resulting model turns out to be closer to dual ideal mixing than to conventional ideal mixing; the scalar mixing angle is roughly -17 degrees in a convention where dual ideal mixing is 0 degrees.

hep-ph↗