Direct CP Violation and Isospin Triangles of B-pipi Decays.pdf
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Direct CP Violation and Isospin Triangles of B → ππ Decays
Zhi-zhong Xing
CCAST (World Laboratory), P.O. Box 8730, Beijing 100080, China
and Institute of High Energy Physics, Chinese Academy of Sciences,
P.O. Box 918 (4), Beijing 100039, China ?
(Electronic address: xingzz@mail.ihep.ac.cn)
Abstract
The recent observation of B0d → π0π0 and B?0d → π0π0 decay modes allows us
to make a fresh isospin analysis of B → ππ transitions. We find that current
experimental data can impose some model-independent constraints on the
parameter space of direct CP violation in Bd → π+π? and Bd → π0π0.
Furthermore, we establish a direct relationship between the weak phase α
and the charge-averaged branching fractions and CP-violating asymmetries
of B → ππ decays.
PACS number(s): 12.15.Ff, 13.25.Hw, 11.30.Er, 14.40.Nd
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?Mailing address
1
The major goal of B-meson factories is to test the Kobayashi-Maskawa mechanism of
CP violation within the standard model and to detect possible new sources of CP violation
beyond the standard model. So far the CP-violating asymmetry in B0d vs B?
0
d → J/ψKS
decays has unambiguously been measured at KEK and SLAC [1], and the experimental result
is compatible very well with the standard-model expectation. Some preliminary evidence
for CP violation in a number of other B decays has also been reported by BaBar and
Belle Collaborations [2]. Further experiments will provide much more precise data on CP
violation in the B-meson system, from which one may cross-check the consistency of the
Kobayashi-Maskawa picture and probe possible new physics.
The charmless two-body nonleptonic decays B?0d → π+π?, B?0d → π0π0 and B?u → π0π?,
which can be related to one another via the isospin triangle [3], have been of great in-
terest in B physics for a stringent test of the factorization hypothesis, a quantitative
analysis of final-state interactions, and a clean determination of the CP-
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