Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Agreement at last: an experimental and theoretical study on the single
  ionization of helium by fast proton impact   Even though ion/atom-collision is a mature field of atomic physics great
discrepancies between experiment and theoretical calculations are still common.
Here we present experimental results with highest momentum resolution on single
ionization of helium induced by 1\,MeV protons and compare these to different
theoretical calculations. The overall agreement is strikingly good and already
the first Born approximation yields good agreement between theory and
experiment. This has been expected since several decades, but so far has not
been accomplished. The influence of projectile coherence effects on the
measured data is shortly discussed in line with an ongoing dispute on the
existence of nodal structures in the electron angular emission distributions.

1
The categories of this paper are: cs
23
The categories of this paper are: solv-int
20
The categories of this paper are: acc-phys
37
The categories of this paper are: supr-con
33
The categories of this paper are: plasm-ph
8
The categories of this paper are: hep-ex
5
The categories of this paper are: gr-qc
16
The categories of this paper are: stat
9
The categories of this paper are: nlin
22
The categories of this paper are: chao-dyn
31
The categories of this paper are: ao-sci
26
The categories of this paper are: bayes-an
30
The categories of this paper are: q-alg
34
The categories of this paper are: chem-ph
28
The categories of this paper are: alg-geom
15
The categories of this paper are: nucl-ex