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/6e39518a-1ded-4202-8439-a11b5a836f9e