Evidence For Direct CP Violation Research Articles

Measurement of the Time-Integrated CP Asymmetry in D^{0}→K^{-}K^{+} Decays.

The time-integrated CP asymmetry in the Cabibbo-suppressed decay D^{0}→K^{-}K^{+} is measured using proton-proton collision data, corresponding to an integrated luminosity of 5.7 fb^{-1} collected at a center-of-mass energy of 13TeV with the LHCb detector. The D^{0} mesons are required to originate from promptly produced D^{*+}→D^{0}π^{+} decays, and the charge of the companion pion is used to determine the flavor of the charm meson at production. The time-integrated CP asymmetry is measured to be A_{CP}(K^{-}K^{+})=[6.8±5.4±1.6]×10^{-4} where the first uncertainty is statistical and the second systematic. The direct CP asymmetries in D^{0}→K^{-}K^{+} and D^{0}→π^{-}π^{+} decays, a_{K^{-}K^{+}}^{d} and a_{π^{-}π^{+}}^{d}, are derived by combining A_{CP}(K^{-}K^{+}) with the time-integrated CP asymmetry difference, ΔA_{CP}=A_{CP}(K^{-}K^{+})-A_{CP}(π^{-}π^{+}), and other inputs, giving a_{K^{-}K^{+}}^{d}=(7.7±5.7)×10^{-4},a_{π^{-}π^{+}}^{d}=(23.2±6.1)×10^{-4},with a correlation coefficient corresponding to ρ=0.88. The compatibility of these results with CP symmetry is 1.4 and 3.8 standard deviations for D^{0}→K^{-}K^{+} and D^{0}→π^{-}π^{+} decays, respectively. This is the first evidence for direct CP violation in a specific D^{0} decay.

Recent results on CP violation at B factories

We review recent results of the Beauty Factories BaBar and Belle on CP violation in the quark sector and constraints on the CKM unitarity triangle. We first present the recent measurement, using BaBar and Belle data, of cos(2β) = cos(2ϕ1) in B0 → D(∗)h0 with $D \rightarrow {K^{0}_{S}} \pi ^{+} \pi ^{-}$ decays, using a combined time-dependent Dalitz plot analysis. The BaBar Dalitz plot analysis of the $B^{+} \rightarrow {K^{0}_{S}} \pi ^{+} \pi ^{0}$ decay is also presented, and shows an evidence for direct CP violation in B+ → K∗(892)π0. A recently published BaBar measurement of the |V ub| CKM matrix element allows to contrain one side of the unitarity triangle. These analyses use the data sets of the BaBar and Belle experiments containing 471 × 106 and 772 × 106 $B\overline {B}$ pairs collected at the Υ(4S) resonance at the asymmetric-energy B factories PEP-II at SLAC and KEKB at KEK, respectively.

Measurement of polarization amplitudes and CP asymmetries in B 0 → ϕK *(892)0

An angular analysis of the decay $B^0 \to \phi K^*(892)^0$ is reported based on a $pp$ collision data sample, corresponding to an integrated luminosity of 1.0 fb$^{-1}$, collected at a centre-of-mass energy of $\sqrt{s} = 7$ TeV with the LHCb detector. The P-wave amplitudes and phases are measured with a greater precision than by previous experiments, and confirm about equal amounts of longitudinal and transverse polarization. The S-wave $K^+ \pi^-$ and $K^+K^-$ contributions are taken into account and found to be significant. A comparison of the $B^0 \to \phi K^*(892)^0$ and $\bar{B}^0 \to \phi \bar{K}^*(892)^0$ results shows no evidence for direct CP violation in the rate asymmetry, in the triple-product asymmetries or in the polarization amplitudes and phases.

Search for direct CP violation in [formula omitted] modes using semileptonic B decays

A search for direct CP violation in D0→h−h+ (where h=K or π) is presented using data corresponding to an integrated luminosity of 1.0 fb−1 collected in 2011 by LHCb in pp collisions at a centre-of-mass energy of 7 TeV. The analysis uses D0 mesons produced in inclusive semileptonic b-hadron decays to the D0μX final state, where the charge of the accompanying muon is used to tag the flavour of the D0 meson. The difference in the CP-violating asymmetries between the two decay channels is measured to beΔACP=ACP(K−K+)−ACP(π−π+)=(0.49±0.30(stat)±0.14(syst))%. This result does not confirm the evidence for direct CP violation in the charm sector reported in other analyses.

Charming CP violation and dipole operators from RS flavor anarchy

Abstract Recently the LHCb collaboration reported evidence for direct CP violation in charm decays. The value is sufficiently large that either substantially enhanced Standard Model contributions or non-Standard Model physics is required to explain it. In the latter case only a limited number of possibilities would be consistent with other existing flavor-changing constraints. We show that warped extra dimensional models that explain the quark spectrum through flavor anarchy can naturally give rise to contributions of the size required to explain the the LHCb result. The D meson asymmetry arises through a sizable CP-violating contribution to a chromomagnetic dipole operator. This happens naturally without introducing inconsistencies with existing constraints in the up quark sector. We discuss some subtleties in the loop calculation that are similar to those in Higgs to γγ. Loop-induced dipole operators in warped scenarios and their composite analogs exhibit non-trivial dependence on the Higgs profile, with the contributions monotonically decreasing when the Higgs is pushed away from the IR brane. We show that the size of the dipole operator quickly saturates as the Higgs profile approaches the IR brane, implying small dependence on the precise details of the Higgs profile when it is quasi IR localized. We also explain why the calculation of the coefficient of the lowest dimension 5D operator is guaranteed to be finite. This is true not only in the charm sector but also with other radiative processes such as electric dipole moments, b → sγ, ϵ ′/ϵ K and μ → eγ. We furthermore discuss the interpretation of this contribution within the framework of partial compositeness in four dimensions and highlight some qualitative differences between the generic result of composite models and that obtained for dynamics that reproduces the warped scenario.

Mini-review of rare charmonium decays at BESIII

Recently, the LHCb experiment announced 3.5σ evidence for direct CP violation in D0 decay by looking at the difference between ACP(D0 → K+K−) and ACP(D0 → π+π−). This is the first evidence of CP violation in a charm system, which may indicate new physics beyond the Standard Model. Motivated by this measurement, we review rare processes in charmonium decay, especially, the weak decay, C or P violated decay, and lepton flavor violated decays. In case the new physics appears in charm sector, these rare decays of charmonium states will provide an opportunity to search for significant contributions from physics beyond the Standard Model. With huge J/ψ and ψ (2S) samples in BESIII experiment, the rare decays may be feasible.

Measurement of the CP-violating phase [formula omitted] in [formula omitted] decays

Measurement of the mixing-induced CP-violating phase ϕs in B¯s0 decays is of prime importance in probing new physics. Here 7421±105 signal events from the dominantly CP-odd final state J/ψπ+π− are selected in 1 fb−1 of pp collision data collected at s=7 TeV with the LHCb detector. A time-dependent fit to the data yields a value of ϕs=−0.019−0.174−0.003+0.173+0.004 rad, consistent with the Standard Model expectation. No evidence of direct CP violation is found.

Measurements of the branching fractions andCPasymmetries ofB±→J/ψπ±andB±→ψ(2S)π±decays

A study of B+ to J/psi pi+ and B+ to psi(2S) pi+ decays is performed with data corresponding to 0.37 fb-1 of proton-proton collisions at sqrt(s)=7 TeV. Their branching fractions are found to be B(B+ to J/psi pi+) = (3.88 +- 0.11 +- 0.15) x 10^{-5} and B(B+ to psi(2S) pi+) = (2.52 +- 0.26 +- 0.15) x 10^{-5}, where the first uncertainty is related to the statistical size of the sample and the second quantifies systematic effects. The measured CP asymmetries in these modes are ACP(J/psi pi) = 0.005 +- 0.027 +- 0.011 and ACP(psi(2S) pi) = 0.048 +- 0.090 +- 0.011 with no evidence of direct CP violation seen.

Search forCPViolation inD±Meson Decays toϕπ±

We search for CP violation in Cabibbo-suppressed charged D meson decays by measuring the difference between the CP violating asymmetries for the Cabibbo-suppressed decays D+ -> K+K-pi+ and the Cabibbo-favored decays Ds -> K+K-pi+ in the K+K- mass region of the phi resonance. Using 955/fb of data collected with the Belle detector we obtain A_CP(D+ -> phi pi+) = (+0.51 +- 0.28 +- 0.05)%. The measurement improves the sensitivity of previous searches by more than a factor of five. We find no evidence for direct CP violation.

Measurement ofCPobservables inB±→DCPK±decays and constraints on the CKM angleγ

Using the entire sample of 467 million Y(4S) --> BBbar decays collected with the BaBar detector at the PEP-II asymmetric-energy B factory at SLAC, we perform a "GLW" analysis of B+- --> D K+- decays, using decay modes in which the neutral D meson decays to either CP-eigenstates or non-CP-eigenstates. We measure the partial decay rate charge asymmetries for CP-even and CP-odd D final states to be A_CP+ = 0.25+-0.06+-0.02 and A_CP- = -0.09+-0.07+-0.02, respectively, where the first error is the statistical and the second is the systematic uncertainty. The parameter A_CP+ is different from zero with a significance of 3.6 standard deviations, constituting evidence for direct CP violation. We also measure the ratios of the charged-averaged B partial decay rates in CP and non-CP decays, R_CP+ = 1.18+-0.09+-0.05 and R_CP- = 1.07+-0.08+-0.04. We infer frequentist confidence intervals for the angle gamma of the (db) unitarity triangle, for the strong phase difference delta_B, and for the amplitude ratio r_B, which are related to the B- --> DK- decay amplitude by r_Be^{i(delta_B-gamma)} = A(B- --> anti-D0 K^-)/A(B- --> D0 K-). Including statistical and systematic uncertainties, we obtain 0.24<r_B<0.45 (0.06<r_B<0.51) and, modulo 180 degrees, 11.3 degrees < gamma < 22.7 degrees or 80.9 degrees < gamma < 99.1 degrees or 157.3 degrees < gamma < 168.7 degrees (7.0 degrees < gamma < 173.0 degrees) at the 68% (95%) confidence level.

Time-dependent Dalitz plot measurement ofCPparameters inB0→KS0π+π−decays

We present a time-dependent Dalitz plot measurement of CP violation parameters in B0 --> Ks Pi+ Pi- decays. These results are obtained from a large data sample that contains 657 million BBbar pairs collected at the Y(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e- collider. For the CP violation parameters, we obtain two consistent solutions that describe the data well. The first of these solutions may be preferred by external information from other measurements. There is no evidence for direct CP violation in B0 --> rho0(770) Ks, B0 --> f0(980) Ks and B0 --> K*+(892) Pi-, while measurements of mixing-induced CP violation in B0 --> rho0(770) Ks, B0 --> f0(980) Ks decays are consistent with that of b --> c cbar s decays. We also measured the phase difference between B0 --> K*+(892) Pi- and B0B --> K*-(892) Pi+ which may be used to extract phi3.

Evidence for directCPviolation from Dalitz-plot analysis ofB±→K±π∓π±

We report a Dalitz-plot analysis of the charmless hadronic decays of charged B mesons to the final state K+/- pi+/- pi-/+. Using a sample of 383.2 +/- 4.2 million BBbar pairs collected by the BaBar detector, we measure CP-averaged branching fractions and direct CP asymmetries for intermediate resonant and nonresonant contributions. We find evidence for direct CP violation in the decay B+ -> rho0(770) K+, with a CP violation parameter A_CP = (+44 +/- 10 +/- 4 +5,-13)%.

Measurements of ϕ1(β) in B decays to charm and charmonium at Belle

We present a measurement of the time-dependent CP violation parameters for B0 → D*+D*-Ks0 and B0 → J/ψKs0 decays obtained from the distribution of proper time intervals between the two B decays. These results are obtained from a data sample of BB pairs collected at the γ (4S) resonance with the Belle detector at the KEKB asymmetric e+e− collider. For B0 → D*+D*-Ks0, we find no evidence for direct or mixing-induced CP violation, and in a fit sensitive to cos2ϕ1, no conclusion can be drawn regarding its sign with current statistics. For B0 → J/ψπ0, we find no evidence for direct CP violation and measure mixing-induced CP violation consistent with Standard Model expectations, with a 2.4σ significance.

Search for direct CP violation in B decays at BABAR

We report on new and updated BABAR measurements of direct CP-violating quantities incharmless B-decays. They have been performed using a sample of about 383 million γ(4S)→Bb̄ decays collected at the PEP-II asymmetric B Factory at SLAC. No evidence of direct CP violation is found in these measurements, all statistically limited.

Branching fraction andCP-violation charge asymmetry measurements forB-meson decays toηK±,ηπ±,η′K,η′π±,ωK, andωπ±

We present measurements of the branching fractions for B0 meson decays to eta'K0 and omegaK0, and of the branching fractions and CP-violation charge asymmetries for B+ meson decays to etapi+, etaK+, eta'pi+, eta'K+, omegapi+, and omegaK+. The data, collected with the BABAR detector at the Stanford Linear Accelerator Center, represent 383 million BBbar pairs produced in e+e- annihilation. The measurements agree with previous results; we find no evidence for direct CP violation.

Studies ofCPViolation inB→J/ψK*Decays

CP violation in $B\to J/\psi K^*$ decays is studied using an angular analysis in a data sample of 253 fb$^{-1}$ recorded with the Belle detector at the KEKB $e^+e^-$ collider. The flavor separated measurements of the decay amplitudes indicate no evidence for direct CP violation. T-odd CP violation is studied using the asymmetries in triple product correlations, and the results are consistent with the Standard Model null predictions. The time-dependent angular analysis gives the following values of CP violating parameters: $\sin 2\phi_1 = 0.24 \pm 0.31 \pm 0.05$ and $\cos 2\phi_1 = 0.56 \pm 0.79 \pm 0.11$.

Measurement ofCPasymmetries inB0→ϕK0andB0→K+K−Ks0decays

We measure the time-dependent CP asymmetry parameters in B0 --> K+ K- K0 based on a data sample of approximately 227 million B-meson pairs recorded at the Upsilon(4S) resonance with the BaBar detector at the PEP-II B-meson Factory at SLAC. We reconstruct two-body B0 decays to Phi(1020) K0S and Phi(1020)K0L, and the three-body decay K+ K- K0S with Phi(1020) K0S excluded. For the B0 --> Phi K0 decays, we measure sin(2 beta_{eff})(Phi K0) = +0.50 +/- 0.25(stat) +0.07/-0.04(syst). The B0 --> K+ K- K0S decays are dominated by K+ K- S-wave, as determined from an angular analysis; we measure sin(2 beta_{eff})(K+ K- K0S) = +0.55 +/- 0.22(stat) +/- 0.04(syst) +/- 0.11(CP), where the last error is due to the uncertainty in the fraction of CP-even contributions to the decay amplitude. We find no evidence for direct CP violation.

Final state interactions in hadronicBdecays

There exist many experimental indications that final-state interactions (FSIs) may play a prominent role not only in charmful B decays but also in charmless B ones. We examine the final-state rescattering effects on the hadronic B decay rates and their impact on direct CP violation. The color-suppressed neutral modes such as $B^0\to D^0\pi^0,\pi^0\pi^0,\rho^0\pi^0,K^0\pi^0$ can be substantially enhanced by long-distance rescattering effects. The direct CP-violating partial rate asymmetries in charmless B decays to $\pi\pi/\pi K$ and $\rho\pi$ are significantly affected by final-state rescattering and their signs are generally different from that predicted by the short-distance approach. For example, direct CP asymmetry in $B^0\to\rho^0\pi^0$ is increased to around 60% due to final state rescattering effects whereas the short-distance picture gives about 1%. Evidence of direct CP violation in the decay $\bar B^0\to K^-\pi^+$ is now established, while the combined BaBar and Belle measurements of $\bar B^0\to\rho^\pm\pi^\mp$ imply a $3.6\sigma$ direct CP asymmetry in the $\rho^+\pi^-$ mode. Our predictions for CP violation agree with experiment in both magnitude and sign, whereas the QCD factorization predictions seem to have some difficulty with the data. Current data on $\pi K$ modes seem to violate the isospin sum rule relation, suggesting the presence of electroweak penguin contributions. We have also investigated whether a large transverse polarization in $B\to \phi K^*$ can arise from the final-state rescattering of $D^{(*)}\bar D_s^{(*)}$ into $\phi K^*$.

Evidence for DirectCPViolation inB0→K+π−Decays

We report evidence for direct CP violation in the decay B0 -> K+-pi-+ with 253/fb of data collected with the Belle detector at the KEKB e+e- collider. Using 275 million B B_bar pairs we observe a B -> K+-pi-+ signal with 2140+-53 events. The measured CP violating asymmetry is Acp(K+-pi-+) = -0.101+-0.025 (stat)+-0.005 (syst), corresponding to a significance of 3.9 sigma including systematics. We also search for CP violation in the decays B+- -> K+-pi0 and B+- -> pi+-pi0. The measured CP violating asymmetries are Acp(K+-pi0) = 0.04+-0.05(stat)+-0.02(syst) and Acp(pi+-pi0) = -0.02+-0.10(stat)+-0.01(syst), corresponding to the intervals -0.05 < Acp(K+-pi0) < 0.13 and -0.18<Acp(pi+-pi0)<0.14 at 90% confidence level.

Observation of large CP violation and evidence for direct CP violation in B0-->pi(+)pi(-) decays.

We report the first observation of CP violation in B0-->pi(+)pi(-) decays based on 152x10(6) gamma (4S)-->BB decays collected with the Belle detector at the KEKB asymmetric-energy e(+)e(-) collider. We reconstruct a B0-->pi(+)pi(-) CP eigenstate and identify the flavor of the accompanying B meson from its decay products. From the distribution of the time intervals between the two B meson decay points, we obtain A(pipi)=+0.58+/-0.15(stat)+/-0.07(syst) and S(pipi)=-1.00+/-0.21(stat)+/-0.07(syst). We rule out the CP-conserving case, A(pipi)=S(pipi)=0, at a level of 5.2 standard deviations. We also find evidence for direct CP violation with a significance at or greater than 3.2 standard deviations for any S(pipi) value.