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Pion

About: Pion is a research topic. Over the lifetime, 23215 publications have been published within this topic receiving 375419 citations. The topic is also known as: pi meson & pi-meson.


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Journal ArticleDOI
TL;DR: In this article, the low energy representation of several Green's functions and form factors and of the na scattering amplitude are calculated in terms of a few constants, which may be identified with the coupling constants of a unique effective low energy Lagrangian.

3,277 citations

Journal ArticleDOI
TL;DR: In this article, the divergence of the axial vector current in β-decay may be proportional to the pion field, and three models of pion-nucleon interaction are presented that have the required property.
Abstract: In order to derive in a convincing manner the formula of Goldberger and Treiman for the rate of charged pion decay, we consider the possibility that the divergence of the axial vector current in β-decay may be proportional to the pion field. Three models of the pion-nucleon interaction (and the weak current) are presented that have the required property. The first, using gradient coupling, has the advantage that it is easily generalized to strange particles, but the disadvantages of being unrenormalizable and of bringing in the vector and axial vector currents in an unsymmetrical way. The second model, using a strong interaction proposed bySchwinger and a weak current proposed byPolkinghorne, is renormalizable and symmetrical betweenV andA, but it involves postulating a new particle and is hard to extend to strange particles. The third model resembles the second one except that it is not necessary to introduce a new particle. (Renormalizability in the usual sense is then lost, however). Further research along these lines is suggested, including consideration of the possibility that the pion decay rate may be plausibly obtained under less stringent conditions.

1,791 citations

Journal ArticleDOI
TL;DR: In this article, it is suggested that the group is in fact U(3)×U(3), exemplified by the symmetrical Sakata model, and the symmetrized Sakata models are used to define the structure of baryons and mesons.
Abstract: The system of strongly interacting particles is discussed, with electromagnetism, weak interactions, and gravitation considered as perturbations. The electric current jα, the weak current Jα, and the gravitational tensor θαβ are all well-defined operators, with finite matrix elements obeying dispersion relations. To the extent that the dispersion relations for matrix elements of these operators between the vacuum and other states are highly convergent and dominated by contributions from intermediate one-meson states, we have relations like the Goldberger-Treiman formula and universality principles like that of Sakurai according to which the ρ meson is coupled approximately to the isotopic spin. Homogeneous linear dispersion relations, even without subtractions, do not suffice to fix the scale of these matrix elements; in particular, for the nonconserved currents, the renormalization factors cannot be calculated, and the universality of strength of the weak interactions is undefined. More information than just the dispersion relations must be supplied, for example, by field-theoretic models; we consider, in fact, the equal-time commutation relations of the various parts of j4 and J4. These nonlinear relations define an algebraic system (or a group) that underlies the structure of baryons and mesons. It is suggested that the group is in fact U(3)×U(3), exemplified by the symmetrical Sakata model. The Hamiltonian density θ44 is not completely invariant under the group; the noninvariant part transforms according to a particular representation of the group; it is possible that this information also is given correctly by the symmetrical Sakata model. Various exact relations among form factors follow from the algebraic structure. In addition, it may be worthwhile to consider the approximate situation in which the strangeness-changing vector currents are conserved and the Hamiltonian is invariant under U(3); we refer to this limiting case as "unitary symmetry." In the limit, the baryons and mesons form degenerate supermultiplets, which break up into isotopic multiplets when the symmetry-breaking term in the Hamiltonian is "turned on." The mesons are expected to form unitary singlets and octets; each octet breaks up into a triplet, a singlet, and a pair of strange doublets. The known pseudoscalar and vector mesons fit this pattern if there exists also an isotopic singlet pseudoscalar meson χ0. If we consider unitary symmetry in the abstract rather than in connection with a field theory, then we find, as an attractive alternative to the Sakata model, the scheme of Ne'eman and Gell-Mann, which we call the "eightfold way"; the baryons N, Λ, Σ, and Ξ form an octet, like the vector and pseudoscalar meson octets, in the limit of unitary symmetry. Although the violations of unitary symmetry must be quite large, there is some hope of relating certain violations to others. As an example of the methods advocated, we present a rough calculation of the rate of K+→μ++ν in terms of that of π+→μ++ν.

1,673 citations

Journal ArticleDOI
TL;DR: In this paper, the results of experimental studies designed to search for the 2m decay of the K, meson were reported, with an upper bound of 1/300 for the fraction of K2's which decay into two charged pions.
Abstract: This Letter reports the results of experimental studies designed to search for the 2m decay of the K, meson. Several previous experiments have served"~ to set an upper limit of 1/300 for the fraction of K2 's which decay into two charged pions. The present experiment, using spark chamber techniques, proposed to extend this limit.

1,542 citations

Journal ArticleDOI
TL;DR: In this article, it was shown that the existence of two-component Pauli spinors satisfying a second order differential equation and the suggestion that in β decay these spinors act without gradient couplings leads to an essentially unique weak four-fermion coupling.
Abstract: The representation of Fermi particles by two-component Pauli spinors satisfying a second order differential equation and the suggestion that in β decay these spinors act without gradient couplings leads to an essentially unique weak four-fermion coupling. It is equivalent to equal amounts of vector and axial vector coupling with two-component neutrinos and conservation of leptons. (The relative sign is not determined theoretically.) It is taken to be "universal"; the lifetime of the μ agrees to within the experimental errors of 2%. The vector part of the coupling is, by analogy with electric charge, assumed to be not renormalized by virtual mesons. This requires, for example, that pions are also "charged" in the sense that there is a direct interaction in which, say, a π0 goes to π- and an electron goes to a neutrino. The weak decays of strange particles will result qualitatively if the universality is extended to include a coupling involving a Λ or Σ fermion. Parity is then not conserved even for those decays like K→2π or 3π which involve no neutrinos. The theory is at variance with the measured angular correlation of electron and neutrino in He6, and with the fact that fewer than 10^-4 pion decay into electron and neutrino.

1,494 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
2023332
2022759
2021354
2020376
2019400
2018430