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Published December 28, 2018 | Published
Journal Article Open

First Evidence for cos 2β > 0 and Resolution of the Cabibbo-Kobayashi-Maskawa Quark-Mixing Unitarity Triangle Ambiguity


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^0_Sπ+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) × 10^6BB pairs recorded by the BABAR detector and (772±11) × 10^6BB 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^0Sπ+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 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.

Additional Information

© 2018 Published by the American Physical Society. Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Funded by SCOAP3. Received 17 April 2018; revised manuscript received 22 August 2018; published 26 December 2018. We thank the PEP-II and KEKB groups for the excellent operation of the accelerators. The BABAR experiment acknowledges the substantial dedicated effort from the computing organizations for their support. The collaborating institutions wish to thank SLAC for its support and kind hospitality. The Belle experiment wishes to acknowledge the KEK cryogenics group for efficient solenoid operations; and the KEK computer group, the NII, and PNNL/EMSL for valuable computing and SINET5 network support. This work was supported by MEXT, JSPS and Nagoya's TLPRC (Japan); ARC (Australia); FWF (Austria); NSERC (Canada); NSFC and CCEPP (China); MSMT (Czechia); CEA and CNRS-IN2P3 (France); BMBF, CZF, DFG, EXC153, and VS (Germany); DST (India); INFN (Italy); MOE, MSIP, NRF, RSRI, FLRFAS project and GSDC of KISTI (Korea); FOM (The Netherlands); NFR (Norway); MNiSW and NCN (Poland); MES and RFAAE (Russia); ARRS (Slovenia); IKERBASQUE and MINECO (Spain); SNSF (Switzerland); MOE and MOST (Taiwan); STFC (United Kingdom); BSF (USA-Israel); and DOE and NSF (USA). Individuals have received support from the Marie Curie EIF (European Union) and the A. P. Sloan Foundation (USA).

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Published - PhysRevLett.121.261801.pdf


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