Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: First measurement of the helicity asymmetry for $\gamma p\rightarrow
  p\pi^0$ in the resonance region   The first measurement of the helicity dependence of the photoproduction cross
section of single neutral pions off protons is reported for photon energies
from 600 to 2300\,MeV, covering nearly the full solid angle. The data are
compared to predictions from the SAID, MAID, and BnGa partial wave analyses.
Strikingly large differences between data and predictions are observed which
are traced to differences in the helicity amplitudes of well known and
established resonances. Precise values for the helicity amplitudes of several
resonances are reported.

22
The categories of this paper are: chao-dyn
18
The categories of this paper are: econ
7
The categories of this paper are: hep-th
9
The categories of this paper are: nlin
32
The categories of this paper are: atom-ph
26
The categories of this paper are: bayes-an
6
The categories of this paper are: astro-ph
25
The categories of this paper are: patt-sol
14
The categories of this paper are: math-ph
29
The categories of this paper are: funct-an
30
The categories of this paper are: q-alg
0
The categories of this paper are: hep-ph
28
The categories of this paper are: alg-geom
24
The categories of this paper are: dg-ga
2
The categories of this paper are: math
37
The categories of this paper are: supr-con