The effective lifetime of the B$^0_\mathrm{s}$ meson in the decay B$^0_\mathrm{s}$$\to$ J/$\psi$K$^0_\mathrm{S}$ is measured using data collected during 2016-2018 with the CMS detector in $\sqrt{s}$ = 13 TeV proton-proton collisions at the LHC, corresponding to an integrated luminosity of 140 fb$^{-1}$. The effective lifetime is determined by performing a two-dimensional unbinned maximum likelihood fit to the B$^0_\mathrm{s}$ meson invariant mass and proper decay time distributions. The resulting value of 1.59 $\pm$ 0.07 (stat) $\pm$ 0.03 (syst) ps is the most precise measurement to date and is in good agreement with the expected value.
The measured effective lifetime for the $\mathrm{B}^{0}_{\mathrm{s}} \to \mathrm{J}/{\psi}\,\mathrm{K}^{0}_{\mathrm{S}}$ decay
We present first data on sub-threshold production of K0 s mesons and {\Lambda} hyperons in Au+Au collisions at $\sqrt{s_{NN}}$ = 2.4 GeV. We observe an universal <Apart> scaling of hadrons containing strangeness, independent of their corresponding production thresholds. Comparing the yields, their <Apart> scaling, and the shapes of the rapidity and the pt spectra to state-of-the-art transport model (UrQMD, HSD, IQMD) predictions, we find that none of the latter can simultaneously describe all observables with reasonable \c{hi}2 values.
Example of $K^{0}_{S}$ signal for 0-40% most central events, over mixed-event background for the bin $-0.05 < y_{cm} < 0.05$ and reduced transverse masses between $80-120 MeV/c^{2}$.
Example of $\Lambda$ signal for 0-40% most central events, over mixed-event background for the bin $-0.05 < y_{cm} < 0.05$ and reduced transverse masses between $100-150 MeV/c^{2}$.
Reduced transverse mass ($m_{t}-m_{0}$) spectra of $K^{0}_{S}$ for the 0-40% most central events. NOTE: The spectra are not scaled by $1/N_{Events}$! To compare the data, divide by $N_{Events} = 2.1997626 x 10^{9}$
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