Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userInterplay of dineutrino modes with semileptonic rare $boldsymbol{B}$-decays
105
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
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.
rate research
Read More
Two of the elements of the Cabibbo-Kobayashi-Maskawa quark mixing matrix, $|V_{ub}|$ and $|V_{cb}|$, are extracted from semileptonic B decays. The results of the B factories, analysed in the light of the most recent theoretical calculations, remain puzzling, because for both $|V_{ub}|$ and $|V_{cb}|$ the exclusive and inclusive determinations are in clear tension. Further, measurements in the $tau$ channels at Belle, Babar, and LHCb show discrepancies with the Standard Model predictions, pointing to a possible violation of lepton flavor universality. LHCb and Belle II have the potential to resolve these issues in the next few years. This article summarizes the discussions and results obtained at the MITP workshop held on April 9--13, 2018, in Mainz, Germany, with the goal to develop a medium-term strategy of analyses and calculations aimed at solving the puzzles. Lattice and continuum theorists working together with experimentalists have discussed how to reshape the semileptonic analyses in view of the much higher luminosity expected at Belle II, searching for ways to systematically validate the theoretical predictions in both exclusive and inclusive B decays, and to exploit the rich possibilities at LHCb.
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.
We study the exclusive semileptonic $B$-meson decays $Bto K(pi)ell^+ell^-$, $Bto K(pi) ubar u$, and $Btopitau u$, computing observables in the Standard model using the recent lattice-QCD results for the underlying form factors from the Fermilab Lattice and MILC Collaborations. These processes provide theoretically clean windows into physics beyond the Standard Model because the hadronic uncertainties are now under good control for suitably binned observables. For example, the resulting partially integrated branching fractions for $Btopimu^+mu^-$ and $Bto Kmu^+mu^-$ outside the charmonium resonance region are 1-2$sigma$ higher than the LHCb Collaborations recent measurements, where the theoretical and experimental errors are commensurate. The combined tension is 1.7$sigma$. Combining the Standard-Model rates with LHCbs measurements yields values for the Cabibbo-Kobayashi-Maskawa (CKM) matrix elements $|V_{td}|=7.45{(69)}times10^{-3}$, $|V_{ts}|=35.7(1.5)times10^{-3}$, and $|V_{td}/V_{ts}|=0.201{(20)}$, which are compatible with the values obtained from neutral $B_{(s)}$-meson oscillations and have competitive uncertainties. Alternatively, taking the CKM matrix elements from unitarity, we constrain new-physics contributions at the electroweak scale. The constraints on the Wilson coefficients ${rm Re}(C_9)$ and ${rm Re}(C_{10})$ from $Btopimu^+mu^-$ and $Bto Kmu^+mu^-$ are competitive with those from $Bto K^* mu^+mu^-$, and display a 2.0$sigma$ tension with the Standard Model. Our predictions for $Bto K(pi) ubar u$ and $Btopitau u$ are close to the current experimental limits.
We discuss a method to construct observables protected against QCD uncertainties based on the angular distribution of the exclusive Bd -> K(*0}(-> Kpi) l+ l- decay. We focus on the identification and the interpretation of all the symmetries of the distribution. They constitute a key ingredient to construct a set of so-called transverse observables. We work in the framework of QCD factorization at NLO supplemented by an estimate of power-suppressed Lambda/mb corrections. A discussion of the new physics properties of two of the transverse asymmetries, AT^{(2)} and AT^{(5)}, is presented. A comparison between the transverse asymmetry AT^{(2)} and the forward-backward asymmetry shows that AT^{(2)} emerges as an improved version of it.
B meson semileptonic decays are a crucial tool in our studies of the quark mixing parameters Vcb and Vub. The interplay between experimental and theoretical challenges to achieve precision in the determination of these fundamental parameters is discussed.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
