A search is presented for additional scalar (H) or pseudoscalar (A) Higgs bosons decaying to a top quark pair in proton-proton collisions at a center-of-mass energy of 13 TeV. The data set analyzed corresponds to an integrated luminosity of 35.9 fb$^{-1}$ collected by the CMS experiment at the LHC. Final states with one or two charged leptons are considered. The invariant mass of the reconstructed top quark pair system and variables that are sensitive to the spin of the particles decaying into the top quark pair are used to search for signatures of the H or A bosons. The interference with the standard model top quark pair background is taken into account. A moderate signal-like deviation compatible with an A boson with a mass of 400 GeV is observed with a global significance of 1.9 standard deviations. New stringent constraints are reported on the strength of the coupling of the hypothetical bosons to the top quark, with the mass of the bosons ranging from 400 to 750 GeV and their total relative width from 0.5 to 25%. The results of the search are also interpreted in a minimal supersymmetric standard model scenario. Values of $m_\mathrm{A}$ from 400 to 700 GeV are probed, and a region with values of $\tan\beta$ below 1.0 to 1.5, depending on $m_\mathrm{A}$, is excluded at 95% confidence level.
A measurement is reported of the jet mass distribution in hadronic decays of boosted top quarks produced in pp collisions at $\sqrt{s} =$ 13 TeV. The data were collected with the CMS detector at the LHC and correspond to an integrated luminosity of 35.9 fb$^{-1}$. The measurement is performed in the lepton+jets channel of $\mathrm{t\bar{t}}$ events, where the lepton is an electron or muon. The products of the hadronic top quark decay t $\to$ bW $\to$ bq$\mathrm{\bar{q}}'$ are reconstructed as a single jet with transverse momentum larger than 400 GeV. The $\mathrm{t\bar{t}}$ cross section as a function of the jet mass is unfolded at the particle level and used to extract a value of the top quark mass of 172.6 $\pm$ 2.5 GeV. A novel jet reconstruction technique is used for the first time at the LHC, which improves the precision by a factor of three relative to an earlier measurement. This highlights the potential of measurements using boosted top quarks, where the new technique will enable future precision measurements.
Measurements of the top quark polarization and top quark pair ($\mathrm{t\bar{t}}$) spin correlations are presented using events containing two oppositely charged leptons (e$^+$e$^-$, e$^\pm\mu^\mp$, or $\mu^+\mu^-$) produced in proton-proton collisions at a center-of-mass energy of 13 TeV. The data were recorded by the CMS experiment at the LHC in 2016 and correspond to an integrated luminosity of 35.9 fb$^{-1}$. A set of parton-level normalized differential cross sections, sensitive to each of the independent coefficients of the spin-dependent parts of the $\mathrm{t\bar{t}}$ production density matrix, is measured for the first time at 13 TeV. The measured distributions and extracted coefficients are compared with standard model predictions from simulations at next-to-leading-order (NLO) accuracy in quantum chromodynamics (QCD), and from NLO QCD calculations including electroweak corrections. All measurements are found to be consistent with the expectations of the standard model. The normalized differential cross sections are used in fits to constrain the anomalous chromomagnetic and chromoelectric dipole moments of the top quark to $-$0.24 $<C_\text{tG}/\Lambda^{2}$ $<$ 0.07 TeV$^{-2}$ and $-$0.33 $< C^{I}_\text{tG}/\Lambda^{2}$ $<$ 0.20 TeV$^{-2}$, respectively, at 95% confidence level.
Jet production in lead-lead (PbPb) and proton-proton (pp) collisions at a nucleon-nucleon center-of-mass energy of 5.02 TeV is studied with the CMS detector at the LHC, using PbPb and pp data samples corresponding to integrated luminosities of 404 $\mu$b$^{-1}$ and 27.4 pb$^{-1}$, respectively. Jets with different areas are reconstructed using the anti-$k_\mathrm{T}$ algorithm by varying the distance parameter $R$. The measurements are performed using jets with transverse momenta ($p_\mathrm{T}$) greater than 200 GeV and in a pseudorapidity range of $|\eta|$$\lt$ 2. To reveal the medium modification of the jet spectra in PbPb collisions, the properly normalized ratio of spectra from PbPb and pp data is used to extract jet nuclear modification factors as functions of the PbPb collision centrality, $p_\mathrm{T}$ and, for the first time, as a function of $R$ up to 1.0. For the most central collisions, a strong suppression is observed for high-$p_\mathrm{T}$ jets reconstructed with all distance parameters, implying that a significant amount of jet energy is scattered to large angles. The dependence of jet suppression on $R$ is expected to be sensitive to both the jet energy loss mechanism and the medium response, and so the data are compared to several modern event generators and analytic calculations. The models considered do not fully reproduce the data.
The second- and third-order azimuthal anisotropy Fourier harmonics of charged particles produced in pPb collisions, at $\sqrt{s_\mathrm{NN}} =$ 8.16 TeV, are studied over a wide range of event multiplicities. Multiparticle correlations are used to isolate global properties stemming from the collision overlap geometry. The second-order "elliptic" harmonic moment is obtained with high precision through four-, six-, and eight-particle correlations and, for the first time, the third-order "triangular" harmonic moment is studied using four-particle correlations. A sample of peripheral PbPb collisions at $\sqrt{s_\mathrm{NN}} =$ 5.02 TeV that covers a similar range of event multiplicities as the pPb results is also analyzed. Model calculations of initial-state fluctuations in pPb and PbPb collisions can be directly compared to the high precision experimental results. This work provides new insight into the fluctuation-driven origin of the $v_3$ coefficients in pPb and PbPb collisions, and into the dominating overall collision geometry in PbPb collisions at the earliest stages of heavy ion interactions.
A combination of four searches for new physics involving signatures with at least one photon and large missing transverse momentum, motivated by generalized models of gauge-mediated supersymmetry (SUSY) breaking, is presented. All searches make use of proton-proton collision data at $\sqrt{s}=$ 13 TeV, which were recorded with the CMS detector at the LHC in 2016, and correspond to an integrated luminosity of 35.9 fb$^{-1}$. Signatures with at least one photon and large missing transverse momentum are categorized into events with two isolated photons, events with a lepton and a photon, events with additional jets, and events with at least one high-energy photon. No excess of events is observed beyond expectations from standard model processes, and limits are set in the context of gauge-mediated SUSY. Compared to the individual searches, the combination extends the sensitivity to gauge-mediated SUSY in both electroweak and strong production scenarios by up to 100 GeV in neutralino and chargino masses, and yields the first CMS result combining various SUSY searches in events with photons at $\sqrt{s}=$ 13 TeV.
For the first time, a search for the rare decay of the W boson to three charged pions has been performed. Proton-proton collision data recorded by the CMS experiment at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 77.3 fb$^{-1}$, have been analyzed. No significant excess is observed above the background expectation. An upper limit of 1.01 $\times$ 10$^{-6}$ is set at 95% confidence level on the branching fraction of the W boson to three charged pions. This provides a strong motivation for theoretical calculations of this branching fraction.
We present the first study of charged-hadron production associated with jets originating from b quarks in proton-proton collisions at a center-of-mass energy of 5.02 TeV. The data sample used in this study was collected with the CMS detector at the CERN LHC and corresponds to an integrated luminosity of 27.4 pb$^{-1}$. To characterize the jet substructure, the differential jet shapes, defined as the normalized transverse momentum distribution of charged hadrons as a function of angular distance from the jet axis, are measured for b jets. In addition to the jet shapes, the per-jet yields of charged particles associated with b jets are also quantified, again as a function of the angular distance with respect to the jet axis. Extracted jet shape and particle yield distributions for b jets are compared with results for inclusive jets, as well as with the predictions from the PYTHIA and HERWIG++ event generators.
A search for nonresonant excesses in the invariant mass spectra of electron and muon pairs is presented. The analysis is based on data from proton-proton collisions at a center-of-mass energy of 13 TeV recorded by the CMS experiment in 2016, corresponding to a total integrated luminosity of 36 fb$^{-1}$. No significant deviation from the standard model is observed. Limits are set at 95% confidence level on energy scales for two general classes of nonresonant models. For a class of fermion contact interaction models, lower limits ranging from 20 to 32 TeV are set on the characteristic compositeness scale $\Lambda$. For the Arkani-Hamed, Dimopoulos, and Dvali model of large extra dimensions, the first results in the dilepton final state at 13 TeV are reported, and values of the ultraviolet cutoff parameter $\Lambda_\mathrm{T}$ below 6.9 TeV are excluded. A combination with recent CMS diphoton results improves this exclusion to $\Lambda_\mathrm{T}$ below 7.7 TeV, providing the most sensitive limits to date in nonhadronic final states.
A search for a light charged Higgs boson (H$^+$) decaying to a W boson and a CP-odd Higgs boson (A) in final states with e$\mu\mu$ or $\mu\mu\mu$ is performed using data from pp collisions at $\sqrt{s}=$ 13 TeV, recorded by the CMS detector at the LHC and corresponding to an integrated luminosity of 35.9 fb$^{-1}$. In this search, it is assumed that the H$^+$ boson is produced in decays of top quarks, and the A boson decays to two oppositely charged muons. The presence of signals for H$^+$ boson masses between 100 and 160 GeV and A boson masses between 15 and 75 GeV is investigated. No evidence for the production of the H$^+$ boson is found. Upper limits at 95% confidence level are obtained on the combined branching fraction for the decay chain t $\to$ bH$^+$ $\to$ bW$^+$A $\to$ bW$^+\mu^+\mu^-$, of 1.9 $\times$ 10$^{-6}$ to 8.6 $\times$ 10$^{-6}$, depending on the masses of the H$^+$ and A bosons. These are the first limits for these decay modes of the H$^+$ and A bosons.
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