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We present a precise calculation of the dilepton invariant-mass spectrum and the decay rate for $B^pm to pi^pm ell^+ ell^-$ ($ell^pm = e^pm, mu^pm $) in the Standard Model (SM) based on the effective Hamiltonian approach for the $b to d ell^+ ell^-$ transitions. With the Wilson coefficients already known in the next-to-next-to-leading logarithmic (NNLL) accuracy, the remaining theoretical uncertainty in the short-distance contribution resides in the form factors $f_+ (q^2)$, $f_0 (q^2)$ and $f_T (q^2)$. Of these, $f_+ (q^2)$ is well measured in the charged-current semileptonic decays $B to pi ell u_ell$ and we use the $B$-factory data to parametrize it. The corresponding form factors for the $B to K$ transitions have been calculated in the Lattice-QCD approach for large-$q^2$ and extrapolated to the entire $q^2$-region using the so-called $z$-expansion. Using an $SU(3)_F$-breaking Ansatz, we calculate the $B to pi$ tensor form factor, which is consistent with the recently reported lattice $B to pi$ analysis obtained at large~$q^2$. The prediction for the total branching fraction ${cal B} (B^pm to pi^pm mu^+ mu^-) = (1.88 ^{+0.32}_{-0.21}) times 10^{-8}$ is in good agreement with the experimental value obtained by the LHCb Collaboration. In the low $q^2$-region, heavy-quark symmetry (HQS) relates the three form factors with each other. Accounting for the leading-order symmetry-breaking effects, and using data from the charged-current process $B to pi ell u_ell$ to determine $f_+ (q^2)$, we calculate the dilepton invariant-mass distribution in the low $q^2$-region in the $B^pm to pi^pm ell^+ ell^-$ decay. This provides a model-independent and precise calculation of the partial branching ratio for this decay.
The hitherto unobserved purely leptonic decays B^pm -> tau^pm u and B^pm -> mu^pm u are of much interest at current and future runs of the e+e- B factories. Such decays are sensitive to charged Higgs bosons (H^pm) at the tree-level and provide esse
A new and simple procedure to measure the angle $gamma$ from $B^{pm} to pi^{pm}pi^+pi^-$ and $B^{pm} to K^{pm}pi^+pi^-$ decays using SU(3) symmetry is presented. It is based on a full Dalitz plot analysis of these decays. All diagrams, including stro
Supposing only Lorentz and the gauge invariances of the Lagrangian, we derive energy and angular distributions for $tau^pm to mu^pm mu^pm mu^mp$ lepton flavor violating decay process. Using these results, we discuss methods to determine the parameter
A model for the $B^pm to pi^-pi^+pi^pm$ decay amplitude is proposed to study the large CP violation observed at the high mass region of the Dalitz plane. A short distance $ b to u $ amplitude with the weak phase $gamma$ is considered together with th
A search for $B^{0}_{s}totau^{pm}mu^{mp}$ and $B^{0}totau^{pm}mu^{mp}$ decays is performed using data corresponding to an integrated luminosity of 3 fb$^{-1}$ of proton-proton collisions, recorded with the LHCb detector in 2011 and 2012. For this sea