arXiv subjects
Publications and source records attributed to Gerhard Buchalla.
We review selected topics in the field of nonleptonic and rare B meson decays. We concentrate in particular on exclusive channels, discussing recent developments based on the concepts of factorization in QCD and the heavy-quark limit.
We discuss a model-independent framework for the analysis of the radiative B-meson decays B -> K* gamma and B -> rho gamma based on the heavy-quark limit of QCD. We present a factorization formula for the treatment of B -> V gamma matrix elements involving charm (or up-quark) loops, which contribute at leading power in Lambda_QCD/m_B to the decay amplitude. Annihilation topologies are power suppressed, but still calculable in some cases. The framework of QCD factorization is necessary to compute exclusive b -> s(d) gamma decays systematically beyond the leading logarithmic approximation. Results to next-to-leading order in QCD and to leading order in the heavy-quark limit are given and phenomenological implications are discussed.
We analyze the double radiative B-meson decays B_s -> gamma gamma and B_d -> gamma gamma in QCD factorization based on the heavy-quark limit m_b >> Lambda_QCD. We systematically discuss the various contributions to these exclusive processes. The dominant effect arises from the magnetic-moment type transition b -> s(d) gamma where an additional photon is emitted from the light quark (one-particle reducible diagram). The contributions from one-particle irreducible diagrams are power suppressed. We argue that they are still calculable within QCD factorization. They are used to compute the CP-asymmetries in B -> gamma gamma and to estimate so-called long-distance contributions in B and D -> gamma gamma. Numerical results are presented for branching ratios and CP asymmetries.
We provide a model-independent framework for the analysis of the radiative B-meson decays B -> K* gamma and B -> rho gamma. In particular, we give a systematic discussion of the various contributions to these exclusive processes based on the heavy-quark limit of QCD. We propose a novel factorization formula for the consistent treatment of B -> V gamma matrix elements involving charm (or up-quark) loops, which contribute at leading power in Lambda_QCD/m_B to the decay amplitude. Annihilation topologies are shown to be power suppressed. In some cases they are nevertheless calculable. The approach is similar to the framework of QCD factorization that has recently been formulated for two-body non-leptonic B decays. These results allow us, for the first time, to compute exclusive b -> s(d) gamma decays systematically beyond the leading logarithmic approximation. We present results for these decays complete to next-to-leading order in QCD and to leading order in the heavy-quark limit. Phenomenological implications for various observables of interest are discussed, including direct CP violation, and isospin and U-spin breaking effects.
These lectures describe the most important theoretical methods in b-physics. We discuss the formalism of effective weak Hamiltonians, heavy quark effective theory, the heavy quark expansion for inclusive decays of b-hadrons and, finally, the more recent ideas of QCD factorization for exclusive nonleptonic B decays. While the main emphasis is put on introducing the basic theoretical concepts, some key applications in phenomenology are also presented for illustration.
The theory of rare $K$ decays is reviewed, emphasizing short-distance processes and the prospects to probe the physics of flavour. A brief overview of the subject is presented, along with a more detailed discussion of the theory of $K\toπν\barν$ decays.
We introduce and discuss basic topics in the theory of kaons and charmed particles. In the first part, theoretical methods in weak decays such as operator product expansion, renormalization group and the construction of effective Hamiltonians are presented, along with an elementary account of chiral perturbation theory. The second part describes the phenomenology of the neutral kaon system, CP violation, $\varepsilon$ and $\varepsilon'/\varepsilon$, rare kaon decays ($K\toπν\barν$, $K_L\toπ^0 e^+e^-$, $K_L\toμ^+μ^-$), and some examples of flavour physics in the charm sector.
We review the status of rare kaon decays, concentrating on modes with sensitivity to short-distance flavour physics.
We summarize both the study of CP violation with $K$ and $B$ mesons, as well as rare decays of kaons, emphasizing recent developments. The topics discussed include the unitarity triangle, $ε'/ε$, $K\toπν\barν$ and other rare $K$ decays, T-odd asymmetries in kaon physics, theoretical aspects of CP violation in B decays, $B\to J/ΨK_S$, $B\toππ$, $B\toπK$ and inclusive CP asymmetries.
We update the Standard Model predictions for the rare decays $K^+\toπ^+ν\barν$ and $K_L\toπ^0ν\barν$. In view of improved limits on $B_s$--$\bar B_s$ mixing we derive a stringent and theoretically clean Standard Model upper limit on $B(K^+\toπ^+ν\barν)$, which is based on the ratio of $B_d$--$\bar B_d$ to $B_s$--$\bar B_s$ mixing, $ΔM_d/ΔM_s$, alone. This method avoids the large hadronic uncertainties present in the usual analysis of the CKM matrix. We find $B(K^+\toπ^+ν\barν)< 1.67\cdot 10^{-10}$, which can be further improved in the future. In addition we consider the extraction of $|V_{td}|$ from a future measurement of $B(K^+\toπ^+ν\barν)$, discussing the various sources of uncertainties involved. We also investigate theoretically clean constraints on $B(K_L\toπ^0ν\barν)$. We take the opportunity to review the next-to-leading order (NLO) QCD corrections to $K\toπν\barν$, $K_L\toμ^+μ^-$, $B\to Xν\barν$ and $B\to l^+l^-$, including a small additional term that had been missed in the original publications. The phenomenological impact of this change is negligible, the corresponding numerical shift being essentially within the small perturbative uncertainties at the NLO level.
The rare decay $B\to X_sl^+l^-$ provides excellent prospects for precision tests of Standard Model flavour dynamics. The process can be computed in perturbation theory with small uncertainty. However, in order to ensure a reliable theoretical prediction, also potentially important effects from non-perturbative QCD have to be controlled with sufficient accuracy. The present article summarizes recent developments related to this topic.
The rare decay $K_L\toπ^0ν\barν$ is dominated by direct CP violation and can be computed with extraordinarily high precision. In principle also a CP conserving contribution to this process can arise within the Standard Model. We clarify the structure of the CP conserving mechanism, analyzing both its short-distance and long-distance components. It is pointed out that the calculation of the CP conserving amplitude, although sensitive in part to nonperturbative physics, is rather well under control. The resulting CP conserving contribution to the rate for $K_L\toπ^0ν\barν$ turns out to be very strongly suppressed due to several factors, which we discuss in detail.
We reconsider the calculation of ${\cal O}(Λ^2_{QCD}/m^2_b)$ nonperturbative corrections to $\bar B\to X_sl^+l^-$ decay. Our analysis confirms the results of Ali et al. for the dilepton invariant mass spectrum, which were in disagreement with an earlier publication, and for the lepton forward-backward asymmetry. We also give expressions for the ${\cal O}(Λ^2_{QCD}/m^2_b)$ corrections to the left-right asymmetry. In addition we discuss the breakdown of the heavy quark expansion near the point of maximal dilepton invariant mass $q^2$ and consider a model independent approach to this region using heavy hadron chiral perturbation theory. The modes $\bar B\to\bar Kl^+l^-$ and $\bar B\to\bar Kπl^+l^-$, which determine the endpoint region of the inclusive decay, are analyzed within this framework. An interpolation is suggested between the region of moderately high $q^2$, where the heavy quark expansion is still valid, and the vicinity of the endpoint described by chiral perturbation theory. We also comment on further nonperturbative effects in $\bar B\to X_sl^+l^-$.
We review basic aspects of the phenomenology of CP violation in the decays of $K$ and $B$ mesons. In particular we discuss the commonly used classification of CP violation -- CP violation in the mass matrix, in the interference of mixing with decay, and in the decay amplitude itself -- and the related notions of direct and indirect CP violation. These concepts are illustrated with explicit examples. We also emphasize the highlights of this field including the clean observables $B(K_L\toπ^0ν\barν)$ and ${\cal A}_{CP}(B\to J/ΨK_S)$. The latter quantity serves to demonstrate the general features of large, mixing induced CP violation in $B$ decays.
We consider for the first time the leading large top mass corrections, arising at higher order in electroweak interactions, to the rare decays $K\toπν\barν$ and the related modes $B\to X_sν\barν$ and $B\to l^+l^-$. Higher order effects of similar type have previously been calculated in the large-$m_t$ limit for key observables of precision electroweak physics at Z-factories. Here we obtain the corresponding corrections of order ${\cal O}(G^2_F m^4_t)$ at the amplitude level for short-distance dominated rare meson decays. This allows us to quantify the importance of higher order electroweak effects for these processes, which can be reliably computed and have very small uncertainties from strong interactions. Simultaneously it becomes possible to remove, to some extent, ambiguities in the definition of electroweak parameters describing the strength of FCNC interactions. The corrections we discuss are at the level of a few percent.
The phenomenology of rare kaon decays is reviewed, with emphasis on tests of standard model flavordynamics.
The present status of CP violation in decays of neutral kaons is reviewed. In addition selected rare decays of both K and B mesons are discussed. The emphasis is in particular on observables that can be reliably calculated and thus offer the possibility of clean tests of standard model flavor physics.
We consider CP violating asymmetries that are induced by particle-antiparticle mixing in inclusive channels of neutral $B$ meson decay. Not only are the branching ratios sizable, at the 1% to 50% level, but some of those asymmetries are expected to be large because of substantial CKM phases. The inclusive sum partially dilutes the asymmetries, but the dilution factor is calculable, assuming local quark-hadron duality, and CKM parameters can be reliably extracted. We discuss in detail the determination of $sin 2α$ from charmless final states in decays of $B_d$ mesons and survey the asymmetries for other inclusive final states. While probably not yet sensitive to standard model predictions, meaningful CP violation studies can be conducted with existing data samples of inclusive neutral $B$ decays.