We extend the framework of QCD factorization to non-leptonic B decays into three light mesons, taking as an example the decay B+→π+π+π−. We discuss the factorization properties of this decay in ...different regions of phase space. We argue that, in the limit of very large b-quark mass, the central region of the Dalitz plot can be described in terms of the B→π form factor and the B and π light-cone distribution amplitudes. The edges of the Dalitz plot, on the other hand, require different non-perturbative input: the B→ππ form factor and the two-pion distribution amplitude. We present the set-up for both regions to leading order in both αs and ΛQCD/mb and discuss how well the two descriptions merge. We argue that for realistic B-meson masses there is no perturbative center in the Dalitz plot, but that a systematic description might be possible in the context of two-pion states. As an example, we estimate the B→ρπ branching fraction beyond the quasi-particle approximation. We also discuss the prospects for studies of three-body and quasi-two-body non-leptonic B decays from QCD.
We calculate the decay width and the τ-lepton energy distribution as well as relevant moments for inclusive B¯→Xcτν¯τ process including power corrections up to order ΛQCD3/mb3 and QCD corrections to ...the partonic level. We compare the result with the sum of the standard-model predictions of the branching fractions of the exclusive semileptonic B¯→(D,D⁎,D⁎⁎)τν¯τ decays as well as with the relevant experimental data. Our prediction is in agreement with the LEP measurement and is consistent with the standard-model calculation of the exclusive modes. We discuss the impact from physics beyond the Standard Model.
Abstract We derive a QCD sum rule for the inverse moment of the B s -meson light-cone distribution amplitude in HQET. Within this method, the SU(3) f l symmetry violation is traced to the strange ...quark mass and to the difference between strange and nonstrange quark condensate densities. We predict the ratio of inverse moments λ Bs /λ B = 1.19 ± 0.14 which can be used in various applications of these distribution amplitudes to the analyses of B s -meson decays, provided an accurate value of λ B is available from other sources, such as the B → ℓν ℓ γ decay.
On the decays B → K(⁎)+ leptonium Fael, Matteo; Mannel, Thomas
Nuclear physics. B,
July 2018, 2018-07-00, 2018-07-01, Volume:
932
Journal Article
Peer reviewed
Open access
We determine the rates of the B meson decays into a K(⁎) and an ℓ+ℓ− bound state, the leptonium, where ℓ=e,μ,τ. The two spin states of the leptonium, the spin singlet and the spin triplet, couple to ...the axial current and to the vector current, respectively, thus probing different helicity structures of the underlying b→sℓ+ℓ− effective Hamiltonian. Since ortho- and para-leptonia have different decay modes, a distinction between the two is relatively easy and these decays may become a cross check for the results of lepton-flavor-violation searches obtained with free leptons. We find that some of the decays involving muon and tau have a branching ratio of the order of 10−13 and they may become accessible at the LHCb with 50 fb−1 of integrated luminosity. In addition, since the tau-pair threshold lies right between the J/ψ and the ψ(2S) resonances, we estimate the charm-loop contribution to the decays B→K(⁎)+tauonium.
We consider weak decays of heavy hadrons (bottom and charmed) where the heavy quark acts as a spectator. These decays are heavily phase-space suppressed but may become experimentally accessible in ...the near future. These decays may be interesting as a QCD laboratory to study the behaviour of the light quarks in the colour-background field of the heavy spectator.
A
bstract
The treatment of the quark mass plays an important role when it comes to increasing the precision of the predictions of the heavy quark expansion for inclusive heavy hadron decays. Various ...short-distance mass schemes have been invented to minimize the uncertainties induced by the quark mass, which needs to be extracted from other, independent observables. We suggest to replace the quark mass directly by an observable such as e.g. the inverse moments of the cross section for
e
+
e
−
→ hadrons. We investigate this alternative strategy and study its impact on the perturbative series.
A
bstract
We extend existing work on reparametrization invariance (RPI) of the heavy-quark expansion (HQE). RPI implies relations between different orders of the HQE. We discuss the total rates of ...inclusive processes and obtain results which have a manifest RPI and can be expressed through matrix elements of operators and states defined in full QCD. This approach leads to a partial re-summation of higher-order terms in the heavy-quark expansion. It has the advantage that for reparametrization-invariant observables it shows that the number of independent non-perturbative parameters can be reduced.
The determination of Vcb relies on the Heavy-Quark Expansion and the extraction of the non-perturbative matrix elements from inclusive b → c decays. The proliferation of these matrix elements ...complicates their extraction at 1/mb4 and higher, thereby limiting the Vcb extraction. Reparametrization invariance links different operators in the Heavy-Quark expansion thus reducing the number of independent operators at 1/mb4 to eight for the total rate. We show that this reduction also holds for spectral moments as long as they are defined by reparametrization invariant weight-functions. This is valid in particular for the leptonic invariant mass spectrum (q2), i.e. the differential rate and its moments. Currently, Vcb is determined by fitting the energy and hadronic mass moments, which do not manifest this parameter reduction and depend on the full set of 13 matrix elements up to 1/mb4. In light of this, we propose an experimental analysis of the q2 moments to open the possibility of a model-independent Vcb extraction from semileptonic decays including the 1/mb4 terms in a fully data-driven way.
We set up a zero recoil sum rule to constrain the form factors of the Λb→Λc transition. Our results are compared with the recent lattice calculation for these transitions. We find the same situation ...as in the case for B→D⁎: The lattice results practically saturate the sum rules, leaving basically no room for excited states.
Abstract The determination of the CKM element V cb from inclusive semileptonic b → cℓ ν ¯ $$ \overline{\nu} $$ decays has reached a high precision thanks to a combination of theoretical and ...experimental efforts. Aiming towards even higher precision, we discuss two processes that contaminate the inclusive V cb determination; the b → u background and the contribution of the tauonic mode: b → c(τ → μν ν ¯ $$ \overline{\nu} $$ ) ν ¯ $$ \overline{\nu} $$ . Both of these contributions are dealt with at the experimental side, using Monte-Carlo methods and momentum cuts. However, these contributions can be calculated with high precision within the Heavy-Quark Expansion. In this note, we calculate the theoretical predictions for these two processes. We compare our b → u results qualitatively with generator-level Monte-Carlo data used at Belle and Belle II. Finally, we suggest to change the strategy for the extraction of V cb by comparing the data on B → Xℓ directly with the theoretical expressions, to which our paper facilitates.
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