The puzzle of the pi -> gamma gamma* transition form factor

Autor(en)
Wolfgang Lucha, Dmitri Melikhov
Abstrakt

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(en)
Teilchenphysik
Externe Organisation(en)
Österreichische Akademie der Wissenschaften (ÖAW), Lomonosov Moscow State University (MSU)
Journal
Journal of Physics G: Nuclear and Particle Physics
Band
39
Anzahl der Seiten
11
ISSN
0954-3899
DOI
https://doi.org/10.1088/0954-3899/39/4/045003
Publikationsdatum
2012
Peer-reviewed
Ja
ÖFOS 2012
103036 Theoretische Physik, 103034 Teilchenphysik
Link zum Portal
https://ucrisportal.univie.ac.at/de/publications/the-puzzle-of-the-pi--gamma-gamma-transition-form-factor(6e39518a-1ded-4202-8439-a11b5a836f9e).html