Publications
1150 results found
Sirunyan AM, Tumasyan A, Adam W, et al., 2018, Search for disappearing tracks as a signature of new long-lived particles in proton-proton collisions at root s=13 TeV, JOURNAL OF HIGH ENERGY PHYSICS, Vol: 2018, ISSN: 1029-8479
A search is presented for long-lived charged particles that decay within the CMS detector and produce the signature of a disappearing track. A disappearing track is an isolated track with missing hits in the outer layers of the silicon tracker, little or no energy in associated calorimeter deposits, and no associated hits in the muon detectors. This search uses data collected with the CMS detector in 2015 and 2016 from proton-proton collisions at a center-of-mass energy of 13 TeV at the LHC, corresponding to an integrated luminosity of 38.4 fb−1. The results of the search are interpreted in the context of the anomaly-mediated supersymmetry breaking model. The data are consistent with the background-only hypothesis. Limits are set on the product of the cross section for direct production of charginos and their branching fraction to a neutralino and a pion, as a function of the chargino mass and lifetime. At 95% confidence level, charginos with masses below 715 (695) GeV are excluded for a lifetime of 3 (7) ns, as are charginos with lifetimes from 0.5 to 60 ns for a mass of 505 GeV. These are the most stringent limits using a disappearing track signature on this signal model for chargino lifetimes above ≈0.7 ns.
Sirunyan AM, Tumasyan A, Adam W, et al., 2018, Measurement of the cross section for top quark pair production in association with a W or Z boson in proton-proton collisions at root s=13 TeV, Journal of High Energy Physics, Vol: 2018, ISSN: 1029-8479
A measurement is performed of the cross section of top quark pair production in association with a W or Z boson using proton-proton collisions at a center-of-mass energy of 13 TeV at the LHC. The data sample corresponds to an integrated luminosity of 35.9 fb−1, collected by the CMS experiment in 2016. The measurement is performed in the same-sign dilepton, three- and four-lepton final states. The production cross sections are measured to be σ(tt⎯⎯W)=0.77+0.12−0.11(stat)+0.13−0.12(syst)pb and σ(tt⎯⎯Z)=0.99+0.09−0.08(stat)+0.12−0.10(syst)pb. The expected (observed) signal significance for the tt⎯⎯W production in same-sign dilepton channel is found to be 4.5 (5.3) standard deviations, while for the tt⎯⎯Z production in three- and four-lepton channels both the expected and the observed significances are found to be in excess of 5 standard deviations. The results are in agreement with the standard model predictions and are used to constrain the Wilson coefficients for eight dimension-six operators describing new interactions that would modify tt⎯⎯W and tt⎯⎯Z production.
Sirunyan AM, Tumasyan A, Adam W, et al., 2018, Measurement of the inelastic proton-proton cross section at root s=13 TeV, JOURNAL OF HIGH ENERGY PHYSICS, Vol: 2018, ISSN: 1029-8479
A measurement of the inelastic proton-proton cross section with the CMS detector at a center-of-mass energy of s√=13 TeV is presented. The analysis is based on events with energy deposits in the forward calorimeters, which cover pseudorapidities of −6.6 < η < −3.0 and +3.0 < η < +5.2. An inelastic cross section of 68.6 ± 0.5(syst) ± 1.6(lumi) mb is obtained for events with MX > 4.1 GeV and/or MY > 13 GeV, where MX and MY are the masses of the diffractive dissociation systems at negative and positive pseudorapidities, respectively. The results are compared with those from other experiments as well as to predictions from high-energy hadron-hadron interaction models.
Sirunyan AM, Tumasyan A, Adam W, et al., 2018, Observation of proton-tagged, central (semi)exclusive production of high-mass lepton pairs in pp collisions at 13 TeV with the CMS-TOTEM precision proton spectrometer, Journal of High Energy Physics, Vol: 2018, ISSN: 1029-8479
The process pp → pℓ+ℓ−p(*), with ℓ+ℓ− a muon or an electron pair produced at midrapidity with mass larger than 110 GeV, has been observed for the first time at the LHC in pp collisions at s√=13 TeV. One of the two scattered protons is measured in the CMS-TOTEM precision proton spectrometer (CT-PPS), which operated for the first time in 2016. The second proton either remains intact or is excited and then dissociates into a low-mass state p*, which is undetected. The measurement is based on an integrated luminosity of 9.4 fb−1 collected during standard, high-luminosity LHC operation. A total of 12 μ+μ− and 8 e+e− pairs with m(ℓ+ℓ−) > 110 GeV, and matching forward proton kinematics, are observed, with expected backgrounds of 1.49 ± 0.07 (stat) ± 0.53 (syst) and 2.36 ± 0.09 (stat) ± 0.47 (syst), respectively. This corresponds to an excess of more than five standard deviations over the expected background. The present result constitutes the first observation of proton-tagged γγ collisions at the electroweak scale. This measurement also demonstrates that CT-PPS performs according to the design specifications.Open image in new window
Sirunyan AM, Tumasyan A, Adam W, et al., 2018, Electroweak production of two jets in association with a Z boson in proton-proton collisions root s =13 TeV, European Physical Journal C: Particles and Fields, Vol: 78, ISSN: 1434-6044
A measurement of the electroweak (EW) production of two jets in association with a Z boson in proton-proton collisions at s√=13TeV is presented, based on data recorded in 2016 by the CMS experiment at the LHC corresponding to an integrated luminosity of 35.9fb--1. The measurement is performed in the ℓℓjj final state with ℓ including electrons and muons, and the jets j corresponding to the quarks produced in the hard interaction. The measured cross section in a kinematic region defined by invariant masses mℓℓ>50GeV, mjj>120GeV, and transverse momenta pTj>25GeV is σEW(ℓℓjj)=534±20(stat)±57(syst) fb, in agreement with leading-order standard model predictions. The final state is also used to perform a search for anomalous trilinear gauge couplings. No evidence is found and limits on anomalous trilinear gauge couplings associated with dimension-six operators are given in the framework of an effective field theory. The corresponding 95% confidence level intervals are −2.6<cWWW/Λ2<2.6TeV−2 and −8.4<cW/Λ2<10.1TeV−2. The additional jet activity of events in a signal-enriched region is also studied, and the measurements are in agreement with predictions.
Sirunyan AM, Tumasyan A, Adam W, et al., 2018, Search for a singly produced third-generation scalar leptoquark decaying to a tau lepton and a bottom quark in proton-proton collisions at root s=13 TeV, Journal of High Energy Physics, Vol: 2018, ISSN: 1029-8479
A search is presented for a singly produced third-generation scalar leptoquark decaying to a τ lepton and a bottom quark. Associated production of a leptoquark and a τ lepton is considered, leading to a final state with a bottom quark and two τ leptons. The search uses proton-proton collision data at a center-of-mass energy of 13 TeV recorded with the CMS detector, corresponding to an integrated luminosity of 35.9 fb−1. Upper limits are set at 95% confidence level on the production cross section of the third-generation scalar leptoquarks as a function of their mass. From a comparison of the results with the theoretical predictions, a third-generation scalar leptoquark decaying to a τ lepton and a bottom quark, assuming unit Yukawa coupling (λ), is excluded for masses below 740 GeV. Limits are also set on λ of the hypothesized leptoquark as a function of its mass. Above λ = 1.4, this result provides the best upper limit on the mass of a third-generation scalar leptoquark decaying to a τ lepton and a bottom quark.
Sirunyan AM, Tumasyan A, Adam W, et al., 2018, Azimuthal correlations for inclusive 2-jet, 3-jet, and 4-jet events in pp collisions at root s=13 TeV, EUROPEAN PHYSICAL JOURNAL C, Vol: 78, ISSN: 1434-6044
Azimuthal correlations between the two jets with the largest transverse momenta pT in inclusive 2-, 3-, and 4-jet events are presented for several regions of the leading jet pT up to 4TeV. For 3- and 4-jet scenarios, measurements of the minimum azimuthal angles between any two of the three or four leading pT jets are also presented. The analysis is based on data from proton–proton collisions collected by the CMS Collaboration at a centre-of-mass energy of 13TeV, corresponding to an integrated luminosity of 35.9fb−1. Calculations based on leading-order matrix elements supplemented with parton showering and hadronization do not fully describe the data, so next-to-leading-order calculations matched with parton shower and hadronization models are needed to better describe the measured distributions. Furthermore, we show that azimuthal jet correlations are sensitive to details of the parton showering, hadronization, and multiparton interactions. A next-to-leading-order calculation matched with parton showers in the MC@NLO method, as implemented in herwig 7, gives a better overall description of the measurements than the powheg method.
Sirunyan AM, Tumasyan A, Adam W, et al., 2018, Nuclear modification factor of D-0 mesons in PbPb collisions at root s(NN)=5.02 TeV, Physics Letters B, Vol: 782, Pages: 474-496, ISSN: 0370-2693
The transverse momentum () spectrum of prompt mesons and their antiparticles has been measured via the hadronic decay channels and in and PbPb collisions at a centre-of-mass energy of 5.02 TeV per nucleon pair with the CMS detector at the LHC. The measurement is performed in the meson range of 2–100 and in the rapidity range of . The (PbPb) dataset used for this analysis corresponds to an integrated luminosity of 27.4 pb−1 (530 μb−1 ). The measured meson spectrum in pp collisions is well described by perturbative QCD calculations. The nuclear modification factor, comparing meson yields in PbPb and collisions, was extracted for both minimum-bias and the 10% most central PbPb interactions. For central events, the meson yield in the PbPb collisions is suppressed by a factor of 5–6 compared to the reference in the range of 6–10. For mesons in the high- range of 60–100, a significantly smaller suppression is observed. The results are also compared to theoretical calculations.
Sirunyan AM, Tumasyan A, Adam W, et al., 2018, Search for new physics in events with two soft oppositely charged leptons and missing transverse momentum in proton-proton collisions at root s=13 TeV, Physics Letters B, Vol: 782, Pages: 440-467, ISSN: 0370-2693
A search is presented for new physics in events with two low-momentum, oppositely charged leptons (electrons or muons) and missing transverse momentum in proton-proton collisions at a centre-of-mass energy of 13 TeV. The data collected using the CMS detector at the LHC correspond to an integrated luminosity of 35.9. The observed event yields are consistent with the expectations from the standard model. The results are interpreted in terms of pair production of charginos and neutralinos ( and ) with nearly degenerate masses, as expected in natural supersymmetry models with light higgsinos, as well as in terms of the pair production of top squarks ( ), when the lightest neutralino and the top squark have similar masses. At 95% confidence level, wino-like masses are excluded up to 230 GeV for a mass difference of 20 GeV relative to the lightest neutralino. In the higgsino-like model, masses are excluded up to 168 GeV for the same mass difference. For pair production, top squark masses up to 450 GeV are excluded for a mass difference of 40 GeV relative to the lightest neutralino.
Sirunyan AM, Tumasyan A, Adam W, et al., 2018, Measurement of the underlying event activity in inclusive Z boson production in proton-proton collisions at root s=13 TeV, Journal of High Energy Physics, Vol: 2018, ISSN: 1029-8479
This paper presents a measurement of the underlying event activity in proton-proton collisions at a center-of-mass energy of 13 TeV, performed using inclusive Z boson production events collected with the CMS experiment at the LHC. The analyzed data correspond to an integrated luminosity of 2.1 fb−1. The underlying event activity is quantified in terms of the charged particle multiplicity, as well as of the scalar sum of the charged particles’ transverse momenta in different topological regions defined with respect to the Z boson direction. The distributions are unfolded to the stable particle level and compared with predictions from various Monte Carlo event generators, as well as with similar CDF and CMS measurements at center-of-mass energies of 1.96 and 7 TeV respectively.
Sirunyan AM, Tumasyan A, Adam W, et al., 2018, Search for a heavy resonance decaying into a Z boson and a vector boson in the v(v)over-barq(q)over-bar final state, Journal of High Energy Physics, Vol: 2018, ISSN: 1029-8479
A search is presented for a heavy resonance decaying into either a pair of Z bosons or a Z boson and a W boson (ZZ or WZ), with a Z boson decaying into a pair of neutrinos and the other boson decaying hadronically into two collimated quarks that are reconstructed as a highly energetic large-cone jet. The search is performed using the data collected with the CMS detector at the CERN LHC during 2016 in proton-proton collisions at a center-of-mass energy of 13 TeV, corresponding to a total integrated luminosity of 35.9 fb−1. No excess is observed in data with regard to background expectations. Results are interpreted in scenarios of physics beyond the standard model. Limits at 95% confidence level on production cross sections are set at 0.9 fb (63 fb) for spin-1 W′ bosons, included in the heavy vector triplet model, with mass 4.0 TeV (1.0 TeV), and at 0.5 fb (40 fb) for spin-2 bulk gravitons with mass 4.0 TeV (1.0 TeV). Lower limits are set on the masses of W′ bosons in the context of two versions of the heavy vector triplet model of 3.1TeV and 3.4 TeV, respectively.
Sirunyan AM, Tumasyan A, Adam W, et al., 2018, Search for a new scalar resonance decaying to a pair of Z bosons in proton-proton collisions at root s=13 TeV, JOURNAL OF HIGH ENERGY PHYSICS, Vol: 2018, ISSN: 1029-8479
A search for a new scalar resonance decaying to a pair of Z bosons is performed in the mass range from 130 GeV to 3 TeV, and for various width scenarios. The analysis is based on proton-proton collisions recorded by the CMS experiment at the LHC in 2016, corresponding to an integrated luminosity of 35.9 fb−1 at a center-of-mass energy of 13 TeV. The Z boson pair decays are reconstructed using the 4ℓ, 2ℓ2q, and 2ℓ2ν final states, where ℓ = e or μ. Both gluon fusion and electroweak production of the scalar resonance are considered, with a free parameter describing their relative cross sections. A dedicated categorization of events, based on the kinematic properties of associated jets, and matrix element techniques are employed for an optimal signal and background separation. A description of the interference between signal and background amplitudes for a resonance of an arbitrary width is included. No significant excess of events with respect to the standard model expectation is observed and limits are set on the product of the cross section for a new scalar boson and the branching fraction for its decay to ZZ for a large range of masses and widths.
Sirunyan AM, Tumasyan A, Adam W, et al., 2018, Search for high-mass resonances in final states with a lepton and missing transverse momentum at root s=13 TeV, JOURNAL OF HIGH ENERGY PHYSICS, Vol: 2018, ISSN: 1029-8479
A search for new high-mass resonances in proton-proton collisions having final states with an electron or muon and missing transverse momentum is presented. The analysis uses proton-proton collision data collected in 2016 with the CMS detector at the LHC at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 35.9 fb−1. The transverse mass distribution of the charged lepton-neutrino system is used as the discriminating variable. No significant deviation from the standard model prediction is found. The best limit, from the combination of electron and muon channels, is 5.2 TeV at 95% confidence level for the mass of a W′ boson with the same couplings as those of the standard model W boson. Exclusion limits of 2.9 TeV are set on the inverse radius of the extra dimension in the framework of split universal extra dimensions. In addition, model-independent limits are set on the production cross section and coupling strength of W′ bosons decaying into this final state. An interpretation is also made in the context of an R parity violating supersymmetric model with a slepton as a mediator and flavor violating decay.
Sirunyan AM, Tumasyan A, Adam W, et al., 2018, Search for high-mass resonances in dilepton final states in proton-proton collisions at root s=13 TeV, JOURNAL OF HIGH ENERGY PHYSICS, Vol: 2018, ISSN: 1029-8479
A search is presented for new high-mass resonances decaying into electron or muon pairs. The search uses proton-proton collision data at a centre-of-mass energy of 13 TeV collected by the CMS experiment at the LHC in 2016, corresponding to an integrated luminosity of 36 fb−1. Observations are in agreement with standard model expectations. Upper limits on the product of a new resonance production cross section and branching fraction to dileptons are calculated in a model-independent manner. This permits the interpretation of the limits in models predicting a narrow dielectron or dimuon resonance. A scan of different intrinsic width hypotheses is performed. Limits are set on the masses of various hypothetical particles. For the Z′SSM(Z′ψ) particle, which arises in the sequential standard model (superstring-inspired model), a lower mass limit of 4.50 (3.90) TeV is set at 95% confidence level. The lightest Kaluza-Klein graviton arising in the Randall-Sundrum model of extra dimensions, with coupling parameters k/MPl of 0.01, 0.05, and 0.10, is excluded at 95% confidence level below 2.10, 3.65, and 4.25 TeV, respectively. In a simplified model of dark matter production via a vector or axial vector mediator, limits at 95% confidence level are obtained on the masses of the dark matter particle and its mediator.
Sirunyan AM, Tumasyan A, Adam W, et al., 2018, Search for the flavor-changing neutral current interactions of the top quark and the Higgs boson which decays into a pair of b quarks at root s=13 TeV, JOURNAL OF HIGH ENERGY PHYSICS, Vol: 2018, ISSN: 1029-8479
A search for flavor-changing neutral currents (FCNC) in events with the top quark and the Higgs boson is presented. The Higgs boson decay to a pair of b quarks is considered. The data sample corresponds to an integrated luminosity of 35.9 fb−1 recorded by the CMS experiment at the LHC in proton-proton collisions at s√=13 TeV. Two channels are considered: single top quark FCNC production in association with the Higgs boson (pp → tH), and top quark pair production with FCNC decay of the top quark (t → qH). Final states with one isolated lepton and at least three reconstructed jets, among which at least two are associated with b quarks, are studied. No significant deviation is observed from the predicted background. Observed (expected) upper limits at 95% confidence level are set on the branching fractions of top quark decays, ℬ(t → uH) < 0.47% (0.34%) and ℬ(t → cH) < 0.47% (0.44%), assuming a single nonzero FCNC coupling.
Sirunyan AM, Tumasyan A, Adam W, et al., 2018, Search for t(t)over-barH production in the all-jet final state in proton-proton collisions root s=13 TeV, Journal of High Energy Physics, Vol: 2018, ISSN: 1029-8479
A search is presented for the associated production of a Higgs boson with a top quark pair in the all-jet final state. Events containing seven or more jets are selected from a sample of proton-proton collisions at s√=13 TeV collected with the CMS detector at the LHC in 2016, corresponding to an integrated luminosity of 35.9 fb−1. To separate the tt⎯⎯H signal from the irreducible tt⎯⎯+bb⎯⎯⎯ background, the analysis assigns leading order matrix element signal and background probability densities to each event. A likelihood-ratio statistic based on these probability densities is used to extract the signal. The results are provided in terms of an observed ttH signal strength relative to the standard model production cross section μ = σ/σSM, assuming a Higgs boson mass of 125 GeV. The best fit value is μˆ=0.9±0.7(stat)±1.3(syst)=0.9±1.5(tot), and the observed and expected upper limits are, respectively, μ < 3.8 and < 3.1 at 95% confidence levels.
Sirunyan AM, Tumasyan A, Adam W, et al., 2018, Measurement of prompt and nonprompt charmonium suppression in PbPb collisions at 5.02 TeV, EUROPEAN PHYSICAL JOURNAL C, Vol: 78, ISSN: 1434-6044
The nuclear modification factors of J/ψ and ψ(2S) mesons are measured in PbPb collisions at a centre-of-mass energy per nucleon pair of sNN−−−√=5.02TeV. The analysis is based on PbPb and pp data samples collected by CMS at the LHC in 2015, corresponding to integrated luminosities of 464μb−1 and 28pb-1, respectively. The measurements are performed in the dimuon rapidity range of |y|<2.4 as a function of centrality, rapidity, and transverse momentum (pT ) from pT=3 GeV/c in the most forward region and up to 50GeV/c. Both prompt and nonprompt (coming from b hadron decays) J/ψ mesons are observed to be increasingly suppressed with centrality, with a magnitude similar to the one observed at sNN−−−√=2.76TeV for the two J/ψ meson components. No dependence on rapidity is observed for either prompt or nonprompt J/ψ mesons. An indication of a lower prompt J/ψ meson suppression at pT>25 GeV/c is seen with respect to that observed at intermediate pT. The prompt ψ(2S) meson yield is found to be more suppressed than that of the prompt J/ψ mesons in the entire pT range.
Sirunyan AM, Tumasyan A, Adam W, et al., 2018, Performance of the CMS muon detector and muon reconstruction with proton-proton collisions at root s=13 TeV, JOURNAL OF INSTRUMENTATION, Vol: 13, ISSN: 1748-0221
The CMS muon detector system, muon reconstruction software, and high-level trigger underwent significant changes in 2013–2014 in preparation for running at higher LHC collision energy and instantaneous luminosity. The performance of the modified system is studied using proton-proton collision data at center-of-mass energy √s=13 TeV, collected at the LHC in 2015 and 2016. The measured performance parameters, including spatial resolution, efficiency, and timing, are found to meet all design specifications and are well reproduced by simulation. Despite the more challenging running conditions, the modified muon system is found to perform as well as, and in many aspects better than, previously. We dedicate this paper to the memory of Prof. Alberto Benvenuti, whose work was fundamental for the CMS muon detector.
Sirunyan AM, Tumasyan A, Adam W, et al., 2018, Measurement of differential cross sections for the production of top quark pairs and of additional jets in lepton plus jets events from pp collisions at root s=13 TeV, PHYSICAL REVIEW D, Vol: 97, ISSN: 2470-0010
Differential and double-differential cross sections for the production of top quark pairs in proton-proton collisions at √s=13 TeV are measured as a function of kinematic variables of the top quarks and the top quark-antiquark (t¯t) system. In addition, kinematic variables and multiplicities of jets associated with the t¯t production are measured. This analysis is based on data collected by the CMS experiment at the LHC in 2016 corresponding to an integrated luminosity of 35.8 fb−1. The measurements are performed in the lepton+jets decay channels with a single muon or electron and jets in the final state. The differential cross sections are presented at the particle level, within a phase space close to the experimental acceptance, and at the parton level in the full phase space. The results are compared to several standard model predictions that use different methods and approximations. The kinematic variables of the top quarks and the t¯t system are reasonably described in general, though none predict all the measured distributions. In particular, the transverse momentum distribution of the top quarks is more steeply falling than predicted. The kinematic distributions and multiplicities of jets are adequately modeled by certain combinations of next-to-leading-order calculations and parton shower models.
Sirunyan AM, Tumasyan A, Adam W, et al., 2018, Bose-Einstein correlations in pp, pPb, and PbPb collisions at root s(NN)=0.9-7 TeV, PHYSICAL REVIEW C, Vol: 97, ISSN: 2469-9985
Quantum-statistical (Bose-Einstein) two-particle correlations are measured in pp collisions at √s=0.9, 2.76, and 7 TeV, as well as in pPb and peripheral PbPb collisions at nucleon-nucleon center-of-mass energies of 5.02 and 2.76 TeV, respectively, using the CMS detector at the Large Hadron Collider. Separate analyses are performed for same-sign unidentified charged particles as well as for same-sign pions and kaons identified via their energy loss in the silicon tracker. The characteristics of the one-, two-, and three-dimensional correlation functions are studied as functions of the pair average transverse momentum (kT) and the charged-particle multiplicity in the event. For all systems, the extracted correlation radii steadily increase with the event multiplicity, and decrease with increasing kT. The radii are in the range 1–5 fm, the largest values corresponding to very high multiplicity pPb interactions and to peripheral PbPb collisions with multiplicities similar to those seen in pPb data. It is also observed that the dependencies of the radii on multiplicity and kT largely factorize. At the same multiplicity, the radii are relatively independent of the colliding system and center-of-mass energy.
Sirunyan AM, Tumasyan A, Adam W, et al., 2018, Search for Physics Beyond the Standard Model in Events with High-Momentum Higgs Bosons and Missing Transverse Momentum in Proton-Proton Collisions at 13 TeV, PHYSICAL REVIEW LETTERS, Vol: 120, ISSN: 0031-9007
A search for physics beyond the standard model in events with one or more high-momentum Higgs bosons, H, decaying to pairs of b quarks in association with missing transverse momentum is presented. The data, corresponding to an integrated luminosity of 35.9 fb−1, were collected with the CMS detector at the LHC in proton-proton collisions at the center-of-mass energy √s=13 TeV. The analysis utilizes a new b quark tagging technique based on jet substructure to identify jets from H→b¯b. Events are categorized by the multiplicity of H-tagged jets, jet mass, and the missing transverse momentum. No significant deviation from standard model expectations is observed. In the context of supersymmetry (SUSY), limits on the cross sections of pair-produced gluinos are set, assuming that gluinos decay to quark pairs, H (or Z), and the lightest SUSY particle, LSP, through an intermediate next-to-lightest SUSY particle, NLSP. With large mass splitting between the NLSP and LSP, and 100% NLSP branching fraction to H, the lower limit on the gluino mass is found to be 2010 GeV.
Sirunyan AM, Tumasyan A, Adam W, et al., 2018, Measurement of angular parameters from the decay B-0 -> K*(0)mu(+)mu(-) in proton-proton collisions at root s=8 TeV, PHYSICS LETTERS B, Vol: 781, Pages: 517-541, ISSN: 0370-2693
Angular distributions of the decay ⁎ are studied using a sample of proton–proton collisions at collected with the CMS detector at the LHC, corresponding to an integrated luminosity of . An angular analysis is performed to determine the and parameters, where the parameter is of particular interest because of recent measurements that indicate a potential discrepancy with the standard model predictions. Based on a sample of 1397 signal events, the and parameters are determined as a function of the dimuon invariant mass squared. The measurements are in agreement with predictions based on the standard model.
Sirunyan AM, Tumasyan A, Adam W, et al., 2018, Search for a massive resonance decaying to a pair of Higgs bosons in the four b quark final state in proton-proton collisions at root s=13 TeV, PHYSICS LETTERS B, Vol: 781, Pages: 244-269, ISSN: 0370-2693
A search for a massive resonance decaying into a pair of standard model Higgs bosons, in a final state consisting of two b quark–antiquark pairs, is performed. A data sample of proton–proton collisions at a centre-of-mass energy of 13 TeV is used, collected by the CMS experiment at the CERN LHC in 2016, and corresponding to an integrated luminosity of 35.9. The Higgs bosons are highly Lorentz-boosted and are each reconstructed as a single large-area jet. The signal is characterized by a peak in the dijet invariant mass distribution, above a background from the standard model multijet production. The observations are consistent with the background expectations, and are interpreted as upper limits on the products of the s-channel production cross sections and branching fractions of narrow bulk gravitons and radions in warped extra-dimensional models. The limits range from 126 to 1.4 fb at 95% confidence level for resonances with masses between 750 and 3000 GeV, and are the most stringent to date, over the explored mass range.
Sirunyan AM, Tumasyan A, Adam W, et al., 2018, Observation of (tt)over-barH production, Physical Review Letters, Vol: 120, ISSN: 0031-9007
The observation of Higgs boson production in association with a top quark-antiquark pair is reported, based on a combined analysis of proton-proton collision data at center-of-mass energies of √s=7, 8, and 13 TeV, corresponding to integrated luminosities of up to 5.1, 19.7, and 35.9 fb−1, respectively. The data were collected with the CMS detector at the CERN LHC. The results of statistically independent searches for Higgs bosons produced in conjunction with a top quark-antiquark pair and decaying to pairs of W bosons, Z bosons, photons, τ leptons, or bottom quark jets are combined to maximize sensitivity. An excess of events is observed, with a significance of 5.2 standard deviations, over the expectation from the background-only hypothesis. The corresponding expected significance from the standard model for a Higgs boson mass of 125.09 GeV is 4.2 standard deviations. The combined best fit signal strength normalized to the standard model prediction is 1.26+0.31−0.26.
Sirunyan AM, Tumasyan A, Adam W, et al., 2018, Search for dark matter in events with energetic, hadronically decaying top quarks and missing transverse momentum at root s=13 TeV, JOURNAL OF HIGH ENERGY PHYSICS, Vol: 2018, ISSN: 1029-8479
A search for dark matter is conducted in events with large missing transverse momentum and a hadronically decaying, Lorentz-boosted top quark. This study is performed using proton-proton collisions at a center-of-mass energy of 13 TeV, in data recorded by the CMS detector in 2016 at the LHC, corresponding to an integrated luminosity of 36 fb−1. New substructure techniques, including the novel use of energy correlation functions, are utilized to identify the decay products of the top quark. With no significant deviations observed from predictions of the standard model, limits are placed on the production of new heavy bosons coupling to dark matter particles. For a scenario with purely vector-like or purely axial-vector-like flavor changing neutral currents, mediator masses between 0.20 and 1.75 TeV are excluded at 95% confidence level, given a sufficiently small dark matter mass. Scalar resonances decaying into a top quark and a dark matter fermion are excluded for masses below 3.4 TeV, assuming a dark matter mass of 100 GeV.
Sirunyan AM, Tumasyan A, Adam W, et al., 2018, Search for single production of vector-like quarks decaying to a b quark and a Higgs boson, Journal of High Energy Physics, Vol: 2018, ISSN: 1029-8479
A search is presented for single production of heavy vector-like quarks (B) that decay to a Higgs boson and a b quark, with the Higgs boson decaying to a highly boosted bb⎯⎯⎯ pair reconstructed as a single collimated jet. The analysis is based on data collected by the CMS experiment in proton-proton collisions at s√=13 TeV, corresponding to an integrated luminosity of 35.9 fb−1. The data are consistent with background expectations, and upper limits at 95% confidence level on the product of the B quark cross section and the branching fraction are obtained in the range 1.28–0.07 pb, for a narrow B quark with a mass between 700 and 1800 GeV. The production of B quarks with widths of 10, 20 and 30% of the resonance mass is also considered, and the sensitivities obtained are similar to those achieved in the narrow width case. This is the first search at the CERN LHC for the single production of a B quark through its fully hadronic decay channel, and the first study considering finite resonance widths of the B quark.
Sirunyan AM, Tumasyan A, Adam W, et al., 2018, Search for excited quarks of light and heavy flavor in gamma plus jet final states in proton-proton collisions at root s=13 TeV, PHYSICS LETTERS B, Vol: 781, Pages: 390-411, ISSN: 0370-2693
A search for dark matter is conducted in events with large missing transverse momentum and a hadronically decaying, Lorentz-boosted top quark. This study is performed using proton-proton collisions at a center-of-mass energy of 13 TeV, in data recorded by the CMS detector in 2016 at the LHC, corresponding to an integrated luminosity of 36 fb−1. New substructure techniques, including the novel use of energy correlation functions, are utilized to identify the decay products of the top quark. With no significant deviations observed from predictions of the standard model, limits are placed on the production of new heavy bosons coupling to dark matter particles. For a scenario with purely vector-like or purely axial-vector-like flavor changing neutral currents, mediator masses between 0.20 and 1.75 TeV are excluded at 95% confidence level, given a sufficiently small dark matter mass. Scalar resonances decaying into a top quark and a dark matter fermion are excluded for masses below 3.4 TeV, assuming a dark matter mass of 100 GeV.
Sirunyan AM, Tumasyan A, Adam W, et al., 2018, Search for lepton flavour violating decays of the Higgs boson to μτ and eτ in proton-proton collisions at s = 13 $$ \sqrt{s}=13 $$ TeV, The Journal of High Energy Physics, Vol: 2018, ISSN: 1029-8479
A search for lepton flavour violating decays of the Higgs boson in the μτ and eτ decay modes is presented. The search is based on a data set corresponding to an integrated luminosity of 35.9 fb−1 of proton-proton collisions collected with the CMS detector in 2016, at a centre-of-mass energy of 13 TeV. No significant excess over the standard model expectation is observed. The observed (expected) upper limits on the lepton flavour violating branching fractions of the Higgs boson are ℬ(H → μτ) < 0.25% (0.25%) and ℬ(H → eτ) < 0.61% (0.37%), at 95% confidence level. These results are used to derive upper limits on the off-diagonal μτ and eτ Yukawa couplings |Yμτ|2+|Yτμ|2−−−−−−−−−−−√<1.43×10−3 and |Yeτ|2+|Yτe|2−−−−−−−−−−−√<2.26×10−3 at 95% confidence level. The limits on the lepton flavour violating branching fractions of the Higgs boson and on the associated Yukawa couplings are the most stringent to date.
Sirunyan AM, Collaboration CMS, Tumasyan A, et al., 2018, Measurement of b hadron lifetimes in pp collisions at root s=8TeV, European Physical Journal C: Particles and Fields, Vol: 78, ISSN: 1434-6044
Measurements are presented of the lifetimes of the B0, B0s, Λ0b, and B+c hadrons using the decay channels B0→J/ψK∗(892)0, B0→J/ψK0S, B0s→J/ψπ+π−, B0s→J/ψϕ(1020), Λ0b→J/ψΛ0, and B+c→J/ψπ+. The data sample, corresponding to an integrated luminosity of 19.7fb-1, was collected by the CMS detector at the LHC in proton–proton collisions at s√=8TeV. The B0 lifetime is measured to be 453.0±1.6(stat)±1.8(syst)μm in J/ψK∗(892)0and 457.8±2.7(stat)±2.8(syst)μm in J/ψK0S, which results in a combined measurement of cτB0=454.1±1.4(stat)±1.7(syst)μm. The effective lifetime of the B0s meson is measured in two decay modes, with contributions from different amounts of the heavy and light eigenstates. This results in two different measured lifetimes: cτB0s→J/ψπ+π−=502.7±10.2(stat)±3.4(syst)μm and cτB0s→J/ψϕ(1020)=443.9±2.0(stat)±1.5(syst)μm. The Λ0b lifetime is found to be 442.9±8.2(stat)±2.8(syst)μm. The precision from each of these channels is as good as or better than previous measurements. The B+c lifetime, measured with respect to the B+ to reduce the systematic uncertainty, is 162.3±7.8(stat)±4.2(syst)±0.1(τB+)μm. All results are in agreement with current world-average values.
Sirunyan AM, Collaboration CMS, Tumasyan A, et al., 2018, Search for heavy neutral leptons in events with three charged leptons in proton-proton collisions at root s=13 TeV, Physical Review Letters, Vol: 120, ISSN: 0031-9007
A search for a heavy neutral lepton N of Majorana nature decaying into a W boson and a charged lepton is performed using the CMS detector at the LHC. The targeted signature consists of three prompt charged leptons in any flavor combination of electrons and muons. The data were collected in proton-proton collisions at a center-of-mass energy of 13 TeV, with an integrated luminosity of 35.9 fb−1. The search is performed in the N mass range between 1 GeV and 1.2 TeV. The data are found to be consistent with the expected standard model background. Upper limits are set on the values of |VeN|2 and |VμN|2, where VℓN is the matrix element describing the mixing of N with the standard model neutrino of flavor ℓ. These are the first direct limits for N masses above 500 GeV and the first limits obtained at a hadron collider for N masses below 40 GeV.
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