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Register a new userTheoretical Status of Rare B Decays with Muons
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Rare B decays allow to investigate fundamental interactions regarding their flavor, chiral, Dirac and CP properties. In anticipation of the large data samples of exclusive B decays into muons from the forthcoming LHC experiments, in particular LHCb, as well as possible super flavor factories, we review the theoretical status and outline future opportunities to explore the borders of the Standard Model and beyond.
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We review the theoretical status of the B --> pi K decays, focusing on recent developments in the QCD factorization and perturbative QCD approaches as well as on the Standard-Model correlation between the mixing-induced and direct CP asymmetries of the B^0 --> pi^0 K^0 mode.
We present a systematic global analysis of dineutrino modes $b to q , u bar u$, $q=d,s$, and charged dilepton $b to q ,ell^+ ell^-$ transitions. We derive improved or even entirely new limits on dineutrino branching ratios including decays $B^0 to (K^0 , X_s), u bar u$, $B_s to phi , u bar u$ and $B^0 to (pi^0, rho^0), u bar u$ from dineutrino modes which presently are best constrained: $B^+ to (K^+,pi^+, rho^+) , u bar u$ and $B^0 to K^{*0} , u bar u$. Using SMEFT we obtain new flavor constraints from the dineutrino modes, which are stronger than the corresponding ones from charged dilepton rare $b$-decay or Drell-Yan data, for $e tau$ and $tau tau$ final states, as well as for $mu tau$ ones in $b to s$ processes. The method also allows to put novel constraints on semileptonic four-fermion operators with top quarks. Implications for ditau modes $b to s , tau^+ tau^-$ and $b to d , tau^+ tau^-$ are worked out. Furthermore, the interplay between dineutrinos and charged dileptons allows for concrete, novel tests of lepton universality in rare $B$-decays. Performing a global fit to $b to s ,mu^+ mu^-, ,s gamma$ transitions we find that lepton universality predicts the ratio of the $B^0 to K^{*0} , u bar u$ to $B^0 to K^0 , u bar u$ ($B^+ to K^+ , u bar u$) branching fractions to be within 1.7 to 2.6 (1.6 to 2.4) at $1,sigma$, a region that includes the standard model, and that can be narrowed with improved charged dilepton data. There is sizable room outside this region where universality is broken and that can be probed with the Belle II experiment. Using results of a fit to $B^0 to mu^+ mu^-$, $B^0_sto bar{K}^{ast 0},mu^+mu^-$ and $ B^+ to pi^+, mu^+ mu^-$ data we obtain an analogous relation for $|Delta b|=|Delta d|=1$ transitions.
The inclusive semileptonic branching ratio is often employed to normalize other inclusive B decays. Using recent determinations of the non-perturbative parameters of the Operator Product Expansion we compute the normalization factor for the branching ratio of B->X_s gamma and find a few percent enhancement with respect to previous determinations.
In this paper, we study the extended Standard Model (SM) with an extra Higgs doublet and right-handed neutrinos. If the symmetry to distinguish the two Higgs doublets is not assigned, flavor changing neutral currents (FCNCs) involving the scalars are predicted even at the tree level. We investigate the constraints on the FCNCs at the one-loop level, and especially study the semileptonic $B$ meson decays, e.g. $B to D^{(*)} tau u$ and $B to K^{(*)} ll$ processes, where the SM predictions are more than $2 sigma$ away from the experimental results. We also consider the flavor-violating couplings involving right-handed neutrinos and discuss if the parameters to explain the excesses of the semileptonic $B$ decays can resolve the discrepancy in the the anomalous muon magnetic moment. Based on the analysis, we propose the smoking-gun signals of our model at the LHC.
Rare inclusive $B$ decays such as $bar{B}to X_{s(d)} ell^+ell^-$ are interesting probes for physics beyond the Standard Model. Due to the complementarity to their exclusive counterparts, they might shed light on the anomalies currently seen in exclusive $b to s$ transitions. Distinguishing new-physics effects from the Standard Model requires precise predictions and necessitates the control of long distance effects. In the present work we revisit and improve the description of various long distance effects in inclusive decays such as charmonium and light-quark resonances, nonfactorisable power corrections, and cascade decays. We then apply these results to a state-of-the-art phenomenological study of $bar{B}to X_d ell^+ell^-$, including also logarithmically enhanced QED corrections and the recently calculated five-body contributions. To fully exploit the new-physics potential of inclusive flavour-changing neutral current decays, the $bar{B}to X_d ell^+ell^-$ observables should be measured in a dedicated Belle II analysis.
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