Publications
1150 results found
Khachatryan V, Sirunyan AM, Tumasyan A, et al., 2015, Search for a Higgs boson decaying into gamma*gamma -> ll gamma with low dilepton mass in pp collisions at root s=8 TeV, Physics Letters B, Vol: 753, Pages: 341-362, ISSN: 0370-2693
Khachatryan V, Sirunyan AM, Tumasyan A, et al., 2015, Angular analysis of the decay B-0 -> K*(0)mu(+)mu(-) from pp collisions at root s=8 TeV, Physics Letters B, Vol: 753, Pages: 424-448, ISSN: 0370-2693
The angular distributions and the differential branching fraction of the decay B0→K⁎(892)0μ+μ− are studied using data corresponding to an integrated luminosity of 20.5 fb−1 collected with the CMS detector at the LHC in pp collisions at View the MathML source. From 1430 signal decays, the forward–backward asymmetry of the muons, the K⁎(892)0 longitudinal polarization fraction, and the differential branching fraction are determined as a function of the dimuon invariant mass squared. The measurements are among the most precise to date and are in good agreement with standard model predictions.
Khachatryan V, Sirunyan AM, Tumasyan A, et al., 2015, Search for exotic decays of a Higgs boson into undetectable particles and one or more photons, Physics Letters B, Vol: 753, Pages: 363-388, ISSN: 0370-2693
Khachatryan V, Sirunyan AM, Tumasyan A, et al., 2015, Search for supersymmetry in the vector-boson fusion topology in proton-proton collisions at √s=8 TeV, Journal of High Energy Physics, Vol: 2015, ISSN: 1126-6708
Khachatryan V, Sirunyan AM, Tumasyan A, et al., 2015, Search for neutral MSSM Higgs bosons decaying to mu(+) mu(-) in pp collisions at root s=7 and 8 TeV, Physics Letters B, Vol: 752, Pages: 221-246, ISSN: 0370-2693
Khachatryan V, Sirunyan AM, Tumasyan A, et al., 2015, Measurement of the differential cross section for top quark pair production in pp collisions at s√=8TeV, European Physical Journal C, Vol: 75, ISSN: 1434-6052
The normalized differential cross section for top quark pair ( tt¯tt¯ ) production is measured in pp collisions at a centre-of-mass energy of 8 TeVTeV at the CERN LHC using the CMS detector in data corresponding to an integrated luminosity of 19.7 fb−1fb−1 . The measurements are performed in the lepton ++ jets ( e/μe/μ ++ jets) and in the dilepton ( e+e−e+e− , μ+μ−μ+μ− , and e±μ∓e±μ∓ ) decay channels. The tt¯tt¯ cross section is measured as a function of the kinematic properties of the charged leptons, the jets associated to b quarks, the top quarks, and the tt¯tt¯ system. The data are compared with several predictions from perturbative quantum chromodynamic up to approximate next-to-next-to-leading-order precision. No significant deviations are observed relative to the standard model predictions.
Khachatryan V, Sirunyan AM, Tumasyan A, et al., 2015, Search for neutral MSSM Higgs bosons decaying into a pair of bottom quarks, Journal of High Energy Physics, Vol: 2015, Pages: 1-43, ISSN: 1126-6708
Khachatryan V, Sirunyan AM, Tumasyan A, et al., 2015, Search for a charged Higgs boson in pp collisions at √s=8 TeV, Journal of High Energy Physics, Vol: 2015, ISSN: 1126-6708
Khachatryan V, Sirunyan AM, Tumasyan A, et al., 2015, A search for pair production of new light bosons decaying into muons, Physics Letters B, Vol: 752, Pages: 146-168, ISSN: 0370-2693
A search for the pair production of new light bosons, each decaying into a pair of muons, is performed with the CMS experiment at the LHC, using a dataset corresponding to an integrated luminosity of 20.7 fb−1 collected in proton–proton collisions at center-of-mass energy of View the MathML source. No excess is observed in the data relative to standard model background expectation and a model independent upper limit on the product of the cross section, branching fraction, and acceptance is derived. The results are compared with two benchmark models, the first one in the context of the next-to-minimal supersymmetric standard model, and the second one in scenarios containing a hidden sector, including those predicting a nonnegligible light boson lifetime.
Khachatryan V, Sirunyan AM, Tumasyan A, et al., 2015, Measurements of the Z Z production cross sections in the 2l2ν channel in proton–proton collisions at s√=7 and 8 TeV and combined constraints on triple gauge couplings, European Physical Journal C, Vol: 75, ISSN: 1434-6052
Measurements of the ZZ ZZ production cross sections in proton–proton collisions at center-of-mass energies of 7 and 8 TeV TeV are presented. Candidate events for the leptonic decay mode ZZ→2l2νZZ→2l2ν , where ll denotes an electron or a muon, are reconstructed and selected from data corresponding to an integrated luminosity of 5.1 (19.6) fb-1fb-1 at 7 (8) TeV TeV collected with the CMS experiment. The measured cross sections, σ(pp→ZZ)=5.1+1.5−1.4(stat)+1.4−1.1(syst)±0.1(lumi)~pbσ(pp→ZZ)=5.1−1.4+1.5(stat)−1.1+1.4(syst)±0.1(lumi)~pb at 7 TeV TeV , and 7.2+0.8−0.8(stat)+1.9−1.5(syst)±0.2(lumi)~pb7.2−0.8+0.8(stat)−1.5+1.9(syst)±0.2(lumi)~pb at 8 TeV TeV , are in good agreement with the standard model predictions with next-to-leading-order accuracy. The selected data are analyzed to search for anomalous triple gauge couplings involving the ZZ ZZ final state. In the absence of any deviation from the standard model predictions, limits are set on the relevant parameters. These limits are then combined with the previously published CMS results for ZZ ZZ in 4 ll final states, yielding the most stringent constraints on the anomalous couplings.
Khachatryan V, Sirunyan AM, Tumasyan A, et al., 2015, Limits on the Higgs boson lifetime and width from its decay to four charged leptons, Physical Review D, Vol: 92, ISSN: 1550-7998
Constraints on the lifetime and width of the Higgs boson are obtained from H→ZZ→4ℓ events using data recorded by the CMS experiment during the LHC run 1 with an integrated luminosity of 5.1 and 19.7 fb−1 at a center-of-mass energy of 7 and 8 TeV, respectively. The measurement of the Higgs boson lifetime is derived from its flight distance in the CMS detector with an upper bound of τH<1.9×10−13 s at the 95% confidence level (C.L.), corresponding to a lower bound on the width of ΓH>3.5×10−9 MeV. The measurement of the width is obtained from an off-shell production technique, generalized to include anomalous couplings of the Higgs boson to two electroweak bosons. From this measurement, a joint constraint is set on the Higgs boson width and a parameter fΛQ that expresses an anomalous coupling contribution as an on-shell cross-section fraction. The limit on the Higgs boson width is ΓH<46 MeV with fΛQ unconstrained and ΓH<26 MeV for fΛQ=0 at the 95% C.L. The constraint fΛQ<3.8×10−3 at the 95% C.L. is obtained for the expected standard model Higgs boson width.
Khachatryan V, Sirunyan AM, Tumasyan A, et al., 2015, Search for a Higgs boson in the mass range from 145 to 1000 GeV decaying to a pair of W or Z bosons, Journal of High Energy Physics, Vol: 2015, ISSN: 1126-6708
Khachatryan V, Sirunyan AM, Tumasyan A, et al., 2015, Comparison of the Z/γ∗ + jets to γ + jets cross sections in pp collisions at √s=8 TeV, Journal of High Energy Physics, Vol: 2015, ISSN: 1126-6708
A comparison of the differential cross sections for the processes Z/γ * + jets and photon (γ)+jets is presented. The measurements are based on data collected with the CMS detector at s√=8s=8 TeV corresponding to an integrated luminosity of 19.7 fb−1. The differential cross sections and their ratios are presented as functions of p T. The measurements are also shown as functions of the jet multiplicity. Differential cross sections are obtained as functions of the ratio of the Z/γ * p T to the sum of all jet transverse momenta and of the ratio of the Z/γ * p T to the leading jet transverse momentum. The data are corrected for detector effects and are compared to simulations based on several QCD calculations.
Khachatryan V, Sirunyan AM, Tumasyan A, et al., 2015, Search for supersymmetry with photons in pp collisions at √s=8 TeV, Physical Review D, Vol: 92, ISSN: 1550-7998
Khachatryan V, Sirunyan AM, Tumasyan A, et al., 2015, Pseudorapidity distribution of charged hadrons in proton-proton collisions at root s=13TeV, Physics Letters B, Vol: 751, Pages: 143-163, ISSN: 0370-2693
Khachatryan V, Sirunyan AM, Tumasyan A, et al., 2015, Search for diphoton resonances in the mass range from 150 to 850 GeV in pp collisions at root s=8 TeV, Physics Letters B, Vol: 750, Pages: 494-519, ISSN: 0370-2693
Khachatryan V, Sirunyan AM, Tumasyan A, et al., 2015, Search for neutral color-octet weak-triplet scalar particles in proton-proton collisions at √s=8 TeV, Journal of High Energy Physics, Vol: 2015, ISSN: 1126-6708
Adam W, Bergauer T, Dragicevic M, et al., 2015, Study of W boson production in pPb collisions at root(NN)-N-S=5.02 TeV, Physics Letters B, Vol: 750, Pages: 565-586, ISSN: 0370-2693
Khachatryan V, Sirunyan AM, Tumasyan A, et al., 2015, Evidence for transverse-momentum- and pseudorapidity-dependent event-plane fluctuations in PbPb and pPb collisions, Physical Review C, Vol: 92, ISSN: 1089-490X
A systematic study of the factorization of long-range azimuthal two-particle correlations into a productof single-particle anisotropies is presented as a function ofpTandηof both particles and as a function of theparticle multiplicity in PbPb andpPb collisions. The data were taken with the CMS detector for PbPb collisions at√sNN=2.76 TeV andpPb collisions at√sNN=5.02 TeV, covering a very wide range of multiplicity. FactorizationisobservedtobebrokenasafunctionofbothparticlepTandη. When measured with particles of differentpT,the magnitude of the factorization breakdown for the second Fourier harmonic reaches 20% for very central PbPbcollisions but decreases rapidly as the multiplicity decreases. The data are consistent with viscous hydrodynamicpredictions, which suggest that the effect of factorization breaking is mainly sensitive to the initial-state conditionsrather than to the transport properties (e.g., shear viscosity) of the medium. The factorization breakdown is alsocomputed with particles of differentη. The effect is found to be weakest for mid-central PbPb events but becomeslarger for more central or peripheral PbPb collisions, and also for very-high-multiplicitypPb collisions. Theη-dependent factorization data provide new insights to the longitudinal evolution of the medium formed in heavyion collisions.
Khachatryan V, Sirunyan AM, Tumasyan A, et al., 2015, Measurement of the underlying event activity using charged-particle jets in proton-proton collisions at √s=2.76 TeV, Journal of High Energy Physics, Vol: 2015, ISSN: 1126-6708
Khachatryan V, Sirunyan AM, Tumasyan A, et al., 2015, Angular coefficients of Z bosons produced in pp collisions at root S=8 TeV and decaying to mu(+)mu(-) as a function of transverse momentum and rapidity, Physics Letters B, Vol: 750, Pages: 154-175, ISSN: 0370-2693
Measurements of the five most significant angular coefficients, A0 through A4, for Z bosons produced in pp collisions at View the MathML source and decaying to μ+μ− are presented as a function of the transverse momentum and rapidity of the Z boson. The integrated luminosity of the dataset collected with the CMS detector at the LHC corresponds to View the MathML source. These measurements provide comprehensive information about the Z boson production mechanisms, and are compared to the QCD predictions at leading order, next-to-leading order, and next-to-next-to-leading order in perturbation theory.
Khachatryan V, Sirunyan AM, Tumasyan A, et al., 2015, Search for the standard model Higgs boson produced through vector boson fusion and decaying to bb¯, Physical Review D, Vol: 92, ISSN: 1550-7998
Khachatryan V, Sirunyan AM, Tumasyan A, et al., 2015, Search for resonant pair production of Higgs bosons decaying to two bottom quark-antiquark pairs in proton-proton collisions at 8TeV, Physics Letters B, Vol: 749, Pages: 560-582, ISSN: 0370-2693
Khachatryan V, Sirunyan AM, Tumasyan A, et al., 2015, Performance of photon reconstruction and identification with the CMS detector in proton-proton collisions at √s = 8 TeV, Journal of Instrumentation, Vol: 10, ISSN: 1748-0221
Khachatryan V, Sirunyan AM, Tumasyan A, et al., 2015, Measurement of the Z boson differential cross section in transverse momentum and rapidity in proton–proton collisions at 8 TeV, Physics Letters B, Vol: 749, Pages: 187-209, ISSN: 0370-2693
Khachatryan V, Sirunyan AM, Tumasyan A, et al., 2015, Search for lepton-flavour-violating decays of the Higgs boson, Physics Letters B, Vol: 749, Pages: 337-362, ISSN: 0370-2693
Khachatryan V, Sirunyan AM, Tumasyan A, et al., 2015, Measurements of the ϒ(1S), ϒ(2S), and ϒ(3S) differential cross sections in pp collisions at root √s = 7 TeV, Physics Letters B, Vol: 749, Pages: 14-34, ISSN: 0370-2693
Differential cross sections as a function of transverse momentum pT are presented for the production of ϒ(nS) (n = 1, 2, 3) states decaying into a pair of muons. Data corresponding to an integrated luminosity of 4.9View the MathML source in pp collisions at View the MathML source were collected with the CMS detector at the LHC. The analysis selects events with dimuon rapidity |y|<1.2 and dimuon transverse momentum in the range View the MathML source. The measurements show a transition from an exponential to a power-law behavior at View the MathML source for the three ϒ states. Above that transition, the ϒ(3S) spectrum is significantly harder than that of the ϒ(1S). The ratios of the ϒ(3S) and ϒ(2S) differential cross sections to the ϒ(1S) cross section show a rise as pT increases at low pT, then become flatter at higher pT.
Khachatryan V, Sirunyan AM, Tumasyan A, et al., 2015, Constraints on the pMSSM, AMSB model and on other models from the search for long-lived charged particles in proton–proton collisions at s√=8TeV, European Physical Journal C, Vol: 75, ISSN: 1434-6052
Stringent limits are set on the long-lived lepton-like sector of the phenomenological minimal supersymmetric standard model (pMSSM) and the anomaly-mediated supersymmetry breaking (AMSB) model. The limits are derived from the results presented in a recent search for long-lived charged particles in proton–proton collisions, based on data collected by the CMS detector at a centre-of-mass energy of 8 TeV at the Large Hadron Collider. In the pMSSM parameter sub-space considered, 95.9 % of the points predicting charginos with a lifetime of at least 10 ns are excluded. These constraints on the pMSSM are the first obtained at the LHC. Charginos with a lifetime greater than 100 ns and masses up to about 800 GeV in the AMSB model are also excluded. The method described can also be used to set constraints on other models.
Khachatryan V, Sirunyan AM, Tumasyan A, et al., 2015, Constraints on the spin-parity and anomalous HVV couplings of the Higgs boson in proton collisions at 7 and 8 TeV, Physical Review D, Vol: 92, ISSN: 1550-7998
The study of the spin-parity and tensor structure of the interactions of the recently discovered Higgs boson is performed using the H→ZZ,Zγ∗,γ∗γ∗→4ℓ, H→WW→ℓνℓν, and H→γγ decay modes. The full data set recorded by the CMS experiment during the LHC run 1 is used, corresponding to an integrated luminosity of up to 5.1 fb−1 at a center-of-mass energy of 7 TeV and up to 19.7 fb−1 at 8 TeV. A wide range of spin-two models is excluded at a 99% confidence level or higher, or at a 99.87% confidence level for the minimal gravitylike couplings, regardless of whether assumptions are made on the production mechanism. Any mixed-parity spin-one state is excluded in the ZZ and WW modes at a greater than 99.999% confidence level. Under the hypothesis that the resonance is a spin-zero boson, the tensor structure of the interactions of the Higgs boson with two vector bosons ZZ, Zγ, γγ, and WW is investigated and limits on eleven anomalous contributions are set. Tighter constraints on anomalous HVV interactions are obtained by combining the HZZ and HWW measurements. All observations are consistent with the expectations for the standard model Higgs boson with the quantum numbers JPC=0++.
Schopper H, Lella LD, 2015, 60 Years of CERN Experiments and Discoveries, Publisher: World Scientific, ISBN: 9789814644167
These problems were solved in 1958 by the first experiment performed at CERN with particles from a CERN accelerator. It was a search for π+ → e+ν decay.29 That experiment, which “put CERN on the map of high energy physics”,30 started ...
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