Narrow Results

Short-distance expansion of the total semileptonic B widths is reviewed for the OPE-conformable scheme employing low-scale running quark masses. The third- and fourth-order BLM corrections are given and the complete resummation of the BLM series presented. The effect of higher perturbative orders with running quark masses is found to be very small. Numerical consequences for |V_cb| are addressed.

We consider effective Lagrangian models of CP-violating vertex structure in which a b→uW vertex, proportional to s₁₃e^-iδ₁₃ with s₁₃ very small (milliweak interaction) and δ₁₃ large, is dynamically generated. A consequent, enhanced CP-violating vertex for b→sg results in an enhanced CP-violating phase in the ratio of amplitudes for . We estimate that this can significantly change the S-parameter from the value expected in the standard model.

We summarize the status of semileptonic and leptonic B decays, including $\left|V_{cb}\right|$ and $\left|V_{ub}\right|$ exclusive and inclusive determinations, decays to excited states of the charm meson spectrum and decays into $\tau$ leptons.

In this paper we examine T-violating triple-product correlations (TP's) in B→V₁V₂ decays. TP's are excellent probes of physics beyond the standard model (SM) for two reasons: (i) within the SM, most TP's are expected to be tiny, and (ii) unlike direct CP asymmetries, TP's are not suppressed by the small strong phases which are expected in B decays. TP's are obtained via the angular analysis of B→V₁V₂. In a general analysis based on factorization, we demonstrate that the most promising decays for measuring TP's in the SM involve excited final-state vector mesons, and we provide estimates of such TP's. We find that there are only a handful of decays in which large TP's are possible, and the size of these TP's depends strongly on the size of nonfactorizable effects. We show that TP's which vanish in the SM can be very large in models with new physics. The measurement of a nonzero TP asymmetry in a decay where none is expected would specifically point to new physics involving large couplings to the right-handed b-quark.

We present results on time-dependent CP asymmetries in neutral B decays. The amplitude of the CP asymmetry, sin2β in the Standard Model, is derived from decay-time distributions from events in which one neutral B meson is fully reconstructed in a final state containing a charmonium meson and the other B meson is determined to be either a B⁰ or from its decay products. Using data collected by the BABAR detector at the PEP-II asymmetric-energy B Factory at SLAC, we measure sin2β = 0.722 ± 0.040(stat) ± 0.023(syst) and , determining the sign of cos2β to be positive at 86% CL.

A brief summary of outstanding theoretical issues and recent results from the QCD factorization approach to exclusive hadronic B decays is provided.

Supersymmetric contributions to the branching ratios and CP asymmetries of B→K π decays are analyzed in view of recent experimental measurements. We show that supersymmetry can still provide a natural solution to the apparent discrepancy between the CP asymmetry results and the Standard Model expectations. We emphasize that chargino contributions may enhance the electroweak penguin effects that can resolve to the puzzle of the CP asymmetries of B→Kπ. We also point out that a nonuniversal A-terms is an essential requirement for this solution.

Several recent key results from the BABAR experiment are presented, most using 383.6 fb⁻¹ of data. In particular, the search for B⁺ → τ⁺ν, inclusive and exclusive measurements of |V_ub|, measurements of b → dγ decays and new observations of rare charmless hadronic decays. The new results provide important experimental constraints on the Standard Model and new physics models.

After briefly introducing the framework of QCD factorization for B → M₁M₂ in the language of the Soft-Collinear Effective Theory, we firstly address the recent efforts on higher-order radiative corrections in QCD factorization. Then we discuss some phenomenologies in B → VV within the framework of QCD factorization.

The decays are analyzed in the standard model (SM) extended to fourth generation of quarks (SM4). The decay rate, forward–backward asymmetry, lepton polarization asymmetries, the helicity fractions of the final state meson and CP asymmetry are discussed using the form factors calculated in the light-cone sum rules (LCSR) approach. We utilized the constraints on different fourth generation parameters obtained from the experimental information on K, B and D decays and from their recent searches at the ATLAS and CMS experiments to explore their impact on the decays. We find that the values of above mentioned physical observables deviate significantly from their minimal SM predications. In the present study, we will also perform the analysis of CP asymmetry in decays within SM4, which is one of the most interesting observable in the study of SM4.

The most common decay used for measuring 2β_s, the phase of mixing, is . This decay is dominated by the color-suppressed tree diagram, but there are other contributions due to gluonic and electroweak penguin diagrams. These are often referred to as "penguin pollution" (PP) because their inclusion in the amplitude leads to a theoretical error in the extraction of 2β_s from the data. In the standard model (SM), it is estimated that the PP is negligible, but there is some uncertainty as to its exact size. Now, (the measured value of 2β_s) is small, in agreement with the SM, but still has significant experimental errors. When these are reduced, if one hopes to be able to see clear evidence of new physics (NP), it is crucial to have the theoretical error under control. In this paper, we show that, using a modification of the angular analysis currently used to measure in , one can reduce the theoretical error due to PP. Theoretical input is still required, but it is much more modest than entirely neglecting the PP. If differs from the SM prediction, this points to NP in the mixing. There is also enough information to test for NP in the decay. This method can be applied to all decays.

The LHCb collaboration has recently reported evidence for nonzero CP asymmetries in B⁺ decays into π⁺K⁺K^-, π⁺π⁺π^-, K⁺K⁺K^- and K⁺π⁺π^-. The branching ratios for these decays have also been measured with different values ranging from 5×10^-6 to 51×10^-6. If flavor SU(3) symmetry is a good symmetry for B decays, in the case that the dominant amplitude is momentum independent it is expected that branching ratios Br and CP violating rate differences satisfy, Br(π⁺π⁺π^-) = 2 Br(π⁺K⁺K^-), Br(K⁺K⁺K^-) = 2 Br(K⁺π⁺π^-) and Δ_CP(π⁺π⁺π^-) = 2Δ_CP(π⁺K⁺K^-) = -Δ_CP(K⁺K⁺K^-) = -2Δ_CP(K⁺π⁺π^-). The experimental data do not exhibit the expected pattern for the branching ratios. The rate differences for B⁺→π⁺π⁺π^- and B⁺→K⁺ K⁺ K^- satisfy the relation between ΔS = 0 and ΔS = 1 as well, but the other two do not, with the CP asymmetries having different signs than expected. In this paper, we study how to include momentum dependent and also SU(3) breaking effects on these decays to explain experimental data. We find that by including only the lowest order derivative terms, in the SU(3) limit, the decay patterns cannot be explained. Large SU(3) breaking effects are needed to explain the data.

We study the rare decays $K_L^0\to {\pi }^0\nu \bar{\nu }$, $B^{+}\to {\pi }^{+}\nu \bar{\nu }$, $B^{+}\to K^{\ast +}\nu \bar{\nu }$ and $B\to X_s\nu \bar{\nu }$ for the search of NSIs. We want to constrain the NSIs by using these reactions. We show that there is a strong dependence of these reactions on new physics free parameter ${ϵ}_{\tau \tau }^{QL}$, where $Q=u$, $c$, $t$. We include second and third generation of quarks in the loop for these decays. We show that the $K_L^0\to {\pi }^0\nu \bar{\nu }$ is providing very precise bounds as compared to all other semileptonic decays, having neutrinos in their final state. We further show that the interference between standard model and NSIs is giving dominant contribution for $B^{+}\to {\pi }^{+}\nu \bar{\nu }$, $B^{+}\to K^{\ast +}\nu \bar{\nu }$ and $B\to X_s\nu \bar{\nu }$. We point out that the constraints for ${ϵ}_{\tau \tau }^{cL}$ and ${ϵ}_{\tau \tau }^{tL}$ are more precise as compared to ${ϵ}_{\tau \tau }^{uL}$. The analysis of $B^{+}\to {\pi }^{+}\nu \bar{\nu }$, $B^{+}\to K^{\ast +}\nu \bar{\nu }$ and $B\to X_s\nu \bar{\nu }$, provide us that the $u$-quark induced Br of NSIs are giving very small contribution. We also compare these decays to the decays of charm and kaons having neutrinos in the final state.

Lepton flavor violating (LFV) decays are forbidden in the Standard Model (SM) and to explore them one has to go beyond it. The flavor changing neutral current induced lepton flavor conserving and LFV decays of $K$ and $B$ mesons is discussed in the gauge group $G=SU{(2)}_L\times U{(1)}_{Y_1}\times SU{(2)}_X$. The lepto-quark $X_{\mu }^{\pm 2/3}$ corresponding to gauge group $SU{(2)}_X$ allows the quark–lepton transitions and hence giving a framework to construct the effective Lagrangian for the LFV decays. The mass of lepto-quark $m_X$ provides a scale at which the gauge group $G$ is broken to the SM gauge group. Using the most stringent experimental limit ${ℬ}(K_L^0\to {\mu }^{\mp }{e}^{\pm })<1.7\times 10^{-12}$, the upper bound on the effective coupling constant ${\left(\frac{G_X}{G_F}\right)}^2<1.1\times 10^{-10}$ is obtained for certain pairing of lepton and quark generations in the representation $(2,\bar{2})$ of the group $G$. Later, the effective Lagrangian for the LFV meson decays for the gauge group $G=[SU{(2)}_L\times SU{(2)}_R\times U{(1)}_{Y_1^{\prime }}]\times SU{(2)}_X$ is constructed. Using ${ℬ}(K^{-}\to {\pi }^{-}\nu \bar{\nu })=(1.7\pm 1.1)\times 10^{-10}$, the bound on the ratio of effective couplings is obtained to be ${\left(\frac{G_X}{G_F}\right)}^2<10^{-10}$. A number of decay modes are discussed which provide a promising area to test this model in the current and future particle physics experiments.

The confidence level limits of the CDF search for the and rare decays and the branching ratio measurement of are presented.

A brief account of the study of rare B decay B → K#ℓ⁺ℓ^- using soft-collinear effective theory (SCET) is presented. Theoretical underpinning of this work is a factorization formula, derived to leading power in 1/m_b and valid to all orders in α_s. Partially integrated branching ratio in the dilepton squared mass range 1 GeV² ≤ q² ≤ 7 GeV² and the forward-backward (FB) asymmetry of the leptons are calculated. For the zero-point of the FB asymmetry, we get . The scale-related uncertainty of is improved compared to the earlier estimate of the same.

A review of recent BABAR results on exclusive B → (ρ/ω)γ, B → πl⁺l^- and B → K(*) l⁺l^- decays is presented. It was found that , at 90% C.L., and . It was also found that different asymmetry measurements are consistent with Standard Model expectations. Based on these results an independent estimate of the |V_td/V_ts| matrix element of the CKM matrix is derived to be . A first evidence of B⁺ → ρ⁺γ decays was found and last year's observation of B⁰ → p⁰γ was confirmed.

We report the results of two studies of exclusive charmless semileptonic B decays at the Belle experiment located at the asymmetric e⁺e^- collider KEKB. In the first analysis, based on a data sample of pairs collected near the ϒ(4S) resonance, the decays B → πℓν and B → ρℓν are searched in events in which the accompanying B meson is reconstructed in the semileptonic mode B → D^(*)ℓν. This tagging technique allows to measure the signal modes with high purity. Even higher purities are achieved in the second analysis which is based on events. In this study, the decays B → πℓν, B → ρℓν and B → ωℓν are measured in events which were tagged by fully reconstructing one of the B mesons in a hadronic decay mode.

We report on five studies of b → c hadronic B decays at Belle. The first observations of three new processes are reported and improved measurements of more than ten processes are presented.

A set of key measurements of B decays which have the potential to uncover New Physics at the LHC is discussed. Together with the general purpose detectors ATLAS and CMS, the LHCb detector, which is devoted to B physics, can study these effects precisely. Due to the large cross section at 14 TeV, LHCb has access to 10¹² B meson decays per year. This allows significant measurements of even very rare B decays and, in particular, the precision study of the B system.