Scalar radius of the pion and γγ → ππ
We make an improvement of the dispersion relation calculation of the quadratic scalar radius of the pion, 〈r2〉s pπ, and the reaction γγ → π0 π0. We solve a previous discrepancy between the the solution of the Muskhelishvili-Omnès equations for the non-strange null isospin (I) pion scalar form factor...
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| Acceso en línea: | http://hdl.handle.net/20.500.12110/paper_18248039_v_n_p_Roca |
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todo:paper_18248039_v_n_p_Roca2023-10-03T16:33:10Z Scalar radius of the pion and γγ → ππ Roca, L. Oller, J.A. Schat, C. Dispersion relations Form factors Isospin Lower energies Approximation theory Dispersions Shear waves Stress intensity factors Hadrons We make an improvement of the dispersion relation calculation of the quadratic scalar radius of the pion, 〈r2〉s pπ, and the reaction γγ → π0 π0. We solve a previous discrepancy between the the solution of the Muskhelishvili-Omnès equations for the non-strange null isospin (I) pion scalar form factor and the Indurain's calculation using an Omnès representation of this form factor. We show that Ynduráin's method is indeed compatible with the determinations from the Muskhelishvili-Omnès equations once a possible zero in the scalar form factor is considered. Once this is accounted for, the resulting value is 〈r2〉 s pπ = 0.63 ±0.05 fm2. Regarding the reaction γγ → π0 π0 we emphasize how the f0(980) signal emerges in γγ → ππ within the dispersive approach and how this fixes to a large extent the phase of the isoscalar S-wave γγ → ππ amplitude above the KK̄ threshold. This allows us to make sharper predictions for the cross section at lower energies and our results could then be used to distinguish between different ππ isoscalar S-wave parameterizations with the advent of new precise data on γγ → π0π0. We also pay special attention to the role played by the σ resonance in γγ → ππ and calculate its coupling and width to γγ, for which we obtain Λ(σ → γγ) = ( 1.68 ± 0.15) KeV. © Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence. CONF info:eu-repo/semantics/openAccess http://creativecommons.org/licenses/by/2.5/ar http://hdl.handle.net/20.500.12110/paper_18248039_v_n_p_Roca |
| institution |
Universidad de Buenos Aires |
| institution_str |
I-28 |
| repository_str |
R-134 |
| collection |
Biblioteca Digital - Facultad de Ciencias Exactas y Naturales (UBA) |
| topic |
Dispersion relations Form factors Isospin Lower energies Approximation theory Dispersions Shear waves Stress intensity factors Hadrons |
| spellingShingle |
Dispersion relations Form factors Isospin Lower energies Approximation theory Dispersions Shear waves Stress intensity factors Hadrons Roca, L. Oller, J.A. Schat, C. Scalar radius of the pion and γγ → ππ |
| topic_facet |
Dispersion relations Form factors Isospin Lower energies Approximation theory Dispersions Shear waves Stress intensity factors Hadrons |
| description |
We make an improvement of the dispersion relation calculation of the quadratic scalar radius of the pion, 〈r2〉s pπ, and the reaction γγ → π0 π0. We solve a previous discrepancy between the the solution of the Muskhelishvili-Omnès equations for the non-strange null isospin (I) pion scalar form factor and the Indurain's calculation using an Omnès representation of this form factor. We show that Ynduráin's method is indeed compatible with the determinations from the Muskhelishvili-Omnès equations once a possible zero in the scalar form factor is considered. Once this is accounted for, the resulting value is 〈r2〉 s pπ = 0.63 ±0.05 fm2. Regarding the reaction γγ → π0 π0 we emphasize how the f0(980) signal emerges in γγ → ππ within the dispersive approach and how this fixes to a large extent the phase of the isoscalar S-wave γγ → ππ amplitude above the KK̄ threshold. This allows us to make sharper predictions for the cross section at lower energies and our results could then be used to distinguish between different ππ isoscalar S-wave parameterizations with the advent of new precise data on γγ → π0π0. We also pay special attention to the role played by the σ resonance in γγ → ππ and calculate its coupling and width to γγ, for which we obtain Λ(σ → γγ) = ( 1.68 ± 0.15) KeV. © Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence. |
| format |
CONF |
| author |
Roca, L. Oller, J.A. Schat, C. |
| author_facet |
Roca, L. Oller, J.A. Schat, C. |
| author_sort |
Roca, L. |
| title |
Scalar radius of the pion and γγ → ππ |
| title_short |
Scalar radius of the pion and γγ → ππ |
| title_full |
Scalar radius of the pion and γγ → ππ |
| title_fullStr |
Scalar radius of the pion and γγ → ππ |
| title_full_unstemmed |
Scalar radius of the pion and γγ → ππ |
| title_sort |
scalar radius of the pion and γγ → ππ |
| url |
http://hdl.handle.net/20.500.12110/paper_18248039_v_n_p_Roca |
| work_keys_str_mv |
AT rocal scalarradiusofthepionandngpp AT ollerja scalarradiusofthepionandngpp AT schatc scalarradiusofthepionandngpp |
| _version_ |
1807319810483159040 |