Displaying publications 21 - 40 of 116 in total

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  1. Sirunyan AM, Tumasyan A, Adam W, Ambrogi F, Asilar E, Bergauer T, et al.
    Eur Phys J C Part Fields, 2018;78(9):707.
    PMID: 30839784 DOI: 10.1140/epjc/s10052-018-6143-z
    A search for pair production of heavy scalar leptoquarks (LQs), each decaying into a top quark and a
    τ
    lepton, is presented. The search considers final states with an electron or a muon, one or two
    τ
    leptons that decayed to hadrons, and additional jets. The data were collected in 2016 in proton-proton collisions at


    s

    =
    13


    Te



    with the CMS detector at the LHC, and correspond to an integrated luminosity of 35.9



    fb

    -
    1



    . No evidence for pair production of LQs is found. Assuming a branching fraction of unity for the decay

    LQ

    t
    τ

    , upper limits on the production cross section are set as a function of LQ mass, excluding masses below 900



    Ge



    at 95% confidence level. These results provide the most stringent limits to date on the production of scalar LQs that decay to a top quark and a
    τ
    lepton.
  2. Sirunyan AM, Tumasyan A, Adam W, Ambrogi F, Asilar E, Bergauer T, et al.
    Eur Phys J C Part Fields, 2018;78(9):697.
    PMID: 30839770 DOI: 10.1140/epjc/s10052-018-6144-y
    Pseudorapidity, transverse momentum, and multiplicity distributions are measured in the pseudorapidity range

    |
    η
    |
    <
    2.4

    for charged particles with transverse momenta satisfying


    p
    T

    >
    0.5

    GeV

    in proton-proton collisions at a center-of-mass energy of


    s

    =
    13

    TeV

    . Measurements are presented in three different event categories. The most inclusive of the categories corresponds to an inelastic
    p

    p
    data set, while the other two categories are exclusive subsets of the inelastic sample that are either enhanced or depleted in single diffractive dissociation events. The measurements are compared to predictions from Monte Carlo event generators used to describe high-energy hadronic interactions in collider and cosmic-ray physics.
  3. Sirunyan AM, Tumasyan A, Adam W, Ambrogi F, Asilar E, Bergauer T, et al.
    Eur Phys J C Part Fields, 2018;78(9):701.
    PMID: 30839773 DOI: 10.1140/epjc/s10052-018-6148-7
    A measurement is presented of the effective leptonic weak mixing angle (


    sin
    2


    θ
    eff



    ) using the forward-backward asymmetry of Drell-Yan lepton pairs (

    μ
    μ

    and
    e

    e
    ) produced in proton-proton collisions at


    s

    =
    8

    TeV

    at the CMS experiment of the LHC. The data correspond to integrated luminosities of 18.8 and

    19.6



    fb

    -
    1




    in the dimuon and dielectron channels, respectively, containing 8.2 million dimuon and 4.9 million dielectron events. With more events and new analysis techniques, including constraints obtained on the parton distribution functions from the measured forward-backward asymmetry, the statistical and systematic uncertainties are significantly reduced relative to previous CMS measurements. The extracted value of


    sin
    2


    θ
    eff



    from the combined dilepton data is


    sin
    2


    θ
    eff


    =
    0.23101
    ±
    0.00036

    (stat)
    ±
    0.00018

    (syst)
    ±
    0.00016

    (theo)
    ±
    0.00031

    (parton distributions in proton)
    =
    0.23101
    ±
    0.00053

    .
  4. Sirunyan AM, Tumasyan A, Adam W, Ambrogi F, Asilar E, Bergauer T, et al.
    Eur Phys J C Part Fields, 2019;79(3):280.
    PMID: 31007587 DOI: 10.1140/epjc/s10052-019-6730-7
    A search for dark matter produced in association with a Higgs boson decaying to a pair of bottom quarks is performed in proton-proton collisions at a center-of-mass energy of 13



    Te



    collected with the CMS detector at the LHC. The analyzed data sample corresponds to an integrated luminosity of 35.9



    fb

    -
    1



    . The signal is characterized by a large missing transverse momentum recoiling against a bottom quark-antiquark system that has a large Lorentz boost. The number of events observed in the data is consistent with the standard model background prediction. Results are interpreted in terms of limits both on parameters of the type-2 two-Higgs doublet model extended by an additional light pseudoscalar boson
    a
    (2HDM+
    a
    ) and on parameters of a baryonic


    Z

    '

    simplified model. The 2HDM+
    a
    model is tested experimentally for the first time. For the baryonic


    Z

    '

    model, the presented results constitute the most stringent constraints to date.
  5. Sirunyan AM, Tumasyan A, Adam W, Ambrogi F, Asilar E, Bergauer T, et al.
    Eur Phys J C Part Fields, 2019;79(4):305.
    PMID: 31007588 DOI: 10.1140/epjc/s10052-019-6800-x
    A search is presented for resonant production of second-generation sleptons (


    μ
    ~

    L

    ,


    ν
    ~

    μ

    ) via the R-parity-violating coupling

    λ
    211
    '

    to quarks, in events with two same-sign muons and at least two jets in the final state. The smuon (muon sneutrino) is expected to decay into a muon and a neutralino (chargino), which will then decay into a second muon and at least two jets. The analysis is based on the 2016 data set of proton-proton collisions at


    s

    =
    13

    TeV

    recorded with the CMS detector at the LHC, corresponding to an integrated luminosity of 35.9



    fb

    -
    1



    . No significant deviation is observed with respect to standard model expectations. Upper limits on cross sections, ranging from 0.24 to 730


    fb

    , are derived in the context of two simplified models representing the dominant signal contributions leading to a same-sign muon pair. The cross section limits are translated into coupling limits for a modified constrained minimal supersymmetric model with

    λ
    211
    '

    as the only nonzero R-parity violating coupling. The results significantly extend restrictions of the parameter space compared with previous searches for similar models.
  6. Sirunyan AM, Tumasyan A, Adam W, Ambrogi F, Asilar E, Bergauer T, et al.
    Phys. Rev. Lett., 2019 Jan 11;122(1):011803.
    PMID: 31012697 DOI: 10.1103/PhysRevLett.122.011803
    A search is performed for dark matter particles produced in association with a top quark pair in proton-proton collisions at sqrt[s]=13  TeV. The data correspond to an integrated luminosity of 35.9  fb^{-1} recorded by the CMS detector at the LHC. No significant excess over the standard model expectation is observed. The results are interpreted using simplified models of dark matter production via spin-0 mediators that couple to dark matter particles and to standard model quarks, providing constraints on the coupling strength between the mediator and the quarks. These are the most stringent collider limits to date for scalar mediators, and the most stringent for pseudoscalar mediators at low masses.
  7. Sirunyan AM, Tumasyan A, Adam W, Ambrogi F, Bergauer T, Brandstetter J, et al.
    Phys. Rev. Lett., 2019 Apr 05;122(13):132001.
    PMID: 31012626 DOI: 10.1103/PhysRevLett.122.132001
    Signals consistent with the B_{c}^{+}(2S) and B_{c}^{*+}(2S) states are observed in proton-proton collisions at sqrt[s]=13  TeV, in an event sample corresponding to an integrated luminosity of 143  fb^{-1}, collected by the CMS experiment during the 2015-2018 LHC running periods. These excited b[over ¯]c states are observed in the B_{c}^{+}π^{+}π^{-} invariant mass spectrum, with the ground state B_{c}^{+} reconstructed through its decay to J/ψπ^{+}. The two states are reconstructed as two well-resolved peaks, separated in mass by 29.1±1.5(stat)±0.7(syst)  MeV. The observation of two peaks, rather than one, is established with a significance exceeding five standard deviations. The mass of the B_{c}^{+}(2S) meson is measured to be 6871.0±1.2(stat)±0.8(syst)±0.8(B_{c}^{+})  MeV, where the last term corresponds to the uncertainty in the world-average B_{c}^{+} mass.
  8. Sirunyan AM, Tumasyan A, Adam W, Ambrogi F, Asilar E, Bergauer T, et al.
    Phys. Rev. Lett., 2019 Apr 05;122(13):132003.
    PMID: 31012605 DOI: 10.1103/PhysRevLett.122.132003
    The observation of single top quark production in association with a Z boson and a quark (tZq) is reported. Events from proton-proton collisions at a center-of-mass energy of 13 TeV containing three charged leptons (either electrons or muons) and at least two jets are analyzed. The data were collected with the CMS detector in 2016 and 2017 and correspond to an integrated luminosity of 77.4fb^{-1}. The increased integrated luminosity, a multivariate lepton identification, and a redesigned analysis strategy improve significantly the sensitivity of the analysis compared to previous searches for tZq production. The tZq signal is observed with a significance well over 5 standard deviations. The measured tZq production cross section is σ(pp→tZq→tℓ^{+}ℓ^{-}q)=111±13(stat)_{-9}^{+11}(syst)  fb, for dilepton invariant masses above 30 GeV, in agreement with the standard model expectation.
  9. Sirunyan AM, Tumasyan A, Adam W, Ambrogi F, Asilar E, Bergauer T, et al.
    Eur Phys J C Part Fields, 2018;78(4):291.
    PMID: 31007582 DOI: 10.1140/epjc/s10052-018-5740-1
    A search for new physics in events with a Z boson produced in association with large missing transverse momentum at the LHC is presented. The search is based on the 2016 data sample of proton-proton collisions recorded with the CMS experiment at


    s

    =
    13

    TeV

    , corresponding to an integrated luminosity of 35.9



    fb

    -
    1



    . The results of this search are interpreted in terms of a simplified model of dark matter production via spin-0 or spin-1 mediators, a scenario with a standard-model-like Higgs boson produced in association with the Z boson and decaying invisibly, a model of unparticle production, and a model with large extra spatial dimensions. No significant deviations from the background expectations are found, and limits are set on relevant model parameters, significantly extending the results previously achieved in this channel.
  10. Sirunyan AM, Tumasyan A, Adam W, Ambrogi F, Asilar E, Bergauer T, et al.
    Eur Phys J C Part Fields, 2018;78(4):287.
    PMID: 31007580 DOI: 10.1140/epjc/s10052-018-5752-x
    A study of the associated production of a
    Z
    boson and a charm quark jet (

    Z
    +
    c

    ), and a comparison to production with a
    b
    quark jet (

    Z
    +
    b

    ), in

    p
    p

    collisions at a centre-of-mass energy of 8


    TeV

    are presented. The analysis uses a data sample corresponding to an integrated luminosity of 19.7



    fb

    -
    1



    , collected with the CMS detector at the CERN LHC. The
    Z
    boson candidates are identified through their decays into pairs of electrons or muons. Jets originating from heavy flavour quarks are identified using semileptonic decays of
    c
    or
    b
    flavoured hadrons and hadronic decays of charm hadrons. The measurements are performed in the kinematic region with two leptons with


    p

    T



    >
    20

    GeV

    ,



    |


    η



    |


    <
    2.1

    ,

    71
    <

    m





    <
    111

    GeV

    , and heavy flavour jets with


    p

    T

    jet

    >
    25

    GeV

    and



    |


    η
    jet


    |


    <
    2.5

    . The

    Z
    +
    c

    production cross section is measured to be

    σ

    (
    p
    p

    Z
    +
    c
    +
    X
    )

    B

    (
    Z



    +



    -

    )

    =
    8.8
    ±
    0.5

    (stat)
    ±
    0.6

    (syst)

    pb

    . The ratio of the

    Z
    +
    c

    and

    Z
    +
    b

    production cross sections is measured to be

    σ
    (
    p
    p

    Z
    +
    c
    +
    X
    )
    /
    σ
    (
    p
    p

    Z
    +
    b
    +
    X
    )
    =
    2.0
    ±
    0.2

    (stat)
    ±
    0.2

    (syst)

    . The

    Z
    +
    c

    production cross section and the cross section ratio are also measured as a function of the transverse momentum of the
    Z
    boson and of the heavy flavour jet. The measurements are compared with theoretical predictions.
  11. Sirunyan AM, Tumasyan A, Adam W, Ambrogi F, Asilar E, Bergauer T, et al.
    Eur Phys J C Part Fields, 2019;79(2):94.
    PMID: 30872972 DOI: 10.1140/epjc/s10052-019-6562-5
    A search is presented for decays of
    Z
    and Higgs bosons to a

    J
    /
    ψ

    meson and a photon, with the subsequent decay of the

    J
    /
    ψ

    to


    μ
    +


    μ
    -


    . The analysis uses data from proton-proton collisions with an integrated luminosity of 35.9



    fb

    -
    1



    at


    s

    =
    13

    TeV

    collected with the CMS detector at the LHC. The observed limit on the

    Z


    J
    /
    ψ

    γ

    decay branching fraction, assuming that the

    J
    /
    ψ

    meson is produced unpolarized, is

    1.4
    ×

    10

    -
    6



    at 95% confidence level, which corresponds to a rate higher than expected in the standard model by a factor of 15. For extreme-polarization scenarios, the observed limit changes from

    -
    13.6

    to

    +
    8.6
    %

    with respect to the unpolarized scenario. The observed upper limit on the branching fraction for

    H


    J
    /
    ψ

    γ

    where the

    J
    /
    ψ

    meson is assumed to be transversely polarized is

    7.6
    ×

    10

    -
    4



    , a factor of 260 larger than the standard model prediction. The results for the Higgs boson are combined with previous data from proton-proton collisions at


    s

    =
    8

    TeV

    to produce an observed upper limit on the branching fraction for

    H


    J
    /
    ψ

    γ

    that is a factor of 220 larger than the standard model value.
  12. Sirunyan AM, Tumasyan A, Adam W, Ambrogi F, Asilar E, Bergauer T, et al.
    Eur Phys J C Part Fields, 2019;79(1):20.
    PMID: 30872964 DOI: 10.1140/epjc/s10052-018-6482-9
    Measurements of inclusive isolated-photon and photon+jet production in proton-proton collisions at


    s

    =
    13

    TeV

    are presented. The analysis uses data collected by the CMS experiment in 2015, corresponding to an integrated luminosity of 2.26



    fb

    -
    1



    . The cross section for inclusive isolated photon production is measured as a function of the photon transverse energy in a fiducial region. The cross section for photon+jet production is measured as a function of the photon transverse energy in the same fiducial region with identical photon requirements and with the highest transverse momentum jet. All measurements are in agreement with predictions from next-to-leading-order perturbative QCD.
  13. Sirunyan AM, Tumasyan A, Adam W, Ambrogi F, Asilar E, Bergauer T, et al.
    Eur Phys J C Part Fields, 2018;78(9):789.
    PMID: 30956565 DOI: 10.1140/epjc/s10052-018-6242-x
    A search is presented for physics beyond the standard model, based on measurements of dijet angular distributions in proton-proton collisions at


    s

    =
    13
    TeV

    . The data collected with the CMS detector at the LHC correspond to an integrated luminosity of 35.9



    fb

    -
    1



    . The observed distributions, corrected to particle level, are found to be in agreement with predictions from perturbative quantum chromodynamics that include electroweak corrections. Constraints are placed on models containing quark contact interactions, extra spatial dimensions, quantum black holes, or dark matter, using the detector-level distributions. In a benchmark model where only left-handed quarks participate, contact interactions are excluded at the 95% confidence level up to a scale of 12.8 or 17.5TeV, for destructive or constructive interference, respectively. The most stringent lower limits to date are set on the ultraviolet cutoff in the Arkani-Hamed-Dimopoulos-Dvali model of extra dimensions. In the Giudice-Rattazzi-Wells convention, the cutoff scale is excluded up to 10.1TeV. The production of quantum black holes is excluded for masses below 5.9 and 8.2TeV, depending on the model. For the first time, lower limits between 2.0 and 4.6TeVare set on the mass of a dark matter mediator for (axial-)vector mediators, for the universal quark coupling


    g
    q

    =
    1.0

    .
  14. Sirunyan AM, Tumasyan A, Adam W, Ambrogi F, Asilar E, Bergauer T, et al.
    Eur Phys J C Part Fields, 2019;79(3):269.
    PMID: 30971865 DOI: 10.1140/epjc/s10052-019-6752-1
    Measurements are presented of associated production of a
    W
    boson and a charm quark (

    W
    +
    c

    ) in proton-proton collisions at a center-of-mass energy of 13



    Te



    . The data correspond to an integrated luminosity of 35.7



    fb

    -
    1



    collected by the CMS experiment at the CERN LHC. The
    W
    bosons are identified by their decay into a muon and a neutrino. The charm quarks are tagged via the full reconstruction of



    D








    (
    2010
    )

    ±


    mesons that decay via




    D








    (
    2010
    )

    ±





    D

    0

    +

    π
    ±




    K



    +

    π
    ±

    +

    π
    ±


    . A cross section is measured in the fiducial region defined by the muon transverse momentum


    p

    T

    μ

    >
    26


    Ge



    , muon pseudorapidity


    |


    η
    μ


    |
    <
    2.4


    , and charm quark transverse momentum


    p

    T

    c

    >
    5


    Ge



    . The inclusive cross section for this kinematic range is

    σ

    (
    W
    +
    c
    )

    =
    1026
    ±
    31

    (stat)





    +
    76







    -
    72






    (syst) pb

    . The cross section is also measured differentially as a function of the pseudorapidity of the muon from the
    W
    boson decay. These measurements are compared with theoretical predictions and are used to probe the strange quark content of the proton.
  15. Sirunyan AM, Tumasyan A, Adam W, Ambrogi F, Asilar E, Bergauer T, et al.
    Phys. Rev. Lett., 2019 Mar 29;122(12):121803.
    PMID: 30978057 DOI: 10.1103/PhysRevLett.122.121803
    This Letter describes a search for Higgs boson pair production using the combined results from four final states: bbγγ, bbττ, bbbb, and bbVV, where V represents a W or Z boson. The search is performed using data collected in 2016 by the CMS experiment from LHC proton-proton collisions at sqrt[s]=13  TeV, corresponding to an integrated luminosity of 35.9  fb^{-1}. Limits are set on the Higgs boson pair production cross section. A 95% confidence level observed (expected) upper limit on the nonresonant production cross section is set at 22.2 (12.8) times the standard model value. A search for narrow resonances decaying to Higgs boson pairs is also performed in the mass range 250-3000 GeV. No evidence for a signal is observed, and upper limits are set on the resonance production cross section.
  16. Sirunyan AM, Tumasyan A, Adam W, Ambrogi F, Asilar E, Bergauer T, et al.
    Eur Phys J C Part Fields, 2018;78(11):965.
    PMID: 30881214 DOI: 10.1140/epjc/s10052-018-6373-0
    The production of a
    Z
    boson, decaying to two charged leptons, in association with jets in proton-proton collisions at a centre-of-mass energy of 13


    TeV

    is measured. Data recorded with the CMS detector at the LHC are used that correspond to an integrated luminosity of 2.19



    fb
    -1


    . The cross section is measured as a function of the jet multiplicity and its dependence on the transverse momentum of the
    Z
    boson, the jet kinematic variables (transverse momentum and rapidity), the scalar sum of the jet momenta, which quantifies the hadronic activity, and the balance in transverse momentum between the reconstructed jet recoil and the
    Z
    boson. The measurements are compared with predictions from four different calculations. The first two merge matrix elements with different parton multiplicities in the final state and parton showering, one of which includes one-loop corrections. The third is a fixed-order calculation with next-to-next-to-leading order accuracy for the process with a
    Z
    boson and one parton in the final state. The fourth combines the fully differential next-to-next-to-leading order calculation of the process with no parton in the final state with next-to-next-to-leading logarithm resummation and parton showering.
  17. Sirunyan AM, Tumasyan A, Adam W, Ambrogi F, Asilar E, Bergauer T, et al.
    Phys. Rev. Lett., 2019 Mar 01;122(8):081804.
    PMID: 30932612 DOI: 10.1103/PhysRevLett.122.081804
    A search for heavy, narrow resonances decaying to a Higgs boson and a photon (Hγ) has been performed in proton-proton collision data at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 35.9  fb^{-1} collected with the CMS detector at the LHC in 2016. Events containing a photon and a Lorentz-boosted hadronically decaying Higgs boson reconstructed as a single, large-radius jet are considered, and the γ+jet invariant mass spectrum is analyzed for the presence of narrow resonances. To increase the sensitivity of the search, events are categorized depending on whether or not the large-radius jet can be identified as a result of the merging of two jets originating from b quarks. Results in both categories are found to agree with the predictions of the standard model. Upper limits on the production rate of Hγ resonances are set as a function of their mass in the range of 720-3250 GeV, representing the most stringent constraints to date.
  18. 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.
  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, 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.
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