Direct CP Asymmetries Research Articles

New physics hints in B decays and collider outlook

There are currently two hints for new physics involving CP violation in b → s transitions: ΔS ≡ S f − S J ϕK ≠ 0, and difference in direct CP asymmetry ΔA Kπ ≡ A K+π 0 − A K+π − ≠ 0. We explore the two scenarios with a large and unique new CP phase in b ↔ s transitions. Motivated by ΔS ≠ 0, we update on the right-handed strange-beauty squark sb 1R at TeV scale. Motivated by ΔA Kπ ≠ 0, we explore sequential fourth generation t′ and b′ quarks. Both scenarios can survive constraints such as SM level b → sγ, sll and B s mixing, and predict sizable CP violation in B s mixing. The fourth generation picture predicts sizable K L → π 0 vv. Direct search for sb R, b′ and t′ at hadronic colliders, such as Tevatron Run II and LHC, can complement further CP violation studies at these machines, as well as at the future Super B factory.

B+ and B0 Direct CP Asymmetries difference in a sequential Fourth Generation scenario

Direct CP violation in B0 → K+π− decay has emerged at −10% level, but the asymmetry in B+ → K+π0 mode is consistent with zero. This difference points towards possible New Physics in the electroweak penguin operator. We point out that a sequential fourth generation, with sizable V*t′s Vt′b and near maximal phase, could be a natural cause. We compare t′ effects on direct CP violation in B+ → K+π0 with b → sl+ l− and Bs mixing. Such large effects in b ↔ s transitions would affect s ↔ d transitions, as kaon constraints would demand Vt′d ≠ 0. Using Γ(Z → b b̄) to bound |Vt′b|, we infer sizable |Vt′s| ≲ |Vt′b| ≲ |Vus|. Imposing ϵK, K+ → π+ v v̄ and ϵ′/ϵ constraints, we find V*t′d Vt′s ∼ few ×104 with large phase, enhancing KL → π0 vv̄ to 5 × 10−10 or even higher. Interestingly, ΔmBd and sin 2ΦBd are not much affected, as |V*t′d Vt′b| << |V*td Vtb| ∼ 0.01.

Measurement of the Branching Fraction and Photon Energy Moments ofB→XsγandACP(B→Xs+dγ)

The photon spectrum in B -> X_s gamma decay, where X_s is any strange hadronic state, is studied using a data sample of 88.5 million e+e- -> Upsilon(4S) -> BBbar decays collected by the BaBar experiment at SLAC. The partial branching fraction, Delta B(B -> X_s gamma)=(3.67 +- 0.29(stat.) +- 0.34(sys.) +- 0.29(model)) times 10^-4, the first moment <E_gamma>=2.288 +- 0.025 +- 0.017 +- 0.015 GeV and the second moment <E_gamma^2> - <E_gamma>^2 =0.0328 +- 0.0040 +- 0.0023 +- 0.0036 GeV^2 are measured for the photon energy range 1.9 GeV < E_gamma < 2.7 GeV. They are also measured for narrower E_gamma ranges. The moments are then fit to recent theoretical calculations to extract the Heavy Quark Expansion parameters, m_b and mu_pi^2, and to extrapolate the partial branching fraction to E_gamma>1.6 GeV. In addition, the direct CP asymmetry A_CP(B -> X_(s+d) gamma) is measured to be -0.110 +- 0.115(stat.) +- 0.017(sys.).

Evidence forB→η′πand Improved Measurements forB→η′K

We report evidence for the exclusive two-body charmless hadronic B meson decay B-->eta'pi, and improved measurements of B-->eta'K. The results are obtained from a data sample of 386x10(6) BB pairs collected at the Upsilon(4S) resonance, with the Belle detector at the KEKB asymmetric-energy e+e- collider. We measure B(B+-->eta'pi+)=[1.76(-0.62)(+0.67)(stat)(-0.14)(+0.15)(syst)]x10(-6) and B(B0-->eta'pi0)=[2.79(-0.96)(+1.02)(stat)(-0.34)(+0.25)(syst)]x10(-6). We also find the ratio of B(B+-->eta'K+)/B(B0-->eta'K0)=1.17+/-0.08(stat)+/-0.03(syst) and measure the direct CP asymmetries for the charged modes.

The rare decays B→K(*)K̄(*) and R-parity violating supersymmetry

We study the branching ratios, the direct CP asymmetries in B→K(*)K̄(*) decays and the polarization fractions of B→K*K̄* decays by employing the QCD factorization in the minimal supersymmetric standard model with R-parity violation. We derive the new upper bounds on the relevant R-parity violating couplings from the latest experimental data of B→K(*)K̄(*), and some of these constraints are stronger than the existing bounds. Using the constrained parameter spaces, we predict the R-parity violating effects on the other quantities in B→K(*)K̄(*) decays which have not been measured yet. We find that the R-parity violating effects on the branching ratios and the direct CP asymmetries could be large; nevertheless their effects on the longitudinal polarizations of B→K*K̄* decays are small. Near future experiments can test these predictions and shrink the parameter spaces.

Spectator scattering at NLO in non-leptonic B decays: Tree amplitudes

We compute the 1-loop ( α s 2 ) correction to hard spectator scattering in non-leptonic B decay tree amplitudes. This forms part of the NNLO contribution to the QCD factorization formula for hadronic B decays, and introduces a new rescattering phase that corrects the leading-order result for direct CP asymmetries. Among the technical issues, we discuss the cancellation of infrared divergences, and the treatment of evanescent four-quark operators. The infrared finiteness of our result establishes factorization of spectator scattering at the 1-loop order. Depending on the values of hadronic input parameters, the new 1-loop correction may have a significant impact on tree-dominated decays such as B → π π .

Direct CP violation in hadronic B decays

There are different approaches for the hadronic B decay calculations, recently. In this paper, we upgrade three of them, namely factorization, QCD factorization and the perturbative QCD approach based on $k_T$ factorization, by using new parameters and full wave functions. Although they get similar results for many of the branching ratios, the direct CP asymmetries predicted by them are different, which can be tested by recent experimental measurements of B factories.

Measurements of branching fractions, rate asymmetries, and angular distributions in the rare decaysB→Kℓ+ℓ−andB→K*ℓ+ℓ−

We present measurements of the flavor-changing neutral current decays B --> Kl+l- and B --> K*l+l-, where l+l- is either an e+e- or mu+mu- pair. The data sample comprises 229 x 10^6 Y(4s) -->to BBbar decays collected with the BaBar detector at the PEP-II e+e- storage ring. Flavor-changing neutral current decays are highly suppressed in the Standard Model and their predicted properties could be significantly modified by new physics at the electroweak scale. We measure the branching fractions B(B --> Kll) = (0.34 +- 0.07 +- 0.02) x 10^{-6}, B(B --> K*ll) = (0.78^{+0.19}_{-0.17} +- 0.11) x 10^{-6}, the direct CP asymmetries of these decays, and the relative abundances of decays to electrons and muons. For two regions in l+l- mass, above and below m(Jpsi), we measure partial branching fractions and the forward-backward angular asymmetry of the lepton pair. In these same regions we also measure the K* longitudinal polarization in B --> K*l+l- decays. Upper limits are obtained for the lepton flavor-violating decays B --> Kemu and B --> K*emu. All measurements are consistent with Standard Model expectations.

Charmless B decays at CDF

In this paper I review the most recent CDF II results in the field of charmless B decays: the measurement of the relative branching fractions of B 0 and B s 0 → h + h ′ − decays, the direct CP asymmetry in the B 0 → K + π − decay, the limits on the Λ b 0 → h + h ′ − branching fractions, the first evidence of B s 0 → ϕ ϕ decay and the measurement of direct CP asymmetry in the B + → ϕ K + decay.

Measurement of angle at the Belle experiment

We present a measurement of the time-dependent CP-violating parameters in B 0 → π + π − decays with 275 millions B B ¯ pairs and B 0 → ρ ± π ± decays with 152 millions B B ¯ pairs collected with the Belle detector at the KEKB asymmetric-energy e + e − collider operating at the ϒ ( 4 S ) resonance. We observe large indirect and direct CP asymmetry and using B 0 → π + π − , we constrain ϕ 2 as 0 ° < ϕ 2 < 19 ° and 71 ° < ϕ 2 < 180 ° at 95.4% C.L. For B 0 → ρ ± π ± decay, although CP asymmetry is not significant due to low statistics, ϕ 2 is calculated as ϕ 2 = ( 102 ± 13 ± 15 ) ° .

Factorization and polarization in two charmed-meson B decays

We provide a comprehensive test of factorization in the heavy–heavy B decays motivated by the recent experimental data from the BELLE and BABAR collaborations. The penguin effects are not negligible in the B decays with two pseudoscalar mesons. The direct CP asymmetries are found to be a few percent. We give estimates on the weak annihilation contributions by analogy to the observed annihilation-dominated processes. The Nc insensitivity of branching ratios indicates that the soft final state interactions are not dominant. We also study the polarizations in B→D*D(s) * decays. The power law shows that the transverse perpendicular polarization fraction is small. The effects of the heavy quark symmetry breaking caused by the perturbative QCD and power corrections on the transverse polarization are also investigated.

Effects of Final-State Interactions in Hadronic B Decays

Final-state rescattering effects on the hadronic B decays and their impact on direct and mixing-induced CP asymmetries are examined. Implications for some phenomenologies are briefly discussed.

Power corrections in charmless B decays

Power corrections seem to play an important role in charmless B decays as indicated by recent analysis using QCD Factorization. In this talk, I would like to report on a recent work on power corrections in charmless B decays. By using the ratio of the branching fraction of B + → π + K *0 to that of B 0 → π − ρ + , for which the theoretical uncertainties are greatly reduced, it is shown in a transparent manner that power corrections in charmless B decays are probably large and that the B 0 → K − ρ + decay could be explained with the annihilation term included. For ratios of direct CP asymmetries, QCD Factorisation with the annihilation terms included would predict the direct CP asymmetry of B → π + π − to be about 3 times larger than that of B → π ± K -+ , with opposite sign. In particular, the large measured value for B → π ± K -+ , CP asymmetry implies naturally a corresponding large B → π + π − CP asymmetry as observed by Belle. Experimentally any significant deviation from this prediction would suggest either new physics or possibly the importance of long-distance rescattering effects.

Study ofB→K*ρ, K*ωdecays with polarization in the perturbative QCD approach

The $B \to K^{*}\rho$, $ K^{*}\omega$ decays are useful to determine the CKM angle $\phi_3=\gamma$. Their polarization fractions are also interesting since the polarization puzzle of the $B\to \phi K^*$ decay. We study these decays in the perturbative QCD approach based on $k_T$ factorization. After calculating of the non-factorizable and annihilation type contributions, in addition to the conventional factorizable contributions, we find that the contributions from the annihilation diagrams are crucial. They give dominant contribution to the strong phases and suppress the longitudinal polarizations. Our results agree with the current existing data. We also predict a sizable direct CP asymmetries in $B^+ \to K^{*+}\rho^0$, $B^0 \to K^{*+}\rho^-$, and $B^+ \to K^{*+}\omega$ decays, which can be tested by the oncoming measurements in the B factory experiments.

The [formula omitted] puzzle and supersymmetric models

In the light of new experimental results on B→Kπ decays, we study the decay processes B→Kπ in the framework of both R-parity conserving (SUGRA) and R-parity violating supersymmetric models. We find that any possible deviations from the Standard Model indicated by the current data for the branching ratios and the direct CP asymmetries of B→Kπ can be explained in both R-parity conserving SUGRA and R-parity violating SUSY models. However, there is a difference between the predictions of both models to the time-dependent CP asymmetry observable SKSπ0 whose current experimental results include large uncertainties. We demonstrate that this difference can be useful for testing both models with more accurate data for SKSπ0 and ACP+− in the near future.

Difference in B^+ and B^0 Direct CP Asymmetry as Effect of a Fourth Generation(SUMMER INSTITUTE 2005)

Difference in B^+ and B^0 Direct CP Asymmetry as Effect of a Fourth Generation(SUMMER INSTITUTE 2005)

Study of B c → D π in the perturbative QCD approach

We investigate the branching ratios and direct CP asymmetries of $B_c^+\to D^0\pi^+$ and $B_c^+\to D^+\pi^0$ decays in the PQCD approach. All the diagrams with emission topology or annihilation topology are calculated strictly. A branching ratio of $10^{-6}$ and $10^{-7}$ for $B_c^+\to D^0\pi^+$ and $B_c^+\to D^+\pi^0$ decay is predicted, respectively. Because of the different weak phase and strong phase from penguin operator and two kinds of tree operator contributions, we predict a possible large direct CP violation: $A^{\rm dir}_{cp} (B_c^\pm \to D^0 \pi^\pm)\approx -50%$ and $A^{\rm dir}_{cp} (B_c^\pm \to D^\pm \pi^0)\approx 25%$ when $\gamma=55^\circ$, which can be tested in the coming LHC.

CP-violating asymmetries inB0decays toK+K−KS(L)0andKS0KS0KS(L)0

Decay rates and time-dependent and direct CP asymmetries in the decays $B^0\to K^+K^-K_{S(L)}$ and $K_S K_S K_{S(L)}$ are studied. Resonant and nonresonant contributions to the three-body decays are carefully investigated. Nonresonant effects on 2-body and 3-body matrix elements are constrained by QCD counting rules. The predicted branching ratios are consistent with the data within the theoretical and experimental errors, though the theoretical central values are somewhat smaller than the experimental ones. Owing to the presence of color-allowed tree amplitudes in $B^0\to K^+K^-K_{S(L)}$, this penguin-dominated mode is subject to a significant tree pollution and the deviation of the mixing-induced \CP asymmetry from that measured in $B\to J/\psi K_S$, namely, $\Delta \sin 2\beta_{K^+K^-K_{S(L)}}\equiv \sin 2\beta_{K^+K^-K_{S(L)}}-\sin 2 \beta_{J/\psi K_S}$, can be as large as O(0.10). In contrast, the $K_SK_SK_{S(L)}$ modes appear theoretically very clean in our picture with negligible $\Delta\sin 2\beta_{K_SK_SK_{S(L)}}$. Direct CP asymmetries in $K^+K^-K_{S(L)}$ and $K_S K_S K_{S(L)}$ modes are found to be very small.

ReexaminingB→ππ,πKdecays in QCD factorization approach

Motivated by the recent experimental data, we have revisited the $B\to \pi K,\pi \pi$ decays in the framework of QCD factorization, with inclusion of the important strong penguin corrections of order $\alpha_s^2$ induced by $b\to D g^\ast g^\ast$ ($D=d$ or $s$ and $g^\ast$ denotes an off-shell gluon) transitions. We find that these higher order strong penguin contributions can provide $\sim 30%$ enhancement to the penguin-dominated $B\to \pi K$ decay rates, and such an enhancement can improve the consistency between the theoretical predictions and the experimental data significantly, while for the tree-dominated $B\to \pi\pi$ decays, these higher order contributions play only a minor role. When these strong penguin contributions are summed, only a small strong phase remains and the direct CP asymmetries get small corrections. We also find patterns of the ratios between the CP-averaged branching fractions remain nearly unaffected even after including these higher order corrections and the $\pi K$ puzzle still persists. Our results may indicate that to resolve the puzzle one would have to resort to new physics contributions in the electroweak penguin sector as found by Buras {\it et al}.

Revisiting the annihilation decay $\bar{B}_{s}\to\pi^{ + }\pi^{-}$

It is very important to know the strength of annihilation contribution in B charmless nonleptonic decays. $\bar{B}_{s}\to \pi^{+}\pi^{-}$ process could serve a good probe of the strength. We have studied the process in QCD factorization framework. Using a gluon mass scale indicted by the studies of infrared behavior of gluon propagators to avoid enhancements in the soft end point regions, we find that the CP averaged branching ratio is about $1.24\times 10^{-7}$, the direct CP asymmetry $C_{\pi\pi}$ is about -0.05, while the mixing-induced CP asymmetry quite large with the value $S_{\pi\pi}$=0.18. The process could be measured at LHC-b experiments in the near future and would deepen our understanding of dynamics of B charmless decays.