Measurement of CP Asymmetries and Branching Fractions in Charmless Two-Body B-Meson Decays to Pions and Kaons
Abstract
We present improved measurements of CP-violation parameters in the decays
B
0
→
π
+
π
−
,
B
0
→
K
+
π
−
, and
B
0
→
π
0
π
0
, and of the branching fractions for
B
0
→
π
0
π
0
and
B
0
→
K
0
π
0
. The results are obtained with the full data set collected at the
Υ(4S)
resonance by the BABAR experiment at the PEP-II asymmetric-energy
B
factory at the SLAC National Accelerator Laboratory, corresponding to
467±5
million
B
B
¯
pairs. We find the CP-violation parameter values and branching fractions
S
π
+
π
−
=−0.68±0.10±0.03,
C
π
+
π
−
=−0.25±0.08±0.02,
A
K
−
π
+
=−0.107±
0.016
+0.006
−0.004
,
C
π
0
π
0
=−0.43±0.26±0.05,Br(
B
0
→
π
0
π
0
)=(1.83±0.21±0.13)×
10
−6
,Br(
B
0
→
K
0
π
0
)=(10.1±0.6±0.4)×
10
−6
,
where in each case, the first uncertainties are statistical and the second are systematic. We observe CP violation with a significance of 6.7 standard deviations for
B
0
→
π
+
π
−
and 6.1 standard deviations for
B
0
→
K
+
π
−
, including systematic uncertainties. Constraints on the Unitarity Triangle angle
α
are determined from the isospin relations among the
B→ππ
rates and asymmetries. Considering only the solution preferred by the Standard Model, we find
α
to be in the range
[
71
∘
,
109
∘
]
at the 68% confidence level.