$\bar{\Lambda ^0_ b } \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \overline{\Lambda} $ mass fit. Top: $\overline{\Lambda}$ is reconstructed using long tracks. Bottom: using the downstream tracks. The plots on the left and on the right used data recorded with different magnet polarities.

The measured $\sigma(pp\rightarrow \Lambda ^0_ b X)\cal B ( \Lambda ^0_ b \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \Lambda )$ in $\rm nb$ for the eight samples. The black vertical bars represent the statistical error, the red limits represent the systematic uncertainty. The green horizontal band represents the average for the two species $\Lambda ^0_ b $ and $\overline{\Lambda} ^0_ b $ . The red horizontal line represent the predictions from the LHCb simulated sample. (1)&(2) stand for the measurement using $\Lambda ^0_ b $ reconstructed with $\Lambda$ daughters as long tracks using data recorded with different polarity of the magnetic field, while (3)&(4) stand for the case in which the $\Lambda$ daughters are reconstructed as downstream tracks.

Animated gif made out of all figures.

Requirements used to select first the $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ $\rightarrow$ $\mu ^+\mu ^-$ then the $\Lambda \rightarrow p \pi $ and finally the $\Lambda ^0_ b \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \Lambda $ candidates. $M$ and $m$ are used to indicate the measured invariant masses and the nominal masses respectively. As the $\Lambda$ can be reconstructed from a pair of long tracks (LL) or downstream tracks (DD) different values are indicated where applied, $\tau$ is the decay time of the particle and IP$_{\chi^2}$ the difference in the $\chi^2$ of the primary vertex measured with and without the respective track. The $ K ^0_{\rm\scriptscriptstyle S}$ background is eliminated from the $\Lambda$ sample by applying a requirement on $|M_{\pi \pi }-m_{ K ^0_{\rm\scriptscriptstyle S} }|$.

Systematic uncertainties for the cross-section measurements in percent. Where the uncertainty is different for the eight sub-samples in which the candidates are divided, the smallest and the largest estimated values are are shown. The total systematic uncertainty is obtained assuming total correlation among the correlated variables.