Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Elastic scattering of low energy pions by nuclei and the in-medium
  isovector pi N amplitude   Measurements of elastic scattering of 21.5 MeV pi+ and pi- by Si, Ca, Ni and
Zr were made using a single arm magnetic spectrometer. Absolute calibration was
made by parallel measurements of Coulomb scattering of muons. Parameters of a
pion-nucleus optical potential were obtained from fits to all eight angular
distributions put together. The `anomalous' s-wave repulsion known from pionic
atoms is clearly observed and could be removed by introducing a
chiral-motivated density dependence of the isovector scattering amplitude,
which also greatly improved the fits to the data. The empirical energy
dependence of the isoscalar amplitude also improves the fits to the data but,
contrary to what is found with pionic atoms, on its own is incapable of
removing the anomaly.

21
The categories of this paper are: adap-org
23
The categories of this paper are: solv-int
14
The categories of this paper are: math-ph
22
The categories of this paper are: chao-dyn
31
The categories of this paper are: ao-sci
24
The categories of this paper are: dg-ga
37
The categories of this paper are: supr-con
7
The categories of this paper are: hep-th
34
The categories of this paper are: chem-ph
33
The categories of this paper are: plasm-ph
36
The categories of this paper are: cmp-lg
12
The categories of this paper are: nucl-th
3
The categories of this paper are: physics
32
The categories of this paper are: atom-ph
8
The categories of this paper are: hep-ex
29
The categories of this paper are: funct-an