CERN Accelerating science

\textcolor{changes}{Contributions to \BuKll decays in the SM and possible new physics models.} A \Bp meson, consisting of \bquarkbar and \uquark quarks, decays into a \Kp, containing \squarkbar and \uquark quarks, and two charged leptons, $\ellp\ellm$. (Left) The SM contribution involves the electroweak bosons $\gamma,~W^+$ and $Z^0$, \textcolor{changes}{and the up-type quarks $\bar{u}$, $\bar{c}$ and $\bar{t}$}. (Right) A possible new physics contribution to the decay with a hypothetical leptoquark ($LQ$) which, unlike the electroweak bosons, could have different interaction strengths with the different types of leptons.

Candidate invariant mass distributions. Distribution of the invariant mass \mKllgeneric for candidates with (left) electron and (right) muon pairs in the final state for the (top) nonresonant \BuKll signal channels and (bottom) resonant \BuJpsiKll decays. The fit projection is superimposed\textcolor{changes}{, with dotted lines describing the signal contribution and solid areas representing each of the background components described in the text and listed in the legend}. In the resonant-mode distributions, some fit components are too small to be visible.

Candidate invariant mass distributions. Distribution of the invariant mass \mKllgeneric for candidates with (left) electron and (right) muon pairs in the final state for the (top) nonresonant \BuKll signal channels and (bottom) resonant \BuJpsiKll decays. The fit projection is superimposed\textcolor{changes}{, with dotted lines describing the signal contribution and solid areas representing each of the background components described in the text and listed in the legend}. In the resonant-mode distributions, some fit components are too small to be visible.

Candidate invariant mass distributions. Distribution of the invariant mass \mKllgeneric for candidates with (left) electron and (right) muon pairs in the final state for the (top) nonresonant \BuKll signal channels and (bottom) resonant \BuJpsiKll decays. The fit projection is superimposed\textcolor{changes}{, with dotted lines describing the signal contribution and solid areas representing each of the background components described in the text and listed in the legend}. In the resonant-mode distributions, some fit components are too small to be visible.

Candidate invariant mass distributions. Distribution of the invariant mass \mKllgeneric for candidates with (left) electron and (right) muon pairs in the final state for the (top) nonresonant \BuKll signal channels and (bottom) resonant \BuJpsiKll decays. The fit projection is superimposed\textcolor{changes}{, with dotted lines describing the signal contribution and solid areas representing each of the background components described in the text and listed in the legend}. In the resonant-mode distributions, some fit components are too small to be visible.

Comparison between \RK measurements. In addition to the LHCb result, the measurements by the BaBar~\cite{RKbabar} and Belle~\cite{RKbelle} collaborations, which combine \BuKll and \BdKSll decays, are also shown.

Comparison between \RK measurements. In addition to the LHCb result, the measurements by the BaBar~\cite{RKbabar} and Belle~\cite{RKbelle} collaborations, which combine \BuKll and \BdKSll decays, are also shown. \textcolor{changes}{The vertical dashed line indicates the SM prediction.}

Simulated $K^+e^-$ mass distributions for signal and various cascade background samples. \textcolor{changes}{The signal is represented by the orange shaded region and the various cascade background contributions by red, dark blue and light blue shaded regions.} The distributions are all normalised to unity. (Left, with log $y$-scale) the bremsstrahlung correction to the momentum of the electron is applied, resulting in a tail to the right. The region to the left of the vertical dashed line is rejected. (Right, with linear $y$-scale) the mass is computed only from the track information. The notation $\pi^-_{[\rightarrow e^-]}$ ($e^-_{[\rightarrow \pi^-]}$) is used to denote an \textcolor{changes}{pion (electron)} that is \textcolor{changes}{reconstructed} as an \textcolor{changes}{electron (pion)}. The region between the dashed vertical lines is rejected.

Simulated $K^+e^-$ mass distributions for signal and various cascade background samples. \textcolor{changes}{The signal is represented by the orange shaded region and the various cascade background contributions by red, dark blue and light blue shaded regions.} The distributions are all normalised to unity. (Left, with log $y$-scale) the bremsstrahlung correction to the momentum of the electron is applied, resulting in a tail to the right. The region to the left of the vertical dashed line is rejected. (Right, with linear $y$-scale) the mass is computed only from the track information. The notation $\pi^-_{[\rightarrow e^-]}$ ($e^-_{[\rightarrow \pi^-]}$) is used to denote an \textcolor{changes}{pion (electron)} that is \textcolor{changes}{reconstructed} as an \textcolor{changes}{electron (pion)}. The region between the dashed vertical lines is rejected.

Candidate invariant mass distributions. Distribution of the invariant mass \mKll for nonresonant candidates in the (left) sample previously analysed~\cite{LHCb-PAPER-2019-009} and (right) the new data sample. The top row shows the fit to the muon modes and the subsequent rows the fits to the electron modes triggered by (second row) one of the electrons, (third row) the kaon and (last row) by other particles in the event. The fit projections are superimposed\textcolor{changes}{, with dotted lines describing the signal contribution and solid areas representing each of the background components described in the text and listed in the legend}.

Candidate invariant mass distributions. Distribution of the invariant mass \mKll for nonresonant candidates in the (left) sample previously analysed~\cite{LHCb-PAPER-2019-009} and (right) the new data sample. The top row shows the fit to the muon modes and the subsequent rows the fits to the electron modes triggered by (second row) one of the electrons, (third row) the kaon and (last row) by other particles in the event. The fit projections are superimposed\textcolor{changes}{, with dotted lines describing the signal contribution and solid areas representing each of the background components described in the text and listed in the legend}.

Candidate invariant mass distributions. Distribution of the invariant mass \mKll for nonresonant candidates in the (left) sample previously analysed~\cite{LHCb-PAPER-2019-009} and (right) the new data sample. The top row shows the fit to the muon modes and the subsequent rows the fits to the electron modes triggered by (second row) one of the electrons, (third row) the kaon and (last row) by other particles in the event. The fit projections are superimposed\textcolor{changes}{, with dotted lines describing the signal contribution and solid areas representing each of the background components described in the text and listed in the legend}.

Candidate invariant mass distributions. Distribution of the invariant mass \mKll for nonresonant candidates in the (left) sample previously analysed~\cite{LHCb-PAPER-2019-009} and (right) the new data sample. The top row shows the fit to the muon modes and the subsequent rows the fits to the electron modes triggered by (second row) one of the electrons, (third row) the kaon and (last row) by other particles in the event. The fit projections are superimposed\textcolor{changes}{, with dotted lines describing the signal contribution and solid areas representing each of the background components described in the text and listed in the legend}.

Candidate invariant mass distributions. Distribution of the invariant mass \mKll for nonresonant candidates in the (left) sample previously analysed~\cite{LHCb-PAPER-2019-009} and (right) the new data sample. The top row shows the fit to the muon modes and the subsequent rows the fits to the electron modes triggered by (second row) one of the electrons, (third row) the kaon and (last row) by other particles in the event. The fit projections are superimposed\textcolor{changes}{, with dotted lines describing the signal contribution and solid areas representing each of the background components described in the text and listed in the legend}.

Candidate invariant mass distributions. Distribution of the invariant mass \mKll for nonresonant candidates in the (left) sample previously analysed~\cite{LHCb-PAPER-2019-009} and (right) the new data sample. The top row shows the fit to the muon modes and the subsequent rows the fits to the electron modes triggered by (second row) one of the electrons, (third row) the kaon and (last row) by other particles in the event. The fit projections are superimposed\textcolor{changes}{, with dotted lines describing the signal contribution and solid areas representing each of the background components described in the text and listed in the legend}.

Candidate invariant mass distributions. Distribution of the invariant mass \mKll for nonresonant candidates in the (left) sample previously analysed~\cite{LHCb-PAPER-2019-009} and (right) the new data sample. The top row shows the fit to the muon modes and the subsequent rows the fits to the electron modes triggered by (second row) one of the electrons, (third row) the kaon and (last row) by other particles in the event. The fit projections are superimposed\textcolor{changes}{, with dotted lines describing the signal contribution and solid areas representing each of the background components described in the text and listed in the legend}.

Candidate invariant mass distributions. Distribution of the invariant mass \mKll for nonresonant candidates in the (left) sample previously analysed~\cite{LHCb-PAPER-2019-009} and (right) the new data sample. The top row shows the fit to the muon modes and the subsequent rows the fits to the electron modes triggered by (second row) one of the electrons, (third row) the kaon and (last row) by other particles in the event. The fit projections are superimposed\textcolor{changes}{, with dotted lines describing the signal contribution and solid areas representing each of the background components described in the text and listed in the legend}.

Candidate invariant mass distributions. Distribution of the invariant mass \mKllconst for resonant candidates in the (left) sample previously analysed~\cite{LHCb-PAPER-2019-009} and (right) the new data sample. The top row shows the fit to the muon modes and the subsequent rows the fits to the electron modes triggered by (second row) one of the electrons, (third row) the kaon and (last row) by other particles in the event. The fit projections are superimposed\textcolor{changes}{, with dotted lines describing the signal contribution and solid areas representing each of the background components described in the text and listed in the legend}.

Candidate invariant mass distributions. Distribution of the invariant mass \mKllconst for resonant candidates in the (left) sample previously analysed~\cite{LHCb-PAPER-2019-009} and (right) the new data sample. The top row shows the fit to the muon modes and the subsequent rows the fits to the electron modes triggered by (second row) one of the electrons, (third row) the kaon and (last row) by other particles in the event. The fit projections are superimposed\textcolor{changes}{, with dotted lines describing the signal contribution and solid areas representing each of the background components described in the text and listed in the legend}.

Candidate invariant mass distributions. Distribution of the invariant mass \mKllconst for resonant candidates in the (left) sample previously analysed~\cite{LHCb-PAPER-2019-009} and (right) the new data sample. The top row shows the fit to the muon modes and the subsequent rows the fits to the electron modes triggered by (second row) one of the electrons, (third row) the kaon and (last row) by other particles in the event. The fit projections are superimposed\textcolor{changes}{, with dotted lines describing the signal contribution and solid areas representing each of the background components described in the text and listed in the legend}.

Candidate invariant mass distributions. Distribution of the invariant mass \mKllconst for resonant candidates in the (left) sample previously analysed~\cite{LHCb-PAPER-2019-009} and (right) the new data sample. The top row shows the fit to the muon modes and the subsequent rows the fits to the electron modes triggered by (second row) one of the electrons, (third row) the kaon and (last row) by other particles in the event. The fit projections are superimposed\textcolor{changes}{, with dotted lines describing the signal contribution and solid areas representing each of the background components described in the text and listed in the legend}.

Candidate invariant mass distributions. Distribution of the invariant mass \mKllconst for resonant candidates in the (left) sample previously analysed~\cite{LHCb-PAPER-2019-009} and (right) the new data sample. The top row shows the fit to the muon modes and the subsequent rows the fits to the electron modes triggered by (second row) one of the electrons, (third row) the kaon and (last row) by other particles in the event. The fit projections are superimposed\textcolor{changes}{, with dotted lines describing the signal contribution and solid areas representing each of the background components described in the text and listed in the legend}.

Candidate invariant mass distributions. Distribution of the invariant mass \mKllconst for resonant candidates in the (left) sample previously analysed~\cite{LHCb-PAPER-2019-009} and (right) the new data sample. The top row shows the fit to the muon modes and the subsequent rows the fits to the electron modes triggered by (second row) one of the electrons, (third row) the kaon and (last row) by other particles in the event. The fit projections are superimposed\textcolor{changes}{, with dotted lines describing the signal contribution and solid areas representing each of the background components described in the text and listed in the legend}.

Candidate invariant mass distributions. Distribution of the invariant mass \mKllconst for resonant candidates in the (left) sample previously analysed~\cite{LHCb-PAPER-2019-009} and (right) the new data sample. The top row shows the fit to the muon modes and the subsequent rows the fits to the electron modes triggered by (second row) one of the electrons, (third row) the kaon and (last row) by other particles in the event. The fit projections are superimposed\textcolor{changes}{, with dotted lines describing the signal contribution and solid areas representing each of the background components described in the text and listed in the legend}.

Candidate invariant mass distributions. Distribution of the invariant mass \mKllconst for resonant candidates in the (left) sample previously analysed~\cite{LHCb-PAPER-2019-009} and (right) the new data sample. The top row shows the fit to the muon modes and the subsequent rows the fits to the electron modes triggered by (second row) one of the electrons, (third row) the kaon and (last row) by other particles in the event. The fit projections are superimposed\textcolor{changes}{, with dotted lines describing the signal contribution and solid areas representing each of the background components described in the text and listed in the legend}.

\textcolor{changes}{Likelihood function from the fit to the nonresonant \BuKll candidates in terms of the ratio between the likelihood value ($L$) and that found by the fit ($L_{\rm max}$) as a function of \RK.} The extent of the dark, medium and light blue regions shows the values allowed for \RK at $1\sigma$, $3\sigma$ and $5\sigma$ levels. The red line indicates the prediction from the SM.

Differential \rjpsi measurement. (Top) distributions of the reconstructed spectra of (left) the angle between the leptons\textcolor{changes}{, $\alpha(\ell^+, \ell^-)$}, and (right) the minimum \pt of the leptons \textcolor{changes}{ for \BuKll and \BuJpsiKll decays}. (Bottom) the single ratio \rjpsi relative to its average value $\left< \rjpsi \right>$ as a function of these variables. In the electron minimum \pt spectra, the structure at 2800\mevc is related to the trigger threshold. \textcolor{changes}{ Uncertainties on the data points are statistical only.}

Double differential \rjpsi measurement. (Left) the value of \rjpsi, relative to the average value of \rjpsi, measured in two-dimensional bins of the maximum lepton momentum, $p(\ell)$, and the opening angle between the two leptons, $\alpha(\ell^+,\ell^-)$. (Right) the bin definition in this two-dimensional space together with the distribution for \BuKee (\BuJpsiKee) decays depicted as red (blue) contours. \textcolor{changes}{Uncertainties on the data points are statistical only.}

Double differential \rjpsi measurement. (Left) the value of \rjpsi, relative to the average value of \rjpsi, measured in two-dimensional bins of the maximum lepton momentum, $p(\ell)$, and the opening angle between the two leptons, $\alpha(\ell^+,\ell^-)$. (Right) the bin definition in this two-dimensional space together with the distribution for \BuKee (\BuJpsiKee) decays depicted as red (blue) contours. \textcolor{changes}{Uncertainties on the data points are statistical only.}