First Evidence for cos2?>0 and Resolution of the Cabibbo-Kobayashi-Maskawa Quark-Mixing Unitarity Triangle Ambiguity

Abstract

We present first evidence that the cosine of the CP-violating weak phase 2? is positive, and hence exclude trigonometric multifold solutions of the Cabibbo-Kobayashi-Maskawa (CKM) Unitarity Triangle using a time-dependent Dalitz plot analysis of B0?D(?)h0 with D?KS0?+?- decays, where h0 {?0,?,?} 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 (4S) resonance at the asymmetric-energy B factories PEP-II at SLAC and KEKB at KEK, respectively. The data samples contain (471�3)�106BB pairs recorded by the BABAR detector and (772�11)�106BB pairs recorded by the Belle detector. The results of the measurement are sin2?=0.80�0.14(stat)�0.06(syst)�0.03(model) and cos2?=0.91�0.22(stat)�0.09(syst)�0.07(model). The result for the direct measurement of the angle ? of the CKM Unitarity Triangle is ?=[22.5�4.4(stat)�1.2(syst)�0.6(model)]�. The measurement assumes no direct CP violation in B0?D(?)h0 decays. The quoted model uncertainties are due to the composition of the D0?KS0?+?- 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 cos2?>0 is 3.7 standard deviations. The trigonometric multifold solution ?/2-?=(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. � 2018 authors. Published by the American Physical Society.