SOKENDAI (The Graduate University for Advanced Studies), Hayama 240-0193, Japan.
High Energy Accelerator Research Organization (KEK), Tsukuba 305-0801, Japan.
Phys Rev Lett. 2018 Dec 28;121(26):261801. doi: 10.1103/PhysRevLett.121.261801.
We present first evidence that the cosine of the CP-violating weak phase 2β is positive, and hence exclude trigonometric multifold solutions of the Cabibbo-Kobayashi-Maskawa (CKM) Unitarity Triangle using a time-dependent Dalitz plot analysis of B^{0}→D^{()}h^{0} with D→K_{S}^{0}π^{+}π^{-} decays, where h^{0}∈{π^{0},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)×10^{6}BB[over ¯] pairs recorded by the BABAR detector and (772±11)×10^{6}BB[over ¯] pairs recorded by the Belle detector. The results of the measurement are sin2β=0.80±0.14(stat)±0.06(syst)±0.03(model) and cos2β=0.91±0.22(stat)±0.09(syst)±0.07(model). The result for the direct measurement of the angle β of the CKM Unitarity Triangle is β=[22.5±4.4(stat)±1.2(syst)±0.6(model)]°. The measurement assumes no direct CP violation in B^{0}→D^{()}h^{0} decays. The quoted model uncertainties are due to the composition of the D^{0}→K_{S}^{0}π^{+}π^{-} decay amplitude model, which is newly established by performing a Dalitz plot amplitude analysis using a high-statistics e^{+}e^{-}→cc[over ¯] data sample. CP violation is observed in B^{0}→D^{(*)}h^{0} 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.
我们首次提供了 CP 破坏弱相角 2β为正的证据，因此排除了 Cabibbo-Kobayashi-Maskawa（CKM）幺正三角形的三角函数多重解，方法是对 B^{0}→D^{()}h^{0}衰变进行时变 Dalitz 图分析，其中 h^{0}∈{π^{0},η,ω}表示轻无味和中性强子。该测量是使用分别位于 SLAC 的 PEP-II 和 KEK 的 KEKB 的 Y(4S)共振，由 BABAR 和 Belle 实验的最终数据集完成的。数据样本包含由 BABAR 探测器记录的（471±3）×10^{6}BB[over ¯]对和由 Belle 探测器记录的（772±11）×10^{6}BB[over ¯]对。测量结果为 sin2β=0.80±0.14(stat)±0.06(syst)±0.03(model) 和 cos2β=0.91±0.22(stat)±0.09(syst)±0.07(model)。CKM 幺正三角形角 β 的直接测量结果为 β=[22.5±4.4(stat)±1.2(syst)±0.6(model)]°。该测量假设 B^{0}→D^{()}h^{0}衰变中没有直接 CP 破坏。所给出的模型不确定性是由于 D^{0}→K_{S}^{0}π^{+}π^{-}衰变幅度模型的组成引起的，该模型是通过使用高统计量 e^{+}e^{-}→cc[over ¯]数据样本进行 Dalitz 图幅度分析新建立的。在 B^{0}→D^{(*)}h^{0}衰变中观察到 CP 破坏，其水平为 5.1 个标准偏差。cos2β>0 的显著性为 3.7 个标准偏差。π/2-β=(68.1±0.7)°的三角函数多重解被排除在 7.3 个标准偏差的水平。该测量解决了 CKM 幺正三角形顶点确定中的一个歧义。
