Publications
1082 results found
Sirunyan AM, Tumasyan A, Adam W, et al., 2018, Search for new physics in events with a leptonically decaying Z boson and a large transverse momentum imbalance in proton-proton collisions at root s=13 TeV, EUROPEAN PHYSICAL JOURNAL C, Vol: 78, ISSN: 1434-6044
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√=13TeV, corresponding to an integrated luminosity of 35.9fb−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.
Sirunyan AM, Tumasyan A, Adam W, et al., 2018, Measurement of normalized differential t(t)over-bar cross sections in the dilepton channel from pp collisions at root s=13 TeV, Journal of High Energy Physics, Vol: 2018, ISSN: 1029-8479
Normalized differential cross sections for top quark pair production are measured in the dilepton (e+e−, μ+μ−, and μ∓e±) decay channels in proton-proton collisions at a center-of-mass energy of 13 TeV. The measurements are performed with data corresponding to an integrated luminosity of 2.1 fb−1 using the CMS detector at the LHC. The cross sections are measured differentially as a function of the kinematic properties of the leptons, jets from bottom quark hadronization, top quarks, and top quark pairs at the particle and parton levels. The results are compared to several Monte Carlo generators that implement calculations up to next-to-leading order in perturbative quantum chromodynamics interfaced with parton showering, and also to fixed-order theoretical calculations of top quark pair production up to next-to-next-to-leading order.
Sirunyan AM, Tumasyan A, Adam W, et al., 2018, Search for pair production of vector-like quarks in the bW(b)over-barW channel from proton-proton collisions at root s=13TeV, PHYSICS LETTERS B, Vol: 779, Pages: 82-106, ISSN: 0370-2693
A search is presented for the production of vector-like quark pairs, or , with electric charge of 2/3 (T) or (Y), in proton–proton collisions at . The data were collected by the CMS experiment at the LHC in 2016 and correspond to an integrated luminosity of . The T and Y quarks are assumed to decay exclusively to a W boson and a b quark. The search is based on events with a single isolated electron or muon, large missing transverse momentum, and at least four jets with large transverse momenta. In the search, a kinematic reconstruction of the final state observables is performed, which would permit a signal to be detected as a narrow mass peak (≈7% resolution). The observed number of events is consistent with the standard model prediction. Assuming strong pair production of the vector-like quarks and a 100% branching fraction to , a lower limit of 1295 GeV at 95% confidence level is set on the T and Y quark masses.
Sirunyan AM, Tumasyan A, Adam W, et al., 2018, Search for massive resonances decaying into WW, WZ, ZZ, qW, and qZ with dijet final states at root s=13 TeV, PHYSICAL REVIEW D, Vol: 97, ISSN: 2470-0010
Results are presented from a search in the dijet final state for new massive narrow resonances decaying to pairs of W and Z bosons or to a W/Z boson and a quark. Results are based on data recorded in proton-proton collisions at √s=13 TeV with the CMS detector at the CERN LHC. The data correspond to an integrated luminosity of 35.9 fb−1. The mass range investigated extends upwards from 1.2 TeV. No excess is observed above the estimated standard model background and limits are set at 95% confidence level on cross sections, which are interpreted in terms of various models that predict gravitons, heavy spin-1 bosons, and excited quarks. In a heavy vector triplet model, W′ and Z′ resonances, with masses below 3.2 and 2.7 TeV, respectively, and spin-1 resonances with degenerate masses below 3.8 TeV are excluded at 95% confidence level. In the case of a singlet W′ resonance masses between 3.3 and 3.6 TeV can be excluded additionally. Similarly, excited quark resonances, q∗, decaying to qW and qZ with masses less than 5.0 and 4.7 TeV, respectively, are excluded. In a narrow-width bulk graviton model, upper limits are set on cross sections ranging from 0.6 fb for high resonance masses above 3.6 TeV, to 36.0 fb for low resonance masses of 1.3 TeV.
Sirunyan AM, Tumasyan A, Adam W, et al., 2018, Search for supersymmetry with Higgs boson to diphoton decays using the razor variables at root s=13 TeV, PHYSICS LETTERS B, Vol: 779, Pages: 166-190, ISSN: 0370-2693
An inclusive search for anomalous Higgs boson production in the diphoton decay channel and in association with at least one jet is presented, using LHC proton–proton collision data collected by the CMS experiment at a center-of-mass energy of 13 TeV and corresponding to an integrated luminosity of . The razor variables and , as well as the momentum and mass resolution of the diphoton system, are used to categorize events into different search regions. The search result is interpreted in the context of strong and electroweak production of supersymmetric particles. We exclude bottom squark pair-production with masses below 450 GeV for bottom squarks decaying to a bottom quark, a Higgs boson, and the lightest supersymmetric particle (LSP) for LSP masses below 250 GeV. For wino-like chargino–neutralino production, we exclude charginos with mass below 170 GeV for LSP masses below 25 GeV. In the GMSB scenario, we exclude charginos with mass below 205 GeV for neutralinos decaying to a Higgs boson and a goldstino LSP with 100% branching fraction.
Sirunyan AM, Tumasyan A, Adam W, et al., 2018, Observation of the Higgs boson decay to a pair of tau leptons with the CMS detector, PHYSICS LETTERS B, Vol: 779, Pages: 283-316, ISSN: 0370-2693
A measurement of the signal strength is performed using events recorded in proton–proton collisions by the CMS experiment at the LHC in 2016 at a center-of-mass energy of . The data set corresponds to an integrated luminosity of . The signal is established with a significance of 4.9 standard deviations, to be compared to an expected significance of 4.7 standard deviations. The best fit of the product of the observed signal production cross section and branching fraction is times the standard model expectation. The combination with the corresponding measurement performed with data collected by the CMS experiment at center-of-mass energies of 7 and leads to an observed significance of 5.9 standard deviations, equal to the expected significance. This is the first observation of Higgs boson decays to τ leptons by a single experiment.
Sirunyan AM, Tumasyan A, Adam W, et al., 2018, Measurement of the associated production of a single top quark and a Z boson in pp collisions at, root s=13 TeV, PHYSICS LETTERS B, Vol: 779, Pages: 358-384, ISSN: 0370-2693
A measurement is presented of the associated production of a single top quark and a Z boson. The study uses data from proton–proton collisions at recorded by the CMS experiment, corresponding to an integrated luminosity of 35.9 fb−1. Using final states with three leptons (electrons or muons), the tZq production cross section is measured to be , where ℓ stands for electrons, muons, or τ leptons, with observed and expected significances of 3.7 and 3.1 standard deviations, respectively.
Aaboud MY, Aad G, Abbott B, et al., 2018, Combination of inclusive and differential t(t)over-bar charge asymmetry measurements using ATLAS and CMS data at root S =7 and 8 TeV, Journal of High Energy Physics, Vol: 2018, ISSN: 1029-8479
This paper presents combinations of inclusive and differential measurements of the charge asymmetry (AC) in top quark pair (tt⎯⎯) events with a lepton+jets signature by the ATLAS and CMS Collaborations, using data from LHC proton-proton collisions at centre-of-mass energies of 7 and 8 TeV. The data correspond to integrated luminosities of about 5 and 20 fb−1 for each experiment, respectively. The resulting combined LHC measurements of the inclusive charge asymmetry are A C CHC7 = 0.005 ± 0.007 (stat) ± 0.006(syst) at 7 TeV and A C CHC8 = 0.0055 ± 0.0023 (stat) ± 0.0025 (syst) at 8 TeV. These values, as well as the combination of AC measurements as a function of the invariant mass of the tt⎯⎯ system at 8 TeV, are consistent with the respective standard model predictions.
Sirunyan AM, Tumasyan A, Adam W, et al., 2018, Measurement of associated Z plus charm production in proton-proton collisions at root s=8TeV, EUROPEAN PHYSICAL JOURNAL C, Vol: 78, ISSN: 1434-6044
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 pp collisions at a centre-of-mass energy of 8TeV are presented. The analysis uses a data sample corresponding to an integrated luminosity of 19.7fb−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 pℓT>20GeV, |ηℓ|<2.1, 71<mℓℓ<111GeV, and heavy flavour jets with pjetT>25GeV and |ηjet|<2.5. The Z+c production cross section is measured to be σ(pp→Z+c+X)B(Z→ℓ+ℓ−)=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(pp→Z+c+X)/σ(pp→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.
Sirunyan AM, Tumasyan A, Adam W, et al., 2018, Measurement of the Splitting Function in &ITpp &ITand Pb-Pb Collisions at root&ITsNN&IT=5.02 TeV, PHYSICAL REVIEW LETTERS, Vol: 120, ISSN: 0031-9007
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.
Sirunyan AM, Tumasyan A, Adam W, et al., 2018, Suppression of Excited gamma States Relative to the Ground State in Pb-Pb Collisions at root s(NN)=5.02 TeV, PHYSICAL REVIEW LETTERS, Vol: 120, ISSN: 0031-9007
The relative yields of Υ mesons produced in pp and Pb-Pb collisions at √sNN=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.
Sirunyan AM, Tumasyan A, Adam W, et al., 2018, Comparing transverse momentum balance of b jet pairs in pp and PbPb collisions at root s(NN)=5.02 TeV, JOURNAL OF HIGH ENERGY PHYSICS, Vol: 2018, ISSN: 1029-8479
The transverse momentum balance of pairs of back-to-back b quark jets in PbPb and pp collisions recorded with the CMS detector at the LHC is reported. The center-of-mass energy in both collision systems is 5.02 TeV per nucleon pair. Compared to the pp collision baseline, b quark jets have a larger imbalance in the most central PbPb collisions, as expected from the jet quenching effect. The data are also compared to the corresponding measurement with inclusive dijets. In the most central collisions, the imbalance of b quark dijets is comparable to that of inclusive dijets.
Sirunyan AM, Tumasyan A, Adam W, et al., 2018, Measurement of differential cross sections in the kinematic angular variable phi* for inclusive Z boson production in pp collisions at root s=8 TeV, JOURNAL OF HIGH ENERGY PHYSICS, Vol: 2018, ISSN: 1029-8479
Measurements of differential cross sections dσ/dϕ* and double-differential cross sections d2σ/dϕ*d|y| for inclusive Z boson production are presented using the dielectron and dimuon final states. The kinematic observable ϕ* correlates with the dilepton transverse momentum but has better resolution, and y is the dilepton rapidity. The analysis is based on data collected with the CMS experiment at a centre-of-mass energy of 8 TeV corresponding to an integrated luminosity of 19.7 fb−1. The normalised cross section (1/σ) dσ/dϕ*, within the fiducial kinematic region, is measured with a precision of better than 0.5% for ϕ* < 1. The measurements are compared to theoretical predictions and they agree, typically, within few percent.
Sirunyan AM, Tumasyan A, Adam W, et al., 2018, Combined search for electroweak production of charginos and neutralinos in proton-proton collisions at root s=13 TeV, JOURNAL OF HIGH ENERGY PHYSICS, Vol: 2018, ISSN: 1029-8479
A statistical combination of several searches for the electroweak production of charginos and neutralinos is presented. All searches use proton-proton collision data at s√=13 TeV, recorded with the CMS detector at the LHC in 2016 and corresponding to an integrated luminosity of 35.9 fb−1. In addition to the combination of previous searches, a targeted analysis requiring three or more charged leptons (electrons or muons) is presented, focusing on the challenging scenario in which the difference in mass between the two least massive neutralinos is approximately equal to the mass of the Z boson. The results are interpreted in simplified models of chargino-neutralino or neutralino pair production. For chargino-neutralino production, in the case when the lightest neutralino is massless, the combination yields an observed (expected) limit at the 95% confidence level on the chargino mass of up to 650 (570) GeV, improving upon the individual analysis limits by up to 40 GeV. If the mass difference between the two least massive neutralinos is approximately equal to the mass of the Z boson in the chargino-neutralino model, the targeted search requiring three or more leptons obtains observed and expected exclusion limits of around 225 GeV on the second neutralino mass and 125 GeV on the lightest neutralino mass, improving the observed limit by about 60 GeV in both masses compared to the previous CMS result. In the neutralino pair production model, the combined observed (expected) exclusion limit on the neutralino mass extends up to 650–750 (550–750) GeV, depending on the branching fraction assumed. This extends the observed exclusion achieved in the individual analyses by up to 200 GeV. The combined result additionally excludes some intermediate gaps in the mass coverage of the individual analyses.
Sirunyan AM, Tumasyan A, Adam W, et al., 2018, Search for electroweak production of charginos and neutralinos in multilepton final states in proton-proton collisions at root s=13 TeV, Journal of High Energy Physics, Vol: 166, ISSN: 1029-8479
Results are presented from a search for the direct electroweak production of charginos and neutralinos in signatures with either two or more leptons (electrons or muons) of the same electric charge, or with three or more leptons, which can include up to two hadronically decaying tau leptons. The results are based on a sample of proton-proton collision data collected at s√=13 TeV, recorded with the CMS detector at the LHC, corresponding to an integrated luminosity of 35.9 fb−1. The observed event yields are consistent with the expectations based on the standard model. The results are interpreted in simplified models of supersymmetry describing various scenarios for the production and decay of charginos and neutralinos. Depending on the model parameters chosen, mass values between 180 GeV and 1150 GeV are excluded at 95% CL. These results significantly extend the parameter space probed for these particles in searches at the LHC. In addition, results are presented in a form suitable for alternative theoretical interpretations.
Sirunyan AM, Tumasyan A, Adam W, et al., 2018, Search for natural supersymmetry in events with top quark pairs and photons in pp collisions at root s=8 TeV, JOURNAL OF HIGH ENERGY PHYSICS, Vol: 2018, ISSN: 1029-8479
Results are presented from a search for natural gauge-mediated supersymmetry (SUSY) in a scenario in which the top squark is the lightest squark, the next-to-lightest SUSY particle is a bino-like neutralino, and the lightest SUSY particle is the gravitino. The strong production of top squark pairs can produce events with pairs of top quarks and neutralinos, with each bino-like neutralino decaying to a photon and a gravitino. The search is performed using a sample of pp collision data accumulated by the CMS experiment at s√=8 TeV, corresponding to an integrated luminosity of 19.7 fb−1. The final state consists of a lepton (electron or muon), jets, and one or two photons. The imbalance in transverse momentum in the events is compared with the expected spectrum from standard model processes. No excess event yield is observed beyond the expected background, and the result is interpreted in the context of a general model of gauge-mediated SUSY breaking that leads to exclusion of top squark masses below 650–730 GeV.
Sirunyan AM, Tumasyan A, Adam W, et al., 2018, Study of dijet events with a large rapidity gap between the two leading jets in pp collisions at root s=7 TeV, EUROPEAN PHYSICAL JOURNAL C, Vol: 78, ISSN: 1434-6044
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 pjetT>40 GeV and pseudorapidity 1.5<|ηjet|<4.7, and to have values of ηjet 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 8pb−1. Events with no charged particles with pT>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 pT 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.
Sirunyan AM, Tumasyan A, Adam W, et al., 2018, Measurement of the inclusive t(t)over-bar cross section in pp collisions root s=5.02 TeV using final states with at least one charged lepton, JOURNAL OF HIGH ENERGY PHYSICS, Vol: 2018, ISSN: 1029-8479
The top quark pair production cross section (σtt¯) is measured for the first time in pp collisions at a center-of-mass energy of 5.02 TeV. The data were collected by the CMS experiment at the LHC and correspond to an integrated luminosity of 27.4 pb−1. The measurement is performed by analyzing events with at least one charged lepton. The measured cross section is σtt¯ = 69.5 ± 6.1 (stat) ± 5.6 (syst) ± 1.6 (lumi) pb, with a total relative uncertainty of 12%. The result is in agreement with the expectation from the standard model. The impact of the presented measurement on the determination of the gluon distribution function is investigated.
Cieri D, Calligaris L, Harder K, et al., 2018, An FPGA-based track finder for the L1 trigger of the CMS experiment at the HL-LHC, Topical Workshop on Electronics for Particle Physics 2017, Publisher: Sissa Medialab srl Partita IVA
A new tracking detector is under development for use by the CMS experiment at the High-Luminosity LHC (HL-LHC). A crucial component of this upgrade will be the ability to reconstruct within a few microseconds all charged particle tracks with transverse momentum above 3 GeV, so they can be used in the Level-1 trigger decision. A concept for an FPGA-based track finder using a fully time-multiplexed architecture is presented, where track candidates are reconstructed using a projective binning algorithm based on the Hough Transform followed by a track fitting based on the linear regression technique. A hardware demonstrator using MP7 processing boards has been assembled to prove the entire system, from the output of the tracker readout boards to the reconstruction of tracks with fitted helix parameters. It successfully operates on one eighth of the tracker solid angle at a time, processing events taken at 40 MHz, each with up to 200 superimposed proton-proton interactions, whilst satisfying latency constraints. The demonstrated track-reconstruction system, the chosen architecture, the achievements to date and future options for such a system will be discussed.
Sirunyan AM, Tumasyan A, Adam W, et al., 2018, Search for new phenomena in final states with two opposite-charge, same-flavor leptons, jets, and missing transverse momentum in pp collisions at root s=13TeV, JOURNAL OF HIGH ENERGY PHYSICS, Vol: 2018, ISSN: 1029-8479
Search results are presented for physics beyond the standard model in final states with two opposite-charge, same-flavor leptons, jets, and missing transverse momentum. The data sample corresponds to an integrated luminosity of 35.9 fb−1 of proton-proton collisions at s√=13 TeV collected with the CMS detector at the LHC in 2016. The analysis uses the invariant mass of the lepton pair, searching for a kinematic edge or a resonant-like excess compatible with the Z boson mass. The search for a kinematic edge targets production of particles sensitive to the strong force, while the resonance search targets both strongly and electroweakly produced new physics. The observed yields are consistent with the expectations from the standard model, and the results are interpreted in the context of simplified models of supersymmetry. In a gauge mediated supersymmetry breaking (GMSB) model of gluino pair production with decay chains including Z bosons, gluino masses up to 1500–1770 GeV are excluded at the 95% confidence level depending on the lightest neutralino mass. In a model of electroweak chargino-neutralino production, chargino masses as high as 610 GeV are excluded when the lightest neutralino is massless. In GMSB models of electroweak neutralino-neutralino production, neutralino masses up to 500-650 GeV are excluded depending on the decay mode assumed. Finally, in a model with bottom squark pair production and decay chains resulting in a kinematic edge in the dilepton invariant mass distribution, bottom squark masses up to 980–1200 GeV are excluded depending on the mass of the next-to-lightest neutralino.
Sirunyan AM, Tumasyan A, Adam W, et al., 2018, Search for pair production of excited top quarks in the lepton + jets final state, Physics Letters B, Vol: 778, Pages: 349-370, ISSN: 0370-2693
A search is performed for the pair production of spin-3/2 excited top quarks, each decaying to a top quark and a gluon. The search uses the data collected with the CMS detector from proton–proton collisions at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 35.9. Events are selected by requiring an isolated muon or electron, an imbalance in the transverse momentum, and at least six jets of which exactly two must be compatible with originating from the fragmentation of a bottom quark. No significant excess over the standard model predictions is found. A lower limit of 1.2 TeV is set at 95% confidence level on the mass of the spin-3/2 excited top quark in an extension of the Randall–Sundrum model, assuming a 100% branching fraction of its decay into a top quark and a gluon. These are the best limits to date in a search for excited top quarks and the first at 13 TeV.
Sirunyan AM, Tumasyan A, Adam W, et al., 2018, Search for ZZ resonances in the 2ℓ2v final state in proton-proton collisions at 13 TeV, Journal of High Energy Physics, Vol: 2018, ISSN: 1029-8479
A search for heavy resonances decaying to a pair of Z bosons is performed using data collected with the CMS detector at the LHC. Events are selected by requiring two oppositely charged leptons (electrons or muons), consistent with the decay of a Z boson, and large missing transverse momentum, which is interpreted as arising from the decay of a second Z boson to two neutrinos. The analysis uses data from proton-proton collisions at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 35.9 fb−1. The hypothesis of a spin-2 bulk graviton (X) decaying to a pair of Z bosons is examined for 600 ≤ mX ≤ 2500 GeV and upper limits at 95% confidence level are set on the product of the production cross section and branching fraction of X → ZZ ranging from 100 to 4 fb. For bulk graviton models characterized by a curvature scale parameter k~=0.5 in the extra dimension, the region mX < 800 GeV is excluded, providing the most stringent limit reported to date. Variations of the model considering the possibility of a wide resonance produced exclusively via gluon-gluon fusion or qq¯¯¯ annihilation are also examined.
Adam W, Bergauer T, Brondolin E, et al., 2018, Test beam demonstration of silicon microstrip modules with transverse momentum discrimination for the future CMS tracking detector, JOURNAL OF INSTRUMENTATION, Vol: 13, ISSN: 1748-0221
Sirunyan AM, Tumasyan A, Adam W, et al., 2018, Observation of Correlated Azimuthal Anisotropy Fourier Harmonics in pp and p + Pb Collisions at the LHC, Physical Review Letters, Vol: 120, ISSN: 0031-9007
The azimuthal anisotropy Fourier coefficients (vn) in 8.16 TeV p þ Pb data are extracted via long-range two-particle correlations as a function of the event multiplicity and compared to corresponding results in pp and PbPb collisions. Using a four-particle cumulant technique, vn correlations are measured for the first time in pp and p þ Pb collisions. The v2 and v4 coefficients are found to be positively correlated in all collision systems. For high-multiplicity p þ Pb collisions, an anticorrelation of v2 and v3 is observed, with a similar correlation strength as in PbPb data at the same multiplicity. The new correlation results strengthen the case for a common origin of the collectivity seen in p þ Pb and PbPb collisions in the measured multiplicity range.
Sirunyan AM, Tumasyan A, Adam W, et al., 2018, Measurements of the pp → ZZ production cross section and the Z → 4ℓ branching fraction, and constraints on anomalous triple gauge couplings at √s = 13TeV, European Physical Journal C: Particles and Fields, Vol: 78, ISSN: 1434-6044
Four-lepton production in proton-proton collisions, pp→(Z/γ∗)(Z/γ∗)→4ℓ , where ℓ=e or μ , is studied at a center-of-mass energy of 13 TeV with the CMS detector at the LHC. The data sample corresponds to an integrated luminosity of 35.9 fb−1 . The ZZ production cross section, σ(pp→ZZ)=17.2±0.5(stat)±0.7(syst)±0.4(theo)±0.4(lumi) pb , measured using events with two opposite-sign, same-flavor lepton pairs produced in the mass region 60<mℓ+ℓ−<120GeV , is consistent with standard model predictions. Differential cross sections are measured and are well described by the theoretical predictions. The Z boson branching fraction to four leptons is measured to be B(Z→4ℓ)=4.8±0.2(stat)±0.2(syst)±0.1(theo)±0.1(lumi)×10−6 for events with a four-lepton invariant mass in the range 80<m4ℓ<100GeV and a dilepton mass mℓℓ>4GeV for all opposite-sign, same-flavor lepton pairs. The results agree with standard model predictions. The invariant mass distribution of the four-lepton system is used to set limits on anomalous ZZZ and ZZ γ couplings at 95% confidence level: −0.0012<fZ4<0.0010 , −0.0010<fZ5<0.0013 , −0.0012<fγ4<0.0013 , −0.0012<fγ5<0.0013 .
Sirunyan AM, Tumasyan A, Adam W, et al., 2018, Observation of Electroweak Production of Same-Sign W Boson Pairs in the Two Jet and Two Same-Sign Lepton Final State in Proton-Proton Collisions at root s=13 TeV, PHYSICAL REVIEW LETTERS, Vol: 120, ISSN: 0031-9007
The first observation of electroweak production of same-sign W boson pairs in proton-proton collisions is reported. The data sample corresponds to an integrated luminosity of 35.9 fb−1 collected at a center-of-mass energy of 13 TeV with the CMS detector at the LHC. Events are selected by requiring exactly two leptons (electrons or muons) of the same charge, moderate missing transverse momentum, and two jets with a large rapidity separation and a large dijet mass. The observed significance of the signal is 5.5 standard deviations, where a significance of 5.7 standard deviations is expected based on the standard model. The ratio of measured event yields to that expected from the standard model at leading order is 0.90±0.22. A cross section measurement in a fiducial region is reported. Bounds are given on the structure of quartic vector boson interactions in the framework of dimension-8 effective field theory operators and on the production of doubly charged Higgs bosons.
Sirunyan AM, Tumasyan A, Adam W, et al., 2018, Search for standard model production of four top quarks with same-sign and multilepton final states in proton-proton collisions at √s = 13TeV, European Physical Journal C: Particles and Fields, Vol: 78, ISSN: 1434-6044
A search for standard model production of four top quarks (tt¯tt¯) 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 tt¯tt¯ cross section is measured to be 16.9⁺¹³·⁸ -₁₁.₄ 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.
Sirunyan AM, Tumasyan A, Adam W, et al., 2018, Search for top squarks and dark matter particles in opposite-charge dilepton final states at root s=13 TeV, PHYSICAL REVIEW D, Vol: 97, ISSN: 2470-0010
A search for new physics is presented in final states with two oppositely charged leptons (electrons or muons), jets identified as originating from b quarks, and missing transverse momentum (pmissT). The search uses proton-proton collision data at √s=13 TeV amounting to 35.9 fb−1 of integrated luminosity collected using the CMS detector in 2016. Hypothetical signal events are efficiently separated from the dominant t¯t background with requirements on pmissT and transverse-mass variables. No significant deviation is observed from the expected background. Exclusion limits are set in the context of simplified supersymmetric models with pair-produced top squarks. For top squarks, decaying exclusively to a top quark and a neutralino, exclusion limits are placed at 95% confidence level on the mass of the lightest top squark up to 800 GeV and on the lightest neutralino up to 360 GeV. These results, combined with searches in the single-lepton and all-jet final states, raise the exclusion limits up to 1050 GeV for the lightest top squark and up to 500 GeV for the lightest neutralino. For top squarks undergoing a cascade decay through charginos and sleptons, the mass limits reach up to 1300 GeV for top squarks and up to 800 GeV for the lightest neutralino. The results are also interpreted in a simplified model with a dark matter (DM) particle coupled to the top quark through a scalar or pseudoscalar mediator. For light DM, mediator masses up to 100 (50) GeV are excluded for scalar (pseudoscalar) mediators. The result for the scalar mediator achieves some of the most stringent limits to date in this model.
Sirunyan AM, Tumasyan A, Adam W, et al., 2018, Inclusive search for a highly boosted Higgs boson decaying to a bottom quark-antiquark pair, Physical Review Letters, Vol: 120, ISSN: 0031-9007
An inclusive search for the standard model Higgs boson (H) produced with large transverse momentum (pT) and decaying to a bottom quark-antiquark pair (b¯b) is performed using a data set of pp collisions at √s = 13 TeV collected with the CMS experiment at the LHC. The data sample corresponds to an integrated luminosity of 35.9 fb -1. A highly Lorentz-boosted Higgs boson decaying to b¯b is reconstructed as a single, large radius jet, and it is identified using jet substructure and dedicated b tagging techniques. The method is validated with Z → b¯b decays. The Z → b¯b process is observed for the first time in the single-jet topology with a local significance of 5.1 standard deviations (5.8 expected). For a Higgs boson mass of 125 GeV, an excess of events above the expected background is observed (expected) with a local significance of 1.5 (0.7) standard deviations. The measured cross section times branching fraction for production via gluon fusion of H → b¯b with reconstructed pT > 450 GeV and in the pseudorapidity range −2.5 < η < 2.5 is 74 ± 48 (stat)+17−10 (syst) fb, which is consistent within uncertainties with the standard model prediction.
Sirunyan AM, Tumasyan A, Adam W, et al., 2018, Search for supersymmetry in events with at least three electrons or muons, jets, and missing transverse momentum in proton-proton collisions at root s=13 TeV, JOURNAL OF HIGH ENERGY PHYSICS, Vol: 2018, ISSN: 1029-8479
A search for new physics is carried out in events with at least three electrons or muons in any combination, jets, and missing transverse momentum. Results are based on the sample of proton-proton collision data produced by the LHC at a center-of-mass energy of 13 TeV and collected by the CMS experiment in 2016. The data sample analyzed corresponds to an integrated luminosity of 35.9 fb−1. Events are classified according to the number of b jets, missing transverse momentum, hadronic transverse momentum, and the invariant mass of same-flavor dilepton pairs with opposite charge. No significant excess above the expected standard model background is observed. Exclusion limits at 95% confidence level are computed for four different supersymmetric simplified models with pair production of gluinos or third-generation squarks. In the model with gluino pair production, with subsequent decays into a top quark-antiquark pair and a neutralino, gluinos with masses smaller than 1610 GeV are excluded for a massless lightest supersymmetric particle. In the case of bottom squark pair production, the bottom squark masses are excluded up to 840 GeV for charginos lighter than 200 GeV. For a simplified model of heavy top squark pair production, the t~2 mass is excluded up to 720, 780, or 710 GeV for models with an exclusive t~2→t~1H decay, an exclusive t~2→t~1Z decay, or an equally probable mix of those two decays. In order to provide a simplified version of the analysis for easier interpretation, a small set of aggregate signal regions also has been defined, providing a compromise between simplicity and analysis sensitivity.
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