Displaying publications 21 - 40 of 104 in total

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  1. Khachatryan V, Sirunyan AM, Tumasyan A, Adam W, Asilar E, Bergauer T, et al.
    Phys. Rev. Lett., 2016 Jul 15;117(3):031802.
    PMID: 27472109 DOI: 10.1103/PhysRevLett.117.031802
    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.
  2. Sirunyan AM, Tumasyan A, Adam W, Asilar E, Bergauer T, Brandstetter J, et al.
    Phys. Rev. Lett., 2017 Aug 25;119(8):082301.
    PMID: 28952777 DOI: 10.1103/PhysRevLett.119.082301
    The production of jets in association with Z bosons, reconstructed via the μ^{+}μ^{-} and e^{+}e^{-} decay channels, is studied in pp and, for the first time, in Pb-Pb collisions. Both data samples were collected by the CMS experiment at the LHC, at a nucleon-nucleon center-of-mass energy of 5.02 TeV. The Pb-Pb collisions were analyzed in the 0%-30% centrality range. The back-to-back azimuthal alignment was studied in both pp and Pb-Pb collisions for Z bosons with transverse momentum p_{T}^{Z}>60  GeV/c and a recoiling jet with p_{T}^{jet}>30  GeV/c. The p_{T} imbalance x_{jZ}=p_{T}^{jet}/p_{T}^{Z}, as well as the average number of jet partners per Z, R_{jZ}, was studied in intervals of p_{T}^{Z}. The R_{jZ} is found to be smaller in Pb-Pb than in pp collisions, which suggests that in Pb-Pb collisions a larger fraction of partons associated with the Z bosons fall below the 30  GeV/c p_{T}^{jet} threshold because they lose energy.
  3. Sirunyan AM, Tumasyan A, Adam W, Ambrogi F, Asilar E, Bergauer T, et al.
    Phys. Rev. Lett., 2017 Sep 15;119(11):111802.
    PMID: 28949210 DOI: 10.1103/PhysRevLett.119.111802
    A search is reported for a narrow vector resonance decaying to quark-antiquark pairs in proton-proton collisions at sqrt[s]=13  TeV, collected with the CMS detector at the LHC. The data sample corresponds to an integrated luminosity of 2.7   fb^{-1}. The vector resonance is produced at large transverse momenta, with its decay products merged into a single jet. The resulting signature is a peak over background in the distribution of the invariant mass of the jet. The results are interpreted in the framework of a leptophobic vector resonance and no evidence is found for such particles in the mass range of 100-300 GeV. Upper limits at 95% confidence level on the production cross section are presented in a region of mass-coupling phase space previously unexplored at the LHC. The region below 140 GeV has not been explored by any previous experiments.
  4. Sirunyan AM, Tumasyan A, Adam W, Ambrogi F, Asilar E, Bergauer T, et al.
    Phys. Rev. Lett., 2018 Apr 06;120(14):142302.
    PMID: 29694107 DOI: 10.1103/PhysRevLett.120.142302
    Data from heavy ion collisions suggest that the evolution of a parton shower is modified by interactions with the color charges in the dense partonic medium created in these collisions, but it is not known where in the shower evolution the modifications occur. The momentum ratio of the two leading partons, resolved as subjets, provides information about the parton shower evolution. This substructure observable, known as the splitting function, reflects the process of a parton splitting into two other partons and has been measured for jets with transverse momentum between 140 and 500 GeV, in pp and PbPb collisions at a center-of-mass energy of 5.02 TeV per nucleon pair. In central PbPb collisions, the splitting function indicates a more unbalanced momentum ratio, compared to peripheral PbPb and pp collisions.. The measurements are compared to various predictions from event generators and analytical calculations.
  5. Sirunyan AM, Tumasyan A, Adam W, Asilar E, Bergauer T, Brandstetter J, et al.
    Phys. Rev. Lett., 2018 Apr 06;120(14):142301.
    PMID: 29694144 DOI: 10.1103/PhysRevLett.120.142301
    The relative yields of ϒ mesons produced in pp and Pb-Pb collisions at sqrt[s_{NN}]=5.02  TeV and reconstructed via the dimuon decay channel are measured using data collected by the CMS experiment. Double ratios are formed by comparing the yields of the excited states, ϒ(2S) and ϒ(3S), to the ground state, ϒ(1S), in both Pb-Pb and pp collisions at the same center-of-mass energy. The double ratios, [ϒ(nS)/ϒ(1S)]_{Pb-Pb}/[ϒ(nS)/ϒ(1S)]_{pp}, are measured to be 0.308±0.055(stat)±0.019(syst) for the ϒ(2S) and less than 0.26 at 95% confidence level for the ϒ(3S). No significant ϒ(3S) signal is found in the Pb-Pb data. The double ratios are studied as a function of collision centrality, as well as ϒ transverse momentum and rapidity. No significant dependencies are observed.
  6. Sirunyan AM, Tumasyan A, Adam W, Asilar E, Bergauer T, Brandstetter J, et al.
    Phys. Rev. Lett., 2017 Oct 06;119(14):141802.
    PMID: 29053305 DOI: 10.1103/PhysRevLett.119.141802
    A search for charged Higgs bosons produced via vector boson fusion and decaying into W and Z bosons using proton-proton collisions at sqrt[s]=13  TeV is presented. The data sample corresponds to an integrated luminosity of 15.2  fb^{-1} collected with the CMS detector in 2015 and 2016. The event selection requires three leptons (electrons or muons), two jets with large pseudorapidity separation and high dijet mass, and missing transverse momentum. The observation agrees with the standard model prediction. Limits on the vector boson fusion production cross section times branching fraction for new charged physical states are reported as a function of mass from 200 to 2000 GeV and interpreted in the context of Higgs triplet models.
  7. Sirunyan AM, Tumasyan A, Adam W, Asilar E, Bergauer T, Brandstetter J, et al.
    Phys. Rev. Lett., 2017 Oct 13;119(15):152301.
    PMID: 29077459 DOI: 10.1103/PhysRevLett.119.152301
    The differential production cross sections of B^{±} mesons are measured via the exclusive decay channels B^{±}→J/ψK^{±}→μ^{+}μ^{-}K^{±} as a function of transverse momentum in pp and Pb-Pb collisions at a center-of-mass energy sqrt[s_{NN}]=5.02  TeV per nucleon pair with the CMS detector at the LHC. The pp(Pb-Pb) data set used for this analysis corresponds to an integrated luminosity of 28.0  pb^{-1} (351  μb^{-1}). The measurement is performed in the B^{±} meson transverse momentum range of 7 to 50  GeV/c, in the rapidity interval |y|<2.4. In this kinematic range, a strong suppression of the production cross section by about a factor of 2 is observed in the Pb-Pb system in comparison to the expectation from pp reference data. These results are found to be roughly compatible with theoretical calculations incorporating beauty quark diffusion and energy loss in a quark-gluon plasma.
  8. Sirunyan AM, Tumasyan A, Adam W, Ambrogi F, Asilar E, Bergauer T, et al.
    Phys. Rev. Lett., 2017 Oct 13;119(15):151802.
    PMID: 29077436 DOI: 10.1103/PhysRevLett.119.151802
    Results are reported from a search for supersymmetric particles in proton-proton collisions in the final state with a single lepton, multiple jets, including at least one b-tagged jet, and large missing transverse momentum. The search uses a sample of proton-proton collision data at sqrt[s]=13  TeV recorded by the CMS experiment at the LHC, corresponding to an integrated luminosity of 35.9  fb^{-1}. The observed event yields in the signal regions are consistent with those expected from standard model backgrounds. The results are interpreted in the context of simplified models of supersymmetry involving gluino pair production, with gluino decay into either on- or off-mass-shell top squarks. Assuming that the top squarks decay into a top quark plus a stable, weakly interacting neutralino, scenarios with gluino masses up to about 1.9 TeV are excluded at 95% confidence level for neutralino masses up to about 1 TeV.
  9. Sirunyan AM, Tumasyan A, Adam W, Ambrogi F, Asilar E, Bergauer T, et al.
    Phys. Rev. Lett., 2018 May 18;120(20):202005.
    PMID: 29864318 DOI: 10.1103/PhysRevLett.120.202005
    A search for resonancelike structures in the B_{s}^{0}π^{±} invariant mass spectrum is performed using proton-proton collision data collected by the CMS experiment at the LHC at sqrt[s]=8  TeV, corresponding to an integrated luminosity of 19.7  fb^{-1}. The B_{s}^{0} mesons are reconstructed in the decay chain B_{s}^{0}→J/ψϕ, with J/ψ→μ^{+}μ^{-} and ϕ→K^{+}K^{-}. The B_{s}^{0}π^{±} invariant mass distribution shows no statistically significant peaks for different selection requirements on the reconstructed B_{s}^{0} and π^{±} candidates. Upper limits are set on the relative production rates of the X(5568) and B_{s}^{0} states times the branching fraction of the decay X(5568)^{±}→B_{s}^{0}π^{±}. In addition, upper limits are obtained as a function of the mass and the natural width of possible exotic states decaying into B_{s}^{0}π^{±}.
  10. Sirunyan AM, Tumasyan A, Adam W, Ambrogi F, Asilar E, Bergauer T, et al.
    Phys. Rev. Lett., 2018 Jun 08;120(23):231801.
    PMID: 29932697 DOI: 10.1103/PhysRevLett.120.231801
    The observation of Higgs boson production in association with a top quark-antiquark pair is reported, based on a combined analysis of proton-proton collision data at center-of-mass energies of sqrt[s]=7, 8, and 13 TeV, corresponding to integrated luminosities of up to 5.1, 19.7, and 35.9  fb^{-1}, respectively. The data were collected with the CMS detector at the CERN LHC. The results of statistically independent searches for Higgs bosons produced in conjunction with a top quark-antiquark pair and decaying to pairs of W bosons, Z bosons, photons, τ leptons, or bottom quark jets are combined to maximize sensitivity. An excess of events is observed, with a significance of 5.2 standard deviations, over the expectation from the background-only hypothesis. The corresponding expected significance from the standard model for a Higgs boson mass of 125.09 GeV is 4.2 standard deviations. The combined best fit signal strength normalized to the standard model prediction is 1.26_{-0.26}^{+0.31}.
  11. Sirunyan AM, Tumasyan A, Adam W, Ambrogi F, Asilar E, Bergauer T, et al.
    Phys. Rev. Lett., 2018 May 18;120(20):202301.
    PMID: 29864330 DOI: 10.1103/PhysRevLett.120.202301
    The prompt D^{0} meson azimuthal anisotropy coefficients, v_{2} and v_{3}, are measured at midrapidity (|y|<1.0) in Pb-Pb collisions at a center-of-mass energy sqrt[s_{NN}]=5.02  TeV per nucleon pair with data collected by the CMS experiment. The measurement is performed in the transverse momentum (p_{T}) range of 1 to 40  GeV/c, for central and midcentral collisions. The v_{2} coefficient is found to be positive throughout the p_{T} range studied. The first measurement of the prompt D^{0} meson v_{3} coefficient is performed, and values up to 0.07 are observed for p_{T} around 4  GeV/c. Compared to measurements of charged particles, a similar p_{T} dependence, but smaller magnitude for p_{T}<6  GeV/c, is found for prompt D^{0} meson v_{2} and v_{3} coefficients. The results are consistent with the presence of collective motion of charm quarks at low p_{T} and a path length dependence of charm quark energy loss at high p_{T}, thereby providing new constraints on the theoretical description of the interactions between charm quarks and the quark-gluon plasma.
  12. Sirunyan AM, Tumasyan A, Adam W, Ambrogi F, Asilar E, Bergauer T, et al.
    Phys. Rev. Lett., 2018 Jun 01;120(22):221801.
    PMID: 29906166 DOI: 10.1103/PhysRevLett.120.221801
    A search for a heavy neutral lepton N of Majorana nature decaying into a W boson and a charged lepton is performed using the CMS detector at the LHC. The targeted signature consists of three prompt charged leptons in any flavor combination of electrons and muons. The data were collected in proton-proton collisions at a center-of-mass energy of 13 TeV, with an integrated luminosity of 35.9  fb^{-1}. The search is performed in the N mass range between 1 GeV and 1.2 TeV. The data are found to be consistent with the expected standard model background. Upper limits are set on the values of |V_{eN}|^{2} and |V_{μN}|^{2}, where V_{ℓN} is the matrix element describing the mixing of N with the standard model neutrino of flavor ℓ. These are the first direct limits for N masses above 500 GeV and the first limits obtained at a hadron collider for N masses below 40 GeV.
  13. Sirunyan AM, Tumasyan A, Adam W, Ambrogi F, Asilar E, Bergauer T, et al.
    Phys. Rev. Lett., 2018 May 18;120(20):201801.
    PMID: 29864370 DOI: 10.1103/PhysRevLett.120.201801
    A search for narrow resonances decaying to bottom quark-antiquark pairs is presented, using a data sample of proton-proton collisions at sqrt[s]=8  TeV corresponding to an integrated luminosity of 19.7  fb^{-1}. The search is extended to masses lower than those reached in typical searches for resonances decaying into jet pairs at the LHC, by taking advantage of triggers that identify jets originating from bottom quarks. No significant excess of events is observed above the background predictions. Limits are set on the product of cross section and branching fraction to bottom quarks for spin 0, 1, and 2 resonances in the mass range of 325-1200 GeV. These results improve on the limits for resonances decaying into jet pairs in the 325-500 GeV mass range.
  14. Sirunyan AM, Tumasyan A, Adam W, Ambrogi F, Asilar E, Bergauer T, et al.
    Phys. Rev. Lett., 2018 Jun 15;120(24):241801.
    PMID: 29956995 DOI: 10.1103/PhysRevLett.120.241801
    A search for physics beyond the standard model in events with one or more high-momentum Higgs bosons, H, decaying to pairs of b quarks in association with missing transverse momentum is presented. The data, corresponding to an integrated luminosity of 35.9  fb^{-1}, were collected with the CMS detector at the LHC in proton-proton collisions at the center-of-mass energy sqrt[s]=13  TeV. The analysis utilizes a new b quark tagging technique based on jet substructure to identify jets from H→bb[over ¯]. Events are categorized by the multiplicity of H-tagged jets, jet mass, and the missing transverse momentum. No significant deviation from standard model expectations is observed. In the context of supersymmetry (SUSY), limits on the cross sections of pair-produced gluinos are set, assuming that gluinos decay to quark pairs, H (or Z), and the lightest SUSY particle, LSP, through an intermediate next-to-lightest SUSY particle, NLSP. With large mass splitting between the NLSP and LSP, and 100% NLSP branching fraction to H, the lower limit on the gluino mass is found to be 2010 GeV.
  15. Khachatryan V, Sirunyan AM, Tumasyan A, Adam W, Asilar E, Bergauer T, et al.
    Eur Phys J C Part Fields, 2017;77(1):15.
    PMID: 28260978 DOI: 10.1140/epjc/s10052-016-4504-z
    A measurement of the top quark pair production ([Formula: see text]) cross section in proton-proton collisions at the centre-of-mass energy of 8[Formula: see text] is presented using data collected with the CMS detector at the LHC, corresponding to an integrated luminosity of 19.6[Formula: see text]. This analysis is performed in the [Formula: see text] decay channels with one isolated, high transverse momentum electron or muon and at least four jets, at least one of which is required to be identified as originating from hadronization of a b quark. The calibration of the jet energy scale and the efficiency of b jet identification are determined from data. The measured [Formula: see text] cross section is [Formula: see text]. This measurement is compared with an analysis of 7[Formula: see text] data, corresponding to an integrated luminosity of 5.0[Formula: see text], to determine the ratio of 8[Formula: see text] to 7[Formula: see text] cross sections, which is found to be [Formula: see text]. The measurements are in agreement with QCD predictions up to next-to-next-to-leading order.
  16. Sirunyan AM, Tumasyan A, Adam W, Ambrogi F, Asilar E, Bergauer T, et al.
    Eur Phys J C Part Fields, 2018;78(2):140.
    PMID: 31265001 DOI: 10.1140/epjc/s10052-018-5607-5
    A search for standard model production of four top quarks (

    t

    t
    ¯

    t

    t
    ¯


    ) is reported using events containing at least three leptons (

    e
    ,
    μ

    ) or a same-sign lepton pair. The events are produced in proton-proton collisions at a center-of-mass energy of 13


    TeV

    at the LHC, and the data sample, recorded in 2016, corresponds to an integrated luminosity of 35.9



    fb

    -
    1



    . Jet multiplicity and flavor are used to enhance signal sensitivity, and dedicated control regions are used to constrain the dominant backgrounds. The observed and expected signal significances are, respectively, 1.6 and 1.0 standard deviations, and the

    t

    t
    ¯

    t

    t
    ¯


    cross section is measured to be

    16
    .

    9

    -
    11.4


    +
    13.8






    fb

    , in agreement with next-to-leading-order standard model predictions. These results are also used to constrain the Yukawa coupling between the top quark and the Higgs boson to be less than 2.1 times its expected standard model value at 95% confidence level.
  17. Sirunyan AM, Tumasyan A, Adam W, Asilar E, Bergauer T, Brandstetter J, et al.
    Eur Phys J C Part Fields, 2018;78(3):242.
    PMID: 31264999 DOI: 10.1140/epjc/s10052-018-5691-6
    Events with no charged particles produced between the two leading jets are studied in proton-proton collisions at


    s

    =
    7




    TeV

    . The jets were required to have transverse momentum


    p

    T

    jet

    >
    40




    GeV

    and pseudorapidity


    1.5
    <
    |


    η
    jet


    |
    <
    4.7


    , and to have values of

    η
    jet

    with opposite signs. The data used for this study were collected with the CMS detector during low-luminosity running at the LHC, and correspond to an integrated luminosity of 8



    pb

    -
    1



    . Events with no charged particles with


    p
    T

    >
    0.2




    GeV

    in the interval

    -
    1
    <
    η
    <
    1

    between the jets are observed in excess of calculations that assume no color-singlet exchange. The fraction of events with such a rapidity gap, amounting to 0.5-1% of the selected dijet sample, is measured as a function of the

    p
    T

    of the second-leading jet and of the rapidity separation between the jets. The data are compared to previous measurements at the Tevatron, and to perturbative quantum chromodynamics calculations based on the Balitsky-Fadin-Kuraev-Lipatov evolution equations, including different models of the non-perturbative gap survival probability.
  18. Sirunyan AM, Tumasyan A, Adam W, Ambrogi F, Asilar E, Bergauer T, et al.
    Eur Phys J C Part Fields, 2019;79(4):364.
    PMID: 31180390 DOI: 10.1140/epjc/s10052-019-6855-8
    A search for the pair production of heavy vector-like partners
    T
    and
    B
    of the top and bottom quarks has been performed by the CMS experiment at the CERN LHC using proton-proton collisions at


    s

    =
    13


    Te



    . The data sample was collected in 2016 and corresponds to an integrated luminosity of 35.9



    fb

    -
    1



    . Final states studied for

    T

    T
    ¯


    production include those where one of the
    T
    quarks decays via

    T

    t
    Z

    and the other via

    T

    b
    W

    ,

    t
    Z

    , or

    t
    H

    , where
    H
    is a Higgs boson. For the

    B

    B
    ¯


    case, final states include those where one of the
    B
    quarks decays via

    B

    b
    Z

    and the other

    B

    t
    W

    ,

    b
    Z

    , or

    b
    H

    . Events with two oppositely charged electrons or muons, consistent with coming from the decay of a
    Z
    boson, and jets are investigated. The number of observed events is consistent with standard model background estimations. Lower limits at 95% confidence level are placed on the masses of the
    T
    and
    B
    quarks for a range of branching fractions. Assuming 100% branching fractions for

    T

    t
    Z

    , and

    B

    b
    Z

    ,
    T
    and
    B
    quark mass values below 1280 and 1130



    Ge



    , respectively, are excluded.
  19. Sirunyan AM, Tumasyan A, Adam W, Ambrogi F, Asilar E, Bergauer T, et al.
    Eur Phys J C Part Fields, 2019;79(5):444.
    PMID: 31265003 DOI: 10.1140/epjc/s10052-019-6926-x
    A search for supersymmetry is presented based on events with at least one photon, jets, and large missing transverse momentum produced in proton-proton collisions at a center-of-mass energy of 13



    Te



    . The data correspond to an integrated luminosity of 35.9



    fb

    -
    1



    and were recorded at the LHC with the CMS detector in 2016. The analysis characterizes signal-like events by categorizing the data into various signal regions based on the number of jets, the number of
    b
    -tagged jets, and the missing transverse momentum. No significant excess of events is observed with respect to the expectations from standard model processes. Limits are placed on the gluino and top squark pair production cross sections using several simplified models of supersymmetric particle production with gauge-mediated supersymmetry breaking. Depending on the model and the mass of the next-to-lightest supersymmetric particle, the production of gluinos with masses as large as 2120



    Ge



    and the production of top squarks with masses as large as 1230



    Ge



    are excluded at 95% confidence level.
  20. Sirunyan AM, Tumasyan A, Adam W, Ambrogi F, Asilar E, Bergauer T, et al.
    Eur Phys J C Part Fields, 2019;79(5):421.
    PMID: 31178657 DOI: 10.1140/epjc/s10052-019-6909-y
    Combined measurements of the production and decay rates of the Higgs boson, as well as its couplings to vector bosons and fermions, are presented. The analysis uses the LHC proton-proton collision data set recorded with the CMS detector in 2016 at


    s

    =
    13


    Te



    , corresponding to an integrated luminosity of 35.9



    fb

    -
    1



    . The combination is based on analyses targeting the five main Higgs boson production mechanisms (gluon fusion, vector boson fusion, and associated production with a
    W
    or
    Z
    boson, or a top quark-antiquark pair) and the following decay modes:

    H

    γ
    γ

    ,

    Z
    Z

    ,

    W
    W

    ,

    τ
    τ

    ,

    b
    b

    , and

    μ
    μ

    . Searches for invisible Higgs boson decays are also considered. The best-fit ratio of the signal yield to the standard model expectation is measured to be

    μ
    =
    1.17
    ±
    0.10

    , assuming a Higgs boson mass of

    125.09


    Ge



    . Additional results are given for various assumptions on the scaling behavior of the production and decay modes, including generic parametrizations based on ratios of cross sections and branching fractions or couplings. The results are compatible with the standard model predictions in all parametrizations considered. In addition, constraints are placed on various two Higgs doublet models.
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