Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userTowards establishing Lepton Flavour Universality violation in $bar{B}to bar{K}^*ell^+ell^-$ decays
207
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
Rare semileptonic $b to s ell^+ ell^-$ transitions provide some of the most promising frameworks to search for new physics effects. Recent analyses of these decays have indicated an anomalous behaviour in measurements of angular distributions of the decay $B^0to K^*mu^+mu^-$ and lepton-flavour-universality observables. Unambiguously establishing if these deviations have a common nature is of paramount importance in order to understand the observed pattern. We propose a novel approach to independently and complementary probe this hypothesis by performing a simultaneous amplitude analysis of $bar{B}^0 to bar{K}^{*0} mu^+mu^-$ and $bar{B}^0 to bar{K}^{*0} e^+e^-$ decays. This method enables the direct determination of observables that encode potential non-equal couplings of muons and electrons, and are found to be insensitive to nonperturbative QCD effects. If current hints of new physics are confirmed, our approach could allow an early discovery of physics beyond the standard model with LHCb run II data sets.
rate research
Read More
A measurement of the ratio of branching fractions of the decays $B^+to K^+mu^+mu^-$ and $B^+to K^+e^+e^-$ is presented. The proton-proton collision data used correspond to an integrated luminosity of $5.0,$fb$^{-1}$ recorded with the LHCb experiment at centre-of-mass energies of $7$, $8$ and $13,$TeV. For the dilepton mass-squared range $1.1 < q^2 < 6.0,$GeV$^2!/c^4$ the ratio of branching fractions is measured to be $R_K = {0.846,^{+,0.060}_{-,0.054},^{+,0.016}_{-,0.014}}$, where the first uncertainty is statistical and the second systematic. This is the most precise measurement of $R_K$ to date and is compatible with the Standard Model at the level of 2.5 standard deviations.
We analyze in detail the angular distributions in $bar{B}to D^*ell bar u$ decays, with a focus on lepton-flavour non-universality. We investigate the minimal number of angular observables that fully describes current and upcoming datasets, and explore their sensitivity to physics beyond the Standard Model (BSM) in the most general weak effective theory. We apply our findings to the current datasets, extract the non-redundant set of angular observables from the data, and compare to precise SM predictions that include lepton-flavour universality violating mass effects. Our analysis shows that the current presentation of the experimental data is not ideal and prohibits the extraction of the full set of relevant BSM parameters, since the number of independent angular observables that can be inferred from data is limited to only four. We uncover a $sim4sigma$ tension between data and predictions that is hidden in the redundant presentation of the Belle 2018 data on $bar{B}to D^*ell bar u$ decays. This tension specifically involves observables that probe $e-mu$ lepton-flavour universality. However, we find inconsistencies in these data, which renders results based on it suspicious. Nevertheless, we discuss which generic BSM scenarios could explain the tension, in the case that the inconsistencies do not affect the data materially. Our findings highlight that $e-mu$ non-universality in the SM, introduced by the finite muon mass, is already significant in a subset of angular observables with respect to the experimental precision.
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.
Lepton flavor universality can be tested in the semileptonic decays $Lambda_bto Lambda_c^{(ast)}$ where $Lambda_c^{(ast)}$ denotes either the ground state $Lambda_c(2286)$ (with $J^P=1/2^+$) or its orbital excitations $Lambda_c(2595)$ (with $J^P=1/2^-$) and $Lambda_c(2625)$ (with $J^P=3/2^-$). We calculate the differential decay rates as well as the branching fractions of these decays for both tauonic and muonic modes with form factors obtained from a covariant confined quark model previously developed by us. We present results for the rate ratios of the tauonic and muonic modes which provide important tests of lepton flavor universality in forthcoming experiments.
A novel approach to reconstruct inclusive $bar{B} to X_{s} ell^{+}ell^{-}$ decays is presented. The method relies on isopsin symmetry to extrapolate the semi-inclusive signature $X_{b}to K^{+} ell^{+}ell^{-} X$ to the fully inclusive rate in $B^{+}$ and $B^{0}$ decays. We investigate the possibility to measure branching fractions and other observables such as lepton universality ratios and $CP$ asymmetries. As a proof of concept, fast simulation is used to compare the $X_{b}to K^{+} ell^{+}ell^{-} X$ signature with a fully inclusive approach. Several experimental advantages are seen which have the potential to make measurements of inclusive $bar{B} to X_{s} ell^{+}ell^{-}$ decays tractable at a hadron collider.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
