Publications (3)0 Total impact
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ABSTRACT: We assess the energy limit up to which Heavy Baryon Chiral Perturbation
Theory can be accurately applied to the process of neutral pion photoproduction
from the proton by analyzing the latest data from the A2 and CB-TAPS
collaborations at Mainz. We find that, within the current experimental status,
the theory works up to $\sim$170 MeV. Above this energy the data call for
further improvement in the theory such as the explicit inclusion of the
$\Delta$(1232). We also find that data and multipoles can be well described up
to $\sim$185 MeV with Taylor expansions in the partial waves up to first order
in pion energy.
12/2012;
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C. Fernandez-Ramirez
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ABSTRACT: It has been commonly assumed that low-energy neutral pion photoproduction from the proton can be described accounting only for S and P waves, and that higher partial waves are irrelevant. We have found that this assumption is not correct and that the inclusion of D waves is necessary to obtain a reliable extraction of the $E_{0+}$ multipole from experimental data. This is due in large measure to the spontaneous breaking of chiral symmetry in QCD which leads to very small S-wave contributions. This makes the usual partial wave expansion less accurate and although D waves are small, their contribution is enhanced through the interference with P waves, which compromises the S-wave extraction from data if D waves are not taken into account. In our work we have used Heavy Baryon Chiral Perturbation Theory to one loop, and up to ${\cal O}(q^4)$, to account for the S and P waves, while D waves are added in an almost model-independent way using standard Born terms and vector mesons. We also show that higher partial waves do not play an important role. Comment: Talk presented in the 6th International Workshop on Chiral Dynamics, July 6-10 2009, Bern, Switzerland. To be published in Proceedings of Science. Uses class Pos.cls (included). 6 pages and 3 figures
12/2009;
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ABSTRACT: The contribution of D waves to physical observables for neutral pion photoproduction in the near threshold region is studied. Heavy Baryon Chiral Perturbation Theory to one loop, and up to ${\cal O}(q^4)$, is used to account for the S and P waves, while D waves are added in an almost model-independent way using standard Born terms and vector mesons. It is found that the inclusion of D waves is necessary to extract the $E_{0+}$ multipole reliably from present and forthcoming data and to assess the low-energy constants of Chiral Perturbation Theory. Arguments are presented demonstrating that F-wave contributions are negligible in the near-threshold region. Comment: 10 pages, 5 figures
02/2009;
