The puzzle of the pi -> gamma gamma* transition form factor
- Author(s)
- Wolfgang Lucha, Dmitri Melikhov
- Abstract
We study the P -> gamma gamma* (P = pi(0), eta, eta') transition form factors by means of the local-duality (LD) version of QCD sum rules. For the case of eta and eta', the conventional LD model provides a good description of the existing data. However, for the pion form factor we find a disagreement with recent BABAR results for high Q(2), even though the accuracy of the LD approximation is expected to increase with Q(2). It remains mysterious why both eta and eta' form factors to virtual photons, on the one hand, and the pi(0) form factor, on the other hand, show a qualitatively different behaviour, corresponding to a violation of LD that rises with Q(2) in the pion case. In a quantum-mechanical example, we show that, for a bound-state size of about 1 fm, the LD sum rule provides an accurate prediction for the form factor for Q(2) larger than a few GeV2.
- Organisation(s)
- Particle Physics
- External organisation(s)
- Österreichische Akademie der Wissenschaften (ÖAW), Anuchin Research Institute and Museum of Anthropology
- Journal
- Journal of Physics G: Nuclear and Particle Physics
- Volume
- 39
- No. of pages
- 11
- ISSN
- 0954-3899
- DOI
- https://doi.org/10.1088/0954-3899/39/4/045003
- Publication date
- 2012
- Peer reviewed
- Yes
- Austrian Fields of Science 2012
- 103036 Theoretical physics, 103034 Particle physics
- Portal url
- https://ucrisportal.univie.ac.at/en/publications/6e39518a-1ded-4202-8439-a11b5a836f9e