Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Measurement of the $B^0\to D^{\ast-} D_s^{\ast+}$ and
  $D_s^+\to\phi\pi^+$ Branching Fractions   We present measurements of the branching fractions $\BR(B^0\to D^{\ast-}
D_s^{\ast+})$ and $\BR(D_s^+\to\phi\pi^+)$, based on $123\times10^6$
Y(4S)->BBbar decays collected by the BaBar detector at the PEP-II
asymmetric-energy $e^+e^-$ B factory. A partial reconstruction technique is
used to measure $\BR(B^0\to D^{\ast-} D_s^{\ast+})$ and the decay chain is
fully reconstructed to measure the branching fraction product $\BR(B^0\to
D^{\ast-} D_s^{\ast+})\times\BR(D_s^+\to\phi\pi^+)$. Comparing these two
measurements provides a model-independent determination of the \Dsphipi\
branching fraction. We obtain $\BR(B^0\to D^{\ast-} D_s^{\ast+}) = (1.88 \pm
0.09 \pm 0.17)%$ and $\BR(D_s^+\to\phi\pi^+) = (4.81 \pm 0.52 \pm 0.38)%$,
where the first uncertainties are statistical and the second systematic.

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The categories of this paper are: cond-mat
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The categories of this paper are: plasm-ph
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The categories of this paper are: dg-ga
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The categories of this paper are: alg-geom
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The categories of this paper are: solv-int
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The categories of this paper are: cs
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The categories of this paper are: ao-sci
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The categories of this paper are: quant-ph
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The categories of this paper are: nlin
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The categories of this paper are: nucl-th
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The categories of this paper are: adap-org
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The categories of this paper are: nucl-ex
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The categories of this paper are: comp-gas
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The categories of this paper are: econ
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The categories of this paper are: astro-ph
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The categories of this paper are: patt-sol