Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Analysis of the J/psi --> pi^0 gamma^* transition form factor   In view of the first measurement of the branching fraction for J/psi --> pi^0
e^+ e^- by the BESIII collaboration, we analyze what can be learnt on the
corresponding transition form factor using dispersion theory. We show that
light-quark degrees of freedom dominate the spectral function, in particular
two-pion intermediate states. Estimating the effects of multi-pion states as
well as charmonium, we arrive at a prediction for the complete form factor that
should be scrutinized experimentally in the future.

37
The categories of this paper are: supr-con
29
The categories of this paper are: funct-an
34
The categories of this paper are: chem-ph
3
The categories of this paper are: physics
26
The categories of this paper are: bayes-an
5
The categories of this paper are: gr-qc
12
The categories of this paper are: nucl-th
30
The categories of this paper are: q-alg
15
The categories of this paper are: nucl-ex
21
The categories of this paper are: adap-org
32
The categories of this paper are: atom-ph
22
The categories of this paper are: chao-dyn
17
The categories of this paper are: q-fin
16
The categories of this paper are: stat
31
The categories of this paper are: ao-sci
20
The categories of this paper are: acc-phys