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CMS Collaboration

Publications and source records attributed to CMS Collaboration.

At least 955 records · Page 53Linked to original sources

arXiv2017

Search for heavy resonances that decay into a vector boson and a Higgs boson in hadronic final states at sqrt(s) = 13 TeV

A search for heavy resonances with masses above 1 TeV, decaying to final states containing a vector boson and a Higgs boson, is presented. The search considers hadronic decays of the vector boson, and Higgs boson decays to b quarks. The decay products are highly boosted, and each collimated pair of quarks is reconstructed as a single, massive jet. The analysis is performed using a data sample collected in 2016 by the CMS experiment at the LHC in proton-proton collisions at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 35.9 inverse femtobarns. The data are consistent with the background expectation and are used to place limits on the parameters of a theoretical model with a heavy vector triplet. In the benchmark scenario with mass-degenerate W' and Z' bosons decaying predominantly to pairs of standard model bosons, for the first time heavy resonances for masses as high as 3.3 TeV are excluded at 95% confidence level, setting the most stringent limit to date on such states decaying into a vector boson and a Higgs boson.

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arXiv2017

Search for leptophobic Z' bosons decaying into four-lepton final states in proton-proton collisions at sqrt(s) = 8 TeV

A search for heavy narrow resonances decaying into four-lepton final states from cascade decays of a Z' boson has been performed using proton-proton collision data at sqrt(s) = 8 TeV collected by the CMS experiment, corresponding to an integrated luminosity of 19.7 inverse femtobarns. No excess of events over the standard model background expectation is observed. Upper limits for a benchmark model on the product of cross section and branching fraction for the production of these heavy narrow resonances are presented. The limit excludes leptophobic Z' bosons with masses below 2.5 TeV within the benchmark model. This is the first result to constrain a leptophobic Z' resonance in the four-lepton channel.

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arXiv2017

Search for a heavy resonance decaying to a top quark and a vector-like top quark at sqrt(s) = 13 TeV

A search is presented for massive spin-1 Z' resonances decaying to a top quark and a heavy vector-like top quark partner T. The search is based on a 2.6 inverse femtobarns sample of proton-proton collisions at 13 TeV collected with the CMS detector at the LHC. The analysis is optimized for final states in which the T quark decays to a W boson and a bottom quark. The focus is on all-jet final states in which both the W boson and the top quark decay into quarks that evolve into jets. The decay products of the top quark and of the W boson are assumed to be highly Lorentz-boosted and cannot be reconstructed as separate jets, but are instead reconstructed as merged, wide jets. Techniques for the identification of jet substructure and jet flavour are used to distinguish signal from background events. Several models for Z' bosons decaying to T quarks are excluded at 95% confidence level, with upper limits on the cross section ranging from 0.13 to 10 pb, depending on the chosen hypotheses. This is the first search for a neutral spin-1 heavy resonance decaying to a top quark and a vector-like T quark in the all-hadronic final state.

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arXiv2017

Search for low mass vector resonances decaying to quark-antiquark pairs in proton-proton collisions at sqrt(s) = 13 TeV

A search is reported for a narrow vector resonance decaying to quark-antiquark pairs in proton-proton collisions at sqrt(s) = 13 TeV, collected with the CMS detector at the LHC. The data sample corresponds to an integrated luminosity of 2.7 inverse femtobarns. The vector resonance is produced at large transverse momenta, with its decay products merged into a single jet. The resulting signature is a peak over background in the distribution of the invariant mass of the jet. The results are interpreted in the framework of a leptophobic vector resonance and no evidence is found for such particles in the mass range of 100-300 GeV. Upper limits at 95% confidence level on the production cross section are presented in a region of mass-coupling phase space previously unexplored at the LHC. The region below 140 GeV has not been explored by any previous experiments.

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arXiv2017

Measurement of the t t-bar production cross section using events with one lepton and at least one jet in pp collisions at sqrt(s) = 13 TeV

A measurement of the t t-bar production cross section at sqrt(s) = 13 TeV is presented using proton-proton collisions, corresponding to an integrated luminosity of 2.2 inverse femtobarns, collected with the CMS detector at the LHC. Final states with one isolated charged lepton (electron or muon) and at least one jet are selected and categorized according to the accompanying jet multiplicity. From a likelihood fit to the invariant mass distribution of the isolated lepton and a jet identified as coming from the hadronization of a bottom quark, the cross section is measured to be sigma(t t-bar) = 888 +/- 2 (stat) +26 -28 (syst) +/- 20 (lumi) pb, in agreement with the standard model prediction. Using the expected dependence of the cross section on the pole mass of the top quark (m[t]), the value of m[t] is found to be 170.6 +/- 2.7 GeV.

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arXiv2017

Search for physics beyond the standard model in events with two leptons of same sign, missing transverse momentum, and jets in proton-proton collisions at sqrt(s) = 13 TeV

A data sample of events from proton-proton collisions with two isolated same-sign leptons, missing transverse momentum, and jets is studied in a search for signatures of new physics phenomena by the CMS Collaboration at the LHC. The data correspond to an integrated luminosity of 35.9 inverse femtobarns, and a center-of-mass energy of 13 TeV. The properties of the events are consistent with expectations from standard model processes, and no excess yield is observed. Exclusion limits at 95% confidence level are set on cross sections for the pair production of gluinos, squarks, and same-sign top quarks, as well as top-quark associated production of a heavy scalar or pseudoscalar boson decaying to top quarks, and on the standard model production of events with four top quarks. The observed lower mass limits are as high as 1500 GeV for gluinos, 830 GeV for bottom squarks. The excluded mass range for heavy (pseudo)scalar bosons is 350-360 (350-410) GeV. Additionally, model-independent limits in several topological regions are provided, allowing for further interpretations of the results.

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arXiv2017

Measurement of the total and differential inclusive B+ hadron cross sections in pp collisions at sqrt(s) = 13 TeV

The differential cross sections for inclusive production of B+ hadrons are measured as a function of the B+ transverse momentum pT[B] and rapidity y[B] in pp collisions at a centre-of-mass energy of 13 TeV, using data collected by the CMS experiment that correspond to an integrated luminosity of 49.4 inverse picobarns. The measurement uses the exclusive decay channel B+ to J/psi K+, with J/psi mesons that decay to a pair of muons. The results show a reasonable agreement with theoretical calculations within the uncertainties.

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arXiv2017

Search for supersymmetry in multijet events with missing transverse momentum in proton-proton collisions at 13 TeV

A search for supersymmetry is presented based on multijet events with large missing transverse momentum produced in proton-proton collisions at a center-of-mass energy of sqrt(s) = 13 TeV. The data, corresponding to an integrated luminosity of 35.9 inverse femtobarns, were collected with the CMS detector at the CERN LHC in 2016. The analysis utilizes four-dimensional exclusive search regions defined in terms of the number of jets, the number of tagged bottom quark jets, the scalar sum of jet transverse momenta, and the magnitude of the vector sum of jet transverse momenta. No evidence for a significant excess of events is observed relative to the expectation from the standard model. Limits on the cross sections for the pair production of gluinos and squarks are derived in the context of simplified models. Assuming the lightest supersymmetric particle to be a weakly interacting neutralino, 95% confidence level lower limits on the gluino mass as large as 1800 to 1960 GeV are derived, and on the squark mass as large as 960 to 1390 GeV, depending on the production and decay scenario.

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arXiv2017

Search for top quark partners with charge 5/3 in proton-proton collisions at sqrt(s) = 13 TeV

A search for the production of heavy partners of the top quark with charge 5/3 (X[5/3]) decaying into a top quark and a W boson is performed with a data sample corresponding to an integrated luminosity of 2.3 inverse femtobarns, collected in proton-proton collisions at a center-of-mass energy of 13 TeV with the CMS detector at the CERN LHC. Final states with either a pair of same-sign leptons or a single lepton, along with jets, are considered. No significant excess is observed in the data above the expected standard model background contribution and an X[5/3] quark with right-handed (left-handed) couplings is excluded at 95% confidence level for masses below 1020 (990) GeV. These are the first limits based on a combination of the same-sign dilepton and the single-lepton final states, as well as the most stringent limits on the X[5/3] mass to date.

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arXiv2017

Measurement of the top quark mass in the dileptonic t t-bar decay channel using the mass observables M[bl], M[T2], and M[blnu] in pp collisions at sqrt(s) = 8 TeV

A measurement of the top quark mass (M[t]) in the dileptonic t t-bar decay channel is performed using data from proton-proton collisions at a center-of-mass energy of 8 TeV. The data was recorded by the CMS experiment at the LHC and corresponding to an integrated luminosity of 19.7 +/- 0.5 inverse femtobarns. Events are selected with two oppositely charged leptons (l = e, mu) and two jets identified as originating from b quarks. The analysis is based on three kinematic observables whose distributions are sensitive to the value of M[t]. An invariant mass observable, M[bl], and a `stransverse mass' observable, M[T2], are employed in a simultaneous fit to determine the value of M[t] and an overall jet energy scale factor (JSF). A complementary approach is used to construct an invariant mass observable, M[blnu], that is combined with M[T2] to measure M[t]. The shapes of the observables, along with their evolutions in M[t] and JSF, are modeled by a nonparametric Gaussian process regression technique. The sensitivity of the observables to the value of M[t] is investigated using a Fisher information density method. The top quark mass is measured to be 172.22 +/- 0.18 (stat) +0.89/-0.93 (syst) GeV.

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arXiv2017

Study of jet quenching with Z+jet correlations in PbPb and pp collisions at sqrt(s[NN]) = 5.02 TeV

The production of jets in association with Z bosons, reconstructed via the mu+mu- and e+e- decay channels, is studied in pp and, for the first time, in PbPb collisions. Both data samples were collected by the CMS experiment at the LHC, at a nucleon-nucleon center-of-mass energy of 5.02 TeV. The PbPb collisions were analyzed in the 0-30% centrality range. The back-to-back azimuthal alignment was studied in both pp and PbPb collisions for Z bosons with transverse momentum p[tz] > 60 GeV/c and a recoiling jet with p[tj] > 30 GeV/c. The pt imbalance, x[jz] = p[tj] / p[tz], as well as the average number of jet partners per Z, R[jz], were studied in intervals of p[tz], in both pp and PbPb collisions. The R[jz] is found to be smaller in PbPb than in pp collisions, which suggests that in PbPb collisions a larger fraction of partons, associated with the Z bosons, lose energy and fall below the 30 GeV/c p[tj] threshold.

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arXiv2017

Measurement of the inclusive energy spectrum in the very forward direction in proton-proton collisions at sqrt(s) = 13 TeV

The differential cross section for inclusive particle production as a function of energy in proton-proton collisions at a center-of-mass energy of 13 TeV is measured in the very forward region of the CMS detector. The measurement is based on data collected with the CMS apparatus at the LHC, and corresponds to an integrated luminosity of 0.35 inverse microbarns. The energy is measured in the CASTOR calorimeter, which covers the pseudorapidity region -6.6 < eta < -5.2. The results are given as a function of the total energy deposited in CASTOR, as well as of its electromagnetic and hadronic components. The spectra are sensitive to the modeling of multiparton interactions in pp collisions, and provide new constraints for hadronic interaction models used in collider and in high energy cosmic ray physics.

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arXiv2017

Coherent J/psi photoproduction in ultra-peripheral PbPb collisions at sqrt(s[NN]) = 2.76 TeV with the CMS experiment

The cross section for coherent J/psi photoproduction accompanied by at least one neutron on one side of the interaction point and no neutron activity on the other side, X[n]0[n], is measured with the CMS experiment in ultra-peripheral PbPb collisions at sqrt(s[NN]) = 2.76 TeV. The analysis is based on a data sample corresponding to an integrated luminosity of 159 inverse microbarns, collected during the 2011 PbPb run. The J/psi mesons are reconstructed in the dimuon decay channel, while neutrons are detected using zero degree calorimeters. The measured cross section is dsigma[coh,X[n]0[n]] / dy(J/psi) = 0.36 +/- 0.04 (stat) +/- 0.04 (syst) mb in the rapidity interval 1.8 < abs(y) < 2.3. Using a model for the relative rate of coherent photoproduction processes, this X[z,n,z] measurement gives a total coherent photoproduction cross section of dsigma[coh] / dy(J/psi) = 1.82 +/- 0.22 (stat) +/- 0.20 (syst) +/- 0.19 (theo) mb. The data strongly disfavour the impulse approximation model prediction, indicating that nuclear effects are needed to describe coherent J/psi photoproduction in gamma + Pb interactions. The data are found to be consistent with the leading twist approximation, which includes nuclear gluon shadowing.

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arXiv2017

Searches for W' bosons decaying to a top quark and a bottom quark in proton-proton collisions at 13 TeV

Searches are presented for heavy gauge bosons decaying into a top and a bottom quark in data collected by the CMS experiment at sqrt(s) = 13 TeV that correspond to an integrated luminosity of 2.2 and 2.6 inverse femtobarns in the leptonic and hadronic analyses, respectively. Two final states are analyzed, one containing a single electron, or muon, and missing transverse momentum, and the other containing multiple jets and no electrons or muons. No evidence is found for a right-handed W' boson (W'[R]) and the combined analyses exclude at 95% confidence level W'[R] with masses below 2.4 TeV if M[W'[R]] >> M[nu[R]] (mass of the right-handed neutrino), and below 2.6 TeV if M[W'[R]] < M[nu[R]]. The results provide the most stringent limits for right-handed W' bosons in the top and bottom quark decay channel.

hep-ex↗

arXiv2017

Search for the third-generation scalar leptoquarks and heavy right-handed neutrinos in final states with two tau leptons and two jets in proton-proton collisions at sqrt(s) = 13 TeV

A search is performed for third-generation scalar leptoquarks and heavy right-handed neutrinos in events containing one electron or muon, one hadronically decaying tau lepton, and at least two jets, using a sqrt(s) = 13 TeV pp collision data sample corresponding to an integrated luminosity of 12.9 inverse femtobarns collected with the CMS detector at the LHC in 2016. The number of observed events is found to be in agreement with the standard model prediction. A limit is set at 95% confidence level on the product of the leptoquark pair production cross section and beta squared where beta is the branching fraction of leptoquark decay to a tau lepton and a bottom quark. Assuming beta = 1, third-generation leptoquarks with masses below 850 GeV are excluded at 95% confidence level. An additional search based on the same event topology involves heavy right-handed neutrinos, N[R], and right-handed W bosons, W[R] , arising in a left-right symmetric extension of the standard model. In this search, W[R] bosons are assumed to decay to a tau lepton and N[R] followed by the decay of the N[R] to a tau lepton and an off-shell W[R] boson. Assuming the mass of the right-handed neutrino to be half of the mass of the right-handed W boson, W[R] boson masses below 2.9 TeV are excluded at 95% confidence level. These results improve on the limits from previous searches for third-generation leptoquarks and heavy right-handed neutrinos with tau leptons in the final state.

hep-ex↗

arXiv2017

Search for new physics in events with high jet multiplicity and low missing transverse momentum in proton-proton collisions at sqrt(s) = 8 TeV

A dedicated search is presented for new phenomena in inclusive eight- and ten-jet final states with low missing transverse momentum, with and without identification of jets originating from b quarks. The analysis is based on data from proton-proton collisions corresponding to an integrated luminosity of 19.6 inverse femtobarns collected with the CMS detector at the LHC at sqrt(s) = 8 TeV. The dominant multijet background expectations are obtained from low jet multiplicity control samples. Data agree well with the standard model background predictions, and limits are set in several benchmark models. Colorons (axigluons) with masses between 0.6 and 0.75 (up to 1.15) TeV are excluded at 95% confidence level. Similar exclusion limits for gluinos in R-parity violating supersymmetric scenarios are from 0.6 up to 1.1 TeV. These results comprise the first experimental probe of the coloron and axigluon models in multijet final states.

hep-ex↗

arXiv2017

Search for supersymmetry in the all-hadronic final state using top quark tagging in pp collisions at sqrt(s) = 13 TeV

A search is presented for supersymmetry in all-hadronic events with missing transverse momentum and tagged top quarks. The data sample was collected by the CMS detector at the LHC and corresponds to an integrated luminosity of 2.3 inverse femtobarns of proton-proton collisions at a center-of-mass energy of 13 TeV. Search regions are defined using the properties of reconstructed jets, the multiplicity of bottom and top quark candidates, and an imbalance in transverse momentum. With no statistically significant excess of events observed beyond the expected contributions from the standard model, we set exclusion limits at 95% confidence level on the masses of new particles in the context of simplified models of direct and gluino-mediated top squark production. For direct top squark production with decays to a top quark and a neutralino, top squark masses up to 740 GeV and neutralino masses up to 240 GeV are excluded. Gluino masses up to 1550 GeV and neutralino masses up to 900 GeV are excluded for a gluino-mediated production case, where each of the pair-produced gluinos decays to a top-antitop quark pair and a neutralino.

hep-ex↗

arXiv2017

Search for single production of vector-like quarks decaying into a b quark and a W boson in proton-proton collisions at sqrt(s) = 13 TeV

A search is presented for a heavy vector-like quark, decaying into a b quark and a W boson, which is produced singly in association with a light flavor quark and a b quark. The analysis is performed using a data sample of proton-proton collisions at a center-of-mass energy of sqrt(s) = 13 TeV collected at the LHC in 2015. The data set used in the analysis corresponds to an integrated luminosity of 2.3 inverse femtobarns. The search is carried out using events containing one electron or muon, at least one b-tagged jet with large transverse momentum, at least one jet in the forward region of the detector, and missing transverse momentum. No excess over the standard model prediction is observed. Upper limits are placed on the production cross section of heavy exotic quarks: a T quark with a charge of 2/3, and a Y quark with a charge of -4/3. For Y quarks with coupling of 0.5 and B(Y to bW) = 100%, the observed (expected) lower mass limits are 1.40 (1.0) TeV. This is the most stringent limit to date on the single production of the Y vector-like quark.

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