Chiral unitary approach to meson meson and meson - baryon interactions and nuclear applications

By using the non-relativistic effective Lagrangian approach to bound states, a complete expression for the isospin-breaking corrections to the energy levels and the decay widths of kaonic hydrogen is obtained up-to-and-including $O(\alpha,m_d-m_u)$ in QCD. It is demonstrated that, although the leading-order corrections at $O(\alpha^{1/2},(m_d-m_u)^{1/2})$ emerging due to the unitarity cusp are huge, they can be expressed solely in terms of the KN S-wave scattering lengths. Consequently, at leading order, it is possible to derive parameter-free modified Deser-type relations, which can be used to extract the scattering lengths from the hadronic atom data.

Spectrum and decays of kaonic hydrogen

Energy levels of light nuclei A = 12

A formalism, based on an isobaric approach using Feynman diagrammatic techniques, which includes the nucleonic (spin \ensuremath{\le} 5/2), hyperonic (spin 1/2), and kaonic resonances, is developed Using this formalism, a thorough investigation of the following electromagnetic strangeness processes, for which experimental results are available, is performed: \ensuremath{\gamma}p\ensuremath{\rightarrow}${\mathit{K}}^{+}$\ensuremath{\Lambda}, ${\mathit{K}}^{+}$${\mathrm{\ensuremath{\Sigma}}}^{0}$, ${\mathit{K}}^{0}$${\mathrm{\ensuremath{\Sigma}}}^{+}$, for ${\mathit{E}}_{\ensuremath{\gamma}}^{\mathrm{lab}}$\ensuremath{\le} 21 GeV, ep\ensuremath{\rightarrow}${\mathit{e}}^{\ensuremath{'}}$${\mathit{K}}^{+}$\ensuremath{\Lambda}, ${\mathit{e}}^{\ensuremath{'}}$${\mathit{K}}^{+}$${\mathrm{\ensuremath{\Sigma}}}^{0}$, and ${\mathit{K}}^{\mathrm{\ensuremath{-}}}$p\ensuremath{\rightarrow}\ensuremath{\gamma}\ensuremath{\Lambda},\ensuremath{\gamma}${\mathrm{\ensuremath{\Sigma}}}^{0}$ A reaction mechanism, describing well enough the data, is found to include a reasonable number of baryonic resonances among a very large number of potential candidates The extracted main kaon-hyperon-nucleon coupling constants are in good agreement with values predicted using SU(3) symmetry The main findings of this model are compared with the results of other recent phenomenological studies Predictions for the upcoming photoproduction polarization and electroproduction observables are presented, and their sensitivity to the phenomenological models ingredients are emphasized \textcopyright{} 1996 The American Physical Society

Electromagnetic production of associated strangeness.

https://escholarship.org/content/qt8r4529qb/qt8r4529qb.pdf

Exploring hyperons and hypernuclei with lattice QCD

The photon spectrum from ${K}^{\mathrm{\ensuremath{-}}}$ stopping in liquid hydrogen has been measured with a high-resolution (1.5% FWHM at 300 MeV) NaI(Tl) detector. The branching ratios for ${K}^{\mathrm{\ensuremath{-}}}$p\ensuremath{\rightarrow}\ensuremath{\Lambda}\ensuremath{\gamma} (${E}_{\ensuremath{\gamma}}$=281.4 MeV) and ${K}^{\mathrm{\ensuremath{-}}}$p\ensuremath{\rightarrow}${\ensuremath{\Sigma}}^{0}$\ensuremath{\gamma} (${E}_{\ensuremath{\gamma}}$=219.5 MEV) were obtained. The results are ${\mathit{R}}_{\mathrm{\ensuremath{\Lambda}}\ensuremath{\gamma}}$=(0.86\ifmmode\pm\else\textpm\fi{}0.${07}_{\mathrm{\ensuremath{-}}0.08}^{+0.1}$)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}3}$ and ${\mathit{R}}_{\mathrm{\ensuremath{\Sigma}}0\ensuremath{\gamma}}$=(1.44\ifmmode\pm\else\textpm\fi{}0.${20}_{\mathrm{\ensuremath{-}}0.10}^{\ifmmode\pm\else\textpm\fi{}0.12}$)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}3}$ where the first error is statistical and the second systematic. These results are not in good agreement with published predictions or with previous \ensuremath{\Lambda}\ensuremath{\gamma} measurements.

Radiative kaon capture at rest in hydrogen

We report the measurement of the differential scattering cross section for coherent photon scattering (nuclear Compton scattering) from /sup 4/He at an average energy of 180 MeV. This represents the first direct observation of the coherent process on a complex nucleus above the pion threshold. The results are compared with the predicton of a claculation utilizing the isobar-hole formalism.

Differential cross section for coherent photon scattering from 4He at 180 MeV.

We have measured the differential cross sections for coherent Compton photon scattering in the reaction /sup 4/He(..gamma..,..gamma..) /sup 4/He at laboratory angles of 24/sup 0/, 30/sup 0/, 45/sup 0/, and 60/sup 0/ with an average laboratory photon energy of 320 MeV, at 22/sup 0/ with 358 MeV, and at 30/sup 0/ with 260 MeV. These measurements are the first unambiguous test of the ..delta..-hole formalism for this reaction near the peak of the cross section for the ..delta.. resonance. The results are compared to theoretical calculations in the isobar-hole model. Agreement is good for data at the energy corresponding to the ..delta.. peak.

Cross sections for the reaction 4He( gamma, gamma ) 4He in the Delta (1232)-resonance region.

We have designed and tested a new high resolution NaI(Tl) total absorption scintillation counter. The detector is a cylinder composed of a 26.7 cm diameter by 55.9 cm long NaI core with a concentric 10.8 cm thick NaI annulus that is divided into quadrants. The NaI detector is surrounded by a 12.7 cm thick plastic scintillator to veto both cosmic rays and events with significant shower leakage from the NaI. High uniformity of light production and collection throughout the detector is required for superior resolution. The detector has a measured resolution of 1.3% and 1.7% FWHM for 130 MeV photons and 330 MeV electrons, respectively. Computer simulations to account for loss of resolution due to pileup and energy spread of the beam indicate that the ultimate experimental resolutions at these energies are 1.2±0.1% and 1.3±0.1%. The resolutions at these two energies are at least a factor of 2 better than that of any other total absorption scintillation counter available today. Based on shower simulations, the detector is expected to have a resolution of approximately 1.3% for collimated 130–2000 MeV photons.

Development of a NaI(Tl) detector with superior photon energy resolution for use above 100 MeV

The branching ratio for the \ensuremath{\Lambda} weak radiative decay has been measured to be B(\ensuremath{\Lambda}\ensuremath{\rightarrow}n+\ensuremath{\gamma})/(\ensuremath{\Lambda}\ensuremath{\rightarrow}anything) =[1.78\ifmmode\pm\else\textpm\fi{}0.24(stat)${\ifmmode\pm\else\textpm\fi{}}_{0.16}^{0.14}$(syst)]\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}3}$. A low-energy kaon beam was used to produce the \ensuremath{\Lambda} hyperons via the reaction ${\mathit{K}}^{\mathrm{\ensuremath{-}}}$+p\ensuremath{\rightarrow}\ensuremath{\Lambda}+${\mathrm{\ensuremath{\pi}}}^{0}$ at rest. Photons from the signal channel and ${\mathrm{\ensuremath{\pi}}}^{0}$ decay were detected with a NaI(Tl) array. The final spectrum contains 287 events after background subtraction, an order of magnitude more events than from the only previous measurement.

E. K. McIntyre

Papers

Radiative kaon capture at rest in hydrogen

Differential cross section for coherent photon scattering from 4He at 180 MeV.

Cross sections for the reaction 4He( gamma, gamma ) 4He in the Delta (1232)-resonance region.

Development of a NaI(Tl) detector with superior photon energy resolution for use above 100 MeV

Measurement of the Λ→ n +γ branching ratio