Invariant mass distribution of the $\Lambda ^0_ b \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \Lambda $ candidates. The histogram shows data, the solid red line is the overall fit function, the dotted blue line represents the sum of the combinatorial and peaking backgrounds and the dash-dotted green line the combinatorial background component.

Invariant mass distribution of the $\Lambda ^0_ b \rightarrow \Lambda \mu ^+\mu ^- $ candidates, integrated over all $ q^2$ values, together with the fit function described in the text. The histogram shows data, the solid red line is the overall fit function and the dotted blue line represents the background component.

Invariant mass distributions for the rare decay $\Lambda ^0_ b \rightarrow \Lambda \mu ^+\mu ^- $ candidates, in six $ q^2$ intervals, together with the fit function described in the text. The histogram shows data, the solid red line is the overall fit function and the dotted blue line represents the background component.

Measured differential branching fraction for the $\Lambda ^0_ b \rightarrow \Lambda \mu ^+\mu ^- $ decay. In regions without a significant signal, the 90 % confidence level upper limits are also shown. The uncertainties due to components that are fully correlated across all $ q^2$ bins, e.g. the branching fraction of the normalisation channel from Ref. [30], are not included in this figure. The dashed red line with the filled area shows the theoretical prediction from Ref. [14].

Animated gif made out of all figures.

Signal ($N_\mathrm{S}$) and background ($N_\mathrm{B}$) decay yields obtained from the $\Lambda ^0_ b \rightarrow \Lambda \mu ^+\mu ^- $ mass fit in each $ q^2$ interval. The integrated yield is the result of a fit without separation of the data into distinct $ q^2$ regions. The statistical significance is calculated as described in the text.

Total relative efficiency, $\varepsilon_{\mathrm{rel}}$, between $\Lambda ^0_ b \rightarrow \Lambda \mu ^+\mu ^- $ and $\Lambda ^0_ b \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \Lambda $ decays. The uncertainties are the combination of both statistical and systematic components, and are dominated by the latter.

Absolute systematic uncertainties on the yields for the $\Lambda ^0_ b \rightarrow \Lambda \mu ^+\mu ^- $ decay.

Absolute systematic uncertainties on the total relative efficiency, $\varepsilon_{\mathrm{rel}}$.

Measured relative differential branching fraction, $(1/\cal B (\Lambda ^0_ b \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \Lambda ))\;\mathrm{d}\cal B (\Lambda ^0_ b \rightarrow \Lambda \mu ^+\mu ^- )/\mathrm{d} q^2 $. The first uncertainty is statistical and the second is systematic. The systematic uncertainty includes the small, correlated component due to $\cal B ( { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \rightarrow \mu ^+\mu ^- )=(5.93\pm0.06)\times10^{-2}$ [30]. The rightmost column gives the 90 % (95 %) confidence level upper limit (UL) on the relative branching fraction in $ q^2$ intervals where no significant signal is observed.

Measured differential branching fraction, $\mathrm{d}\cal B (\Lambda ^0_ b \rightarrow \Lambda \mu ^+\mu ^- )/\mathrm{d} q^2 $, for $\cal B$ ( $\Lambda ^0_ b \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \Lambda $ )$ = (6.2\pm1.4)\times10^{-4}$ [30], where the first uncertainty is statistical, the second systematic and the third from the uncertainty in $\cal B$ ( $\Lambda ^0_ b \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \Lambda $ ). The rightmost column gives the 90 % (95 %) confidence level upper limit (UL) on the branching fraction in $ q^2$ intervals where no significant signal is observed.

Supplementary material full pdf

This ZIP file contains supplemetary material for the publication LHCb-PAPER-2013-025. The files are: supplementary.pdf : An overview of the extra figures *.pdf, *.png, *.eps : The figures in variuous formats