First Evidence for cos2β>0 and Resolution of the Cabibbo-Kobayashi-Maskawa Quark-Mixing Unitarity Triangle Ambiguity

Physical Review Letters. 2018. Vol. 121. No. 26. P. 1–11.

Aushev T., Mizuk R., Pakhlov P., Pakhlova G., Uglov T.

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 B0→D(∗)h0 with D→KS0π+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 (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 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 B0→D(∗)h0 decays. The quoted model uncertainties are due to the composition of the D0→KS0π+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. © 2018 authors. Published by the American Physical Society.

Keywords: Supersymmetry, Belle experiments, Uncertainty analysis