Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The Standard model prediction for K(e2)/K_(mu2) and pi(e2)/pi(mu2)   We have calculated the ratios $R_{e/\mu}^{(P)} \equiv \Gamma(P \to e
\bar{\nu}_e [\gamma])/ \Gamma(P \to \mu \bar{\nu}_\mu [\gamma])$ ($P=\pi,K$) in
Chiral Perturbation Theory up to $\mathcal{O}(e^2p^4)$, finding
$R_{e/\mu}^{(\pi)} = (1.2352 \pm 0.0001) \times 10^{-4}$ and $R_{e/\mu}^{(K)} =
(2.477 \pm 0.001) \times 10^{-5}$. This observable is helicity suppressed in
the Standard Model, so that it is a sensitive probe of all Standard Model
extensions that induce pseudoscalar currents and nonuniversal corrections to
the lepton couplings. Ongoing experimental searches plan to reach uncertainties
that are comparable to these results. At the moment $R_{e/\mu}^{(K)}$ is in
agreement with the final result by the KLOE Collaboration at DAFNE and it is at
$1.4 \sigma$ of the preliminary result by the NA62 Experiment at CERN. New
measurements of $R_{e/\mu}^{(\pi)}$ are under way by the PEN Collaboration at
PSI and by the PIENU Collaboration at TRIUMF.

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The categories of this paper are: hep-ex
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The categories of this paper are: econ
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The categories of this paper are: math
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The categories of this paper are: plasm-ph
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The categories of this paper are: astro-ph
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The categories of this paper are: alg-geom
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The categories of this paper are: cmp-lg
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The categories of this paper are: physics
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The categories of this paper are: dg-ga
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The categories of this paper are: cond-mat
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The categories of this paper are: patt-sol
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The categories of this paper are: nlin
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The categories of this paper are: ao-sci
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The categories of this paper are: atom-ph
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The categories of this paper are: q-fin
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The categories of this paper are: adap-org