Direct CP Asymmetries Research Articles

CP and charge asymmetries at CDF

We present CDF results on the branching fractions and time-integrated direct CP asymmetries for B0 and Bs0 decay modes into pairs of charmless charged hadrons (pions or kaons). We report also the first observation of Bs0 → Ds±K± mode and the measurement of its branching fraction.

Measurement of theB→Xsγbranching fraction and photon energy spectrum using the recoil method

We present a measurement of the branching fraction and photon energy spectrum for the decay B --> X_s gamma using data from the BaBar experiment. The data sample corresponds to an integrated luminosity of 210 fb^{-1}, from which approximately 680 000 BB events are tagged by a fully reconstructed hadronic decay of one of the B mesons. In the decay of the second B meson, an isolated high--energy photon is identified. We measure BR(B --> X_s gamma) = (3.66 +- 0.85_{stat} +- 0.60_{syst}) x 10^{-4} for photon energies E_gamma above 1.9 GeV in the B rest frame. From the measured spectrum we calculate the first and second moments for different minimum photon energies, which are used to extract the heavy-quark parameters m_b and mu_{pi}^2. In addition, measurements of the direct CP asymmetry and isospin asymmetry are presented.

QCD Approach to B → Dπ Decays and CP Violation

The branching ratios and CP violations of the B → Dπ decays, including both the color-allowed and the color-suppressed modes, are investigated in detail within QCD framework by considering all diagrams that lead to three effective currents of two quarks. An intrinsic mass scale as a dynamical gluon mass is introduced to treat the infrared divergence caused by the soft collinear approximation in the endpoint regions, and the Cutkosky rule is adopted to deal with a physical-region singularity of the on mass-shell quark propagators. When the dynamical gluon mass μg is regarded as a universal scale, it is extracted to be around μg = 440 MeV from one of the well-measured B → Dπ decay modes. The resulting predictions for all branching ratios are in agreement with the current experimental measurements. As these decays have no penguin contributions, there are no direct CP asymmetries. Due to interference between the Cabibbo-suppressed and the Cabibbo-favored amplitudes, mixing-induced CP violations are predicted in the B → D±π∓ decays to be consistent with the experimental data at 1-σ level. More precise measurements will be helpful to extracting weak angle 2β + γ.

Flavors and phases in unparticle physics

Inspired by the recent Georgi's unparticle proposal, we study the flavor structures of the Standard Model (SM) particles when they couple to unparticles. At a very high energy scale, we introduce BZ charges for the SM particles, which are universal for each generation and allow BZ fields to distinguish flavor generations. At the ΛU scale, BZ operators and charges are matched onto unparticle operators and charges, respectively. In this scenario, we find that tree flavor changing neutral currents (FCNCs) can be induced by the rediagonalizations of the SM fermions. As an illustration, we employ the Fritzsch ansatz to the SM fermion mass matrices and we find that the FCNC effects could be simplified to be associated with the mass ratios denoted by mimj/m32, where m3 is the mass of the heaviest particle in each type of fermion generations and i, j are the flavor indices. In addition, we show that there is no new CP violating phase for FCNCs in down type quarks beside the unique one in the CKM matrix. We use B¯q→ℓ+ℓ− as examples to display the new FCNC effects. In particular, we demonstrate that the direct CP asymmetries in the decays can be O(10%) due to the peculiar CP conserving phase in the unparticle propagator.

Probing the unparticle signal in [formula omitted] penguin processes

We investigate the effect of unparticles in the pure b→d penguin processes B0→K0K¯0 and B+,0→ϕπ+,0. Since these processes receive dominant contributions due to the top quark in the loop, direct and mixing-induced CP asymmetry parameters in these processes are expected to be vanishingly small in the Standard Model. We find that due to the unparticle effect sizable nonzero CP violation could be possible in these channels.

Observation of the DecayB+→K+K−π+

We report the observation of charmless hadronic decays of charged B mesons to the final state K+K-pi+. Using a data sample of 347.5 fb^-1 collected at the Y(4S) resonance with the BABAR detector, we observe 429+/-43 signal events with a significance of 9.6 sigma. We measure the inclusive branching fraction BF(B+ --> K+K-pi+) = [5.0+/-0.5(stat)+/-0.5(syst)]x10^-6. Inspection of the Dalitz plot of signal candidates shows a broad structure peaking near 1.5 GeV/c^2 in the K+K- invariant mass distribution. We find the direct CP asymmetry to be consistent with zero.

A solution to [formula omitted] puzzle and [formula omitted

The large ratio of color-suppressed tree amplitude to color-allowed one in B→ππ decays is difficult to understand within the Standard Model, which is known as the “B→ππ puzzle”. The two tree diagrams contain the up- and charm-quark component of penguin amplitude, Puc, which cannot be separated by measuring B→ππ decays alone. We show that the measurements of the branching ratio and direct CP asymmetry of B+→K+K0¯ decay enable one to disentangle the Puc with two-fold ambiguity. One of the two degenerate solutions of the Puc can solve the B→ππ puzzle by giving |C/T|∼0.3 which is consistent with the expectation in the Standard Model. We also show that the two solutions can be discriminated by the measurement of the indirect CP asymmetry of B0→K0K0¯. We point out that the corresponding puzzle in B→πK decays is not solved in this way.

Possible signatures of unparticles in rare annihilation typeBdecays

We investigate the effect of unparticles in the pure annihilation type decays B{sup -}{yields}D{sub s}{sup -}{phi} and D{sub s}{sup -}K*{sup 0}. Since these decays have only annihilation contributions their branching ratios are expected to be very small in the standard model and the direct CP asymmetry parameters to be zero. We find that due to the unparticle effect these branching ratios can be significantly enhanced from their standard model values. Furthermore, sizable nonzero direct CP violation could also be possible in these channels due to the presence of intrinsic CP conserving phase in the unparticle propagator.

NNLO vertex corrections in charmless hadronic B decays: Imaginary part

We compute the imaginary part of the 2-loop vertex corrections in the QCD factorization framework for hadronic two-body decays as B → π π . This completes the NNLO calculation of the imaginary part of the topological tree amplitudes and represents an important step towards an NNLO prediction of direct CP asymmetries in QCD factorization. Concerning the technical aspects, we find that soft and collinear infrared divergences cancel in the hard-scattering kernels which demonstrates factorization at the 2-loop order. All results are obtained analytically including the dependence on the charm quark mass. The numerical impact of the NNLO corrections is found to be significant, in particular they lead to an enhancement of the strong phase of the colour-suppressed tree amplitude.

D–[formula omitted] mixing and rare D decays in the littlest Higgs model with non-unitarity matrix

We study the D–D¯ mixing and rare D decays in the littlest Higgs model. As the new weak singlet quark with the electric charge of 2/3 is introduced to cancel the quadratic divergence induced by the top quark, the standard unitary 3×3 Cabibbo–Kobayashi–Maskawa matrix is extended to a non-unitary 4×3 matrix in the quark charged currents and Z-mediated flavor changing neutral currents are generated at tree level. In this model, we show that the D–D¯ mixing parameter can be as large as the current experimental value and the decay branching ratio (BR) of D→Xuγ is small but its direct CP asymmetry could be O(10%). In addition, we find that the BRs of D→Xuℓ+ℓ−, D→Xuνν¯ and D→μ+μ− could be enhanced to be O(10−9), O(10−8) and O(10−9), respectively.

To the origin of the difference of FSI phases in [formula omitted] and [formula omitted] decays

The final state interactions (FSI) model in which soft rescattering of low mass intermediate states dominates is suggested. It explains why the strong interaction phases are large in the B d → π π channel and are considerably smaller in the B d → ρ ρ one. Direct CP asymmetries of B d → π π decays which are determined by FSI phases are considered as well.

Branching Fractions and Direct CP Asymmetries of Charmless B Decay Modes at the Tevatron

We present new CDF results on the branching fractions and time-integrated direct CP asymmetries for $B^{0}$ and $B^{0}_{s}$ decay modes into pairs of charmless charged hadrons (pion or kaon). The data set for this update amounts to 1 fb$^{-1}$ of $\bar{p}p$ collisions at $\sqrt{s}=1.96 \rm{TeV}$. We report the first observation of the $B^{0}_{s} \to K^{-}\pi^{+}$ mode and a measurement of its branching fraction and direct CP asymmetry. We also observe for the first time two charmless decays of $b$-baryon: $\Lambda^{0}_{b} \to p\pi^{-}$ and $\Lambda^{0}_{b} \to pK^{-}$.

FINDING γ FROM THE η-η′ MIXING WITHIN QCD FACTORIZATION

We propose a method to determine the weak CP violating angle γ by analyzing the charmless nonleptonic B→(η, η′)K decay within the QCD factorization framework. We obtain constraints in the γ–θ (the octet-singlet mixing angle in η-η′ sector) contour plane by using the world average data of direct CP-asymmetry Acp(B→(η, η′)K) and the branching ratio BR (B+→(η, η′)K+). For Acp(B→η(η′)K) = -0.33±0.12(0.031±0.021), we find that γ lies in between 60°(20°) and 160°(160°) for θ = -21.3° for μ = mb/2, whereas for μ = mband the same θ, it lies in between 75°(20°) and 150°(160°). We discuss the two mixing angles scenario arised in the SU (3)Fsymmetry breaking limit. We also include the effect of the power corrections in our analysis and found those not so significant in the present case.

On puzzles and non-puzzles in B→ππ,πK decays

Recently, we have seen interesting progress in the exploration of CP violation in B0 d→π+π-: the measurements of mixing-induced CP violation by the BaBar and Belle collaborations are now in good agreement with each other, whereas the picture of direct CP violation is still unclear. Using the branching ratio and direct CP asymmetry of B0 d→π-K+, this situation can be clarified. We predict $\mathcal{A}_{CP}^{\text{dir}}(B_d\to\pi^+\pi^-)=-0.24\pm0.04$ , which favours the BaBar result, and we extract γ=(70.0+3.8 -4.3)°, which agrees with the unitarity triangle fits. Extending our analysis to other B→πK modes and B0 s→K+K- with the help of the SU(3) flavour symmetry and plausible dynamical assumptions, we find that all observables with colour-suppressed electroweak penguin contributions are measured to be in excellent agreement with the standard model. As far as the ratios Rc,n of the charged and neutral B→πK branching ratios are concerned, which are sizeably affected by electroweak penguin contributions, our standard-model predictions have almost unchanged central values but significantly reduced errors. Since the new data have moved quite a bit towards these results, the “B→πK puzzle” for the CP conserving quantities has been significantly reduced. However, the mixing-induced CP violation of B0 d→π0KS does look puzzling; if confirmed by future measurements, this effect could be accommodated through a modified electroweak penguin sector with a large CP violating new-physics phase. Finally, we point out that the established difference between the direct CP asymmetries of B±→π0K± and Bd→π∓K± appears to be generated by hadronic and not by new physics.

Measurement ofBdecays toϕKγ

We search for the decays B- -> phi K- gamma and B0bar -> phi K0bar gamma in a data sample of 228 million BBbar pairs collected at the Upsilon(4S) resonance with the BaBar detector. We measure the branching fraction B(B- -> phi K- gamma) = (3.5 +/- 0.6 +/- 0.4) x 10^-6 and set an upper limit B(B0bar -> phi K0bar gamma) < 2.7 x 10^-6 at the 90% confidence level. We also measure the direct CP asymmetry in B- -> phi K- gamma, A_CP = (-26 +/- 14 +/- 5)%. The uncertainties are statistical and systematic, respectively.

Study of K* 0(1430) and a0(980) from B→K* 0(1430)π and B→a0(980)K decays

We use the decay modes B→K* 0(1430)π and B→a0(980)K to study the scalar mesons K* 0(1430) and a0(980) within the framework of perturbative QCD. For B→K* 0(1430)π, we perform our calculation in two scenarios for the scalar meson spectrum. The results indicate that scenario II is more favored by the experimental data than scenario I. The important contribution from annihilation diagrams can enhance the branching ratios by about 50% in scenario I and about 30% in scenario II. The direct CP-asymmetries in B→K* 0(1430)π are small, which is consistent with the present experiments. The predicted branching ratio of B→a0(980)K in scenario I differs from the experiments by a factor of 2, which indicates that a0(980) cannot be interpreted as q̄q.

Penguin pollution in theB0→J/ψKSdecay

We present the most complete analysis of the penguin correction to the extraction of the standard-model parameter sin(2\phi_1) from the B^0 -> J/psi K_S decay up to leading power in 1/m_b and to next-to-leading order in \alpha_s, \phi_1 being the weak phase, m_b the b quark mass, and \alpha_s the strong coupling constant. The deviation \Delta S_{J/psi K_S} of the mixing-induced CP asymmetry from sin(2\phi_1) and the direct CP asymmetry A_{J/psi K_S} are both found to be of O(10^{-3}) in a formalism that combines the QCD-improved factorization and perturbative QCD approaches. The above results, different from those of O(10^{-4}) and of O(10^{-2}) obtained in the previous calculations, provide an important standard-model reference for verifying new physics from the B^0 -> J/psi K_S data.

B→ππ decays

The branching ratios and CP asymmetries of $B\to \pi\pi$ decays measured in B factory experiments indicate a large ratio of color-suppressed ($C$) to color-allowed ($T$) tree contributions and a large relative phase between the tree and penguin amplitude. In this talk, I would like to report on a recent analysis to see whether the large $C/T$ ratio can be explained within the QCD based model with i) a large contribution from the annihilation terms or with ii) large final-state-interaction phase between two different isospin amplitudes. We show that the current experimental data do not exclude either possibility but we may be able to distinguish these two effects in future measurements of direct CP asymmetry in $B\to \pi^{0}\pi^{0}$ decay.

Bs0→K+K−andBs0→K0bar K0decays within supersymmetry

We compute the supersymmetric (SUSY) contributions to the observables in Bs-->K+K- and Bs-->K0 anti-K0 decays. The hadronic parameters in the standard-model (SM) amplitudes are obtained from the Bd-->K0 anti-K0 decay using a recent approach that combines flavor SU(3) symmetry and a controlled input from QCD factorization. The latest experimental data for BR(Bs-->K+K-) is in agreement with the SM prediction. We study how the branching ratios and the direct and mixing-induced CP asymmetries of both Bs-->KK decay modes are affected with the inclusion of SUSY, after imposing constraints from BR(B--> Xs gamma), B--> pi K and Delta Ms over the parameter space. While the branching ratios remain unaffected by SUSY, we identify the CP asymmetries of the Bs-->KK decays as the most promising observables to look for large deviations from the SM.

Puzzles in B physics

I discuss some puzzles observed in exclusive B-meson decays, concentrating on the large difference between the direct CP asymmetries in the B0 → π−K= and B± → π0K± modes, the large B0 → π0π0 branching ratio, and the large deviation of the mixing-induced CP asymmetries in the b → sqq penguins from those in the b → ccs trees.