385 Search Results

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 25 GeV relative to the lightest SUSY particle, assumed to be a bino-likemore » neutralino. In the top squark $$ \left(\overset{\sim }{\mathrm{t}}\right) $$ NLSP model, the NLSP is a long-lived $$ \overset{\sim }{\mathrm{t}} $$, 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 $$ \overset{\sim }{\mathrm{t}} $$ and bino-wino NLSP models.[graphic not available: see fulltext]« less

The results of a search for the production of two scalar bosons in final states with two photons and two tau leptons are presented. The search considers both nonresonant production of a Higgs boson pair, HH, and resonant production via a new boson X which decays either to HH or to H and a new scalar Y. The analysis uses up to 138 fb$$^{−1}$$ of proton-proton collision data, recorded between 2016 and 2018 by the CMS experiment at the LHC at a center-of-mass energy of 13 TeV. No evidence for signal is found in the data. For the nonresonant production,more » the observed (expected) upper limit at 95% confidence level (CL) on the HH production cross section is set at 930 (740) fb, corresponding to 33 (26) times the standard model prediction. At 95% CL, HH production is observed (expected) to be excluded for values of κ$$_{λ}$$ outside the range between −12 (−9.4) and 17 (15). Observed (expected) upper limits at 95% CL for the X → HH cross section are found to be within 160 to 2200 (200 to 1800) fb, depending on the mass of X. In the X → Y(ττ)H(γγ) search, the observed (expected) upper limits on the product of the production cross section and decay branching fractions vary between 0.059–1.2 fb (0.087–0.68 fb). For the X → Y(γγ)H(ττ) search the observed (expected) upper limits on the product of the production cross section and Y → γγ branching fraction vary between 0.69–15 fb (0.73–8.3 fb) in the low Y mass search, tightening constraints on the next-to-minimal supersymmetric standard model, and between 0.64–10 fb (0.70–7.6 fb) in the high Y mass search.[graphic not available: see fulltext]« less

A measurement of the angular structure of inclusive jets and those containing a prompt D$$^{0}$$ meson in proton-proton collisions at the LHC at a center-of-mass energy of 5.02 TeV is presented. The data corresponding to an integrated luminosity of 301 pb$$^{−1}$$ were collected by the CMS experiment in 2017. Two jet grooming algorithms, late-k$$_{T}$$ and soft drop, are used to study the intrajet radiation pattern using iterative Cambridge-Aachen declustering. The splitting-angle distributions of jets with transverse momentum (p$$_{T}$$) of around 100 GeV, obtained with these two algorithms, show that there is a shift of the distribution for jets containing amore » prompt D$$^{0}$$ meson with respect to inclusive jets. The suppression of emissions at small angles observed in the late-k$$_{T}$$ grooming approach is consistent with the dead-cone effect, whereas the similar suppression for splittings selected with the soft-drop algorithm appears to be induced by gluon splitting to charm quark-antiquark pairs at large angles. The measured distributions are corrected to the particle level and can be used to constrain model predictions for the substructure of high-p$$_{T}$$ charm quark jets.[graphic not available: see fulltext]« less

A search for pairs of light neutral pseudoscalar bosons ( $A$ ) resulting from the decay of a Higgs boson is performed. The search is conducted using LHC proton-proton collision data at $\sqrt{s}=13\mathrm{TeV}$ , collected with the CMS detector in 2016–2018 and corresponding to an integrated luminosity of $138{\mathrm{fb}}^{-1}$ . The $A$ boson decays into a highly collimated electron-positron pair. A novel multivariate algorithm usingmore » tracks and calorimeter information is developed to identify these distinctive signatures, and events are selected with two such merged electron-positron pairs. No significant excess above the standard model background predictions is observed. Upper limits on the branching fraction for $H\to AA\to 4e$ are set at 95% confidence level, for masses between 10 and 100 MeV and proper decay lengths below $100\mathrm{\mu }\mathrm{m}$ , reaching branching fraction sensitivities as low as ${10}^{-5}$ . This is the first search for Higgs boson decays to four electrons via light pseudoscalars at the LHC. It significantly improves the experimental sensitivity to axionlike particles with masses below 100 MeV .« less

A search for heavy long-lived charged particles at the LHC is presented. Particles interacting with the CMS muon detector across several bunch crossings are searched for using a data sample of proton-proton collisions at $$\sqrt{s}$$ = 13.6 TeV collected with the CMS detector in 2024, corresponding to an integrated luminosity of 3.7 fb$$^{-1}$$. This is the first search relying on the novel level-1 trigger scouting data set collected without any trigger selection, allowing correlations between bunch crossings to be analyzed. The results are interpreted as upper limits on the cross sections of several benchmark processes with pair production of heavymore » long-lived charged particles. Upper limits on the fiducial cross section of a heavy long-lived charged particle with $$p_\mathrm{T}$$$$\gt$$ 500 GeV and $$\lvertη\rvert$$$$\lt$$ 0.83 are also set in different ranges of $β=v/c$. This analysis is a crucial proof of concept for the level-1 trigger data scouting system and complements existing searches for heavy long-lived charged particles by extending the sensitivity to lower $$β$$ values.« less

A pioneering machine-learning-based flavor-tagging algorithm combining same-side and opposite-side tagging is used to obtain the equivalent of 27$$\,$$000 tagged B$$^0_\mathrm{s}$$$$\to$$ J/$$\psi\, \phi$$(1020) decays from pp collisions at $$\sqrt{s} =$$ 13 TeV, collected by the CMS experiment and corresponding to an integrated luminosity of 96.5 fb$$^{-1}$$. A time- and flavor-dependent angular analysis of the $$\mu^+\mu^-$$K$$^+$$K$$^-$ final state is used to measure parameters of the $$\mathrm{B}^0_\mathrm{s}$$-$$\overline{\mathrm{B}}^0_\mathrm{s}$$ system. The weak phase is measured to be $$\phi_\mathrm{s}$$ = $$-$$73 $$\pm$$ 23 (stat) $$\pm$$ 7 (syst) mrad, which, combined with a $$\sqrt{s}$$ = 8 TeV CMS result, gives $$\phi_\mathrm{s}$$ = $$-$$74 $$\pm$$ 23 mrad. Thismore » value differs from zero by 3.2 standard deviations, providing evidence for $CP$ violation in B$$^0_\mathrm{s}$$$$\to$$ J/$$\psi\,\phi$$(1020) decays. All measured physics parameters are found to agree with standard model predictions where available.« less

The first observation of electroweak production of a photon in association with two forward jets in proton-proton collisions is presented. The measurement uses data recorded by the CMS experiment at the LHC during 2016–2018 at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 138 fb$$^{−1}$$. The analysis is performed in a region enriched in photon production via vector boson fusion, with a requirement on the transverse momentum of the photon to exceed 200 GeV. The cross section is measured to be $$ {202}_{-32}^{+36} $$ fb, at a significance with respect to the null hypothesis that exceedsmore » five standard deviations. This is in agreement with the standard model prediction of $$ {177}_{-12}^{+13} $$ fb. Differential cross sections are measured as a function of various observables. Limits are set on dimension-6 effective field theory operators that contribute to the WWγ interaction. The observed 95% confidence intervals for the corresponding Warsaw basis Wilson coefficients c$$_{W}$$ and c$$_{HWB}$$ are [−0.11, 0.16] and [−1.6, 1.5], respectively.[graphic not available: see fulltext]« less

A search for dark matter particles produced in association with a Higgs boson decaying to a bottom quark-antiquark pair in proton-proton collisions at $$\sqrt{s}$$ = 13 TeV is presented. The data, collected with the CMS detector at the LHC, correspond to an integrated luminosity of 101 fb$$^{-1}$$. The analysis is performed in exclusive categories targeting both Lorentz-boosted (merged) and resolved b jet pair topologies, covering a wide range of Higgs boson transverse momentum. A statistical combination is made with a previous search using data collected in 2016 and corresponding to an integrated luminosity of 35.9 fb$$^{-1}$$. The observed data agreemore » with the standard model background predictions. Constraints are placed on models predicting new particles or interactions, such as those in the simplified frameworks of baryonic-Z' and 2HDM+a, where the latter is a type-II two-Higgs-doublet model featuring a heavy pseudoscalar with an additional light pseudoscalar. Upper limits at 95% confidence level are set on the production cross section for these models. For the baryonic-Z' model, Z' boson masses below 2.25 TeV are excluded for a dark matter particle candidate mass of 1 GeV. In the 2HDM+a model, heavy pseudoscalar masses between 850 and 1300 GeV are excluded for a light pseudoscalar mass of 350 GeV.« less

We present a search for the pair production of Higgsinos in final states with large missing transverse momentum and either two reconstructed muons or a reconstructed lepton (muon or electron) and an isolated track. The analyzed data correspond to proton-proton collisions with an integrated luminosity of $137{\mathrm{fb}}^{-1}$ , collected by the CMS experiment at $\sqrt{s}=13\mathrm{TeV}$ in 2016, 2017, and 2018. The signal scenario assumes four nearly mass degenerate Higgsino mass eigenstates: two neutralino states ${\tilde{\chi }}_2^{more »}$ 0 and ${\tilde{\chi }}_1^0$ with a small mass difference in the range 1–10 GeV and two chargino states ${\tilde{\chi }}_1^{\pm }$ with an intermediate mass. The analysis focuses on the decay of the heavier neutralino into the lighter one and a virtual $Z$ boson, which decays into two same-flavor leptons. The leptons have small transverse momentum and/or a small opening angle between the identified muons. An isolated track is used to recover events in which only one of the two leptons is identified. Multivariate discriminants are used to enhance the sensitivity by efficiently rejecting backgrounds from SM processes or misreconstructed tracks and/or leptons. The search explores a unique phase space and probes a previously unexplored region of the signal model parameter space. Mass differences between the two neutralinos are probed down to 1.5 GeV, assuming a Higgsino mass of 100 GeV. The maximum excluded Higgsino mass is 115 GeV.« less

A search for new physics in events featuring a single photon and missing transverse momentum is presented, using proton-proton √𝑠 =13 TeV collision data corresponding to an integrated luminosity of 101 fb⁻¹ collected by the CMS experiment at the CERN LHC between 2017 and 2018. This analysis, combined with a previous study of 36 fb⁻¹ of 2016 data (totaling 137 fb⁻¹), reveals no significant deviations from standard model expectations. The results are then used to establish 95% confidence level limits on parameters in theoretical models involving dark matter and large extra dimensions. Compared to the 2016-only analysis, this search achievesmore » up to a 14% improvement in exclusion reach for mediator masses in simplified dark matter models, along with 11% and 10% enhancements in the limits on the effective field theory suppression scale and the fundamental Planck scale, respectively. These results are the most stringent constraints on these parameters to date.« less