Light antiprotonic atoms

Gotta, D.

doi:10.1063/1.2121980

Cited by 13 publications

(14 citation statements)

References 17 publications

(34 reference statements)

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“…Note that the sign of β is observable, not just its magnitude, and agrees with what is expected. The best experimental value of a(π − p → π 0 n) = −(0.122 ± 0.002)/m π + , obtained from the observed width in the 1s state of pionic hydrogen [31], was used. This is in excellent agreement with HBCHPT predictions of −(0.130 ± 0.006)/m π + [32].…”

Section: A Multipole Extraction From the Experimental Datamentioning

confidence: 99%

Unexpected impact ofDwaves in low-energy neutral pion photoproduction from the proton and the extraction of multipoles

2009

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Contributions of D waves to physical observables for neutral pion photoproduction from the proton in the near-threshold region are studied and means to isolate them are proposed. Various approaches to describe the multipoles are employed-a phenomenological one, a unitary one, and heavy baryon chiral perturbation theory. The results of these approaches are compared and found to yield essentially the same answers. D waves are seen to enter together with S waves in a way that any means which attempt to obtain the E 0+ multipole accurately must rely on knowledge of D waves and that consequently the latter cannot be dismissed in analyses of low-energy pion photoproduction. It is shown that D waves have a significant impact on double-polarization observables that can be measured. This importance of D waves is due to the soft nature of the S wave and is a direct consequence of chiral symmetry and the Nambu-Goldstone nature of the pion. F -wave contributions are shown to be negligible in the near-threshold region.

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Section: A Multipole Extraction From the Experimental Datamentioning

confidence: 99%

Unexpected impact ofDwaves in low-energy neutral pion photoproduction from the proton and the extraction of multipoles

2009

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“…Lattice calculations have confirmed the low energy constants used in ChPT [31][Lellouch], validating that they closely approximate QCD. For the πN s wave scattering lengths there also has been excellent experimental [20] and theoretical [21] progress. There is good agreement between the results Amount of experimental data The polarized photon asymmetry Σ at 90 • versus photon energy for the γ p → π 0 p reaction [25].…”

Section: Discussionmentioning

confidence: 99%

“…We have reached a new era in the prediction and experimental determination of the π 0 lifetime [8,9,10], although more needs to be done to bring the experiments up to the level of accuracy of the ChPT calculation. Progress has also been impressive in the γπN sector, both in experiment [20] and in ChPT calculations [21][Meissner] which take isospin breaking into account. Some ChPT calculations have started to include dispersion relations to take account of the neglected higher order terms [42,43] as has been done in ππ scattering [17].…”

Section: Discussionmentioning

confidence: 99%

“…There has also been a very impressive experimental effort at PSI to measure the level shifts and widths of pionic hydrogen and deuterium [20], as well as a parallel theoretical effort [21][Meissner]. The experimental accuracy has improved to the point where the isospin breaking effects due to the mass difference of the up and down quarks [7], first pointed out by Weinberg [23], had to be taken into account [21][Meissner]; these were required to bring the π-N scattering lengths extracted from the pionic-hydrogen and deuterium results into agreement with each other.…”

Section: ππ and πN Scatteringmentioning

confidence: 99%

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Outlook

Bernstein¹

2013

Proceedings of the 7th International Workshop on Chiral Dynamics — PoS(CD12)

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Based on the spontaneous breaking of chiral symmetry, chiral perturbation theory (ChPT) is believed to approximate confinement scale QCD. Dedicated and increasingly accurate experiments and improving lattice calculations are confirming this belief, and we are entering a new era in which we can test confinement scale QCD in some well chosen reactions. This is demonstrated with an overview of low energy experimental tests of ChPT predictions of ππ scattering, pion properties, πN scattering and electromagnetic pion production. These predictions have been shown to be consistent with QCD in the meson sector by increasingly accurate lattice calculations. At present there is good agreement between experiment and ChPT calculations, including the ππ and πN s wave scattering lengths and the π 0 lifetime. Recent, accurate pionic atom data are in agreement with chiral calculations once isospin breaking effects due to the mass difference of the up and down quarks are taken into account, as was required to extract the ππ scattering lengths. In addition to tests of the theory, comparisons between ππ and πN interactions based on general chiral principles are discussed. Lattice calculations are now providing results for the fundamental, long and inconclusively studied, πN σ term and the contribution of the strange quark to the mass of the proton. Increasingly accurate experiments in electromagnetic pion production experiments from the proton which test ChPT calculations (and their energy region of validity) are presented. These experiments are also beginning to measure the final state πN interaction.

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“…[2]. Interest was rekindled due to the precision measurements of pionic hydrogen and deuterium at PSI [3]. In the framework of covariant baryon CHPT, [4] the elastic π − p amplitude was calculated at threshold to third (leading one-loop) order in the chiral expansion.…”

Section: Isospin-breaking In the Pionnucleon Scattering Lengthsmentioning

confidence: 99%