Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Quasifree Eta Photoproduction from Nuclei   Quasifree $\eta$ photoproduction from nuclei is studied in the Distorted Wave
Impulse Approximation (DWIA). The elementary eta production operator contains
Born terms, vector meson and nucleon resonance contributions and provides an
excellent description of the recent low energy Mainz measurements on the
nucleon. The resonance sector includes the $S_{11}(1535)$, $P_{11}(1440)$ and
$D_{13}(1520)$ states whose couplings are fixed by independent electromagnetic
and hadronic data. Different models for the $\eta N$ t-matrix are used to
construct a simple $\eta A$ optical potential based on a $t
\rho$-approximation. We find that the exclusive $A(\gamma,\eta N)B$ process can
be used to study medium modifications of the $N^*$ resonances, particularly if
the photon asymmetry can be measured. The inclusive $A(\gamma, \eta)X$ reaction
is compared to new data obtained on $^{12}C$, $^{40}Ca$, and is found to
provide a clear distinction between different models for the $\eta N$ t-matrix.

15
The categories of this paper are: nucl-ex
30
The categories of this paper are: q-alg
36
The categories of this paper are: cmp-lg
37
The categories of this paper are: supr-con
18
The categories of this paper are: econ
27
The categories of this paper are: comp-gas
1
The categories of this paper are: cs
29
The categories of this paper are: funct-an
34
The categories of this paper are: chem-ph
22
The categories of this paper are: chao-dyn
32
The categories of this paper are: atom-ph
11
The categories of this paper are: hep-lat
7
The categories of this paper are: hep-th
0
The categories of this paper are: hep-ph
31
The categories of this paper are: ao-sci
13
The categories of this paper are: quant-ph