Publications
1150 results found
Khachatryan V, Sirunyan AM, Tumasyan A, et al., 2016, Measurement of electroweak production of a W boson and two forward jets in proton-proton collisions at root s=8 TeV, Journal of High Energy Physics, Vol: 2016, ISSN: 1029-8479
A measurement is presented of the cross section for the electroweak production of a W boson in association with two jets in proton-proton collisions at a center-of-mass energy of 8 TeV. The data set was collected with the CMS detector and corresponds to an integrated luminosity of 19.3 fb−1. The measured fiducial cross section for W bosons decaying to electrons or muons and for pTj1> 60 GeV, pTj2> 50 GeV, |ηj| < 4.7, and mjj> 1000 GeV is 0.42 ± 0.04 (stat) ± 0.09 (syst) ± 0.01 (lumi) pb. This result is consistent with the standard model leading-order prediction of 0.50 ± 0.02 (scale) ± 0.02 (PDF) pb obtained with MadGraph5_amc@nlo 2.1 interfaced to pythia 6.4. This is the first cross section measurement for this process.
Virdee TS, 2016, The long journey to the Higgs boson and beyond at the LHC: Emphasis on CMS, INTERNATIONAL JOURNAL OF MODERN PHYSICS A, Vol: 31, ISSN: 0217-751X
Ruiz Vargas JC, Khachatryan V, Sirunyan AM, et al., 2016, Decomposing transverse momentum balance contributions for quenched jets in PbPb collisions at root s(NN)=2.76 TeV, The Journal of High Energy Physics, Vol: 2016, ISSN: 1029-8479
Interactions between jets and the quark-gluon plasma produced in heavy ion collisions are studied via the angular distributions of summed charged-particle transverse momenta (pT) with respect to both the leading and subleading jet axes in high-pT dijet events. The contributions of charged particles in different momentum ranges to the overall event pT balance are decomposed into short-range jet peaks and a long-range azimuthal asymmetry in charged-particle pT. The results for PbPb collisions are compared to those in pp collisions using data collected in 2011 and 2013, at collision energy sNN−−−−√=2.76sNN=2.76 TeV with integrated luminosities of 166 μb−1 and 5.3 pb−1, respectively, by the CMS experiment at the LHC. Measurements are presented as functions of PbPb collision centrality, charged-particle pT, relative azimuth, and radial distance from the jet axis for balanced and unbalanced dijets.
Khachatryan V, Sirunyan AM, Tumasyan A, et al., 2016, Observation of the decay B+ → ψ(2S)ϕ(1020)K+ in pp collisions at √s = 8TeV, Physics Letters B, Vol: 764, Pages: 66-86, ISSN: 0370-2693
ThedecayB+→ψ(2S)φ(1020)K+isobservedforthefirsttimeusingdatacollectedfromppcollisionsat√s=8TeV bytheCMSexperimentattheLHC,correspondingtoanintegratedluminosityof19.6 fb−1.Thebranchingfractionofthisdecayismeasured,usingthemodeB+→ψ(2S)K+asnormalization,tobe(4.0±0.4(stat)±0.6(syst)±0.2(B))×10−6,wherethethirduncertaintyisfromthemeasuredbranchingfractionofthenormalizationchannel.
Khachatryan V, Sirunyan AM, Tumasyan A, et al., 2016, Measurement of the ZZ production cross section and Z -> l(+)l(-)l '(+)l '(-) branching fraction in pp collisions at root s=13TeV, Physics Letters B, Vol: 763, Pages: 280-303, ISSN: 0370-2693
Four-lepton production in proton–proton collisions, pp → (Z/γ ∗)(Z/γ ∗) → +−+−, where , = eor μ, is studied at a center-of-mass energy of 13 TeV with the CMS detector at the LHC. The data samplecorresponds to an integrated luminosity of 2.6 fb−1. The ZZ production cross section, σ(pp → ZZ) =14.6+1.9−1.8 (stat) +0.5−0.3 (syst)±0.2 (theo)±0.4 (lumi) pb, is measured for events with two opposite-sign, same-flavor lepton pairs produced in the mass region 60 < m+− ,m+− < 120 GeV. The Z boson branchingfraction to four leptons is measured to be B(Z → +−+−) = 4.9+0.8−0.7 (stat)+0.3−0.2 (syst)+0.2−0.1 (theo) ±0.1 (lumi)×10−6 for the four-lepton invariant mass in the range 80 < m+−+− < 100 GeV and dileptonmass m+− > 4 GeV for all opposite-sign, same-flavor lepton pairs. The results are in agreement withstandard model predictions.
Khachatryan V, Sirunyan AM, Tumasyan A, et al., 2016, Phenomenological MSSM interpretation of CMS searches in pp collisions at s√=7 and 8 TeV, Journal of High Energy Physics, Vol: 2016, ISSN: 1029-8479
Searches for new physics by the CMS collaboration are interpreted in the framework of the phenomenological minimal supersymmetric standard model (pMSSM). The data samples used in this study were collected at s√=7 and 8 TeV and have integrated luminosities of 5.0 fb−1 and 19.5 fb−1, respectively. A global Bayesian analysis is performed, incorporating results from a broad range of CMS supersymmetry searches, as well as constraints from other experiments. Because the pMSSM incorporates several well-motivated assumptions that reduce the 120 parameters of the MSSM to just 19 parameters defined at the electroweak scale, it is possible to assess the results of the study in a relatively straightforward way. Approximately half of the model points in a potentially accessible subspace of the pMSSM are excluded, including all pMSSM model points with a gluino mass below 500 GeV, as well as models with a squark mass less than 300 GeV. Models with chargino and neutralino masses below 200 GeV are disfavored, but no mass range of model points can be ruled out based on the analyses considered. The nonexcluded regions in the pMSSM parameter space are characterized in terms of physical processes and key observables, and implications for future searches are discussed.
Khachatryan V, Sirunyan AM, Tumasyan A, et al., 2016, Measurement of the integrated and differential t(t)over-bar production cross sections for high-p(T) top quarks in pp collisions at root s=8 TeV, Physical Review D, Vol: 94, ISSN: 1550-7998
The cross section for pair production of top quarks (t¯t) with high transverse momenta is measured in pp collisions, collected with the CMS detector at the LHC with ffiffi s p ¼ 8 TeV in data corresponding to anintegrated luminosity of 19.7 fb−1. The measurement is performed using lepton þ jets events, where one top quark decays semileptonically, while the second top quark decays to a hadronic final state. The hadronic decay is reconstructed as a single, large-radius jet, and identified as a top quark candidate using jet substructure techniques. The integrated cross section and the differential cross sections as a function of top quark pT and rapidity are measured at particle level within a fiducial region related to the detector-level requirements and at parton level. The particle-level integrated cross section is found to be σt¯t ¼ 0.499 0.035ðstat þ systÞ 0.095ðtheoÞ 0.013ðlumiÞ pb for top quark pT > 400 GeV. The parton-level measurement is σt¯t ¼ 1.44 0.10ðstat þ systÞ 0.29ðtheoÞ 0.04ðlumiÞ pb. The integrated and differential cross section results are compared to predictions from several event generators.
Khachatryan V, Sirunyan AM, Tumasyan A, et al., 2016, Measurement of the W boson helicity fractions in the decays of top quark pairs to lepton plus jets final states produced in pp collisions at root s=8 TeV, Physics Letters B, Vol: 762, Pages: 512-534, ISSN: 0370-2693
The W boson helicity fractions from top quark decays in tt events are measured using data from proton–proton collisions at a centre-of-mass energy of 8 TeV. The data were collected in 2012 with the CMSdetector at the LHC, corresponding to an integrated luminosity of 19.8 fb−1. Events are reconstructedwith either one muon or one electron, along with four jets in the final state, with two of the jetsbeing identified as originating from b quarks. The measured helicity fractions from both channels arecombined, yielding F0 = 0.681 ± 0.012 (stat) ± 0.023 (syst), FL = 0.323 ± 0.008 (stat) ± 0.014 (syst), andFR = −0.004 ± 0.005 (stat) ± 0.014 (syst) for the longitudinal, left-, and right-handed components of thehelicity, respectively. These measurements of the W boson helicity fractions are the most accurate to dateand they agree with the predictions from the standard model.
Khachatryan V, Sirunyan AM, Tumasyan A, et al., 2016, Search for lepton flavour violating decays of the Higgs boson to e tau and e mu in proton-proton collisions at root s=8 TeV, Physics Letters B, Vol: 763, Pages: 472-500, ISSN: 0370-2693
A direct search for lepton flavour violating decays of the Higgs boson (H) in the H → eτ and H → eμchannels is described. The data sample used in the search was collected in proton–proton collisionsat √s = 8 TeV with the CMS detector at the LHC and corresponds to an integrated luminosity of19.7 fb−1. No evidence is found for lepton flavour violating decays in either final state. Upper limitson the branching fractions, B(H → eτ ) < 0.69% and B(H → eμ) < 0.035%, are set at the 95% confidencelevel. The constraint set on B(H → eτ ) is an order of magnitude more stringent than the existing indirectlimits. The limits are used to constrain the corresponding flavour violating Yukawa couplings, absent inthe standard model
Khachatryan V, Sirunyan AM, Tumasyan A, et al., 2016, Search for new physics with the M-T2 variable in all-jets final states produced in pp collisions at root √s=13 Tev, Journal of High Energy Physics, Vol: 6, ISSN: 1126-6708
A search for new physics is performed using events that contain one or more jets, no isolated leptons, and a large transverse momentum imbalance, as measured through the MT2 variable, which is an extension of the transverse mass in events with two invisible particles. The results are based on a sample of proton-proton collisions collected at a center-of-mass energy of 13 TeV with the CMS detector at the LHC, and that corresponds to an integrated luminosity of 2.3 fb−1. The observed event yields in the data are consistent with predictions for the standard model backgrounds. The results are interpreted using simplified models of supersymmetry and are expressed in terms of limits on the masses of potential new colored particles. Assuming that the lightest neutralino is stable and has a mass less than about 500 GeV, gluino masses up to 1550-1750 GeV are excluded at 95% confidence level, depending on the gluino decay mechanism. For the scenario of direct production of squark-antisquark pairs, top squarks with masses up to 800 GeV are excluded, assuming a 100% branching fraction for the decay to a top quark and neutralino. Similarly, bottom squark masses are excluded up to 880 GeV, and masses of light-flavor squarks are excluded up to 600-1260 GeV, depending on the degree of degeneracy of the squark masses.
Khachatryan V, Sirunyan AM, Tumasyan A, et al., 2016, Measurement of dijet azimuthal decorrelation in pp collisions at root s=8 TeV, European Physical Journal C, Vol: 76, ISSN: 1434-6052
A measurement of the decorrelation of azimuthal angles between the two jets with the largest transverse momenta is presented for seven regions of leading jet transverse momentum up to 2.2 TeVTeV . The analysis is based on the proton-proton collision data collected with the CMS experiment at a centre-of-mass energy of 8 TeVTeV corresponding to an integrated luminosity of 19.7 fb−1fb−1 . The dijet azimuthal decorrelation is caused by the radiation of additional jets and probes the dynamics of multijet production. The results are compared to fixed-order predictions of perturbative quantum chromodynamics (QCD), and to simulations using Monte Carlo event generators that include parton showers, hadronization, and multiparton interactions. Event generators with only two outgoing high transverse momentum partons fail to describe the measurement, even when supplemented with next-to-leading-order QCD corrections and parton showers. Much better agreement is achieved when at least three outgoing partons are complemented through either next-to-leading-order predictions or parton showers. This observation emphasizes the need to improve predictions for multijet production.
Khachatryan V, Sirunyan AM, Tumasyan A, et al., 2016, Search for two Higgs bosons in final states containing two photons and two bottom quarks in proton-proton collisions at 8 TeV, Physical Review D, Vol: 94, ISSN: 2470-0029
A search is presented for the production of two Higgs bosons in final states containing two photons and two bottom quarks. Both resonant and nonresonant hypotheses are investigated. The analyzed data correspond to an integrated luminosity of 19.7 fb−1 of proton-proton collisions at s√=8 TeV collected with the CMS detector. Good agreement is observed between data and predictions of the standard model (SM). Upper limits are set at 95% confidence level on the production cross section of new particles and compared to the prediction for the existence of a warped extra dimension. When the decay to two Higgs bosons is kinematically allowed, assuming a mass scale ΛR=1 TeV for the model, the data exclude a radion scalar at masses below 980 GeV. The first Kaluza-Klein excitation mode of the graviton in the RS1 Randall-Sundrum model is excluded for masses between 325 and 450 GeV. An upper limit of 0.71 pb is set on the nonresonant two-Higgs-boson cross section in the SM-like hypothesis. Limits are also derived on nonresonant production assuming anomalous Higgs-boson couplings.
Khachatryan V, Sirunyan AM, Tumasyan A, et al., 2016, Search for Higgs boson off-shell production in proton-proton collisions at 7 and 8 TeV and derivation of constraints on its total decay width, Journal of High Energy Physics, Vol: 51, Pages: 1-44, ISSN: 1029-8479
A search is presented for the Higgs boson off-shell production in gluon fusionand vector boson fusion processes with the Higgs boson decaying into a W+W− pair and theW bosons decaying leptonically. The data observed in this analysis are used to constrainthe Higgs boson total decay width. The analysis is based on the data collected by the CMSexperiment at the LHC, corresponding to integrated luminosities of 4.9 fb−1 at a centre-ofmassenergy of 7 TeV and 19.4 fb−1 at 8 TeV, respectively. An observed (expected) upperlimit on the off-shell Higgs boson event yield normalised to the standard model predictionof 2.4 (6.2) is obtained at the 95% CL for the gluon fusion process and of 19.3 (34.4) forthe vector boson fusion process. Observed and expected limits on the total width of 26and 66 MeV are found, respectively, at the 95% confidence level (CL). These limits arecombined with the previous result in the ZZ channel leading to observed and expected 95%CL upper limits on the width of 13 and 26 MeV, respectively.
The CMSC, Khachatryan V, Sirunyan AM, et al., 2016, Search for Higgs boson off-shell production in proton-proton collisions at 7 and 8 TeV and derivation of constraints on its total decay width, Journal of High Energy Physics, Vol: 2016, ISSN: 1126-6708
A search is presented for the Higgs boson off-shell production in gluon fusion and vector boson fusion processes with the Higgs boson decaying into a W+W− pair and the W bosons decaying leptonically. The data observed in this analysis are used to constrain the Higgs boson total decay width. The analysis is based on the data collected by the CMS experiment at the LHC, corresponding to integrated luminosities of 4.9 fb−1 at a centre-of-mass energy of 7 TeV and 19.4 fb−1 at 8 TeV, respectively. An observed (expected) upper limit on the off-shell Higgs boson event yield normalised to the standard model prediction of 2.4 (6.2) is obtained at the 95% CL for the gluon fusion process and of 19.3 (34.4) for the vector boson fusion process. Observed and expected limits on the total width of 26 and 66 MeV are found, respectively, at the 95% confidence level (CL). These limits are combined with the previous result in the ZZ channel leading to observed
Khachatryan V, Sirunyan AM, Tumasyan A, et al., 2016, Measurement of the differential cross sections for top quark pair production as a function of kinematic event variables in pp collisions at root s=7 and 8 TeV, Physical Review D, Vol: 94, ISSN: 1550-7998
Measurements are reported of the normalized differential cross sections for top quark pair production with respect to four kinematic event variables: the missing transverse energy; the scalar sum of the jet transverse momentum (pT); the scalar sum of the pT of all objects in the event; and the pT of leptonically decaying W bosons from top quark decays. The data sample, collected using the CMS detector at the LHC, consists of 5.0 fb−1 of proton-proton collisions at s√=7 TeV and 19.7 fb−1 at s√=8 TeV. Top quark pair events containing one electron or muon are selected. The results are presented after correcting for detector effects to allow direct comparison with theoretical predictions. No significant deviations from the predictions of several standard model event simulation generators are observed.
Khachatryan V, Sirunyan AM, Tumasyan A, et al., 2016, Search for s channel single top quark production in pp collisions at root s=7 and 8 TeV, Journal of High Energy Physics, Vol: 2016, ISSN: 1126-6708
A search is presented for single top quark production in the s channel in proton-proton collisions with the CMS detector at the CERN LHC in decay modes of the top quark containing a muon or an electron in the final state. The signal is extracted through a maximum-likelihood fit to the distribution of a multivariate discriminant defined using boosted decision trees to separate the expected signal contribution from background processes. The analysis uses data collected at centre-of-mass energies of 7 and 8 TeV and corresponding to integrated luminosities of 5.1 and 19.7 fb−1, respectively. The measured cross sections of 7.1 ± 8.1 pb (at 7 TeV) and 13.4 ± 7.3 pb (at 8 TeV) result in a best fit value of 2.0 ± 0.9 for the combined ratio of the measured and expected values. The signal significance is 2.5 standard deviations, and the upper limit on the rate relative to the standard model expectation is 4.7 at 95% confidence level.
Virdee TS, 2016, Beyond the standard model of particle physics., Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, Vol: 374, ISSN: 1364-503X
The Large Hadron Collider (LHC) at CERN and its experiments were conceived to tackle open questions in particle physics. The mechanism of the generation of mass of fundamental particles has been elucidated with the discovery of the Higgs boson. It is clear that the standard model is not the final theory. The open questions still awaiting clues or answers, from the LHC and other experiments, include: What is the composition of dark matter and of dark energy? Why is there more matter than anti-matter? Are there more space dimensions than the familiar three? What is the path to the unification of all the fundamental forces? This talk will discuss the status of, and prospects for, the search for new particles, symmetries and forces in order to address the open questions.This article is part of the themed issue 'Unifying physics and technology in light of Maxwell's equations'.
The CMSC, Khachatryan V, Sirunyan AM, et al., 2016, Azimuthal decorrelation of jets widely separated in rapidity in pp collisions at √s = 7 TeV, Journal of High Energy Physics, Vol: 2016, ISSN: 1126-6708
The decorrelation in the azimuthal angle between the most forward and the most backward jets (Mueller-Navelet jets) is measured in data collected in pp collisions with the CMS detector at the LHC at s=7 TeV. The measurement is presented in the form of distributions of azimuthal-angle differences, Δϕ, between the Mueller-Navelet jets, the average cosines of (π − Δϕ), 2(π − Δϕ), and 3(π − Δϕ), and ratios of these cosines. The jets are required to have transverse momenta, pT, in excess of 35 GeV and rapidities, |y|, of less than 4.7. The results are presented as a function of the rapidity separation, Δy, between the Mueller-Navelet jets, reaching Δy up to 9.4 for the first time. The results are compared to predictions of various Monte Carlo event generators and to analytical predictions based on the DGLAP and BFKL parton evolution schemes.[Figure not available: see fulltext.]
Khachatryan VY, Sirunyan AM, Tumasyan A, et al., 2016, Measurement of the differential cross section and charge asymmetry for inclusive pp -> W-+/- + X production at root s=8 TeV, European Physical Journal C, Vol: 76, ISSN: 1434-6052
The differential cross section and charge asymmetry for inclusive pp→W±+X→μ±ν+Xpp→W±+X→μ±ν+X production at s√=8TeVs=8TeV are measured as a function of muon pseudorapidity. The data sample corresponds to an integrated luminosity of 18.8 fb−1fb−1 recorded with the CMS detector at the LHC. These results provide important constraints on the parton distribution functions of the proton in the range of the Bjorken scaling variable x from 10−310−3 to 10−110−1 .
The CMSC, Khachatryan V, Sirunyan AM, et al., 2016, Evidence for exclusive γγ → W<sup>+</sup> W<sup>−</sup> production and constraints on anomalous quartic gauge couplings in pp collisions at √s = 7 and 8 TeV, Journal of High Energy Physics, Vol: 2016, ISSN: 1126-6708
A search for exclusive or quasi-exclusive γγ → W+W− production, via pp → p(*)W+W−p(*) → p(*)μ±e∓p(*) at √s = 8 TeV, is reported using data corresponding to an integrated luminosity of 19.7 fb−1. Events are selected by requiring the presence of an electron-muon pair with large transverse momentum pT(μ±e∓) > 30 GeV, and no associated charged particles detected from the same vertex. The 8 TeV results are combined with the previous 7 TeV results (obtained for 5.05 fb−1 of data). In the signal region, 13 (2) events are observed over an expected background of 3.9 ± 0.6 (0.84 ± 0.15) events for 8 (7) TeV, resulting in a combined excess of 3.4σ over the background-only hypothesis. The observed yields and kinematic distributions are compatible with the standard model prediction for exclusive and quasi-exclusive γγ → W+W− production. Upper limits on the anomalous quartic gauge coupling operators a0,CW (dimension-6) and fM0,1,2,3 (dimension-8), the most stringent to date, are derived from the measured dilepton transverse momentum spectrum.
Khachatryan V, Sirunyan AM, Tumasyan A, et al., 2016, Search for supersymmetry in pp collisions at root s=13 TeV in the single-lepton final state using the sum of masses of large-radius jets, Journal of High Energy Physics, Vol: 2016, ISSN: 1126-6708
Khachatryan V, Sirunyan AM, Tumasyan A, et al., 2016, Search for direct pair production of supersymmetric top quarks decaying to all-hadronic final states in pp collisions at root s=8 TeV, European Physical Journal C: Particles and Fields, Vol: 76, ISSN: 1434-6044
Results are reported from a search for the pairproduction of top squarks, the supersymmetric partners oftop quarks, in final states with jets and missing transversemomentum. The data sample used in this search was collectedby the CMS detector and corresponds to an integrated luminosityof 18.9 fb−1 of proton-proton collisions at a centreof-massenergy of 8 TeV produced by the LHC. The searchfeatures novel background suppression and prediction methods,including a dedicated top quark pair reconstruction algorithm.The data are found to be in agreement with the predictedbackgrounds. Exclusion limits are set in simplifiedsupersymmetry models with the top squark decaying to jetsand an undetected neutralino, either through a top quark orthrough a bottom quark and chargino. Models with the topsquark decaying via a top quark are excluded for top squarkmasses up to 755 GeV in the case of neutralino masses below200 GeV. For decays via a chargino, top squark masses upto 620 GeV are excluded, depending on the masses of thechargino and neutralino.
Khachatryan V, Sirunyan AM, Tumasyan A, et al., 2016, Measurement of the double-differential inclusive jet cross section in proton–proton collisions at s√=13TeV, EUROPEAN PHYSICAL JOURNAL C, Vol: 76, ISSN: 1434-6044
A measurement of the double-differential inclusive jet cross section as a function of jet transverse momentum pT and absolute jet rapidity |y| is presented. The analysis is based on proton–proton collisions collected by the CMS experiment at the LHC at a centre-of-mass energy of 13TeV. The data samples correspond to integrated luminosities of 71 and 44pb-1 for |y|<3 and 3.2<|y|<4.7, respectively. Jets are reconstructed with the anti-kt clustering algorithm for two jet sizes, R, of 0.7 and 0.4, in a phase space region covering jet pT up to 2TeV and jet rapidity up to |y| = 4.7. Predictions of perturbative quantum chromodynamics at next-to-leading order precision, complemented with electroweak and nonperturbative corrections, are used to compute the absolute scale and the shape of the inclusive jet cross section. The cross section difference in R, when going to a smaller jet size of 0.4, is best described by Monte Carlo event generators with next-to-leading order predictions matched to parton showering, hadronisation, and multiparton interactions. In the phase space accessible with the new data, this measurement provides a first indication that jet physics is as well understood at s√=13TeV as at smaller centre-of-mass energies.
Aad G, Abbott B, Abdallah J, et al., 2016, Measurements of the Higgs boson production and decay rates and constraints on its couplings from a combined ATLAS and CMS analysis of the LHC pp collision data at √s = 7 and 8 TeV, Journal of High Energy Physics, Vol: 2016, ISSN: 1126-6708
Combined ATLAS and CMS measurements of the Higgs boson production and decay rates, as well as constraints on its couplings to vector bosons and fermions, are presented. The combination is based on the analysis of five production processes, namely gluon fusion, vector boson fusion, and associated production with a W or a Z boson or a pair of top quarks, and of the six decay modes H → ZZ, W W, γγ, ττ, bb, and μμ. All results are reported assuming a value of 125.09 GeV for the Higgs boson mass, the result of the combined measurement by the ATLAS and CMS experiments. The analysis uses the CERN LHC proton-proton collision data recorded by the ATLAS and CMS experiments in 2011 and 2012, corresponding to integrated luminosities per experiment of approximately 5 fb−1 at √s = 7 TeV and 20 fb−1 at √s = 8 TeV. The Higgs boson production and decay rates measured by the two experiments are combined within the context of three generic parameterisations: two based on cross sections and branching fractions, and one on ratios of coupling modifiers. Several interpretations of the measurements with more model-dependent parameterisations are also given. The combined signal yield relative to the Standard Model prediction is measured to be 1.09 ± 0.11. The combined measurements lead to observed significances for the vector boson fusion production process and for the H → ττ decay of 5.4 and 5.5 standard deviations, respectively. The data are consistent with the Standard Model predictions for all parameterisations considered.
Khachatryan V, Sirunyan AM, Tumasyan A, et al., 2016, Search for new physics in same-sign dilepton events in proton-proton collisions at √s = 13 TeV, European Physical Journal C, Vol: 76, ISSN: 1434-6052
A search for new physics is performed using events with two isolated same-sign leptons, two or more jets, and missing transverse momentum. The results are based on a sample of proton–proton collisions at a center-of-mass energy of 13TeV recorded with the CMS detector at the LHC, corresponding to an integrated luminosity of 2.3 fb1. Multiple search regions are defined by classifying events in terms of missing transverse momentum, the scalar sum of jet transverse momenta, the transverse mass associated with a W boson candidate, the number of jets, the number of b quark jets, and the transverse momenta of the leptons in the event. The analysis is sensitive to a wide variety of possible signals beyond the standard model. No excess above the standard model background expectation is observed. Constraints are set on various supersymmetric models, with gluinos and bottom squarks excluded for masses up to 1300 and 680GeV, respectively, at the 95 % confidence level. Upper limits on the cross sections for the production of two top quark-antiquark pairs (119fb) and two same-sign top quarks (1.7pb) are also obtained. Selection efficiencies and model independent limits are provided to allow further interpretations of the results.
The CMSC, Khachatryan V, Sirunyan AM, et al., 2016, Measurement of the tt¯ production cross section in the eμ channel in proton-proton collisions at √s=7 and 8 TeV, Journal of High Energy Physics, Vol: 2016, ISSN: 1126-6708
© 2016, The Author(s).Abstract: The inclusive cross section for top quark pair production is measured in proton-proton collisions at s=7 and 8 TeV, corresponding to 5.0 and 19.7 fb−1, respectively, with the CMS experiment at the LHC. The cross sections are measured in the electron-muon channel using a binned likelihood fit to multi-differential final state distributions related to identified b quark jets and other jets in the event. The measured cross section values are 173.6 ± 2.1(stat)− 4.0+ 4.5(syst) ± 3.8(lumi)pb at s=7 TeV, and 244.9 ± 1.4(stat)− 5.5+ 6.3(syst) ± 6.4(lumi)pb at s=8 TeV, in good agreement with QCD calculations at next-to-next-to-leading-order accuracy. The ratio of the cross sections measured at 7 and 8 TeV is determined, as well as cross sections in the fiducial regions defined by the acceptance requirements on the two charged leptons in the final state. The cross section results are used to determine the top quark pole mass via the dependence of the theoretically predicted cross section on the mass, giving a best result of 173. 8− 1.8+ 1.7 GeV. The data at s=8 TeV are also used to set limits, for two neutralino mass values, on the pair production of supersymmetric partners of the top quark with masses close to the top quark mass.[Figure not available: see fulltext.]
Khachatryan V, Sirunyan AM, Tumasyan A, et al., 2016, ϒ(nS) polarizations versus particle multiplicity in pp collisions at s=7 TeV, Physics Letters B, Vol: 761, Pages: 31-52, ISSN: 0370-2693
The polarizations of the ϒ(1S), ϒ(2S), and ϒ(3S) mesons are measured as a function of the charged particle multiplicity in proton–proton collisions at s=7 TeV. The measurements are performed with a dimuon data sample collected in 2011 by the CMS experiment, corresponding to an integrated luminosity of 4.9 fb−1. The results are extracted from the dimuon decay angular distributions, in two ranges of ϒ(nS) transverse momentum (10–15 and 15–35 GeV), and in the rapidity interval |y|>1.2. The results do not show significant changes from low- to high-multiplicity pp collisions, although large uncertainties preclude definite statements in the ϒ(2S) and ϒ(3S) cases.
Khachatryan V, Sirunyan AM, Tumasyan A, et al., 2016, Search for Resonant Production of High-Mass Photon Pairs in Proton-Proton Collisions at √s=8 and 13 TeV, Physical Review Letters, Vol: 117, ISSN: 1079-7114
A search for the resonant production of high-mass photon pairs is presented. The analysis is based on samples of proton-proton collision data collected by the CMS experiment at center-of-mass energies of 8 and 13 TeV, corresponding to integrated luminosities of 19.7 and 3.3 fb−1, respectively. The interpretation of the search results focuses on spin-0 and spin-2 resonances with masses between 0.5 and 4 TeV and with widths, relative to the mass, between 1.4×10−4 and 5.6×10−2. Limits are set on scalar resonances produced through gluon-gluon fusion, and on Randall-Sundrum gravitons. A modest excess of events compatible with a narrow resonance with a mass of about 750 GeV is observed. The local significance of the excess is approximately 3.4 standard deviations. The significance is reduced to 1.6 standard deviations once the effect of searching under multiple signal hypotheses is considered. More data are required to determine the origin of this excess.
Khachatryan V, Sirunyan AM, Tumasyan A, et al., 2016, Measurement of the W+W- cross section in pp collisions at root s=8 TeV and limits on anomalous gauge couplings, EUROPEAN PHYSICAL JOURNAL C, Vol: 76, ISSN: 1434-6044
A measurement of the W boson pair production cross section in proton-proton collisions at s√=8 TeV is presented. The data collected with the CMS detector at the LHC correspond to an integrated luminosity of 19.4fb-1. The W+W− candidates are selected from events with two charged leptons, electrons or muons, and large missing transverse energy. The measured W+W− cross section is 60.1±0.9(stat)±3.2(exp)±3.1(theo)±1.6(lumi)\,pb=60.1±4.8\,pb, consistent with the standard model prediction. The W+W− cross sections are also measured in two different fiducial phase space regions. The normalized differential cross section is measured as a function of kinematic variables of the final-state charged leptons and compared with several perturbative QCD predictions. Limits on anomalous gauge couplings associated with dimension-six operators are also given in the framework of an effective field theory. The corresponding 95 % confidence level intervals are −5.7<cWWW/Λ2<5.9TeV−2, −11.4<cW/Λ2<5.4TeV−2, −29.2<cB/Λ2<23.9TeV−2, in the HISZ basis.
Khachatryan V, Sirunyan AM, Tumasyan A, et al., 2016, Search for Narrow Resonances in Dijet Final States at √s=8 TeV with the Novel CMS Technique of Data Scouting, Physical Review Letters, Vol: 117, ISSN: 1079-7114
A search for narrow resonances decaying into dijet final states is performed on data from proton-proton collisions at a center-of-mass energy of 8 TeV, corresponding to an integrated luminosity of 18.8 fb−1. The data were collected with the CMS detector using a novel technique called data scouting, in which the information associated with these selected events is much reduced, permitting collection of larger data samples. This technique enables CMS to record events containing jets at a rate of 1 kHz, by collecting the data from the high-level-trigger system. In this way, the sensitivity to low-mass resonances is increased significantly, allowing previously inaccessible couplings of new resonances to quarks and gluons to be probed. The resulting dijet mass distribution yields no evidence of narrow resonances. Upper limits are presented on the resonance cross sections as a function of mass, and compared with a variety of models predicting narrow resonances. The limits are translated into upper limits on the coupling of a leptophobic resonance Z′B to quarks, improving on the results obtained by previous experiments for the mass range from 500 to 800 GeV.
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