Abelian anomaly and neutral pion production

Journal Article · Wed Dec 15 00:00:00 EST 2010 · Physical Review. C, Nuclear Physics

DOI:https://doi.org/10.1103/PHYSREVC.82.065202· OSTI ID:21499289

Roberts, H L. L. ^[1]; Roberts, C D ^[1]; Bashir, A; Gutierrez-Guerrero, L X ^[2]; Tandy, P C ^[3]

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1. Physics Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States)
2. Instituto de Fisica y Matematicas, Universidad Michoacana de San Nicolas de Hidalgo, Apartado Postal 2-82, Morelia, Michoacan 58040 (Mexico)
3. Center for Nuclear Research, Department of Physics, Kent State University, Kent Ohio 44242 (United States)

We show that in fully self-consistent treatments of the pion, namely, its static properties and elastic and transition form factors, the asymptotic limit of the product Q{sup 2}G{sub {gamma}}{sup *}{sub {gamma}{pi}}{sup 0}(Q{sup 2}), determined a priori by the interaction employed, is not exceeded at any finite value of spacelike momentum transfer. Furthermore, in such a treatment of a vector-vector contact-interaction one obtains a {gamma}{sup *{gamma}{yields}{pi}0} transition form factor that disagrees markedly with all available data. We explain that the contact interaction produces a pion distribution amplitude that is flat and nonvanishing at the endpoints. This amplitude characterizes a pointlike pion bound state. Such a state has the hardest possible form factors (i.e., form factors that become constant at large momentum transfers and hence are in striking disagreement with completed experiments). However, interactions with QCD-like behavior produce soft pions, a valence-quark distribution amplitude that vanishes as {approx}(1-x){sup 2} for x{approx}1, and results that agree with the bulk of existing data. Our analysis supports a view that the large-Q{sup 2} data obtained by the BaBar Collaboration is not an accurate measure of the {gamma}*{gamma}{yields}{pi}{sup 0} form factor.

• OSTI ID: 21499289
• Journal Information: Physical Review. C, Nuclear Physics, Vol. 82, Issue 6; Other Information: DOI: 10.1103/PhysRevC.82.065202; (c) 2010 American Institute of Physics; ISSN 0556-2813
• Country of Publication: United States
• Language: English

Related Subjects

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
ASYMPTOTIC SOLUTIONS
BOUND STATE
DISTRIBUTION
FORM FACTORS
INTERACTIONS
MOMENTUM TRANSFER
PARTICLE PRODUCTION
PIONS NEUTRAL
QUANTUM CHROMODYNAMICS
QUARKS
BOSONS
DIMENSIONLESS NUMBERS
ELEMENTARY PARTICLES
FERMIONS
FIELD THEORIES
HADRONS
MATHEMATICAL SOLUTIONS
MESONS
PARTICLE PROPERTIES
PIONS
PSEUDOSCALAR MESONS
QUANTUM FIELD THEORY