Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Improved Evidence for Direct CP Violation in B0 --> pi+ pi- Decays and
  Model-Independent Constraints on phi_2   We present a new measurement of the time-dependent CP-violating parameters in
B0 --> pi+ pi- decays with 275 x 10^6 BB-bar pairs collected with the Belle
detector at the KEKB asymmetric-energy e+e- collider operating at the
Upsilon(4S) resonance. We find 666 +/- 43 B0 --> pi+ pi- events and measure the
CP-violating parameters: S_pipi = -0.67 +/- 0.16(stat) +/- 0.06(syst) and
A_pipi = +0.56 +/- 0.12(stat) +/- 0.06(syst). We find evidence for large direct
CP-violation with a significance greater than 4 standard deviations for any
S_pipi value. Using isospin relations, we obtain 95.4% confidence intervals for
the CKM angle phi_2 of 0 deg. < phi_2 < 19 deg. and 71 deg. < phi_2 < 180 deg.

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The categories of this paper are: astro-ph
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The categories of this paper are: nlin
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The categories of this paper are: atom-ph
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The categories of this paper are: acc-phys
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The categories of this paper are: solv-int
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The categories of this paper are: plasm-ph
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The categories of this paper are: q-alg
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The categories of this paper are: dg-ga
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The categories of this paper are: cmp-lg
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The categories of this paper are: eess
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The categories of this paper are: stat
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The categories of this paper are: bayes-an
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The categories of this paper are: alg-geom
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The categories of this paper are: patt-sol
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The categories of this paper are: quant-ph
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The categories of this paper are: gr-qc