We present a measurement of the time-dependent CP violation of B 0 → D(∗) CPh0 decays, where the light neutral hadron h0 is a π0, η or ω meson, and the neutral D meson decays to the two-body CP eigenstates K+K−, K0 Sπ0 or K0 Sω. The measurement is performed by combining the ﬁnal data sets of (471±3)×106 BB pairs collected by the BaBar experiment and (772±11)×106 BB pairs by the Belle experiment in a single physics analysis. In this ﬁrst measurement performed on a data sample of more than 1ab−1, we report a ﬁrst observation of CP violation in B 0 → D(∗) CPh0 decays governed by mixing-induced CP violation according to the weak phase β. We measure the CP asymmetry parameters −ηfS = +0 .66±0 .10(stat.)±0.06(syst.) and C = −0.02±0.07(stat.)±0.03(syst.)

Rohrken, M.

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DOI 10.1393/ncc/i2016-16327-5Colloquia: La Thuile 2016IL NUOVO CIMENTO 39 C (2016) 327Combined CP violation measurements by the BaBarand Belle CollaborationsM. Röhrken on behalf of the BaBar and Belle CollaborationsCalifornia Institute of Technology - Pasadena, CA, USAreceived 26 July 2016Summary. — We present a measurement of the time-dependent CP violation ofB0 → D(∗)CP h0 decays, where the light neutral hadron h0 is a π0, η or ω meson, andthe neutral D meson decays to the two-body CP eigenstates K+K−, K0Sπ0 or K0Sω.The measurement is performed by combining the final data sets of (471±3)×106 BBpairs collected by the BaBar experiment and (772±11)×106 BB pairs by the Belleexperiment in a single physics analysis. In this first measurement performed on adata sample of more than 1 ab−1, we report a first observation of CP violationin B0 → D(∗)CP h0 decays governed by mixing-induced CP violation according tothe weak phase β. We measure the CP asymmetry parameters −ηfS = +0.66 ±0.10 (stat.) ± 0.06 (syst.) and C = −0.02 ± 0.07 (stat.) ± 0.03 (syst.).In the Standard Model, the only source of CP violation is an irreducible complex phasein the three-family Cabibbo-Kobayashi-Maskawa (CKM) quark-mixing matrix [1,2]. TheB factory experiments BaBar at SLAC in the US and Belle at KEK in Japan estab-lished CP violation in the neutral and charged B meson system [3-6]. Both experimentsprecisely measured the angle β of the Unitarity Triangle, defined by the CKM matrixelements Vij as arg[−VcdV ∗cb/VtdV ∗tb], using the time-dependent CP violation in b → cc̄stransitions [7, 8]. The current world average is sin(2β) = 0.68 ± 0.02 [9]. The time-dependent CP violation of b → cc̄s transitions is associated with theoretical uncertaintiesdue to possible penguin contributions.A complementary and theoretically clean probe for β is provided by B0 → D(∗)h0decays, where h0 ∈ {π0, η, ω} denotes a light neutral hadron. These decays are mediatedonly by tree-level amplitudes that are dominated by CKM-favored b → cūd transitions.In B0 → D(∗)h0 decays, an interference between the decay amplitudes with and withoutB0-B0oscillations emerges if the neutral D meson decays to a CP eigenstate DCP . Inthis case, the time evolution of B0 → D(∗)CP h0 decays is governed only by the weak phaseβ [10]. The measurement of the time-dependent CP violation of B0 → D(∗)CP h0 decaysallows for a determination of β that is theoretically more clean than using b → cc̄stransitions, and can provide a new gold standard reference for the new physics searchesCreative Commons Attribution 4.0 License (http://creativecommons.org/licenses/by/4.0) 12 M. RÖHRKEN on behalf of the BABAR and BELLE COLLABORATIONSin the mixing-induced CP violation of b → s penguin-mediated B meson decays. Anysizable deviation in the CP violation of B0 → D(∗)CP h0 decays from b → s penguintransitions would point to physics beyond the Standard Model which could be caused, forexample, by unobserved heavy particles or additional CP violating phases contributingto loop diagrams in b → s penguin transitions [11].However, the measurements of B0 → D(∗)h0 decays are experimentally challengingbecause of low B and D meson branching fractions (O(10−4) and O(≤ 10−2), respec-tively), low reconstruction efficiencies, and large backgrounds. Previous measurementscarried out separately by the BaBar and Belle collaborations using two-body [12] andthree-body D meson decays [13,14] were not sensitive enough to establish CP violationin B0 → D(∗)h0 decays.In this article, we present a time-dependent CP violation measurement of B0 →D(∗)CP h0 decays. In this measurement, we combine for the first time the large final datasets of (471 ± 3) × 106 BB pairs collected by the BaBar experiment and (772 ± 11) ×106 BB pairs by the Belle experiment in a single physics analysis. The novel approachincreases the achievable experimental precision and enables time-dependent CP violationmeasurements in the neutral B meson system with unprecedented sensitivity.In B0 → D(∗)CP h0 decays, the light neutral hadron h0 is reconstructed as a π0, η or ωmeson and the neutral D meson is reconstructed in the decays to two-body CP eigen-states K+K−, K0Sπ0 and K0Sω. D∗0 mesons are reconstructed in the decays to D0π0. Inthe measurement, twelve final states are reconstructed in total, among them seven (five)CP -even (CP -odd) states. Continuum e+e− → qq (q ∈ {u, d, s, c}) events are the dom-inant source of background. This background is reduced by selection requirements onmultivariate classifiers provided by neural networks trained on variables characterizingthe event shapes. The B0 → D(∗)CP h0 signal yields are estimated by unbinned maximumlikelihood fits to the beam-constrained mass defined as Mbc ≡√(E∗beam/c2)2 − (p∗B/c)2,where E∗beam is the energy of the beam and p∗B is the momentum of reconstructed Bmeson candidates in the e+e− center-of-mass frame. A signal yield of 508±31 (757±44)events is obtained for BaBar (Belle). The signal yields split into decay modes and ex-periments are summarized in table I. The Mbc data distributions and projections of thefits are shown in fig. 1.The time-dependent CP violation analysis is performed by combining the BaBarand Belle flavor-tagged proper decay time distributions on the likelihood level. In theTable I. – Summary of B0 → D(∗)CP h0 signal yields.Decay mode BaBar BelleB0 → DCP π0 241 ± 22 345 ± 25B0 → DCP η 106 ± 14 148 ± 18B0 → DCP ω 66 ± 10 151 ± 17B0 → D∗CP π0 72 ± 12 80 ± 14B0 → D∗CP η 39 ± 8 39 ± 10B0 → D(∗)CP h0 total 508 ± 31 757 ± 44COMBINED CP VIOLATION MEASUREMENTS BY THE BABAR AND BELLE COLLABORATIONS 3Fig. 1. – The Mbc data distributions (data points with error bars) and projections of the fits(solid line) of B0 → D(∗)CP h0 decays for (a) BaBar and (b) Belle. The dashed and dotted linesrepresent projections of the signal and background components of the fits, respectively.measurement, the following log-likelihood function is maximized:(1) lnL =∑ilnPBaBari +∑jlnPBellej .The indices i and j denote events reconstructed from BaBar and Belle data, respec-tively. The probability density functions for signal are constructed from the convolutionof experiment-specific resolution functions accounting for the finite B meson vertex res-olution with the decay rate of a neutral B meson decaying to a CP eigenstate, definedasg(Δt) =e−|Δt|/τB04τB0{1 + q[S sin(ΔmdΔt) − C cos(ΔmdΔt)]} ,(2)where Δt is the the proper time interval between the decays of the two B mesons producedin an Υ(4S) decay, and S and C, respectively, measure mixing-induced and direct CPviolation. The q = +1 (−1) denotes the b-flavor content when the accompanying Bmeson is tagged as a B0 (B0) meson. The neutral B meson lifetime is represented byτB0 , and the B0 −B0mixing frequency by Δmd. The experimental flavor-tagged properdecay time distributions for BaBar and Belle for the CP -even and CP -odd final statesand projections of the fit are shown in fig. 2.The result of the measurement including statistical and systematic uncertainties is−ηfCP S = +0.66 ± 0.10 (stat.) ± 0.06 (syst.)(3)C = −0.02 ± 0.07 (stat.) ± 0.03 (syst.),where ηfCP is the CP eigenvalue of the final state. The individual sources contributingto the systematic uncertainties are summarized in table II.4 M. RÖHRKEN on behalf of the BABAR and BELLE COLLABORATIONSFig. 2. – The proper time interval distributions of B0 → D(∗)CP h0 decays (data points with errorbars) for B0 tags (red) and B0tags (blue) and the corresponding CP violating asymmetries for(a)-(b) BaBar and (c)-(d) Belle for candidates associated with high-quality flavor tags.Table II. – Systematic uncertainties of the measured time-dependent CP violation parametersof B0 → D(∗)CP h0 decays (in units of 10−2).Source S CBackground Δt PDFs 0.4 0.1Δt resolution functions 2.0 0.4Flavor-tagging 0.3 0.3Peaking background 4.9 0.9Physics parameters 0.2 < 0.1Possible fit bias 0.6 0.8Signal purity 0.6 0.3Tag-side interference 0.1 1.4Vertex reconstruction 1.5 1.4Total 5.6 2.5COMBINED CP VIOLATION MEASUREMENTS BY THE BABAR AND BELLE COLLABORATIONS 5The statistical significance of the result is estimated by a likelihood-ratio approach. In-cluding systematic uncertainties, the measurement excludes the hypothesis of no mixing-induced CP violation in B0 → D(∗)CP h0 decays at a confidence level of 1−6.6×10−8. Thiscorresponds to a significance of 5.4 standard deviations, establishing an observation of CPviolation in B0 → D(∗)CP h0 decays for the first time. The result agrees well with the Stan-dard Model prediction of S = −ηfCP sin(2β) and C = 0. The measured mixing-inducedCP violation is compatible with the current world average of sin(2β) = 0.68 ± 0.02 [9]within 0.2 standard deviations.In summary, we combine for the first time the final data sets of the BaBar and Belleexperiments in a single physics analysis to measure the time-dependent CP violationof B0 → D(∗)CP h0 decays. In this first measurement performed on a data sample ofmore than 1 ab−1, we observe for the first time CP violation in B0 → D(∗)CP h0 decaysdriven by mixing-induced CP violation, and we measure sin(2β) = 0.66 ± 0.10 (stat.) ±0.06 (syst.). The result is consistent within 0.2 standard deviations with the more preciseworld average of sin(2β) = 0.68 ± 0.02 [9] measured from b → cc̄s transitions. Atthe expected precision of the upcoming high-luminosity B factory experiment Belle II,B0 → D(∗)CP h0 decays will provide a new new gold standard reference for the new physicssearches in the mixing-induced CP violation of b → s penguin-mediated B meson decays.REFERENCES[1] Cabibbo N., Phys. Rev. Lett., 10 (1963) 531.[2] Kobayashi M. and Maskawa T., Prog. Theor. Phys., 49 (1973) 652.[3] BaBar Collaboration (Aubert B. et al.), Phys. Rev. Lett., 87 (2001) 091801.[4] Belle Collaboration (Abe K. et al.), Phys. Rev. Lett., 87 (2001) 091802.[5] BaBar Collaboration (Aubert B. et al.), Phys. Rev. Lett., 93 (2004) 131801.[6] Belle Collaboration (Chao Y. et al.), Phys. Rev. Lett., 93 (2004) 191802.[7] BaBar Collaboration (Aubert B. et al.), Phys. Rev. D, 79 (2009) 072009.[8] Belle Collaboration (Adachi I. et al.), Phys. Rev. Lett., 108 (2012) 171802.[9] Heavy Flavor Averaging Group (Amhis Y. et al.), arXiv:1412.7515 (2014).[10] Fleischer R., Phys. Lett. B, 562 (2003) 234; Fleischer R., Nucl. Phys. B, 659 (2003)321.[11] Grossman Y. and Worah M. P., Phys. Lett. B, 395 (1997) 241; London D. and SoniA., Phys. Lett. B, 407 (1997) 61; Moroi T., Phys. Lett. B, 493 (2000) 366; Baek S.,Goto T., Okada Y. and Okumura K. I., Phys. Rev. D, 64 (2001) 095001; Chang D.,Masiero A. and Murayama H., Phys. Rev. D, 67 (2003) 075013.[12] BaBar Collaboration (Aubert B. et al.), Phys. Rev. Lett., 99 (2007) 081801.[13] Belle Collaboration (Krokovny P. et al.), Phys. Rev. Lett., 97 (2006) 081801.[14] BaBar Collaboration (Aubert B. et al.), Phys. Rev. Lett., 99 (2007) 231802.

Combined CP violation measurements by the BaBar and Belle Collaborations

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Combined CP violation measurements by the BaBar and Belle Collaborations

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