Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Improved Search for Heavy Neutrinos and a Test of Lepton Universality in
  the Decay $\pi^+ \rightarrow \mbox{e}^+ \nu$   Two results from the PIENU Experiment are presented reporting a test of
lepton universality in pion decay and improved limits on heavy neutrinos
coupling to positrons. The status of the full analysis for the $\pi^+
\rightarrow \mbox{e}^+ \nu$ branching ratio measurement is summarized.

18
The categories of this paper are: econ
4
The categories of this paper are: cond-mat
0
The categories of this paper are: hep-ph
6
The categories of this paper are: astro-ph
13
The categories of this paper are: quant-ph
9
The categories of this paper are: nlin
12
The categories of this paper are: nucl-th
29
The categories of this paper are: funct-an
14
The categories of this paper are: math-ph
35
The categories of this paper are: mtrl-th
7
The categories of this paper are: hep-th
1
The categories of this paper are: cs
21
The categories of this paper are: adap-org
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The categories of this paper are: dg-ga
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The categories of this paper are: eess
28
The categories of this paper are: alg-geom