A search for the lepton flavor violating $\tau \to $ 3$\mu$ decay is performed using proton-proton collision events at a center-of-mass energy of 13 TeV collected by the CMS experiment at the LHC in 2017-2018, corresponding to an integrated luminosity of 97.7 fb$^{-1}$. Tau leptons produced in both heavy-flavor hadron and W boson decays are exploited in the analysis. No evidence for the decay is observed. The results of this search are combined with an earlier null result based on data collected in 2016 to obtain a total integrated luminosity of 131 fb$^{-1}$. The observed (expected) upper limits on the branching fraction $\mathcal{B}$($\tau \to $ 3$\mu$) at confidence levels of 90 and 95% are 2.9$\times$10$^{-8}$ (2.4$\times$10$^{-8}$) and 3.6$\times$10$^{-8}$ (3.0$\times$10$^{-8}$), respectively.

The first observation of the decay $\Xi^-_\mathrm{b}$$\to$$\psi$(2S)$\Xi^-$ and measurement of the branching ratio of $\Xi^-_\mathrm{b}$$\to$$\psi$(2S)$\Xi^-$ to $\Xi^-_\mathrm{b}$$\to$ J/$\psi$$\Xi^-$ are presented. The J/$\psi$ and $\psi$(2S) mesons are reconstructed using their dimuon decay modes. The results are based on proton-proton colliding beam data from the LHC collected by the CMS experiment at $\sqrt{s}$ = 13 TeV in 2016-2018, corresponding to an integrated luminosity of 140 fb$^{-1}$. The branching fraction ratio is measured to be $\mathcal{B}$($\Xi^-_\mathrm{b}$$\to$$\psi$(2S)$\Xi^-$)/$\mathcal{B}$($\Xi^-_\mathrm{b}$$\to$ J/$\psi$$\Xi^-$) = 0.84$^{+0.21}_{-0.19}$ (stat) $\pm$ 0.10 (syst) $\pm$ 0.02 ($\mathcal{B}$), where the last uncertainty comes from the uncertainties in the branching fractions of the charmonium states. New measurements of the $\Xi_\mathrm{b}^{\ast{}0}$ baryon mass and natural width are also presented, using the $\Xi_\mathrm{b}^-\pi^+$ final state, where the $\Xi^-_\mathrm{b}$ baryon is reconstructed through the decays J/$\psi \Xi^-$, $\psi$(2S)$\Xi^-$, J/$\psi \Lambda$K$^-$, and J/$\psi \Sigma^0$K$^-$. Finally, the fraction of the $\Xi^-_\mathrm{b}$ baryons produced from $\Xi_\mathrm{b}^{\ast{}0}$ decays is determined.

A test of lepton flavor universality in B$^{\pm}$$\to$ K$^{\pm}\mu^+\mu^-$ and B$^{\pm}$$\to$ K$^{\pm}$e$^+$e$^-$ decays, as well as a measurement of differential and integrated branching fractions of a nonresonant B$^{\pm}$$\to$ K$^{\pm}\mu^+\mu^-$ decay are presented. The analysis is made possible by a dedicated data set of proton-proton collisions at $\sqrt{s}$ = 13 TeV recorded in 2018, by the CMS experiment at the LHC, using a special high-rate data stream designed for collecting about 10 billion unbiased b hadron decays. The ratio of the branching fractions $\mathcal{B}$(B$^{\pm}$$\to$ K$^{\pm}\mu^+\mu^-$) to $\mathcal{B}$(B$^{\pm}$$\to$ K$^{\pm}$e$^+$e$^-$) is determined from the measured double ratio $R$(K) of these decays to the respective branching fractions of the B$^\pm$$\to$ J/$\psi$K$^\pm$ with J/$\psi$$\to$$\mu^+\mu^-$ and e$^+$e$^-$ decays, which allow for significant cancellation of systematic uncertainties. The ratio $R$(K) is measured in the range 1.1 $\lt q^2 \lt$ 6.0 GeV$^2$, where $q$ is the invariant mass of the lepton pair, and is found to be $R$(K) = 0.78$^{+0.47}_{-0.23}$, in agreement with the standard model expectation $R$(K) $\approx$ 1. This measurement is limited by the statistical precision of the electron channel. The integrated branching fraction in the same $q^2$ range, $\mathcal{B}$(B$^{\pm}$$\to$ K$^{\pm}\mu^+\mu^-$) = (12.42 $\pm$ 0.68) $\times$ 10$^{-8}$, is consistent with the present world-average value and has a comparable precision.

The results of a search for pair production of the scalar partners of bottom quarks in 2.05 fb^-1 of pp collisions at sqrt{s} = 7 TeV using the ATLAS experiment are reported. Scalar bottoms are searched for in events with large missing transverse momentum and two jets in the final state, where both jets are identified as originating from a b-quark. In an R-parity conserving minimal supersymmetric scenario, assuming that the scalar bottom decays exclusively into a bottom quark and a neutralino, 95% confidence-level upper limits are obtained in the tilde{b}_1 - tilde{chi}^0_1 mass plane such that for neutralino masses below 60 GeV scalar bottom masses up to 390 GeV are excluded.

The $B_\mathrm{c}^+$ meson is observed for the first time in heavy ion collisions. Data from the CMS detector are used to study the production of the $B_\mathrm{c}^+$ meson in lead-lead (PbPb) and proton-proton (pp) collisions at a center-of-mass energy per nucleon pair of $\sqrt{s_{\mathrm{NN}}} =$ 5.02 TeV, via the $B_\mathrm{c}^+ \to (J/\psi\to\mu^+\mu^-)\mu^+\nu_\mu$ decay. The $B_\mathrm{c}^+$ nuclear modification factor, derived from the PbPb-to-pp ratio of production cross sections, is measured in two bins of the trimuon transverse momentum and of the PbPb collision centrality. The B$_\mathrm{c}^+$ meson is shown to be less suppressed than quarkonia and most of the open heavy-flavor mesons, suggesting that effects of the hot and dense nuclear matter created in heavy ion collisions contribute to its production. This measurement sets forth a promising new probe of the interplay of suppression and enhancement mechanisms in the production of heavy-flavor mesons in the quark-gluon plasma.

Measurements are presented of the B$^0_\mathrm{S}$$\to$$\mu^+\mu^-$ branching fraction and effective lifetime, as well as results of a search for the B$^0$$\to$$\mu^+\mu^-$ decay in proton-proton collisions at $\sqrt{s}$ = 13 TeV at the LHC. The analysis is based on data collected with the CMS detector in 2016-2018 corresponding to an integrated luminosity of 140 fb$^{-1}$. The branching fraction of the B$^0_\mathrm{S}$$\to$$\mu^+\mu^-$ decay and the effective B$^0_\mathrm{S}$ meson lifetime are the most precise single measurements to date. No evidence for the B$^0$$\to$$\mu^+\mu^-$ decay has been found. All results are found to be consistent with the standard model predictions and previous measurements.

Three of the most significant measured deviations from standard model predictions, the enhanced decay rate for B $\to$ D$^{(*)}\tau\nu$, hints of lepton universality violation in B $\to$ K$^{(*)}\ell\ell$ decays, and the anomalous magnetic moment of the muon, can be explained by the existence of leptoquarks (LQs) with large couplings to third-generation quarks and masses at the TeV scale. The existence of these states can be probed at the LHC in high energy proton-proton collisions. A novel search is presented for pair production of LQs coupled to a top quark and a muon using data at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 35.9 fb$^{-1}$, recorded by the CMS experiment. No deviation from the standard model prediction has been observed and scalar LQs decaying exclusively into t$\mu$ are excluded up to masses of 1420 GeV. The results of this search are combined with those from previous searches for LQ decays into t$\tau$ and b$\nu$, which excluded scalar LQs below masses of 900 and 1080 GeV. Vector LQs are excluded up to masses of 1190 GeV for all possible combinations of branching fractions to t$\mu$, t$\tau$ and b$\nu$. With this analysis, all relevant couplings of LQs with an electric charge of -1/3 to third-generation quarks are probed for the first time.

The ratios of the production cross sections between the excited $\Upsilon$(2S) and $\Upsilon$(3S) mesons and the $\Upsilon$(1S) ground state, detected via their decay into two muons, are studied as a function of the number of charged particles in the event. The data are from proton-proton collisions at $\sqrt{s} =$ 7 TeV, corresponding to an integrated luminosity of 4.8 fb$^{-1}$, collected with the CMS detector at the LHC. Evidence of a decrease in these ratios as a function of the particle multiplicity is observed, more pronounced at low transverse momentum $p_\mathrm{T}^{\mu\mu}$. For $\Upsilon$(nS) mesons with $p_\mathrm{T}^{\mu\mu}$ $\gt$ 7 GeV, where most of the data were collected, the correlation with multiplicity is studied as a function of the underlying event transverse sphericity and the number of particles in a cone around the $\Upsilon$(nS) direction. The ratios are found to be multiplicity independent for jet-like events. The mean $p_\mathrm{T}^{\mu\mu}$ values for the $\Upsilon$(nS) states as a function of particle multiplicity are also measured and found to grow more steeply as their mass increases.

The dependence of the ratio between the B$_\mathrm{s}^0$ and B$^+$ hadron production fractions, $f_\mathrm{s} / f_\mathrm{u}$, on the transverse momentum ($p_\mathrm{T}$) and rapidity of the B mesons is studied using the decay channels B$_\mathrm{s}^0$$\to$ J$/\psi\,\phi$ and B$^+$$\to$ J$/\psi$ K$^+$. The analysis uses a data sample of proton-proton collisions at a center-of-mass energy of 13 TeV, collected by the CMS experiment in 2018 and corresponding to an integrated luminosity of 61.6 fb$^{-1}$. The $f_\mathrm{s} / f_\mathrm{u}$ ratio is observed to depend on the B $p_\mathrm{T}$ and to be consistent with becoming asymptotically constant at large $p_\mathrm{T}$. No rapidity dependence is observed. The ratio of the B$^0$ to B$^+$ hadron production fractions, $f_\mathrm{d} / f_\mathrm{u}$, measured using the B$^0$$\to$ J$/\psi$ K$^{*0}$ decay channel, is found to be consistent with unity and independent of $p_\mathrm{T}$ and rapidity, as expected from isospin invariance.

The observation of the $\Lambda_\mathrm{b}^0 \to$J/$\psi \Lambda \phi$ decay is reported using proton-proton collision data collected at $\sqrt{s} =$ 13 TeV by the CMS experiment at the LHC in 2018, corresponding to an integrated luminosity of 60 fb$^{-1}$. The ratio of the branching fractions $\mathcal{B}(\Lambda_\mathrm{b}^0 \to$J/$\psi \Lambda \phi)/\mathcal{B}(\Lambda_\mathrm{b}^0\to\psi \Lambda)$ is measured to be (8.26$\pm$0.90 (stat) $\pm$ 0.68 (syst) $\pm$ 0.11 $(\mathcal{B}))\times $10$^{-2}$, where the first uncertainty is statistical, the second is systematic, and the last uncertainty reflects the uncertainties in the world-average branching fractions of $\phi$ and $\psi$(2S) decays to the reconstructed final states.