Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: First evidence for the two-body charmless baryonic decay $B^0 \to p
  \bar{p}$   The results of a search for the rare two-body charmless baryonic decays $B^0
\to p \bar{p}$ and $B_s^0 \to p \bar{p}$ are reported. The analysis uses a data
sample, corresponding to an integrated luminosity of 0.9 fb$^{-1}$, of $pp$
collision data collected by the LHCb experiment at a centre-of-mass energy of 7
TeV. An excess of $B^0 \to p \bar{p}$ candidates with respect to background
expectations is seen with a statistical significance of 3.3 standard
deviations. This is the first evidence for a two-body charmless baryonic $B^0$
decay. No significant $B_s^0 \to p \bar{p}$ signal is observed, leading to an
improvement of three orders of magnitude over previous bounds. If the excess
events are interpreted as signal, the 68.3% confidence level intervals on the
branching fractions are {eqnarray} \cal{B}(B^0 \to p \bar{p}) & = & (1.47
\,^{+0.62}_{-0.51} \,^{+0.35}_{-0.14}) \times 10^{-8} \,, *{0.3cm}
\cal{B}(B_s^0 \to p \bar{p}) & = & (2.84 \,^{+2.03}_{-1.68} \,^{+0.85}_{-0.18})
\times 10^{-8} \,, {eqnarray} where the first uncertainty is statistical and
the second is systematic.

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The categories of this paper are: physics
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The categories of this paper are: plasm-ph
34
The categories of this paper are: chem-ph
15
The categories of this paper are: nucl-ex
37
The categories of this paper are: supr-con
16
The categories of this paper are: stat
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The categories of this paper are: hep-lat
28
The categories of this paper are: alg-geom
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The categories of this paper are: math-ph
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The categories of this paper are: astro-ph
35
The categories of this paper are: mtrl-th
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The categories of this paper are: econ
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The categories of this paper are: chao-dyn
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The categories of this paper are: hep-th
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The categories of this paper are: cond-mat
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The categories of this paper are: q-alg