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Register a new userOn the S-wave pollution of B-> K* l+l- observables
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Joaquim Matias
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It has been argued recently that transverse asymmetries that are expected to be shielded from the presence of the S-wave (Kpi) pairs originating from the decay of a scalar K0* meson, are indeed affected by this pollution due to the impossibility to extract cleanly the normalization for these observables. In this short note we show how using folded distributions, which is nowadays the preferred method to obtain the information from the 4-body decay mode B-> K*(-> Kpi) l+l-, one can easily bypass this problem and extract the clean observables P_{1,2,3} and also P_{4,5,6} in a way completely free from this pollution including all lepton mass corrections. We also show that in case one insists in using uniangular distributions to extract these observables it is possible to reduce this pollution to just lepton mass suppressed terms. On the contrary, the S_i observables, that are by definition normalized by the full differential decay distribution, will indeed suffer from this pollution via their normalization. Finally, we also present a procedure to minimize the error associated to neglecting lepton mass corrections in the distribution defining a massless-improved limit.
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We present results from a search for the flavor-changing neutral current decays $Bto Kell^+ell^-$ and $Bto K^*ell^+ell^-$, where $ell^+ell^-$ is either an $e^+e^-$ or $mu^+mu^-$ pair. The data sample comprises $22.7times 10^6$ $Upsilon(4S)to Bbar B$ decays collected with the BABAR detector at the PEP-II $B$ Factory. We obtain the 90% C.L. upper limits ${mathcal B}(Bto Kell^+ell^-)< 0.50times 10^{-6}$ and ${mathcal B}(Bto K^*ell^+ell^-)<2.9times 10^{-6}$, close to Standard Model predictions for these branching fractions. We have also obtained limits on the lepton-family-violating decays $Bto Ke^{pm}mu^{mp}$ and $Bto K^{*}e^{pm}mu^{mp}$.
This report was prepared in the context of the LPCC Electroweak Precision Measurements at the LHC WG and summarizes the activity of a subgroup dedicated to the systematic comparison of public Monte Carlo codes, which describe the Drell-Yan processes at hadron colliders, in particular at the CERN Large Hadron Collider (LHC). This work represents an important step towards the definition of an accurate simulation framework necessary for very high-precision measurements of electroweak (EW) observables such as the $W$ boson mass and the weak mixing angle. All the codes considered in this report share at least next-to-leading-order (NLO) accuracy in the prediction of the total cross sections in an expansion either in the strong or in the EW coupling constant. The NLO fixed-order predictions have been scrutinized at the technical level, using exactly the same inputs, setup and perturbative accuracy, in order to quantify the level of agreement of different implementations of the same calculation. A dedicated comparison, again at the technical level, of three codes that reach next-to-next-to-leading-order (NNLO) accuracy in quantum chromodynamics (QCD) for the total cross section has also been performed. These fixed-order results are a well-defined reference that allows a classification of the impact of higher-order sets of radiative corrections. Several examples of higher-order effects due to the strong or the EW interaction are discussed in this common framework. Also the combination of QCD and EW corrections is discussed, together with the ambiguities that affect the final result, due to the choice of a specific combination recipe.
We study logarithmically enhanced electromagnetic corrections to the decay rate in the high dilepton invariant mass region as well as corrections to the forward backward asymmetry (FBA) of the inclusive rare decay $bar{B} to X_s ell^+ ell^-$. As expected, the relative effect of these corrections in the high dilepton mass region is around -8% for the muonic final state and therefore much larger than in the low dilepton mass region. We also present a complete phenomenological analysis, to improved NNLO accuracy, of the dilepton mass spectrum and the FBA integrated in the low dilepton mass region, including a new approach to the zero of the FBA. The latter represents one of the most precise predictions in flavour physics with a theoretical uncertainty of order 5%. We find $(q_0^2)_{mumu} = (3.50 pm 0.12) gev^2$. For the high dilepton invariant mass region, we have ${cal B}(bar Bto X_smumu)_{rm high} = (2.40^{+0.69}_{-0.62}) times 10^{-7}$. The dominant uncertainty is due to the $1/m_b$ corrections and can be significantly reduced in the future. For the low dilepton invariant mass region, we confirm previous results up to small corrections.
This talk covers recent theoretical progress in exclusive semileptonic rare B-decays at low hadronic recoil. The efficient parametric suppression of the 1/mb corrections in this region provides opportunities to probe the Standard Model and beyond at precision level. Notably, angular analysis allows to simultaneously access electroweak flavor physics and hadronic matrix elements, the latter of which constitute the leading source of theoretical uncertainty. Ratios of B ->K* form factors can already be extracted from present data. A comparison with existing theoretical determinations by lattice QCD and light cone sum rules gives a consistent picture over the whole kinematic range. In the future improved analyses will advance our understanding of non-perturbative methods for QCD and of |Delta B|=1 transitions.
By borrowing the results from a Large Hadron Collider (LHC) analysis performed with $36.1~text{fb}^{-1}$ of Run 2 data intended to search for $A$ production followed by $ZH$ decay in turn yielding $l^+l^-bbar b$ ($l=e,mu$) final states in the context of the standard four Yukawa types of the 2-Higgs Doublet Model (2HDM), we recast it in terms of sensitivity reaches for the similar process $ppto Hto ZAto l^+l^-bbar b$. This simple exercise across the two processes, which is possible because the only kinematic difference between these are different widths for the Higgs bosons, in turn affecting minimally the efficiency of an experimental selection, enables us to expand the region of parameter space that can be tested to the case when $m_Hge m_A+m_Z$. Furthermore, we extrapolate our results to full Run 3 data samples. We conclude that, while the high energy and luminosity stage of the LHC can afford one with increased sensitivity to the 2HDM in general, the recast analysis does not add anything to what already probed through the actual one.
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