We report on measurements of time-dependent CP-violation asymmetries in neutral B meson decays to charmonium and charm final states. The results are obtained from a data sample of (467 {+-} 5) x 10{sup 6} {Upsilon}(4S) {yields} B{bar B} decays collected with the BABAR detector at the PEP-II B factory

Chen, Chunhui

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Work supported in part by US Department of Energy contract DE-AC02-76SF00515arXiv:0809.3423 [hep-ex]SLAC-PUB-13402CP Violation in B0 decays to Charmonium and Charm Final States at BABARChunhui ChenDepartment of Physics, University of Maryland, College Park, Maryland 20742-4111, U.S.ARepresenting the BABAR CollaborationWe report on measurements of time-dependent CP -violation asymmetries in neutral B meson decays to charmoniumand charm final states. The results are obtained from a data sample of (467± 5)× 106 Υ(4S) → BB decays collectedwith the BABAR detector at the PEP-II B factory.1. IntroductionIn the Standard Model (SM), CP violation is described by the Cabibbo-Kobayashi-Maskawa (CKM) quark mixingmatrix, V [1]. In particular an irreducible complex phase in the 3 × 3 mixing matrix is the source of all the SMCP violation. Measurements of time-dependent CP asymmetries in the B0 meson decays, through the interferencebetween decays with and without B0−B0 mixing, have provides stringent test on the mechanism of CP violation inthe SM.In this paper, we present the most updated measurements of CP violation in neutral B meson decays to charmoniumand charm final states at BABAR . The data used in this analysis were collected with the BABAR detector operating atthe PEP-II B Factory located at the Stanford Linear Accelerator Center. The BABAR dataset comprises (467±5)×106BB pairs collected from 1999 to 2007 at the center-of-mass (CM) energy√s = 10.58 GeV, corresponding to the Υ(4S)resonance.2. Analysis TechniqueTo measure time-dependent CP asymmetries, we typically fully reconstruct a neutral B meson decaying to acommon final state (Brec). We identify (tag) the initial flavor of the Brec candidate using information from theother B meson (Btag) in the event. The decay rate g+ (g−) for a neutral B meson decaying to a CP eigenstateaccompanied by a B0 (B0) tag can be expressed asg±(∆t) =e−|∆t|/τB04τB0{(1∓∆w)± (1− 2w)×[− ηfS sin(∆md∆t)− C cos(∆md∆t)]}(1)whereS = −ηf 2 Imλ1 + |λ|2 , C =1− |λ|21 + |λ|2 , (2)the CP eigenvalue ηf = +1 (−1) for a CP even (odd) final state, ∆t ≡ trec− ttag is the difference between the properdecay times of Brec and Btag, τB0 is the neutral B lifetime, and ∆md is the mass difference of the B meson masseigenstates determined from B0-B0 oscillations [2]. We assume that the corresponding decay-width difference ∆Γdis zero. Here, λ = (q/p)(A¯/A), where q and p are complex constants that relate the B-meson flavor eigenstates tothe mass eigenstates, and A¯/A is the ratio of amplitudes of the decay without mixing of a B0 or B0 to the finalstate under study. The average mistag probability w describes the effect of incorrect tags, and ∆w is the differencebetween the mistag probabilities for B0 and B0 mesons. The sine term in Eq. 1 results from the interference betweenSeptember 2008Invited talk/Presented at the 34th International Conference On High Energy Physics , 7/30/2008 to 8/5/2008, Philadelphia, PA, USAdirect decay and decay after B0 −B0 oscillation. A non-zero cosine term arises from the interference between decayamplitudes with different weak and strong phases (direct CP violation |A¯/A| 6= 1) or from CP violation in B0 −B0mixing (|q/p| 6= 1).In the SM, CP violation in mixing is negligible. When only one diagram contributes to the decay process and noother weak phase appears in the process, we expect C = 0 and S = −ηf sin2β for B0 decay that is governed by ab→ c transition, where β ≡ arg [−VcdV ∗cb/VtdV ∗tb].3. B0 → (cc¯)K(∗)0In the SM, the decay B0 → (cc¯)K(∗)0 is dominated by a color-suppressed b→ ccs tree diagram and the dominatepenguin diagram has the same weak phase. As a result, the parameter C = 0 and S = −ηf sin2β are valid to a goodaccuracy. Recent theoretical calculations suggest that the correction on S is of the order of 10−3 − 10−4 [3], wellbelow the precision of the current experimental measurement.At BABAR , we reconstruct B0 decays to the final states J/ψK0S , J/ψK0L, ψ(2S)K0S , χc1K0S , ηcK0S , and J/ψK∗0(K(∗)0 → K0Spi0). The J/ψK0L final state is CP even, and the J/ψK∗0 final state is an admixture of CP evenand CP odd amplitudes. Ignoring the angular information in J/ψK∗0 results in a dilution of the measured CPasymmetry by a factor 1 − 2R⊥, where R⊥ is the fraction of the L=1 contribution. In Ref. [4] we have measuredR⊥ = 0.233 ± (stat) ± 0.005 (syst), which gives an effective ηf = 0.504 ± 0.033 for f = J/ψK∗0, after acceptancecorrections. By assuming the same CP asymmetries for all the final states, we measure [5]Sf = 0.691± 0.029 (stat)± 0.014 (syst),Cf = 0.026± 0.020 (stat)± 0.016 (syst),where we define Cf = ηfC and Sf = ηfS to be consistent with other time-dependent CP asymmetry measurements.In addition, BABAR also performs measurements, including systematic uncertainties, using individual mode, becausethe theoretical corrections could in principle be different among those modes. The complete results can be found inreference [5]. Our result is consistent with the SM expectation that Cf = 0 and Sf = sin2β, as well as our previousmeasurement [6]. Figure 1 shows the ∆t distributions and asymmetries in yields between B0 tags and B0 tags forthe ηf = −1 and ηf = +1 samples as a function of ∆t, overlaid with the projection of the likelihood fit result.Events / ( 0.4 ps )200400Events / ( 0.4 ps )  tags0B   tags0 BBABARpreliminarya)t (ps)∆-5 0 5Raw Asymmetry-0.4-0.200.20.4Raw Asymmetryb)Events / ( 0.4 ps )100200300Events / ( 0.4 ps )  tags0B   tags0 BBABARpreliminarya)t (ps)∆-5 0 5Raw Asymmetry-0.4-0.200.20.4Raw Asymmetryb)Figure 1: Left: a) Number of ηf = −1 candidates (J/ψK0S, ψ(2S)K0S, χc1K0S, and ηcK0S) in the signal region with a B0 tag(NB0 ) and with a B0 tag (NB0), and b) the raw asymmetry, (NB0 − NB0 )/(NB0 + NB0 ), as functions of ∆t; Right: thecorresponding distributions for the ηf = +1 mode J/ψK0L. The solid (dashed) curves represent the fit projections in ∆t forB0 (B0) tags. The shaded regions represent the estimated background contributions.Invited talk/Presented at the 34th International Conference On High Energy Physics , 7/30/2008 to 8/5/2008, Philadelphia, PA, USA4. B0 → D(∗)±D(∗)∓The B0 → D(∗)±D(∗)∓ decays are dominated by a color-allowed tree-level b→ ccd transition. When neglecting thepenguin (loop) amplitude, the mixing-induced CP asymmetry of B0 → D(∗)±D(∗)∓ is also determined by sin2β [7].The effect of this assumption has been estimated in models based on factorization and heavy quark symmetry, andthe corrections are expected to be a few percent [8, 9]. A large deviation of S in B0 → D(∗)±D(∗)∓ with respect tosin2β determined from b→ (cc)s transition could indicate physics beyond the SM [10–12].The final state D+D− is a CP eigenstate so S = − sin2β and C = 0 in the SM when neglecting the penguincontribution. Most recently, the Belle collaboration reported evidence of large direct CP violation in B0 → D+D−where CD+D− = −0.91 ± 0.23 (stat) ± 0.06 (syst) [13], in contradiction to the SM expectation. This has not beenobserved by BABAR nor is it verified by the other B0 → D∗±D(∗)∓ decay modes [14, 15] which involve the samequark-level diagrams. We updated our measurement with the complete Υ(4S) data sample collected at BABAR andfind [16]SD+D− = −0.63± 0.36 (stat)± 0.05 (syst),CD+D− = −0.07± 0.23 (stat)± 0.03 (syst),which is consistent with the SM with small penguin contributions.The final state D∗±D∗∓ is a mixture of CP even and CP odd states. The fraction of CP odd component RT isdetermined to be RT = 0.158±0.028(stat)±0.006(syst) using a transversity analysis at BABAR [16] . We performed acombined analysis of the angular distribution and its time-dependence to extract the time-dependent CP asymmetry.We measure [16]S+ = −0.76± 0.16 (stat)± 0.04 (syst),C+ = 0.02± 0.12 (stat)± 0.02 (syst),S⊥ = −1.81± 0.71 (stat)± 0.16 (syst),C⊥ = 0.41± 0.50 (stat)± 0.08 (syst),where S+ and C+ are the CP asymmetries of the CP even component, and S⊥ and C⊥ are the CP asymmetries of theCP odd component. In the absence of penguin contribution, S+ = S⊥ = − sin2β and C+ = C⊥ = 0. Additionallywe fit the data constraining S+ = S⊥ = SD∗+D∗− and C+ = C⊥ = CD∗+D∗ and find [16]SD∗+D∗− = −0.71± 0.16 (stat)± 0.03 (syst),CD∗+D∗− = 0.05± 0.09 (stat)± 0.02 (syst).Because B0 → D∗±D∓ is not a CP eigenstate, the expressions for S and C are related, SD∗±D∓ =−√1− CD∗±D∓ sin(2βeff± δ), where δ is the strong phase difference between B0 → D∗+D− and B0 → D+D∗− [17].When neglecting the penguin contributions, βeff = β, and CD∗+D− = −CD+D∗− . We measure [16]SD∗+D− = −0.62± 0.21 (stat)± 0.03 (syst),SD+D∗− = −0.73± 0.23 (stat)± 0.05 (syst),CD∗+D− = 0.08± 0.17 (stat)± 0.04 (syst),CD−D∗+ = 0.00± 0.17 (stat)± 0.03 (syst) .All of the S parameters of B0 → D(∗)±D(∗)∓ measured in BABAR are consistent with the value of sin2β measuredin b→ ccs transitions and with the expectation from the SM for small penguin contributions. The C parameters areconsistent with zero in all modes. In particular, we see no evidence of the large direct CP violation reported by theBelle Collaboration in the B0 → D+D− channel.Invited talk/Presented at the 34th International Conference On High Energy Physics , 7/30/2008 to 8/5/2008, Philadelphia, PA, USA5. B0 → J/ψ pi0The B0 → J/ψpi0 decay has the same quark level diagrams as J/ψK0 except that the s quark in b → ccs issubstituted by a d quark. Therefore, the dominant tree diagram is Cabibbo suppressed compared to that of J/ψK0.However, unlike J/ψK0, the dominant penguin diagram in J/ψpi0, whose CKM element factor is in the same orderas the tree, has a different weak phase from the tree. Therefore the deviation in S from the sin2β of J/ψK0could be substantial. This mode is also useful to constrain the penguin pollution in B0 → (cc)K0 mode in a moremodel-independent way (assuming SU(3) symmetry) [18].BABAR has recently updated the CP violation measurement in this decay. We measure [19]S = −1.23± 0.21 (stat)± 0.04 (syst),C = −0.20± 0.19 (stat)± 0.03 (syst).The significance of S or C being nonzero has been estimated to be 4.0σ using ensembles of MC simulated experimentsincluding the systematic uncertainties. This constitutes evidence of the CP violation in B0 → J/ψpi0 decay. Thenumerical values of S and C are consistent with the SM expectations for a tree-dominated b→ ccd transition.6. ConclusionWe have presented most unadapted measurements of time-dependent CP -violation asymmetries in neutral B mesondecays to charmonium and charm final states from BABAR experiment. The results are in a good agreement with theSM expectations.References[1] N. Cabibbo, Phys. Rev. Lett. 10, 531 (1963); M. Kobayashi and T. Maskawa, Prog. Theor. Phys. 49, 652 (1973).[2] W. M. Yao et al. (Particle Data Group), J. Phys. G 33 (2006) 1.[3] H. Boos, T. Mannel and J. Reuter, Phys. Rev. D 70, 036006 (2004).[4] B. Aubert et al., (BABAR Collaboration), Phys. Rev. D 76, 031102(R) (2007).[5] B. Aubert et al., (BABAR Collaboration), arXiv:0808.1903 [hep-ex].[6] B. Aubert et al., (BABAR Collaboration), Phys. Rev. Lett. 99, 171803 (2007).[7] A. I. Sanda and Z. z. Xing, Phys. Rev. D 56, 341 (1997).[8] Z. z. Xing, Phys. Lett. B 443, 365 (1998).[9] Z. z. Xing, Phys. Rev. D 61, 014010 (2000).[10] Y. Grossman and M. P. Worah, Phys. Lett. B 395, 241 (1997).[11] M. Gronau, J. L. Rosner and D. Pirjol, Phys. Rev. D 78, 033011 (2008).[12] R. Zwicky, Phys. Rev. D 77, 036004 (2008).[13] S. Fratina et al., (Belle Collaboration), Phys. Rev. Lett. 98, 221802 (2007).[14] B. Aubert et al., (BABAR Collaboration), Phys. Rev. D 76, 111102 (2007).[15] B. Aubert et al., (BABAR Collaboration), Phys. Rev. Lett. 99, 071801 (2007).[16] B. Aubert et al., (BABAR Collaboration), arXiv:0808.1866 [hep-ex].[17] R. Aleksan, A. Le Yaouanc, L. Oliver, O. Pene and J. C. Raynal, Phys. Lett. B 317, 173 (1993).[18] M. Ciuchini, M. Pierini and L. Silvestrini, Phys. Rev. Lett. 95, 221804 (2005).[19] B. Aubert et al., (BABAR Collaboration), Phys. Rev. Lett. 101, 021801 (2008).Invited talk/Presented at the 34th International Conference On High Energy Physics , 7/30/2008 to 8/5/2008, Philadelphia, PA, USA

CP Violation in B0 decays to Charmonium and Charm Final States

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CP Violation in B0 decays to Charmonium and Charm Final States

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