Publications
1367 results found
Scandale W, Arduini G, Butcher M, et al., 2015, Observation of strong leakage reduction in crystal assisted collimation of the SPS beam, Physics Letters B, Vol: 748, Pages: 451-454, ISSN: 0370-2693
In ideal two-stage collimation systems, the secondary collimator–absorber should have its length sufficient to exclude practically the exit of halo particles with large impact parameters. In the UA9 experiments on the crystal assisted collimation of the SPS beam a 60 cm long tungsten bar is used as a secondary collimator–absorber which is insufficient for the full absorption of the halo protons. Multi-turn simulation studies of the collimation allowed to select the position for the beam loss monitor downstream the collimation area where the contribution of particles deflected by the crystal in channeling regime but emerging from the secondary collimator–absorber is considerably reduced. This allowed observation of a strong leakage reduction of halo protons from the SPS beam collimation area, thereby approaching the case with an ideal absorber.
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++.
Khachatryan V, Sirunyan AM, Tumasyan A, et al., 2015, Search for narrow high-mass resonances in proton-proton collisions at root s=8 TeV decaying to a Z and a Higgs boson, Physics Letters B, Vol: 748, Pages: 255-277, ISSN: 0370-2693
Khachatryan V, Sirunyan AM, Tumasyan A, et al., 2015, Search for a pseudoscalar boson decaying into a Z boson and the 125 GeV Higgs boson in l(+)l(-)b(b)over-bar final states, Physics Letters B, Vol: 748, Pages: 221-243, ISSN: 0370-2693
Khachatryan V, Sirunyan AM, Tumasyan A, et al., 2015, Search for third-generation scalar leptoquarks in the tτ channel 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, Measurement of diffractive dissociation cross sections in pp collisions at √s=7 TeV, Physical Review D, Vol: 92, ISSN: 1550-7998
Khachatryan V, Sirunyan AM, Tumasyan A, et al., 2015, Search for heavy Majorana neutrinos in mu(+/-)mu(+/-) + jets events inproton-proton collisions at root s=8TeV, Physics Letters B, Vol: 748, Pages: 144-166, ISSN: 0370-2693
Khachatryan V, Sirunyan AM, Tumasyan A, et al., 2015, Distributions of topological observables in inclusive three- and four-jet events in pp collisions at s√=7 TeV, European Physical Journal C, Vol: 75, ISSN: 1434-6052
This paper presents distributions of topological observables in inclusive three- and four-jet events produced in pp collisions at a centre-of-mass energy of 7 TeVTeV with a data sample collected by the CMS experiment corresponding to a luminosity of 5.1 fb−1fb−1 . The distributions are corrected for detector effects, and compared with several event generators based on two- and multi-parton matrix elements at leading order. Among the considered calculations, MadGraph interfaced with pythia6 displays the overall best agreement with data.
Khachatryan V, Sirunyan AM, Tumasyan A, et al., 2015, Measurement of the cross section ratio sigma(t(t)over-barb(b)over-bar)/sigma(t(t)over-barjj) in pp collisions at root √s=8 TeV, Physics Letters B, Vol: 746, Pages: 132-153, ISSN: 0370-2693
Khachatryan V, Sirunyan AM, Tumasyan A, et al., 2015, Evidence for Collective Multiparticle Correlations in p-Pb Collisions, Physical Review Letters, Vol: 115, ISSN: 1079-7114
Khachatryan V, Sirunyan AM, Tumasyan A, et al., 2015, Constraints on parton distribution functions and extraction of the strong coupling constant from the inclusive jet cross section in pp collisions at s√=7 TeV, European Physical Journal C, Vol: 75, ISSN: 1434-6052
The inclusive jet cross section for proton–proton collisions at a centre-of-mass energy of 7 TeVTeV was measured by the CMS Collaboration at the LHC with data corresponding to an integrated luminosity of 5.0 fb−1fb−1 . The measurement covers a phase space up to 2 TeVTeV in jet transverse momentum and 2.5 in absolute jet rapidity. The statistical precision of these data leads to stringent constraints on the parton distribution functions of the proton. The data provide important input for the gluon density at high fractions of the proton momentum and for the strong coupling constant at large energy scales. Using predictions from perturbative quantum chromodynamics at next-to-leading order, complemented with electroweak corrections, the constraining power of these data is investigated and the strong coupling constant at the Z boson mass MZMZ is determined to be αS(MZ)=0.1185±0.0019(exp)+0.0060−0.0037(theo)αS(MZ)=0.1185±0.0019(exp)−0.0037+0.0060(theo) , which is in agreement with the world average.
Khachatryan V, Sirunyan AM, Tumasyan A, et al., 2015, Search for the production of dark matter in association with top-quark pairs in the single-lepton final state 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, Searches for third-generation squark production in fully hadronic final states in proton-proton collisions at √s=8 TeV, Journal of High Energy Physics, Vol: 2015, ISSN: 1126-6708
Searches for third-generation squarks in fully hadronic final states are presented using data samples corresponding to integrated luminosities of 19.4 or 19.7 fb−1, collected at a centre-of-mass energy of 8 TeV with the CMS detector at the LHC. Three mutually exclusive searches are presented, each optimized for a different decay topology. They include a multijet search requiring one fully reconstructed top quark, a dijet search requiring one or two jets originating from b quarks, and a monojet search. No excesses above the standard model expectations are seen, and limits are set on top and bottom squark production in the context of simplified models of supersymmetry.
Khachatryan V, Sirunyan AM, Tumasyan A, et al., 2015, Search for vector-like T quarks decaying to top quarks and Higgs bosons in the all-hadronic channel using jet substructure, Journal of High Energy Physics, Vol: 2015, ISSN: 1126-6708
Khachatryan V, Sirunyan AM, Tumasyan A, et al., 2015, Performance of electron reconstruction and selection 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, Search for a standard model Higgs boson produced in association with a top-quark pair and decaying to bottom quarks using a matrix element method, European Physical Journal C, Vol: 75, ISSN: 1434-6052
Khachatryan V, Sirunyan AM, Tumasyan A, et al., 2015, Observation of the rare B-s(0)->mu(+)mu(-) decay from the combined analysis of CMS and LHCb data, Nature, Vol: 522, Pages: 68-72, ISSN: 0028-0836
The standard model of particle physics describes the fundamental particles and their interactions via the strong, electromagnetic and weak forces. It provides precise predictions for measurable quantities that can be tested experimentally. The probabilities, or branching fractions, of the strange B meson ( ) and the B0 meson decaying into two oppositely charged muons (μ+ and μ−) are especially interesting because of their sensitivity to theories that extend the standard model. The standard model predicts that the and decays are very rare, with about four of the former occurring for every billion mesons produced, and one of the latter occurring for every ten billion B0 mesons1. A difference in the observed branching fractions with respect to the predictions of the standard model would provide a direction in which the standard model should be extended. Before the Large Hadron Collider (LHC) at CERN2 started operating, no evidence for either decay mode had been found. Upper limits on the branching fractions were an order of magnitude above the standard model predictions. The CMS (Compact Muon Solenoid) and LHCb (Large Hadron Collider beauty) collaborations have performed a joint analysis of the data from proton–proton collisions that they collected in 2011 at a centre-of-mass energy of seven teraelectronvolts and in 2012 at eight teraelectronvolts. Here we report the first observation of the µ+µ− decay, with a statistical significance exceeding six standard deviations, and the best measurement so far of its branching fraction. Furthermore, we obtained evidence for the µ+µ− decay with a statistical significance of three standard deviations. Both measurements are statistically compatible with standard model predictions and allow stringent constraints to be placed on theories beyond the standard model. The LHC experiments will resume taking data in 2015, recording proton–proton collisions at a centre-o
Khachatryan V, Sirunyan AM, Tumasyan A, et al., 2015, Study of final-state radiation in decays of Z bosons produced in pp collisions at 7 TeV, Physical Review D, Vol: 91, ISSN: 1550-7998
Khachatryan V, Sirunyan AM, Tumasyan A, et al., 2015, Search for dark matter, extra dimensions, and unparticles in monojet events in proton-proton collisions at √s=8 TeV, European Physical Journal C, Vol: 75, ISSN: 1434-6052
Results are presented from a search for particle dark matter (DM), extra dimensions, and unparticles using events containing a jet and an imbalance in transverse momentum. The data were collected by the CMS detector in proton–proton collisions at the LHC and correspond to an integrated luminosity of 19.7fb-1at a centre-of-mass energy of 8TeV. The number of observed events is found to be consistent with the standard model prediction. Limits are placed on the DM-nucleon scattering cross section as a function of the DM particle mass for spin-dependent and spin-independent interactions. Limits are also placed on the scale parameter MD in the Arkani-Hamed, Dimopoulos, and Dvali (ADD) model of large extra dimensions, and on the unparticle model parameter ΛU. The constraints on ADD models and unparticles are the most stringent limits in this channel and those on the DM-nucleon scattering cross section are an improvement over previous collider results.
Khachatryan V, Sirunyan AM, Tumasyan A, et al., 2015, Nuclear effects on the transverse momentum spectra of charged particles in pPb collisions at √sNN=5.02 TeV, European Physical Journal C, Vol: 75, ISSN: 1434-6052
Khachatryan V, Sirunyan AM, Tumasyan A, et al., 2015, Search for physics beyond the standard model in final states with a lepton and missing transverse energy in proton-proton collisions at √s=8 TeV, Physical Review D, Vol: 91, ISSN: 1550-7998
Chatrchyan S, Khachatryan V, Sirunyan AM, et al., 2015, Erratum to: Measurement of jet multiplicity distributions in tt¯ production in pp collisions at √s=7TeV, European Physical Journal C, Vol: 75, ISSN: 1434-6052
Aad G, Abbott B, Abdallah J, et al., 2015, Combined measurement of the Higgs Boson mass in pp collisions at root s=7 and 8 TeV with the ATLAS and CMS experiments, Physical Review Letters, Vol: 114, ISSN: 1079-7114
A measurement of the Higgs boson mass is presented based on the combined data samples of the ATLAS and CMS experiments at the CERN LHC in the H→γγ and H→ZZ→4ℓ decay channels. The results are obtained from a simultaneous fit to the reconstructed invariant mass peaks in the two channels and for the two experiments. The measured masses from the individual channels and the two experiments are found to be consistent among themselves. The combined measured mass of the Higgs boson is mH=125.09±0.21 (stat)±0.11 (syst) GeV.
Khachatryan V, Sirunyan AM, Tumasyan A, et al., 2015, Searches for supersymmetry using the MT2 variable in hadronic events produced in pp collisions at 8 TeV, Journal of High Energy Physics, Vol: 2015, ISSN: 1126-6708
Khachatryan V, Sirunyan AM, Tumasyan A, et al., 2015, Precise determination of the mass of the Higgs boson and tests of compatibility of its couplings with the standard model predictions using proton collisions at 7 and 8 TeV, European Physical Journal C, Vol: 75, ISSN: 1434-6052
Properties of the Higgs boson with mass near 125GeV are measured in proton-proton collisions with the CMS experiment at the LHC. Comprehensive sets of production and decay measurements are combined. The decay channels include γγ, ZZ, WW, ττ, bb, and μμ pairs. The data samples were collected in 2011 and 2012 and correspond to integrated luminosities of up to 5.1fb-1 at 7TeV and up to 19.7fb-1 at 8TeV. From the high-resolution γγ and ZZ channels, the mass of the Higgs boson is determined to be 125.02+0.26−0.27(stat)+0.14−0.15(syst)GeV. For this mass value, the event yields obtained in the different analyses tagging specific decay channels and production mechanisms are consistent with those expected for the standard model Higgs boson. The combined best-fit signal relative to the standard model expectation is 1.00±0.09(stat)+0.08−0.07(theo)±0.07(syst) at the measured mass. The couplings of the Higgs boson are probed for deviations in magnitude from the standard model predictions in multiple ways, including searches for invisible and undetected decays. No significant deviations are found.
Khachatryan V, Sirunyan AM, Tumasyan A, et al., 2015, Measurement of J/ψ and ψ(2S) Prompt Double-Differential Cross Sections in pp Collisions at √s=7 TeV, Physical Review Letters, Vol: 114, ISSN: 1079-7114
Khachatryan V, Sirunyan AM, Tumasyan A, et al., 2015, Measurement of the inclusive 3-jet production differential cross section in proton–proton collisions at 7 TeV and determination of the strong coupling constant in the TeV range, European Physical Journal C, Vol: 75, ISSN: 1434-6052
Scandale W, Arduini G, Butcher M, et al., 2015, Comparative results on the deflection of positively and negatively charged particles by multiple volume reflections in a multi-strip silicon deflector, JETP LETTERS, Vol: 101, Pages: 679-684, ISSN: 0021-3640
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