796 results found
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
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 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 .
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.
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 ATLASC, Aad G, Abbott B, 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.
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.
Khachatryan V, Sirunyan AM, Tumasyan A, et al., 2016, Measurement of the Z gamma -> nu(nu)over-bar gamma production cross section in pp collisions at root s=8 TeV and limits on anomalous ZZ gamma and Z gamma gamma trilinear gauge boson couplings, Physics Letters B, Vol: 760, Pages: 448-468, ISSN: 0370-2693
Khachatryan V, Sirunyan AM, Tumasyan A, et al., 2016, Measurements of tt charge asymmetry using dilepton final states in ppcollisions at √s=8 TeV, Physics Letters B, Vol: 760, Pages: 365-386, ISSN: 0370-2693
The charge asymmetry in View the MathML source events is measured using dilepton final states produced in pp collisions at the LHC at View the MathML source. The data sample, collected with the CMS detector, corresponds to an integrated luminosity of View the MathML source. The measurements are performed using events with two oppositely charged leptons (electrons or muons) and two or more jets, where at least one of the jets is identified as originating from a bottom quark. The charge asymmetry is measured from differences in kinematic distributions, unfolded to the parton level, of positively and negatively charged top quarks and leptons. The View the MathML source and leptonic inclusive charge asymmetries are found to be View the MathML source and View the MathML source, respectively. These results, as well as charge asymmetry measurements made as a function of the invariant mass, rapidity, and transverse momentum of the View the MathML source system, are in agreement with predictions of the standard model.
Khachatryan V, Sirunyan AM, Tumasyan A, et al., 2016, Measurement of tt¯ production with additional jet activity, including b quark jets, in the dilepton decay channel using pp collisions at √s=8TeV, European Physical Journal C, Vol: 76, ISSN: 1434-6052
Jet multiplicity distributions in top quark pair (tt¯tt¯) events are measured in pp collisions at a centre-of-mass energy of 8 TeV with the CMS detector at the LHC using a data set corresponding to an integrated luminosity of 19.7fb-1fb-1. The measurement is performed in the dilepton decay channels (e+e−e+e−, μ+μ−μ+μ−, and e±μ∓e±μ∓). The absolute and normalized differential cross sections for tt¯tt¯ production are measured as a function of the jet multiplicity in the event for different jet transverse momentum thresholds and the kinematic properties of the leading additional jets. The differential tt¯btt¯b and tt¯bb¯¯¯tt¯bb¯ cross sections are presented for the first time as a function of the kinematic properties of the leading additional bb jets. Furthermore, the fraction of events without additional jets above a threshold is measured as a function of the transverse momenta of the leading additional jets and the scalar sum of the transverse momenta of all additional jets. The data are compared and found to be consistent with predictions from several perturbative quantum chromodynamics event generators and a next-to-leading order calculation.
Khachatryan V, Sirunyan AM, Tumasyan A, et al., 2016, Search for direct pair production of scalar top quarks in the single- and dilepton channels in proton-proton collisions at root s=8 TeV, Journal of High Energy Physics, Vol: 2016, ISSN: 1029-8479
Results are reported from a search for the top squark t~1, the lighter of the two supersymmetric partners of the top quark. The data sample corresponds to 19.7 fb−1 of proton-proton collisions at s√=8 TeV collected with the CMS detector at the LHC. The search targets t~1→bχ~±1 and t~1→t(∗)χ~01 decay modes, where χ~±1 and χ~01 are the lightest chargino and neutralino, respectively. The reconstructed final state consists of jets, b jets, missing transverse energy, and either one or two leptons. Leading backgrounds are determined from data. No significant excess in data is observed above the expectation from standard model processes. The results exclude a region of the two-dimensional plane of possible t~1 and χ~01 masses. The highest excluded t~1 and χ~01 masses are about 700 GeV and 250 GeV, respectively.
Khachatryan V, Sirunyan AM, Tumasyan A, et al., 2016, Measurement of inclusive jet production and nuclear modifications in pPb collisions at √SNN=5.02TeV, European Physical Journal C, Vol: 76, ISSN: 1434-6052
Inclusive jet production in pPb collisions at a nucleon–nucleon (NN) center-of-mass energy of sNN−−−√=5.02TeVsNN=5.02TeV is studied with the CMS detector at the LHC. A data sample corresponding to an integrated luminosity of 30.1 nb −1−1 is analyzed. The jet transverse momentum spectra are studied in seven pseudorapidity intervals covering the range −2.0<ηCM<1.5−2.0<ηCM<1.5 in the NN center-of-mass frame. The jet production yields at forward and backward pseudorapidity are compared and no significant asymmetry about ηCM=0ηCM=0 is observed in the measured kinematic range. The measurements in the pPb system are compared to reference jet spectra obtained by extrapolation from previous measurements in pp collisions at s√=7TeVs=7TeV . In all pseudorapidity ranges, nuclear modifications in inclusive jet production are found to be small, as predicted by next-to-leading order perturbative QCD calculations that incorporate nuclear effects in the parton distribution functions.
Khachatryan V, Sirunyan AM, Tumasyan A, et al., 2016, Search for heavy resonances decaying to two Higgs bosons in final states containing four b quarks, European Physical Journal C: Particles and Fields, Vol: 76, ISSN: 1124-1861
A search is presented for narrow heavy resonancesX decaying into pairs of Higgs bosons (H) in protonprotoncollisions collected by the CMS experiment at theLHC at √s = 8 TeV. The data correspond to an integratedluminosity of 19.7 fb−1. The search considers HH resonanceswith masses between 1 and 3 TeV, having final states of twob quark pairs. Each Higgs boson is produced with largemomentum, and the hadronization products of the pair ofb quarks can usually be reconstructed as single large jets.The background from multijet and tt events is significantlyreduced by applying requirements related to the flavor of thejet, its mass, and its substructure. The signal would be identi-fied as a peak on top of the dijet invariant mass spectrum of theremaining background events. No evidence is observed forsuch a signal. Upper limits obtained at 95 % confidence levelfor the product of the production cross section and branchingfraction σ (gg → X) B(X → HH → bbbb) range from 10to 1.5 fb for the mass of X from 1.15 to 2.0 TeV, significantlyextending previous searches. For a warped extra dimensiontheory with a mass scaleR = 1 TeV, the data exclude radionscalar masses between 1.15 and 1.55 TeV.
Khachatryan V, Sirunyan AM, Tumasyan A, et al., 2016, Search for the associated production of a Higgs boson with a single top quark in proton-proton collisions at √s=8 TeV, Journal of High Energy Physics, Vol: 2016, ISSN: 1126-6708
This paper presents the search for the production of a Higgs boson in association with a single top quark (tHq), using data collected in proton-proton collisions at a center-of-mass energy of 8 TeV corresponding to an integrated luminosity of 19.7 fb−1. The search exploits a variety of Higgs boson decay modes resulting in final states with photons, bottom quarks, and multiple charged leptons, including tau leptons, and employs a variety of multivariate techniques to maximize sensitivity to the signal. The analysis is optimized for the opposite sign of the Yukawa coupling to that in the standard model, corresponding to a large enhancement of the signal cross section. In the absence of an excess of candidate signal events over the background predictions, 95% confidence level observed (expected) upper limits on anomalous tHq production are set, ranging between 600 (450) fb and 1000 (700) fb depending on the assumed diphoton branching fraction of the Higgs boson. This is the first time that results on anomalous tHq production have been reported.
Khachatryan V, Sirunyan AM, Tumasyan A, et al., 2016, Search for R-parity violating decays of a top squark in proton–proton collisions at s=8 TeV, Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics, Vol: 760, Pages: 178-201, ISSN: 0370-2693
The results of a search for a supersymmetric partner of the top quark (top squark), pair-produced in proton–proton collisions at s=8 TeV, are presented. The search, which focuses on R-parity violating, chargino-mediated decays of the top squark, is performed in final states with low missing transverse momentum, two oppositely charged electrons or muons, and at least five jets. The analysis uses a data sample corresponding to an integrated luminosity of 19.7 fb−1 collected with the CMS detector at the LHC in 2012. The data are found to be in agreement with the standard model expectation, and upper limits are placed on the top squark pair production cross section at 95% confidence level. Assuming a 100% branching fraction for the top squark decay chain, t˜→tχ˜1±,χ˜1±→ℓ±+jj, top squark masses less than 890 (1000) GeV for the electron (muon) channel are excluded for the first time in models with a single nonzero R-parity violating coupling λijk′ (i,j,k≤2), where i,j,k correspond to the three generations.
Khachatryan V, Sirunyan AM, Tumasyan A, et al., 2016, Measurement of the inelastic cross section in proton-lead collisions at √sNN = 5.02 TeV, Physics Letters B, Vol: 759, Pages: 641-662, ISSN: 0370-2693
The inelastic hadronic cross section in proton–lead collisions at a centre-of-mass energy per nucleon pair of 5.02 TeV is measured with the CMS detector at the LHC. The data sample, corresponding to an integrated luminosity of L=12.6±0.4 nb−1, has been collected with an unbiased trigger for inclusive particle production. The cross section is obtained from the measured number of proton–lead collisions with hadronic activity produced in the pseudorapidity ranges 3<η<5 and/or −5<η<−3, corrected for photon-induced contributions, experimental acceptance, and other instrumental effects. The inelastic cross section is measured to be σinel(pPb)=2061±3(stat)±34(syst)±72(lumi) mb. Various Monte Carlo generators, commonly used in heavy ion and cosmic ray physics, are found to reproduce the data within uncertainties. The value of σinel(pPb) is compatible with that expected from the proton–proton cross section at 5.02 TeV scaled up within a simple Glauber approach to account for multiple scatterings in the lead nucleus, indicating that further net nuclear corrections are small.
Khachatryan V, Sirunyan AM, Tumasyan A, et al., 2016, Search for pair-produced vectorlike B quarks in proton-proton collisions at root s=8 TeV, Physical Review D, Vol: 93, ISSN: 1550-7998
A search for the production of a heavy B quark, having electric charge −1/3 and vector couplings to W, Z, and H bosons, is carried out using proton-proton collision data recorded at the CERN LHC by the CMS experiment, corresponding to an integrated luminosity of 19.7 fb−1. The B quark is assumed to be pair produced and to decay in one of three ways: to tW, bZ, or bH. The search is carried out in final states with one, two, and more than two charged leptons, as well as in fully hadronic final states. Each of the channels in the exclusive final-state topologies is designed to be sensitive to specific combinations of the B quark-antiquark pair decays. The observed event yields are found to be consistent with the standard model expectations in all the final states studied. A statistical combination of these results is performed, and upper limits are set on the cross section of the strongly produced B quark-antiquark pairs as a function of the B quark mass. Lower limits on the B quark mass between 740 and 900 GeV are set at a 95% confidence level, depending on the values of the branching fractions of the B quark to tW, bZ, and bH. Overall, these limits are the most stringent to date.
Khachatryan V, Sirunyan AM, Tumasyan A, et al., 2016, Forward-backward asymmetry of Drell-Yan lepton pairs in pp collisions at root s=8 TeV, European Physical Journal C, Vol: 76, ISSN: 1434-6052
A measurement of the forward–backward asymmetry AFBAFB of oppositely charged lepton pairs ( μμμμ and eeee ) produced via Z/γ∗Z/γ∗ boson exchange in pp collisions at s√=8s=8 TeVTeV is presented. The data sample corresponds to an integrated luminosity of 19.7 fb−1fb−1 collected with the CMS detector at the LHC. The measurement of AFBAFB is performed for dilepton masses between 40 GeVGeV and 2 TeVTeV and for dilepton rapidity up to 5. The AFBAFB measurements as a function of dilepton mass and rapidity are compared with the standard model predictions.
Khachatryan V, Sirunyan AM, Tumasyan A, et al., 2016, Search for lepton flavour violating decays of heavy resonances and quantum black holes to an eμ pair in proton–proton collisions at √s = 8 TeV, The European Physical Journal C, Vol: 76, ISSN: 1434-6044
A search for narrow resonances decaying to an electron and a muon is presented. The eμ mass spectrum is also investigated for non-resonant contributions from the production of quantum black holes (QBHs). The analysis is performed using data corresponding to an integrated luminosity of 19.7 fb-1 collected in proton-proton collisions at a centre-of-mass energy of 8 TeV with the CMS detector at the LHC. With no evidence for physics beyond the standard model in the invariant mass spectrum of selected eμ pairs, upper limits are set at 95 % confidence level on the product of cross section and branching fraction for signals arising in theories with charged lepton flavour violation. In the search for narrow resonances, the resonant production of a τ sneutrino in R-parity violating supersymmetry is considered. The τ sneutrino is excluded for masses below 1.28 TeV for couplings λ132=λ231=λ′311=0.01, and below 2.30 TeV for λ132=λ231=0.07 and λ′311=0.11. These are the most stringent limits to date from direct searches at high-energy colliders. In addition, the resonance searches are interpreted in terms of a model with heavy partners of the Z boson and the photon. In a framework of TeV-scale quantum gravity based on a renormalization of Newton’s constant, the search for non-resonant contributions to the eμ mass spectrum excludes QBH production below a threshold mass Mth of 1.99 TeV. In models that invoke extra dimensions, the bounds range from 2.36 TeV for one extra dimension to 3.63 TeV for six extra dimensions. This is the first search for QBHs decaying into the eμ final state.
Khachatryan V, Sirunyan AM, Tumasyan A, et al., 2016, Combined search for anomalous pseudoscalar HVV couplings in VH(H→bb‾) production and H → VV decay, Physics Letters B, Vol: 759, Pages: 672-696, ISSN: 0370-2693
A search for anomalous pseudoscalar couplings of the Higgs boson H to electroweak vector bosons V (=W or Z) in a sample of proton–proton collision events corresponding to an integrated luminosity of 18.9 fb−1 at a center-of-mass energy of 8 TeV is presented. Events consistent with the topology of associated VH production, where the Higgs boson decays to a pair of bottom quarks and the vector boson decays leptonically, are analyzed. The consistency of data with a potential pseudoscalar contribution to the HVV interaction, expressed by the effective pseudoscalar cross section fractions fa3, is assessed by means of profile likelihood scans. Results are given for the VH channels alone and for a combined analysis of the VH and previously published H→VV channels. Under certain assumptions, fa3ZZ>0.0034 is excluded at 95% confidence level in the combination. Scenarios in which these assumptions are relaxed are also considered.
Khachatryan V, Sirunyan AM, Tumasyan A, et al., 2016, Search for supersymmetry in electroweak production with photonsand large missing transverse energy in pp collisions at √s = 8 TeV, Physics Letters B, Vol: 759, Pages: 479-500, ISSN: 0370-2693
Results are reported from a search for supersymmetry with gauge-mediated supersymmetry breaking in electroweak production. Final states with photons and large missing transverse energy ( ETmiss) were examined. The data sample was collected in pp collisions at √s=8TeV with the CMS detector at the LHC and corresponds to 7.4fb-1. The analysis focuses on scenarios in which the lightest neutralino has bino- or wino-like components, resulting in decays to photons and gravitinos, where the gravitinos escape undetected. The data were obtained using a specially designed trigger with dedicated low thresholds, providing good sensitivity to signatures with photons, ETmiss, and low hadronic energy. No excess of events over the standard model expectation is observed. The results are interpreted using the model of general gauge mediation. With the wino mass fixed at 10GeV above that of the bino, wino masses below 710GeV are excluded at 95% confidence level. Constraints are also set in the context of two simplified models, for which the analysis sets the lowest cross section limits on the electroweak production of supersymmetric particles.
Khachatryan V, Sirunyan AM, Tumasyan A, et al., 2016, Search for neutral resonances decaying into a Z boson and a pair of b jets or τ leptons, Physics Letters B, Vol: 759, Pages: 369-394, ISSN: 0370-2693
A search is performed for a new resonance decaying into a lighter resonance and a Z boson. Two channels are studied, targeting the decay of the lighter resonance into either a pair of oppositely charged τ leptons or a bb pair. The Z boson is identified via its decays to electrons or muons. The search exploits data collected by the CMS experiment at a centre-of-mass energy of 8 TeV, corresponding to an integrated luminosity of 19.8 fb-1. No significant deviations are observed from the standard model expectation and limits are set on production cross sections and parameters of two-Higgs-doublet models.
Khachatryan V, Sirunyan AM, Tumasyan A, et al., 2016, Search for supersymmetry in pp collisions at √s=8 TeV in final states with boosted W bosons and b jets using razor variables, Physical Review D, Vol: 93, ISSN: 1550-7998
Khachatryan V, Sirunyan AM, Tumasyan A, et al., 2016, Study of Z boson production in pPb collisions at √sNN = 5.02 TeV, Physics Letters B, Vol: 759, Pages: 36-57, ISSN: 0370-2693
The production of Z bosons in pPb collisions at sNN=5.02 TeV is studied by the CMS experiment via the electron and muon decay channels. The inclusive cross section is compared to pp collision predictions, and found to scale with the number of elementary nucleon-nucleon collisions. The differential cross sections as a function of the Z boson rapidity and transverse momentum are measured. Though they are found to be consistent within uncertainty with theoretical predictions both with and without nuclear effects, the forward-backward asymmetry suggests the presence of nuclear effects at large rapidities. These results provide new data for constraining nuclear parton distribution functions.
Khachatryan V, Sirunyan AM, Tumasyan A, et al., 2016, Search for supersymmetry in events with soft leptons, low jet multiplicity, and missing transverse energy in proton-proton collisions at s=8 TeV, Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics, Vol: 759, Pages: 9-35, ISSN: 0370-2693
Results are presented from a search for supersymmetric particles in scenarios with small mass splittings. The data sample corresponds to 19.7 fb-1 of proton-proton collisions recorded by the CMS experiment at s=8 TeV. The search targets top squark (t~) pair production in scenarios with mass differences δm=m(t~)-m(χ~10) below the W-boson mass and with top-squark decays in the four-body mode (t~→bℓνχ~10), where the neutralino (χ~10) is assumed to be the lightest supersymmetric particle (LSP). The signature includes a high transverse momentum (pT) jet associated with initial-state radiation, one or two low-pT leptons, and significant missing transverse energy. The event yields observed in data are consistent with the expected background contributions from standard model processes. Limits are set on the cross section for top squark pair production as a function of the t~ and LSP masses. Assuming a 100% branching fraction for the four-body decay mode, top-squark masses below 316 GeV are excluded for δm=25 GeV at 95% CL. The dilepton data are also interpreted under the assumption of chargino-neutralino production, with subsequent decays to sleptons or sneutrinos. Assuming a difference between the common χ~1+/χ~20 mass and the LSP mass of 20 GeV and a τ-enriched decay scenario, masses in the range m(χ~1+)<307 GeV are excluded at 95% CL.
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