The spectra of strange hadrons are measured in proton-proton collisions, recorded by the CMS experiment at the CERN LHC, at centre-of-mass energies of 0.9 and 7 TeV. The K^0_s, Lambda, and Xi^- particles and their antiparticles are reconstructed from their decay topologies and the production rates are measured as functions of rapidity and transverse momentum. The results are compared to other experiments and to predictions of the PYTHIA Monte Carlo program. The transverse momentum distributions are found to differ substantially from the PYTHIA results and the production rates exceed the predictions by up to a factor of three.
Results from fitting the Tsallis function to the data at 0.9 TeV. See text of paper for details.
Results from fitting the Tsallis function to the data at 7 TeV. See text of paper for details.
An inclusive search for the standard model Higgs boson ($\mathrm{H}$) produced with large transverse momentum ($p_\mathrm{T}$) and decaying to a bottom quark-antiquark pair ($\mathrm{b}\overline{\mathrm{b}}$) is performed using a data set of pp collisions at $\sqrt{s}=$ 13 TeV collected with the CMS experiment at the LHC. The data sample corresponds to an integrated luminosity of 35.9 fb$^{-1}$. A highly Lorentz-boosted Higgs boson decaying to $\mathrm{b}\overline{\mathrm{b}}$ is reconstructed as a single, large radius jet and is identified using jet substructure and dedicated $\mathrm{b}$ tagging techniques. The method is validated with $\mathrm{Z}\to\mathrm{b}\overline{\mathrm{b}}$ decays. The $\mathrm{Z}\to\mathrm{b}\overline{\mathrm{b}}$ process is observed for the first time in the single-jet topology with a local significance of 5.1 standard deviations (5.8 expected). For a Higgs boson mass of 125 GeV, an excess of events above the expected background is observed (expected) with a local significance of 1.5 (0.7) standard deviations. The measured cross section times branching fraction for production via gluon fusion of $\mathrm{H} \rightarrow \mathrm{b}\overline{\mathrm{b}}$ with $p_\mathrm{T} > $450 GeV and in the pseudorapidity range $-$2.5 $< \eta <$ 2.5 is 74 $\pm$ 48 (stat) $_{-10}^{+17}$ (syst) fb, which is consistent within uncertainties with the standard model prediction.
The $m_{SD}$ distributions in data for the failing (left) and passing (right) regions and combined $p_{T}$ categories. The QCD multijet background in the passing region is predicted using the failing region and the pass-fail ratio $R_{p/f}$. The features at 166 and 180 GeV in the $m_{SD}$ distribution are due to the kinematic selection on $\rho$, which affects each $p_{T}$ category differently. In the bottom panel, the ratio of the data to its statistical uncertainty, after subtracting the nonresonant backgrounds, is shown.
The $m_{SD}$ distributions in data for the failing (left) and passing (right) regions and combined $p_{T}$ categories. The QCD multijet background in the passing region is predicted using the failing region and the pass-fail ratio $R_{p/f}$. The features at 166 and 180 GeV in the $m_{SD}$ distribution are due to the kinematic selection on $\rho$, which affects each $p_{T}$ category differently. In the bottom panel, the ratio of the data to its statistical uncertainty, after subtracting the nonresonant backgrounds, is shown.
A first measurement of the top quark mass using the decay channel t to (W to l nu) (b to J/psi + X to mu+ mu- + X) is presented. The analysis uses events selected from the proton-proton collisions recorded with the CMS detector at the LHC at a center-of-mass energy of 8 TeV. The data correspond to an integrated luminosity of 19.7 inverse femtobarns, with 666 t t-bar and single top quark candidate events containing a reconstructed J/psi candidate decaying into an oppositely-charged muon pair. The mass of the (J/psi + l) system, where l is an electron or a muon from W boson decay, is used to extract a top quark mass of 173.5 +/- 3.0 (stat) +/- 0.9 (syst) GeV.
Number of selected events from simulations and observed in data. The uncertainties are statistical.
Summary of the impact of systematic uncertainties on the top quark mass according to the contributions from each source.
A search is presented for narrow heavy resonances X decaying into pairs of Higgs bosons (H) in proton-proton collisions collected by the CMS experiment at the LHC at sqrt(s) = 8 TeV. The data correspond to an integrated luminosity of 19.7 inverse femtobarns. The search considers HH resonances with masses between 1 and 3 TeV, having final states of two b quark pairs. Each Higgs boson is produced with large momentum, and the hadronization products of the pair of b quarks can usually be reconstructed as single large jets. The background from multijet and t t-bar events is significantly reduced by applying requirements related to the flavor of the jet, its mass, and its substructure. The signal would be identified as a peak on top of the dijet invariant mass spectrum of the remaining background events. No evidence is observed for such a signal. Upper limits obtained at 95% confidence level for the product of the production cross section and branching fraction sigma(gg to X) B(X to HH to b b-bar b b-bar) range from 10 to 1.5 fb for the mass of X from 1.15 to 2.0 TeV, significantly extending previous searches. For a warped extra dimension theory with a mass scale Lambda[R] = 1 TeV, the data exclude radion scalar masses between 1.15 and 1.55 TeV.
Observed $m_\mathrm{jj}$ spectrum (black points) compared with a background estimate (black line), obtained in background only hypothesis, for HPHP category. The simulated radion resonances of $m_\mathrm{X} = 1.5$ and 2 TeV are also shown.
Observed $m_\mathrm{jj}$ spectrum (black points) compared with a background estimate (black line), obtained in background only hypothesis, for HPLP category. The simulated radion resonances of $m_\mathrm{X} = 1.5$ and 2 TeV are also shown.
Observed $m_\mathrm{jj}$ spectrum (black points) compared with a background estimate (black line), obtained in background only hypothesis, for LPHP category. The simulated radion resonances of $m_\mathrm{X} = 1.5$ and 2 TeV are also shown.
A search for the production of a heavy B quark, having electric charge -1/3 and vector couplings to W, Z, and H bosons, is carried out using proton-proton collision data recorded at the CERN LHC by the CMS experiment, corresponding to an integrated luminosity of 19.7 inverse femtobarns. The B quark is assumed to be pair produced and to decay in one of three ways: to tW, bZ, or bH. The search is carried out in final states with one, two, and more than two charged leptons, as well as in fully hadronic final states. Each of the channels in the exclusive final-state topologies is designed to be sensitive to specific combinations of the B quark-antiquark pair decays. The observed event yields are found to be consistent with the standard model expectations in all the final states studied. A statistical combination of these results is performed and upper limits are set on the cross section of the strongly produced B quark-antiquark pairs as a function of the B quark mass. Lower limits on the B quark mass between 740 and 900 GeV are set at a 95% confidence level, depending on the values of the branching fractions of the B quark to tW, bZ, and bH. Overall, these limits are the most stringent to date.
Event yields for the multilepton event categories Explanation of categories: C1 - 3 lepton, 0 tau, 1 OSSF, >=1 b-tag, off-Z, ST in 600 to 1000 C2 - 3 lepton, 0 tau, 0 OSSF, >=1 b-tag, ST in 600 to 1000 C3 - 3 lepton, 0 tau, 1 OSSF, >=1 b-tag, off-Z, ST in 1000 to 1500 C4 - 3 lepton, 0 tau, 0 OSSF, >=1 b-tag, ST in 1000 to 1500 C5 - 3 lepton, 0 tau, 1 OSSF, 0 b-tag, off-Z, ST in 600 to 1000 C6 - 3 lepton, 0 tau, 1 OSSF, >=1 b-tag, off-Z, ST in 600 to 1000 C7 - 3 lepton, 1 tau, 0 OSSF, >=1 b-tag, ST in 600 to 1000 C8 - 3 lepton, 1 tau, 0 OSSF, >=1 b-tag, ST in 1000 to 1500 C9 - 3 lepton, 0 tau, 0 OSSF, 0 b-tag, ST in 600 to 1000 C10 - 3 lepton, 0 tau, 1 OSSF, 0 b-tag, off-Z, ST in 1000 to 1500 C11 - 3 lepton, 0 tau, 1 OSSF, >=1 b-tag, off-Z, ST in 1000 to 1500 C12 - 3 lepton, 0 tau, 1 OSSF, >=1 b-tag, on-Z, ST in 600 to 1000 C13 - 3 lepton, 0 tau, 0 OSSF, 0 b-tag, ST in 1000 to 1500 C14 - 3 lepton, 1 tau, 1 OSSF, >=1 b-tag, off-Z, ST in 600 to 1000 C15 - 3 lepton, 1 tau, 0 OSSF, 0 b-tag, ST in 600 to 1000 C16 - 3 lepton, 1 tau, 1 OSSF, >=1 b-tag, off-Z, ST in 1000 to 1500 C17 - 4 lepton, 1 tau, 1 OSSF, >=1 b-tag, off-Z, ST in 600 to 1000 C18 - 4 lepton, 0 tau, 1 OSSF, >=1 b-tag, off-Z, ST in 600 to 1000 C19 - 3 lepton, 1 tau, 0 OSSF, 0 b-tag, ST in 100 to 1500 C20 - 4 lepton, 0 tau, 2 OSSF, >=1 b-tag, off-Z, ST in 600 to 1000 C21 - 3 lepton, 0 tau, 1 OSSF, >=1 b-tag, on-Z, ST in 1000 to 1500 C22 - 3 lepton, 0 tau, 1 OSSF, >=1 b-tag, off-Z, ST in 300 to 600 C23 - 3 lepton, 0 tau, 1 OSSF, >=1 b-tag, off-Z, ST in 1500 to 2000 C24 - 3 lepton, 1 tau, 1 OSSF, >=1 b-tag, off-Z, ST in 600 to 1000 C25 - 3 lepton, 0 tau, 1 OSSF, 0 b-tag, off-Z, ST in 600 to 1000 C26 - 4 lepton, 1 tau, 1 OSSF, >=1 b-tag, off-Z, ST in 300 to 600 Note: "n/a" signifies a category which does not contribute for a given signal hypothesis.
Measurements of the cross sections for top quark pairs produced in association with a W or Z boson are presented, using 8 TeV pp collision data corresponding to an integrated luminosity of 19.5 inverse femtobarns, collected by the CMS experiment at the LHC. Final states are selected in which the associated W boson decays to a charged lepton and a neutrino or the Z boson decays to two charged leptons. Signal events are identified by matching reconstructed objects in the detector to specific final state particles from ttW or ttZ decays. The ttW cross section is measured to be 382 +117 -102 fb with a significance of 4.8 standard deviations from the background-only hypothesis. The ttZ cross section is measured to be 242 +65 -55 fb with a significance of 6.4 standard deviations from the background-only hypothesis. These measurements are used to set bounds on five anomalous dimension-six operators that would affect the ttW and ttZ cross sections.
Expected yields after the final fit, compared to the observed data for OS t$\bar{\mathrm{t}}$Z final states. Here ``hf'' and ``lf'' stand for heavy and light flavors, respectively.
Expected yields after the final fit, compared to the observed data for SS t$\bar{\mathrm{t}}$W final states. The multiboson process includes WWW, WWZ, and W$^{\pm}$W$^{\pm}$; t$\mathrm{\bar{t}}$+X includes t$\mathrm{\bar{t}}\gamma$, t$\mathrm{\bar{t}}\gamma^{*}$, and t$\bar{\mathrm{t}}$WW.
Expected yields after the final fit, compared to the observed data for 3$\ell$ t$\bar{\mathrm{t}}$W and three and 4$\ell$ t$\bar{\mathrm{t}}$Z final states. The 4$\ell$ ``Z-veto'' channel has exactly one lepton pair consistent with a Z boson decay; the ``Z'' channel has two. The multiboson process includes WWW and WWZ; t$\mathrm{\bar{t}}$+X includes t$\mathrm{\bar{t}}\gamma$, t$\mathrm{\bar{t}}\gamma^{*}$, and t$\bar{\mathrm{t}}$WW.
A search is performed for events consistent with the pair production of a new heavy particle that acts as a mediator between a dark sector and normal matter, and that decays to a light quark and a new fermion called a dark quark. The search is based on data corresponding to an integrated luminosity of 16.1 fb$^{-1}$ from proton-proton collisions at $\sqrt{s} =$ 13 TeV collected by the CMS experiment at the LHC in 2016. The dark quark is charged only under a new quantum-chromodynamics-like force, and forms an "emerging jet" via a parton shower, containing long-lived dark hadrons that give rise to displaced vertices when decaying to standard model hadrons. The data are consistent with the expectation from standard model processes. Limits are set at 95% confidence level excluding dark pion decay lengths between 5 and 225 mm for dark mediators with masses between 400 and 1250 GeV. Decay lengths smaller than 5 mm and greater than 225 mm are also excluded in the lower part of this mass range. The dependence of the limit on the dark pion mass is weak for masses between 1 and 10 GeV. This analysis is the first dedicated search for the pair production of a new particle that decays to a jet and an emerging jet.
Distributions of $\langle IP_{\mathrm{2D}}\rangle$ for background (black) and for signals with a mediator mass of 1 TeV and a dark pion proper decay length of 25 mm, for various dark pion masses.
Distributions of $\alpha_\mathrm{3D}$ for background (black) and for signals with a mediator mass of 1 TeV and a dark pion mass of 5 GeV for dark pion proper decay lengths ranging from 1 to 300 mm.
The signal acceptance A, defined as the fraction of simulated signal events passing the selection criteria, for models with a dark pion mass $m_{\pi_\mathrm{DK}}$ of 5 GeV as a function of the mediator mass $m_{\mathrm{X_{DK}}}$ and the dark pion proper decay length $c\tau_{\pi_\mathrm{DK}}$. The corresponding selection set number for each model is indicated as text on the plot.
Characteristics of multi-particle production in proton-proton collisions at $\sqrt{s}$=7 TeV are studied as a function of the charged-particle multiplicity, $N_{ch}$. The produced particles are separated into two classes: those belonging to jets and those belonging to the underlying event. Charged particles are measured with pseudorapidity |η|<2.4 and transverse momentum $p_T$ > 0.25 GeV/c. Jets are reconstructed from charged-particles only and required to have $p_T$ > 5 GeV/c. The distributions of jet $p_T$, average $p_T$ of charged particles belonging to the underlying event or to jets, jet rates, and jet shapes are presented as functions of $N_{ch}$ and compared to the predictions of the PYTHIA and HERWIG event generators. Predictions without multi-parton interactions fail completely to describe the $N_{ch}$-dependence observed in the data. For increasing $N_{ch}$, PYTHIA systematically predicts higher jet rates and harder $p_T$ spectra than seen in the data, whereas HERWIG shows the opposite trends. At the highest multiplicity, the data–model agreement is worse for most observables, indicating the need for further tuning and/or new model ingredients.
Mean $p_T$, all charged particles.
Mean $p_T$, UE charged particles.
Mean $p_T$, in-jet charged particles.
A search for new long-lived particles decaying to leptons is presented using proton-proton collisions produced by the LHC at sqrt(s) = 8 TeV. Data used for the analysis were collected by the CMS detector and correspond to an integrated luminosity of 19.7 inverse femtobarns. Events are selected with an electron and a muon that have transverse impact parameter values between 0.02 cm and 2 cm. The search has been designed to be sensitive to a wide range of models with nonprompt e-mu final states. Limits are set on the "displaced supersymmetry" model, with pair production of top squarks decaying into an e-mu final state via R-parity-violating interactions. The results are the most restrictive to date on this model, with the most stringent limit being obtained for a top squark lifetime corresponding to c tau = 2 cm, excluding masses below 790 GeV at 95% confidence level.
Electron transverse impact parameter distribution for data and expected background processes after the preselection requirements have been applied. The event yields per bin have been rescaled to account for the varying bin sizes. The rightmost bin contains the overflow entries.
Muon transverse impact parameter distribution for data and expected background processes after the preselection requirements have been applied. The event yields per bin have been rescaled to account for the varying bin sizes. The rightmost contains the overflow entries.
Numbers of expected and observed events in the three search regions (see the text for the definitions of these regions). Background and signal expectations are quoted as $N_{\text{exp}} \pm 1\sigma$ stat $\pm 1\sigma$ syst. If the estimated background is zero in a particular search region, the estimate is instead taken from the preceding region. Since this should always overestimate the background, we denote this by a preceding "<".
A search for supersymmetry is presented based on proton-proton collision events containing identified hadronically decaying top quarks, no leptons, and an imbalance $p_\mathrm{T}^\text{miss}$ in transverse momentum. The data were collected with the CMS detector at the CERN LHC at a center-of-mass energy of 13 TeV, and correspond to an integrated luminosity of 35.9 fb$^{-1}$. Search regions are defined in terms of the multiplicity of bottom quark jet and top quark candidates, the $p_\mathrm{T}^\text{miss}$, the scalar sum of jet transverse momenta, and the $m_{\mathrm{T2}}$ mass variable. No statistically significant excess of events is observed relative to the expectation from the standard model. Lower limits on the masses of supersymmetric particles are determined at 95% confidence level in the context of simplified models with top quark production. For a model with direct top squark pair production followed by the decay of each top squark to a top quark and a neutralino, top squark masses up to 1020 GeV and neutralino masses up to 430 GeV are excluded. For a model with pair production of gluinos followed by the decay of each gluino to a top quark-antiquark pair and a neutralino, gluino masses up to 2040 GeV and neutralino masses up to 1150 GeV are excluded. These limits extend previous results.
Figure 8. The 95% CL upper limit on the production cross section of the T2tt simplified model as a function of the top squark and LSP masses. No interpretation is provided for signal models for which |mStop−mLSP−mTop|≤ 25 GeV and mStop≤ 275 GeV because signal events are essentially indistinguishable from SM ttbar events in this region, rendering the signal event acceptance difficult to model.
Figure 8. Observed exclusion region at 95% CL assuming 100% branching fraction.
Figure 8. Expected exclusion region at 95% CL assuming 100% branching fraction.
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