First evidence for cos 2β>0 and resolution of the CKM Unitarity Triangle ambiguity by a time-dependent Dalitz plot analysis of B⁰ → D^(*) h⁰ with D → K_S⁰ π⁺ π^- decays

2018/04/17 by The BaBar, Belle Collaborations, : +422 · 1 voice
Physics and Astronomy · #hep-ex

paper · pdf · doi:10.1103/physrevlett.121.261801

published as Phys. Rev. Lett. 121, 261801 (2018) · To be submitted to Physical Review Letters

arxiv created 2018/04/17 · arxiv published 2018/04/17 · arxiv updated 2019/01/02

Abstract

We present first evidence that the cosine of the CP-violating weak phase 2β is positive, and hence exclude trigonometric multifold solutions of the CKM Unitarity Triangle using a time-dependent Dalitz plot analysis of B⁰ → D^(*) h⁰ with D → K_S⁰ π⁺ π^- decays, where h⁰ ∈ \π⁰, η, ω\ denotes a light unflavored and neutral hadron. The measurement is performed combining the final data sets of the BaBar and Belle experiments collected at the Υ(4S) resonance at the asymmetric-energy B factories PEP-II at SLAC and KEKB at KEK, respectively. The data samples contain ( 471 ± 3 )× 10⁶ BB pairs recorded by the BaBar detector and ( 772 ± 11 )× 10⁶ BB pairs recorded by the Belle detector. The results of the measurement are sin2β = 0.80 ± 0.14 (\rmstat.) ± 0.06 (\rmsyst.) ± 0.03 (\rmmodel) and cos2β = 0.91 ± 0.22 (\rmstat.) ± 0.09 (\rmsyst.) ± 0.07 (\rmmodel). The result for the direct measurement of the angle β of the CKM Unitarity Triangle is β= ( 22.5 ± 4.4 (\rmstat.) ± 1.2 (\rmsyst.) ± 0.6 (\rmmodel) )^∘. The quoted model uncertainties are due to the composition of the D⁰ → K_S⁰ π⁺ π^- decay amplitude model, which is newly established by performing a Dalitz plot amplitude analysis using a high-statistics e⁺e^- → cc data sample. CP violation is observed in B⁰ → D^(*) h⁰ decays at the level of 5.1 standard deviations. The significance for cos2β>0 is 3.7 standard deviations. The trigonometric multifold solution π/2 - β= (68.1 ± 0.7)^∘ is excluded at the level of 7.3 standard deviations. The measurement resolves an ambiguity in the determination of the apex of the CKM Unitarity Triangle.

Discussions

• That's nice: A combined analysis of #Belle and #BaBar data authored by both experiments. Read the #preprints at https://arxiv.org/abs/1804.06152 https://arxiv.org/abs/1804.06153 (there are 2 as there [bsky, 2 points, 1 comments]

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