What is the reason for a wide B$_S$ peak in dimuon plot? Why is the B$_s$ meson peak in dimuon invariant mass spectrum wider than the others? Upsilon meson has a lifetime of several orders of magnitude shorter, which by my intution should lead the wider peak.


Fig 3.8 .Dimuon mass distribution collected with various dimuon triggers, during the 25 ns running period at 13 TeV in 2015.  The coloured paths correspond to dedicated dimuon triggers with low $p_T$ thresholds, in specific mass windows, while the light gray continuous distribution represents events collected with  a dimuon trigger with high $p_T$ thresholds

 A: There is no $B_s$ peak in this plot, and nor would you expect there to be. The decay $B_s \to \mu^+ \mu^-$ is very rare, with a branching fraction of about $2\times 10^{-9}$.
The legend on the plot is a strong clue to what is happening. Each colour is a different dimuon trigger. With the exception of the grey 'double muon inclusive', they each have a different invariant mass window. Within these windows, events are selected with greater efficiency, which appears as a step function on top of the 'double muon inclusive' distribution.
A: After adding the caption it is evident that this is a composite plot. If you notice , there is a flat background around below each resonance ( cut off from that particular experiments data),on the background the resonance peak appears, or not, as in the case of the $B_s$. It is flat because no signal was found when looking with an appropriate trigger at that region. Only the pointed figures have a signal over a flat background.
The general gray background and figures are the ones to look at for resonances. The colored are specialized looks with more data at that area.
