A search for long-lived particles using final states including a displaced vertex with low-momentum tracks, large missing transverse momentum, and a jet from initial-state radiation is presented. This search uses proton-proton collision data at a center-of-mass energy of 13 TeV collected by the CMS experiment at the CERN LHC in 2017 and 2018, with a total integrated luminosity of 100 fb$^{-1}$. This analysis adopts specific supersymmetric (SUSY) coannihilation scenarios as benchmark signal models, characterized by a next-to-lightest SUSY particle (NLSP) with a mass difference of less than 25GeV relative to the lightest SUSY particle, assumed to be a bino-like neutralino. In the top squark ($\tilde{\mathrm{t}}$) NLSP model, the NLSP is a long-lived $\tilde{\mathrm{t}}$, while in the bino-wino NLSP scenario, the mass-degenerate NLSPs are a wino-like long-lived neutralino and a short-lived chargino. The search excludes top squarks with masses less than 400$-$1100 GeV and wino-like neutralinos with masses less than 220$-$550 GeV, depending on the signal parameters, including the mass difference, mass, and lifetime of the long-lived particle. It sets the most stringent limits to date for the $\tilde{\mathrm{t}}$ and bino-wino NLSP models.
The number of observed and predicted background events after the fit to the regions of the search planes. In addition, two representative signals are shown. The predicted background is shown with its associated uncertainties. The observed data are displayed with the 68% confidence level Poisson confidence intervals. The lower panel shows the fractional difference between the observed data and the predicted background.
Observed 95% CL upper limits on the $\tilde{t}$ production cross section, as functions of $m_{\tilde{t}}$ and $\Delta m$, for $\mathcal{B}(\tilde{t} \to bf\overline{f}'\tilde{\chi}^{0}_{1})$ of 10%. The observed (solid black) and expected (dashed red) exclusion curves are overlaid on the plots. The search excludes the region to the left of the exclusion curves.
Observed 95% CL upper limits on the $\tilde{t}$ production cross section, as functions of $m_{\tilde{t}}$ and $\Delta m$, for $\mathcal{B}(\tilde{t} \to bf\overline{f}'\tilde{\chi}^{0}_{1})$ of 10%. The observed (solid black) and expected (dashed red) exclusion curves are overlaid on the plots. The search excludes the region to the left of the exclusion curves.
A search for signatures of a dark analog to quantum chromodynamics is performed. The analysis targets long-lived dark mesons that decay into standard-model particles, with a high branching fraction of the dark mesons decaying into muons. The dark mesons are formed by the hadronisation of dark partons, which are produced by a decay of the Higgs boson. The search is performed using a data set corresponding to an integrated luminosity of 41.6 fb$^{-1}$, which was collected in proton-proton collisions at $\sqrt{s}$ = 13 TeV by the CMS experiment at the CERN LHC in 2018 using non-prompt muon triggers. The search is based on resonant muon pair signatures. Machine-learning techniques are employed in the analysis, utilising boosted decision trees to discriminate between signal and background. No significant excess is observed above the standard model expectation. Upper limits on the branching fraction of the Higgs boson decaying to dark partons are determined to be as low as 10$^{-4}$ at 95% confidence level, surpassing and extending the existing limits on models with dark $\tildeω$ mesons for mean proper decay lengths of less than 500 mm and for $\tildeω$ masses down to 0.3 GeV. First limits are set for extended dark-shower models with two dark flavours that contain dark photons, probing their masses down to 0.33 GeV.
Dimuon invariant mass distributions in mass windows around $0.67~\textrm{GeV}$ in the single-vertex category with $1~\textrm{cm}<l_{xy}<10~\textrm{cm}$ and $\textrm{pointing angle}<0.2$. The background fit is shown together with the signal expected for a representative Scenario A model. A branching fraction of 0.01 is assumed for the Higgs boson decaying into dark partons for illustrating the signals. The lower panel in each plot shows the pull distribution, defined as the difference between the data and the background fit in each bin divided by the statistical uncertainty.
Dimuon invariant mass distributions in mass windows around $1.33~\textrm{GeV}$ in the single-vertex category with $1~\textrm{cm}<l_{xy}<10~\textrm{cm}$ and $\textrm{pointing angle}<0.2$. The background fit is shown together with the signal expected for a representative Scenario B1 model. A branching fraction of 0.01 is assumed for the Higgs boson decaying into dark partons for illustrating the signals. The lower panel in each plot shows the pull distribution, defined as the difference between the data and the background fit in each bin divided by the statistical uncertainty.
Upper limits at 95% CL on the branching fraction $\mathcal{B}\left(\textrm{H}\rightarrow\psi\overline{\psi}\right)$ as a function of the $\tilde{\omega}$ meson $c\tau$ for $m_{\tilde{\omega}}=2~\textrm{GeV}$ and $\mathcal{B}(\tilde{\omega}\to\mu\mu)=0.25$ in the vector portal model. It is assumed that $m_{\tilde{\omega}}=\tilde{\Lambda}=m_{\tilde{\eta}}$, where $m_{\tilde{\omega}}$, $\tilde{\Lambda}$, and $m_{\tilde{\eta}}$ are parameters of the dark sector: the mass of the spin-one meson, confinement scale, and the mass of the spin-zero meson, respectively.
A search for a new neutral gauge boson, Z', produced in association with one or two jets, including at least one b jet, and decaying into a pair of muons is presented. The analysis uses proton-proton collision data collected with the CMS detector at $\sqrt{s}$ = 13 TeV, corresponding to an integrated luminosity of 138 fb$^{-1}$. No significant deviation from background expectations is observed. Upper limits at 95% confidence level on the product of cross section, branching fraction to dimuons, acceptance, and efficiency, from 0.2 to 2 fb, are set for Z' boson masses between 125 and 350 GeV. Process-dependent products of acceptance and efficiency, and model-independent limits on the signal yield are provided. These are the only results to date in the 125$-$200 GeV mass range and the most stringent for b quark fusion production modes in the 200$-$350 GeV range, complementing inclusive Z' boson searches.
Distributions of $m_{\ell\ell}$ in the $\mathrm{SR_{b}^{mm}}$ SR. Events are divided by the bin width. Simulated signal shapes for $Z'$ boson masses of 125, 200, and 350 GeV are shown. The "Stat + syst" band shows the envelope of the fit variations with statistical uncertainties. The ratio of the nominal MC background values (dashed line) and data to the ABCD prediction is shown as a dashed line in the ratio plot. The MC background uncertainties are not shown for visual clarity.
Distributions of $m_{\ell\ell}$ in the $\mathrm{SR_{b+\textrm{j}/b}^{mm}}$ SR. Events are divided by the bin width. Simulated signal shapes for $Z'$ boson masses of 125, 200, and 350 GeV are shown. The "Stat + syst" band shows the envelope of the fit variations with statistical uncertainties. The ratio of the nominal MC background values (dashed line) and data to the ABCD prediction is shown as a dashed line in the ratio plot. The MC background uncertainties are not shown for visual clarity.
Data vs. the ABCD method background prediction for 2016 in $\mathrm{SR_{b}^{mm}}$. Events are divided by the bin width, hence fractional data counts. Error bars show statistical uncertainties of data. The blue band shows the propagated uncertainty of all individual fit variations in a given bin, which we consider to be uncorrelated. The lower panels show the ratio of the observed data to the background estimation.
A search for heavy resonances decaying into a Higgs boson (H) or a Z boson and a photon ($γ$), with the H or Z bosons decaying to a bottom quark-antiquark pair ($\mathrm{b\bar{b}}$) is presented. The analysis is performed using proton-proton collision data at $\sqrt{s}$ = 13 TeV collected by the CMS experiment at the CERN Large Hadron Collider, corresponding to an integrated luminosity of 138 fb$^{-1}$. The analyzed events contain a photon and a massive large-radius jet originating from a Lorentz-boosted $\mathrm{b\bar{b}}$ system. An advanced transformer-based algorithm classifies jets according to their substructure and quark flavors, forming a tagger that identifies jets as candidates from H/Z $\to$$\mathrm{b\bar{b}}$ decays. A set of parametric functions is used to fit the photon-jet invariant mass spectrum and to extract potential signals. No significant excess is observed above the standard model expectations. The results set upper limits at 95% confidence level on the product of the cross section and the branching fraction for spin-1 H$γ$ resonances and spin-0 Z$γ$ resonances, below 0.1 and 0.3 fb, respectively, representing the most stringent limits to date.
Figure 6. Postfit $m_{j\gamma}$ spectra in the SRH1. The lower panel shows the pull distributions with respect to the best-fit function. The signals with the largest local significances are shown normalized to the observed cross section upper limits.
Figure 6. Postfit $m_{j\gamma}$ spectra in the SRZ1. The lower panel shows the pull distributions with respect to the best-fit function. The signals with the largest local significances are shown normalized to the observed cross section upper limits.
Figure 6. Postfit $m_{j\gamma}$ spectra in the SRH2. The lower panel shows the pull distributions with respect to the best-fit function. The signals with the largest local significances are shown normalized to the observed cross section upper limits.
The target asymmetry T, recoil asymmetry P, and beam-target double polarization observable H were determined in exclusive $\pi ^0$ and $\eta $ photoproduction off quasi-free protons and, for the first time, off quasi-free neutrons. The experiment was performed at the electron stretcher accelerator ELSA in Bonn, Germany, with the Crystal Barrel/TAPS detector setup, using a linearly polarized photon beam and a transversely polarized deuterated butanol target. Effects from the Fermi motion of the nucleons within deuterium were removed by a full kinematic reconstruction of the final state invariant mass. A comparison of the data obtained on the proton and on the neutron provides new insight into the isospin structure of the electromagnetic excitation of the nucleon. Earlier measurements of polarization observables in the $\gamma p \rightarrow \pi ^0 p$ and $\gamma p \rightarrow \eta p$ reactions are confirmed. The data obtained on the neutron are of particular relevance for clarifying the origin of the narrow structure in the $\eta n$ system at $W = 1.68\ \textrm{GeV}$. A comparison with recent partial wave analyses favors the interpretation of this structure as arising from interference of the $S_{11}(1535)$ and $S_{11}(1650)$ resonances within the $S_{11}$-partial wave.
Target asymmetry T, recoil asymmetry P, and polarization observable H for $\gamma p \to \pi^0 p$ as a function of the polar center-of-mass angle for bins at the given centroid c.m. energies.
Target asymmetry T, recoil asymmetry P, and polarization observable H for $\gamma n \to \pi^0 n$ as a function of the polar center-of-mass angle for bins at the given centroid c.m. energies.
Target asymmetry T, recoil asymmetry P, and polarization observable H for $\gamma p \to \eta p$ as a function of the polar center-of-mass angle for bins at the given centroid c.m. energies.