diff --git a/draft.tex b/draft.tex index 65a92ed..bf4151a 100644 --- a/draft.tex +++ b/draft.tex @@ -169,7 +169,7 @@ In order to study the sensitivity to different NP scenarios, we generated a large number of toys using the following set of parameters: -the correlator parameters for each polarisation as in~\cite{Danny_2017}, +the non-local hadronic parameters as in~\cite{Danny_2017}, the form factor parameters as determined from~\cite{Straub:2015ica}, but with twice the stated uncertainty, and the CKM Wolfenstein parameters~\cite{Bona:2006ah}; all the above-mentioned parameters @@ -200,18 +200,20 @@ of the fitted parameters. The authors of~\cite{Danny_2017} proposed a SM prediction of the non-local -correlators $\mathcal{H}_\lambda(z)$, where $\lambda=\perp, \para,0$ is -the polarization of the \Kstarz, assuming the analytic expansion to be cut at -the order $z^2$. +hadronic matrix elements $\mathcal{H}_\lambda(z)$, where $\lambda=\perp, \para,0$ +is the polarization of the \Kstarz, operating an analytic expansion in the ``conformal” +variable $z(q^2)$ and assuming a truncation at the order $z^2$ (in the following we refer +to the analytic expansion of $\mathcal{H}_\lambda$ truncated at the order $z^n$ +as $\mathcal{H}_\lambda[z^n]$). In order to test the validity of the adopted parametrizations we repeat the fit with different configurations: \begin{itemize} - \item We include the $\mathcal{H}_\lambda(z)$ SM prediction + \item We include the $\mathcal{H}_\lambda[z^2]$ SM prediction from~\cite{Danny_2017} as gaussian contraint to the fit. - \item We remove any theoretical assumption on $\mathcal{H}_\lambda(z)$ - and let free-floating all the parameters up to the order $z^2$. - \item We increase the order of the analytical expansion of $\mathcal{H}_\lambda(z)$ + \item We remove any theoretical assumption on $\mathcal{H}_\lambda[z^2]$ + and let free-floating all the parameters. + \item We increase the order of the analytical expansion of $\mathcal{H}_\lambda$ up to the (free-floating) order of $z^3$ and $z^4$. \item We re-parametrize the description of the non-local hadronic matrix element as proposed in~\cite{Christoph}. @@ -255,9 +257,37 @@ Fig.~\ref{fig:DeltaC9C10} shows the sensitivity to the two NP scenarios, NP$_{\WC_9}$ and NP$_{\WC_9-\WC_{10}}$ in terms of the two model-independent LFU-breaking difference of Wilson coefficients $\Delta\WC_9$ and $\Delta\WC_{10}$. +We quantify the maximal expected significance to the SM as $4.6\,(5.3)\,\sigma$ for +the \lhcb RunII, $xx(yy)\,\sigma$ for the \belle II 50~ab$^{-1}$ dataset and +$xx(yy)\,\sigma$ for the \lhcb 50~fb$^{-1}$ Upgrade for the NP$_{\WC_9}$ +(NP$_{\WC_9-\WC_{10}}$) scenario respectively. +Modelling detector effects as \qsq and angles resolution or detector acceptance and +efficiency is hardly possible without access to (non-public) information of the current +$B$~physics experiments. +A first rudimentary study on the impact of a finite \qsq resolution is preformed +assuming a \qsq-constant asymmetric smearing of the di-lepton invariant mass +in the electron mode; the size and asymmetry of such smearing is naively chosen +to reproduce the mass fits of~\cite{LHCB-PAPER-2017-013}. +Despite the low \qsq asymmetric tail, the determination of $\Delta\WC_9$ and +$\Delta\WC_{10}$ remains unbiased. +An other important test to probe the stability of the model consists in changing the +description of the non-local hadronic effects in the generation of the pseudo-experiments. +In this way we analyse the potential issue that can rise if the truncation +$\mathcal{H}_\lambda[z^2]$ is not a good description of nature. +We proceed as follows: we generate toys with non-zero coefficients for +$\mathcal{H}_\lambda[z^3]$ and $\mathcal{H}_\lambda[z^4]$ and we perform the fit +with $\mathcal{H}_\lambda[z^2]$. +We vary the choice of the $\mathcal{H}_\lambda[z^{3(4)}]$ generated parameters, +including a ``provocative" set of values that minimize the tension with the $P_5'$ +``anomaly"~\cite{LHCb-PAPER-2015-051} while keeping $\WC_9^{(\mu)}$ and +$\WC_{10}^{(\mu)}$ at their SM values. +Despite the mis-modelling of the non-local hadronic effects in the fit, we observe +that the determination of $\Delta\WC_9$ and $\Delta\WC_{10}$ is always unbiased, +thanks to the relative cancellation of all the shared parameters between the two channels, +while {\color{red} test bias in C10 and Upgrade} \begin{figure}[tbh] @@ -267,16 +297,35 @@ $3\,\sigma$ contours in the $\Delta\WC_9$ - $\Delta\WC_{10}$ plane obtained for different parametrizations of the non-local hadronic effects from a large number of toys generated with the NP$_{\WC_9}$ (top) and NP$_{\WC_9-\WC_{10}}$ (bottom) - scenario and the expected statistics after the \lhcb Run2. + scenario and the expected statistics after the \lhcb RunII. \label{fig:DeltaC9C10} } \end{figure} +In conclusion, we propose a clean, robust and model-independent method to combine +all the available information from $\Bz \to \Kstarz \ellell$ decays for a precise +determination of LFU-breaking difference of Wilson coefficients $\Delta\WC_9$ +and $\Delta\WC_{10}$. +Fig.~\ref{fig:allComponents} shows the contribution of all the single constituents of +the analysis and how the proposed method takes advantage of the complete description +of the decay. +This approach exploits possible differences between the muon and electron channels, +by mean of a shared parametrization of all the common local (form-factors) and non-local +($\mathcal{H}_\lambda$) hadronic matrix elements. +This results in a clean simultaneous analysis of the two channels, independent on any +theoretical uncertainty; in addition, this method doesn't suffer from the limited +statistics of the electron channel, that would make impossible to perform a complete +angular analysis of the single $\Bz \to \Kstarz e^+ e^-$ decay channel. + + + \begin{figure}[tbh] \includegraphics[width=.4\textwidth]{plots/B2Kstll_summary.pdf} \caption{% - . + Sensitivity to the NP$_{\WC_9-\WC_{10}}$ scenario for the expected statistics after the \lhcb RunII. + The relative contribution ($1,\,2,\,3\,\sigma$ contours) of each step of the analysis is shown in different colors, together with the + result of full amplitude method proposed in this letter. \label{fig:allComponents} } \end{figure}