A0 Resonances Research Articles

Two-photon production of f0 and a0 resonances as hadronic molecules composed of two vector mesons

Ascribed as ρρ and K*K¯* molecular states, respectively, isoscalar f0(1500) and f0(1710) states are expected to have isovector partners, potentially identified as a0(1450) and a0(1710). The predicted dominant decay modes for these two a0 resonances are a0(1450)→ωππ and a0(1710)→ωππ,ϕππ. We estimate cross sections for two-photon production of these four resonances within hadronic molecular picture, and demonstrate that SuperKEKB’s luminosity is sufficient for their observation and more precise parameter measurements. Published by the American Physical Society 2024

K[formula omitted]K[formula omitted] and K[formula omitted]K± femtoscopy in pp collisions at [formula omitted] and 13 TeV

Femtoscopic correlations with the particle pair combinations KS0KS0 and KS0K± are studied in pp collisions at s=5.02 and 13 TeV by the ALICE experiment. At both energies, boson source parameters are extracted for both pair combinations, by fitting models based on Gaussian size distributions of the sources, to the measured two-particle correlation functions. The interaction model used for the KS0KS0 analysis includes quantum statistics and strong final-state interactions through the f0(980) and a0(980) resonances. The model used for the KS0K± analysis includes only the final-state interaction through the a0 resonance. Source parameters extracted in the present work are compared with published values from pp collisions at s=7 TeV and the different pair combinations are found to be consistent. From the observation that the strength of the KS0KS0 correlations is significantly greater than the strength of the KS0K± correlations, the new results are compatible with the a0 resonance being a tetraquark state of the form (q1,q2‾,s,s‾), where q1 and q2 are u or d quarks.

The a0(980) and f0(980) in the process [formula omitted

In this work, we have investigated the process Ds+→K+K−π+, taking into account the contributions from the S-wave pseudoscalar-pseudoscalar interaction within the chiral unitary approach, and also the intermediate ϕ resonance. By analyzing the BESIII and BABAR measurements, we conclude that the f0(980) state, dynamically generated from the S-wave pseudoscalar-pseudoscalar interaction, gives the dominant contribution close to the K+K− threshold in the K+K− invariant mass distribution of the decay Ds+→K+K−π+ in S-wave. On the other hand, our results imply that the lineshape adopted by BESIII and BABAR for the resonances a0(980) and f0(980) is not advisable in the fit to the data close to the K+K− threshold.

NEW PARAMETERIZATION OF THE RESONANT PRODUCTION AMPLITUDES NEAR AN INELASTIC THRESHOLD

New formulae for the resonant scattering and the production amplitudes near an inelastic threshold are derived. It is shown that the Flatté formula, frequently used in experimental analyses, is not sufficiently accurate. Its application to data analysis can lead to a substantial distortion of the effective mass spectra and of the resonance pole positions. A unitary parameterization, satisfying a generalized Watson theorem for the production amplitudes, is proposed. It can be easily applied to study production processes, multichannel meson-meson interactions and the resonance properties, including among others the scalar resonances a0(980) and f0(980).

IS THE a0(980) RESONANCE A $K\overline{K}$ BOUND STATE?

We have analysed properties of two resonances a0(980) and a0(1450) using the πη and [Formula: see text] coupled channel model. Although the forces in the scalar-isovector [Formula: see text] channel are attractive the a0(980) resonance cannot be interpreted as a kaon-antikaon bound state within our model.

Properties of the a0 resonances

We present results following from the coupled channel model of two ao resonances decaying into the πη and K K mesons. The a 0(980) resonance can be described by two distinct poles. It is shown that the discrepancy in the a 0(980) mass position between the Crystal Barrel Collaboration and the E852 Group can be explained and removed. In our model with parameters fixed by the present experimental data the a 0(980) cannot be interpreted as a bound K K state although the K K forces in the S-wave isovector channel are attractive.

Coupled channel study of a0 resonances

The coupled channel model of the a 0(980) and a 0(1450) resonances has been constructed using the separable πη and K K interactions. We have shown that two S-matrix poles corresponding to the a 0(980) meson have significantly different widths in the complex energy plane. The K K to πη branching ratio, predicted in our model near the a 0(1450) mass, is in agreement with the result of the Crystal Barrel Collaboration. The K K interaction in the S-wave isovector state is not sufficiently attractive to create a bound a 0(980) meson.

K-matrix analysis of the Kπ S-wave in the mass region 900–2100 MeV and nonet classification of scalar qq̄-states

Abstract A K-matrix re-analysis of the Kπ S-wave is performed in the mass region 900 – 2100 MeV, and solutions which describe the data well are found. The solution with two resonances in the IJ P = 1 2 0 + -wave has poles at (1415 ± 25) − i(165 ± 25) MeV, and (1820 ± 40) − i(125 ± 50) MeV, close to the previous result of D. Aston et al., Nucl. Phys. B 296 (1988) 493. The corresponding bare states, which are the subjects of a q q classification, are: K0bare(1220−60+50) and K0bare(1885−80+50). Within the restored bare states, a construction of the 1 3 P 0 q q nonets is completed. The three resonance solutions are analysed as well, the corresponding bare states are found, and the qq-nonet classification is suggested. In all variants of our qq-classification, the resonances a0(980) and f0(980) (or their bare counterparts) are non-exotic, and an extra scalar/isoscalar state exists in the mass region 1300–1700 MeV, being a good candidate for the lightest scalar glueball.

INADEQUACY OF NARROW RESONANCE APPROXIMATION IN THE ϕ→γa0 AND ϕ→γf0 DECAYS

It is shown that the approximation of the narrow widths of the f0 and a0 resonances, which is used in both theoretical and experimental investigations of the radiative decays ϕ→γa0 and ϕ→γf0, is not valid. We will explain that there is a need to take into account the corrections for finite widths.

Acoustic scattering from free field and buried spherical shells

A measurement was conducted to investigate the effect of sediment loading on the characteristic elastic response of an object. Backscattered form functions were obtained for free field and buried 2% and 11% spherical shells. The results have shown that the free‐field form function for the 2% shell is dominated by the nondispersive s0 mode while the 11% shell is dominated by the antisymmetric Lamb mode a0. Upon sediment loading, the a0 resonances shifted to higher frequencies. The results of this experiment are in good agreement with theoretical calculations.