Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Single \pi^- production in np collisions for excess energies up to 90
  MeV   The quasifree reaction $np\to pp\pim$ was studied in a kinematically complete
experiment by bombarding a liquid hydrogen target with a deuteron beam of
momentum 1.85 GeV/c and analyzing the data along the lines of the spectator
model. In addition to the three charged ejectiles the spectator proton was also
detected in the large-acceptance time-of-flight spectrometer COSY-TOF. It was
identified by its momentum and flight direction thus yielding access to the
Fermi motion of the bound neutron and to the effective neutron 4-momentum
vector $\mathbb{P}_n$ which differed from event to event. A range of almost 90
MeV excess energy above threshold was covered. Energy dependent angular
distributions, invariant mass spectra as well as fully covered Dalitz plots
were deduced. Sizeable $pp$ FSI effects were found as were contributions of $p$
and $d$ partial waves. The behavior of the elementary cross section
$\sigma_{01}$ close to threshold is discussed in view of new cross section
data. In comparison with existing literature data the results provide a
sensitive test of the spectator model.

16
The categories of this paper are: stat
6
The categories of this paper are: astro-ph
36
The categories of this paper are: cmp-lg
34
The categories of this paper are: chem-ph
1
The categories of this paper are: cs
23
The categories of this paper are: solv-int
30
The categories of this paper are: q-alg
0
The categories of this paper are: hep-ph
13
The categories of this paper are: quant-ph
18
The categories of this paper are: econ
28
The categories of this paper are: alg-geom
33
The categories of this paper are: plasm-ph
29
The categories of this paper are: funct-an
24
The categories of this paper are: dg-ga
11
The categories of this paper are: hep-lat
4
The categories of this paper are: cond-mat