Search

A search is performed for long-lived massive neutral particles decaying to quark-antiquark pairs. The experimental signature is a distinctive topology of a pair of jets, originating at a secondary vertex. Events were collected with the CMS detector at the CERN LHC in proton-proton collisions at a center-of-mass energy of 8 TeV. The data analyzed correspond to an integrated luminosity of $18.5{\mathrm{fb}}^{-1}$. No significant excess is observed above standard model expectations. Upper limits at 95% confidence level are set on the production cross section of a heavy neutral scalar particle, $H$, in the mass range of 200 to 1000 GeV, decaying promptly into a pair of long-lived neutral $X$ particles in the mass range of 50 to 350 GeV, each in turn decaying into a quark-antiquark pair. For $X$ with mean proper decay lengths of 0.4 to 200 cm, the upper limits are typically $0.5–200\mathrm{fb}$. The results are also interpreted in the context of an R-parity-violating supersymmetric model with long-lived neutralinos decaying into a quark-antiquark pair and a muon. For pair production of squarks that promptly decay to neutralinos with mean proper decay lengths of $2–40\mathrm{cm}$, the upper limits on the cross section are typically $0.5–3\mathrm{fb}$. The above limits are the most stringent on these channels to date.

The inclusive jet cross section is measured in $pp$ collisions with a center-of-mass energy of 7 TeV at the Large Hadron Collider using the CMS experiment. The data sample corresponds to an integrated luminosity of $34{\mathrm{pb}}^{-1}$. The measurement is made for jet transverse momenta in the range 18–1100 GeV and for absolute values of rapidity less than 3. The measured cross section extends to the highest values of jet $p_T$ ever observed and, within the experimental and theoretical uncertainties, is generally in agreement with next-to-leading-order perturbative QCD predictions.

We report an investigation of the invariant mass spectrum of the two jets with highest transverse momentum in $pp\to W+2$-jet and $W+3$-jet events to look for resonant enhancement. The data sample corresponds to an integrated luminosity of $5.0{\mathrm{fb}}^{-1}$ collected with the CMS detector at $\sqrt{s}=7\mathrm{TeV}$. We find no evidence for the anomalous structure reported by the CDF Collaboration, and establish an upper limit of 5.0 pb at 95% confidence level on the production cross section for a generic Gaussian signal with mass near 150 GeV. Additionally, we exclude two theoretical models that predict a CDF-like dijet resonance near 150 GeV.

This Letter describes the search for an enhanced production rate of events with a charged lepton and a neutrino in high-energy $pp$ collisions at the LHC. The analysis uses data collected with the CMS detector, with an integrated luminosity of $5.0{\mathrm{fb}}^{-1}$ at $\sqrt{s}=7\mathrm{TeV}$, and a further $3.7{\mathrm{fb}}^{-1}$ at $\sqrt{s}=8\mathrm{TeV}$. No evidence is found for an excess. The results are interpreted in terms of limits on a heavy charged gauge boson ($W^{\prime }$) in the sequential standard model, a split universal extra dimension model, and contact interactions in the helicity-nonconserving model. For the last, values of the binding energy below 10.5 (8.8) TeV in the electron (muon) channel are excluded at a 95% confidence level. Interpreting the $\ell \nu$ final state in terms of a heavy $W^{\prime }$ with standard model couplings, masses below 2.90 TeV are excluded.

A search for neutral minimal supersymmetric standard model (MSSM) Higgs bosons in $pp$ collisions at the LHC at a center-of-mass energy of 7 TeV is presented. The results are based on a data sample corresponding to an integrated luminosity of $36{\mathrm{pb}}^{-1}$ recorded by the CMS experiment. The search uses decays of the Higgs bosons to tau pairs. No excess is observed in the tau-pair invariant-mass spectrum. The resulting upper limits on the Higgs boson production cross section times branching fraction to tau pairs, as a function of the pseudoscalar Higgs boson mass, yield stringent new bounds in the MSSM parameter space.

A search for physics beyond the standard model in events with at least three leptons is presented. The data sample, corresponding to an integrated luminosity of $19.5{\mathrm{fb}}^{-1}$ of proton-proton collisions with center-of-mass energy $\sqrt{s}=8\mathrm{TeV}$, was collected by the CMS experiment at the LHC during 2012. The data are divided into exclusive categories based on the number of leptons and their flavor, the presence or absence of an opposite-sign, same-flavor lepton pair (OSSF), the invariant mass of the OSSF pair, the presence or absence of a tagged bottom-quark jet, the number of identified hadronically decaying $\tau$ leptons, and the magnitude of the missing transverse energy and of the scalar sum of jet transverse momenta. The numbers of observed events are found to be consistent with the expected numbers from standard model processes, and limits are placed on new-physics scenarios that yield multilepton final states. In particular, scenarios that predict Higgs boson production in the context of supersymmetric decay chains are examined. We also place a 95% confidence level upper limit of 1.3% on the branching fraction for the decay of a top quark to a charm quark and a Higgs boson ($t\to cH$), which translates to a bound on the left- and right-handed top-charm flavor-violating Higgs Yukawa couplings, ${\lambda }_{tc}^H$ and ${\lambda }_{ct}^H$, respectively, of $\sqrt{|{\lambda }_{tc}^H{|}^2+|{\lambda }_{ct}^H{|}^2}<0.21$.

A search for pair-produced heavy vectorlike charge-$2/3$ quarks, $T$, in $pp$ collisions at a center-of-mass energy of 7 TeV, is performed with the CMS detector at the LHC. Events consistent with the flavor-changing-neutral-current decay of a $T$ quark to a top quark and a $Z$ boson are selected by requiring two leptons from the $Z$-boson decay, as well as an additional isolated charged lepton. In a data sample corresponding to an integrated luminosity of $1.14{\mathrm{fb}}^{-1}$, the number of observed events is found to be consistent with the standard model background prediction. Assuming a branching fraction of 100% for the decay $T\to tZ$, a $T$ quark with a mass less than $475\mathrm{GeV}/c^2$ is excluded at the 95% confidence level.

Results are presented from a search for the pair production of third-generation scalar and vector leptoquarks, as well as for top squarks in $R$-parity-violating supersymmetric models. In either scenario, the new, heavy particle decays into a $\tau$ lepton and a $b$ quark. The search is based on a data sample of $pp$ collisions at $\sqrt{s}=7\mathrm{TeV}$, which is collected by the CMS detector at the LHC and corresponds to an integrated luminosity of $4.8{\mathrm{fb}}^{-1}$. The number of observed events is found to be in agreement with the standard model prediction, and exclusion limits on mass parameters are obtained at the 95% confidence level. Vector leptoquarks with masses below 760 GeV are excluded and, if the branching fraction of the scalar leptoquark decay to a $\tau$ lepton and a $b$ quark is assumed to be unity, third-generation scalar leptoquarks with masses below 525 GeV are ruled out. Top squarks with masses below 453 GeV are excluded for a typical benchmark scenario, and limits on the coupling between the top squark, $\tau$ lepton, and $b$ quark, ${\lambda }_{333}^{\prime }$ are obtained. These results are the most stringent for these scenarios to date.

We present a measurement of the underground decoherence function using multi-muon events observed in the MACRO detector at Gran Sasso at an average depth of $3800\hspace{0.5em}\mathrm{hg}/{\mathrm{cm}}^2.$ Muon pair separations up to 70 m have been measured, corresponding to parent mesons with $P_{\perp }<~1$–$2\hspace{0.5em}\mathrm{GeV}/c.\mathrm{}$ Improved selection criteria are used to reduce detector effects mainly in the low distance separation region of muon pairs. Special care is given to a new unfolding procedure designed to minimize systematic errors in the numerical algorithm. The accuracy of the measurement is such that the possible contribution of rare processes, such as ${\mu }^{\pm }+\overrightarrow{N}{\mu }^{\pm }+N+{\mu }^{+}+{\mu }^{-},$ can be experimentally studied. The measured decoherence function is compared with the predictions of the hadronic interaction model of the HEMAS Monte Carlo code. Good agreement is obtained. We interpret this agreement to indicate that no anomalous $P_{\perp }$ components in soft hadron-nucleus and nucleus-nucleus collisions are required by the MACRO experimental data. Preliminary comparisons with other Monte Carlo codes point out that the uncertainties associated with the hadronic interaction model may be as large as 20%, depending on the energy. MACRO data can be used as a benchmark for future work on the discrimination of shower models in the primary energy region around and below the knee of the spectrum.

A first measurement of the polarization of $W$ bosons with large transverse momenta in $pp$ collisions is presented. The measurement is based on $36{\mathrm{pb}}^{-1}$ of data recorded at $\sqrt{s}=7\mathrm{TeV}$ by the CMS detector at the LHC. The left-handed, right-handed, and longitudinal polarization fractions ($f_L$, $f_R$, and $f_0$, respectively) of $W$ bosons with transverse momenta larger than 50 GeV are determined by using decays to both electrons and muons. The muon final state yields the most precise measurement: $(f_L-f_R{)}^{-}=0.240\pm 0.036(\mathrm{stat})\pm 0.031(\mathrm{syst})$ and $f_0^{-}=0.183\pm 0.087(\mathrm{stat})\pm 0.123(\mathrm{syst})$ for negatively charged $W$ bosons and $(f_L-f_R{)}^{+}=0.310\pm 0.036(\mathrm{stat})\pm 0.017(\mathrm{syst})$ and $f_0^{+}=0.171\pm 0.085(\mathrm{stat})\pm 0.099(\mathrm{syst})$ for positively charged $W$ bosons. This establishes, for the first time, that $W$ bosons produced in $pp$ collisions with large transverse momenta are predominantly left-handed, as expected in the standard model.

The transverse energy ($E_{\mathrm{T}}$) in Pb-Pb collisions at 2.76 TeV nucleon-nucleon center-of-mass energy ($\sqrt{s_{\mathrm{NN}}}$) has been measured over a broad range of pseudorapidity ($\eta$) and collision centrality by using the CMS detector at the LHC. The transverse energy density per unit pseudorapidity ($d{E}_{\mathrm{T}}/d\eta$) increases faster with collision energy than the charged particle multiplicity. This implies that the mean energy per particle is increasing with collision energy. At all pseudorapidities, the transverse energy per participating nucleon increases with the centrality of the collision. The ratio of transverse energy per unit pseudorapidity in peripheral to central collisions varies significantly as the pseudorapidity increases from $\eta =0$ to $|\eta |=5.0$. For the 5% most central collisions, the energy density per unit volume is estimated to be about $14\mathrm{GeV}/{\mathrm{fm}}^3$ at a time of $1\mathrm{fm}/c$ after the collision. This is about 100 times larger than normal nuclear matter density and a factor of 2.6 times higher than the energy density reported at $\sqrt{s_{\mathrm{NN}}}=200\mathrm{GeV}$ at the Relativistic Heavy Ion Collider.

We present the analysis of multiple-muon events collected with one supermodule (1013 h live time) and two supermodules (1195 h live time) of the MACRO detector at Gran Sasso, Italy. Multimuon rates are shown to be sensitive to primary-cosmic-ray energies between ∼50 TeV and several thousand TeV. Experimental data are compared with the expected rates from two composition models: a light (i.e., proton-rich) and a heavy (i.e., Fe-rich) composition. The predictions are based on a Monte Carlo simulation of the hadronic interactions of cosmic-ray nuclei, followed by a detailed tracking of the muons through the rock and the experimental apparatus. The results show good sensitivity of the MACRO detector to primary composition. The data exhibit a preference towards the light composition model.

The first observation of the associated production of a single top quark and a $W$ boson is presented. The analysis is based on a data set corresponding to an integrated luminosity of $12.2{\mathrm{fb}}^{-1}$ of proton-proton collisions at $\sqrt{s}=8\mathrm{TeV}$ recorded by the CMS experiment at the LHC. Events with two leptons and a jet originating from a $b$ quark are selected. A multivariate analysis based on kinematic and topological properties is used to separate the signal from the dominant $t\overline{t}$ background. An excess consistent with the signal hypothesis is observed, with a significance which corresponds to 6.1 standard deviations above a background-only hypothesis. The measured production cross section is $23.4\pm 5.4\text{pb}$, in agreement with the standard model prediction.

Spin correlations and polarization in the top quark–antiquark system are measured using dilepton final states produced in $pp$ collisions at the LHC at $\sqrt{s}=7\mathrm{TeV}$. The data correspond to an integrated luminosity of $5.0{\mathrm{fb}}^{-1}$ collected with the CMS detector. The measurements are performed using events with two oppositely charged leptons (electrons or muons), a significant imbalance in transverse momentum, and two or more jets, where at least one of the jets is identified as originating from a $b$ quark. The spin correlations and polarization are measured through asymmetries in angular distributions of the two selected leptons, unfolded to the parton level. All measurements are found to be in agreement with predictions of the standard model.

The differential cross section for the inclusive production of isolated prompt photons has been measured as a function of the photon transverse energy $E_T^{\gamma }$ in $pp$ collisions at $\sqrt{s}=7\mathrm{TeV}$ using data recorded by the CMS detector at the LHC. The data sample corresponds to an integrated luminosity of $2.9{\mathrm{pb}}^{-1}$. Photons are required to have a pseudorapidity $|{\eta }^{\gamma }|<1.45$ and $E_T^{\gamma }>21\mathrm{GeV}$, covering the kinematic region $0.006<x_T<0.086$. The measured cross section is found to be in agreement with next-to-leading-order perturbative QCD calculations.

A comparison of the relative yields of ${\rm Y}$ resonances in the ${\mu }^{+}{\mu }^{-}$ decay channel in Pb-Pb and $pp$ collisions at a center-of-mass energy per nucleon pair of 2.76 TeV is performed with data collected with the CMS detector at the LHC. Using muons of transverse momentum above $4\mathrm{GeV}/c$ and pseudorapidity below 2.4, the double ratio of the ${\rm Y}(2S)$ and ${\rm Y}(3S)$ excited states to the ${\rm Y}(1S)$ ground state in Pb-Pb and $pp$ collisions, $[{\rm Y}(2S+3S)/{\rm Y}(1S){]}_{\mathrm{Pb}\mathrm{\text{−}}\mathrm{Pb}}/[{\rm Y}(2S+3S)/{\rm Y}(1S){]}_{pp}$, is found to be ${0.31}_{-0.15}^{+0.19}(\mathrm{stat})\pm 0.03(\mathrm{syst})$. The probability to obtain the measured value, or lower, if the true double ratio is unity, is calculated to be less than 1%.

Searches are presented for heavy scalar ($H$) and pseudoscalar ($A$) Higgs bosons posited in the two doublet model (2HDM) extensions of the standard model (SM). These searches are based on a data sample of $pp$ collisions collected with the CMS experiment at the LHC at a center-of-mass energy of $\sqrt{s}=8\mathrm{TeV}$ and corresponding to an integrated luminosity of $19.5{\mathrm{fb}}^{-1}$. The decays $H\to hh$ and $A\to Zh$, where $h$ denotes an SM-like Higgs boson, lead to events with three or more isolated charged leptons or with a photon pair accompanied by one or more isolated leptons. The search results are presented in terms of the $H$ and $A$ production cross sections times branching fractions and are further interpreted in terms of 2HDM parameters. We place 95% C.L. cross section upper limits of approximately 7 pb on $\sigma \mathcal{B}$ for $H\to hh$ and 2 pb for $A\to Zh$. Also presented are the results of a search for the rare decay of the top quark that results in a charm quark and an SM Higgs boson, $t\to ch$, the existence of which would indicate a nonzero flavor-changing Yukawa coupling of the top quark to the Higgs boson. We place a 95% C.L. upper limit of 0.56% on $\mathcal{B}(t\to ch)$.

This article presents a study of single ${\pi }^{+}$ production in neutrino neutral-current interactions ($\mathrm{NC}1{\pi }^{+}$) using the FGD1 hydrocarbon target of the ND280 detector of the T2K experiment. We report the largest sample of such events selected by any experiment, providing the first new data for this channel in over four decades and the first using a sub-GeV neutrino flux. The signal selection strategy and its performance are detailed together with validations of a robust cross section extraction methodology. The measured flux-averaged integrated cross-section is $\sigma =(6.07\pm 1.22)\times {10}^{-41}{\mathrm{cm}}^2/\mathrm{nucleon}$, $1.3\sigma$ above the NEUT v5.4.0 expectation.

We report the first measurement of neutron capture multiplicity in neutrino-oxygen neutral-current quasielasticlike interactions at the gadolinium-loaded Super-Kamiokande detector using the T2K neutrino beam, which has a peak energy of about 0.6 GeV. A total of 30 neutral-current quasielasticlike event candidates were selected from T2K data corresponding to an exposure of $1.76\times {10}^{20}$ protons on target. The $\gamma$ ray signals resulting from neutron captures were identified using a neural network. The flux-averaged mean neutron capture multiplicity was measured to be ${1.37\pm 0.33(\mathrm{stat}.)}_{-0.27}^{+0.17}(\mathrm{syst}.)$, which is compatible within 2.3 sigma than predictions obtained using our nominal simulation. We discuss potential sources of systematic uncertainty in the prediction and demonstrate that a significant portion of this discrepancy arises from the modeling of hadron-nucleus interactions in the detector medium.

The Super-Kamiokande and T2K Collaborations present a joint measurement of neutrino oscillation parameters from their atmospheric and beam neutrino data. It uses a common interaction model for events overlapping in neutrino energy and correlated detector systematic uncertainties between the two datasets, which are found to be compatible. Using 3244.4 days of atmospheric data and a beam exposure of $19.7(16.3)\times {10}^{20}$ protons on target in (anti)neutrino mode, the analysis finds a $1.9\sigma$ exclusion of $CP$ conservation (defined as $J_{CP}=0$) and a $1.2\sigma$ exclusion of the inverted mass ordering.