Recursos de colección

Caltech Authors (160.918 recursos)

Repository of works by Caltech published authors.

Group = CMS@Caltech

Mostrando recursos 1 - 20 de 123

  1. Measurements of the associated production of a Z boson and b jets in pp collisions at √s = 8 TeV

    Khachatryan, V.; Anderson, D.; Apresyan, A.; Bendavid, J.; Bornheim, A.; Bunn, J.; Chen, Y.; Duarte, J.; Mott, A.; Newman, H. B.; Pena, C.; Spiropulu, M.; Vlimant, J. R.; Xie, S.; Zhu, R. Y.; Dubinin, M.
    Measurements of the associated production of a Z boson with at least one jet originating from a b quark in proton–proton collisions at √s = 8 TeV are presented. Differential cross sections are measured with data collected by the CMS experiment corresponding to an integrated luminosity of 19.8fb^(-1). Z bosons are reconstructed through their decays to electrons and muons. Cross sections are measured as a function of observables characterizing the kinematics of the b jet and the Z boson. Ratios of differential cross sections for the associated production with at least one b jet to the associated production with any...

  2. Measurements of properties of the Higgs boson decaying into the four-lepton final state in pp collisions at √s = 13 TeV

    Sirunyan, A. M.; Anderson, D.; Bendavid, J.; Bornheim, A.; Lawhorn, J. M.; Newman, H. B.; Nguyen, T.; Pena, C.; Spiropulu, M.; Vlimant, J. R.; Xie, S.; Zhang, Z.; Zhu, R. Y.; Dubinin, M.
    Properties of the Higgs boson are measured in the H → ZZ → 4ℓ (ℓ = e, μ) decay channel. A data sample of proton-proton collisions at √s = 13 TeV, collected with the CMS detector at the LHC and corresponding to an integrated luminosity of 35.9 fb^(−1) is used. The signal strength modifier μ, defined as the ratio of the observed Higgs boson rate in the H → ZZ → 4ℓ decay channel to the standard model expectation, is measured to be μ = 1.05_(− 0.17)^(+ 0.19) at m_H = 125.09 GeV, the combined ATLAS and CMS measurement of the Higgs boson mass....

  3. Search for associated production of dark matter with a Higgs boson decaying to bb or γγ at √s = 13 TeV

    Sirunyan, A. M.; Anderson, D.; Bendavid, J.; Bornheim, A.; Bunn, J.; Duarte, J.; Lawhorn, J. M.; Mott, A.; Newman, H. B.; Pena, C.; Spiropulu, M.; Vlimant, J. R.; Xie, S.; Zhu, R. Y.; Dubinin, M.
    A search for dark matter is performed looking for events with large missing transverse momentum and a Higgs boson decaying either to a pair of bottom quarks or to a pair of photons. The data from proton-proton collisions at a center-of-mass energy of 13 TeV, collected in 2015 with the CMS detector at the LHC, correspond to an integrated luminosity of 2.3 fb^(−1). Results are interpreted in the context of a Z′-two-Higgs-doublet model, where the gauge symmetry of the standard model is extended by a U(1)_Z ′ group, with a new massive Z′ gauge boson, and the Higgs sector is extended...

  4. Particle-flow reconstruction and global event description with the CMS detector

    Sirunyan, A. M.; Anderson, D.; Bendavid, J.; Bornheim, A.; Bunn, J.; Duarte, J.; Lawhorn, J. M.; Mott, A.; Newman, H. B.; Pena, C.; Spiropulu, M.; Vlimant, J. R.; Xie, S.; Zhu, R. Y.; Dubinin, M.
    The CMS apparatus was identified, a few years before the start of the LHC operation at CERN, to feature properties well suited to particle-flow (PF) reconstruction: a highly-segmented tracker, a fine-grained electromagnetic calorimeter, a hermetic hadron calorimeter, a strong magnetic field, and an excellent muon spectrometer. A fully-fledged PF reconstruction algorithm tuned to the CMS detector was therefore developed and has been consistently used in physics analyses for the first time at a hadron collider. For each collision, the comprehensive list of final-state particles identified and reconstructed by the algorithm provides a global event description that leads to unprecedented CMS...

  5. Measurement of the triple-differential dijet cross section in proton-proton collisions at √s = 8 TeV and constraints on parton distribution functions

    Sirunyan, A. M.; Anderson, D.; Bendavid, J.; Bornheim, A.; Bunn, J.; Duarte, J.; Lawhorn, J. M.; Mott, A.; Newman, H. B.; Pena, C.; Spiropulu, M.; Vlimant, J. R.; Xie, S.; Zhu, R. Y.; Dubinin, M.
    A measurement is presented of the triple-differential dijet cross section at a centre-of-mass energy of 8TeV using 19.7fb^(-1) of data collected with the CMS detector in proton-proton collisions at the LHC. The cross section is measured as a function of the average transverse momentum, half the rapidity separation, and the boost of the two leading jets in the event. The cross section is corrected for detector effects and compared to calculations in perturbative quantum chromodynamics at next-to-leading order accuracy, complemented with electroweak and nonperturbative corrections. New constraints on parton distribution functions are obtained and the inferred value of the strong...

  6. Search for a light pseudoscalar Higgs boson produced in association with bottom quarks in pp collisions at √s = 8 TeV

    Sirunyan, A. M.; Anderson, D.; Bendavid, J.; Bornheim, A.; Lawhorn, J. M.; Newman, H. B.; Nguyen, T.; Pena, C.; Spiropulu, M.; Vlimant, J. R.; Xie, S.; Zhang, Z.; Zhu, R. Y.; Dubinin, M.
    A search for a light pseudoscalar Higgs boson (A) produced in association with bottom quarks and decaying into a muon pair is reported. The search uses 19.7 fb^(−1) of proton-proton collisions at a center-of-mass energy of 8 TeV, collected by the CMS experiment. No signal is observed in the dimuon mass range from 25 to 60 GeV. Upper limits on the cross section times branching fraction, σ(pp→bbA)B(A→μμ), are set.

  7. Measurement of the differential cross sections for the associated production of a W boson and jets in proton-proton collisions at √s = 13  TeV

    Sirunyan, A. M.; Anderson, D.; Bendavid, J.; Bornheim, A.; Lawhorn, J. M.; Newman, H. B.; Nguyen, T.; Pena, C.; Spiropulu, M.; Vlimant, J. R.; Xie, S.; Zhang, Z.; Zhu, R. Y.; Dubinin, M.
    A measurement of the differential cross sections for a W boson produced in association with jets in the muon decay channel is presented. The measurement is based on 13 TeV proton-proton collision data corresponding to an integrated luminosity of 2.2  fb^(-1), recorded by the CMS detector at the LHC. The cross sections are reported as functions of jet multiplicity, jet transverse momentum p_T, jet rapidity, the scalar p_T sum of the jets, and angular correlations between the muon and each jet for different jet multiplicities. The measured cross sections are in agreement with predictions that include multileg leading-order (LO) and next-to-LO...

  8. Search for new phenomena with the M_(T2) variable in the all-hadronic final state produced in proton–proton collisions at √s = 13 TeV

    Sirunyan, A. M.; Anderson, D.; Bendavid, J.; Bornheim, A.; Lawhorn, J. M.; Newman, H. B.; Nguyen, T.; Pena, C.; Spiropulu, M.; Vlimant, J. R.; Xie, S.; Zhang, Z.; Zhu, R. Y.; Dubinin, M.
    A search for new phenomena is performed using events with jets and significant transverse momentum imbalance, as inferred through the M_(T2) variable. The results are based on a sample of proton–proton collisions collected in 2016 at a center-of-mass energy of 13TeV with the CMS detector and corresponding to an integrated luminosity of 35.9fb^(-1). No excess event yield is observed above the predicted standard model background, and the results are interpreted as exclusion limits at 95% confidence level on the masses of predicted particles in a variety of simplified models of R-parity conserving supersymmetry. Depending on the details of the model,...

  9. Measurement of the B^± Meson Nuclear Modification Factor in Pb-Pb Collisions at √S_(NN) = 5.02  TeV

    Sirunyan, A. M.; Anderson, D.; Bendavid, J.; Bornheim, A.; Lawhorn, J. M.; Newman, H. B.; Pena, C.; Spiropulu, M.; Vlimant, J. R.; Xie, S.; Zhu, R. Y.
    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 √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...

  10. Measurements of jet charge with dijet events in pp collisions at √s = 8 TeV

    Sirunyan, A. M.; Anderson, D.; Bendavid, J.; Bornheim, A.; Bunn, J.; Duarte, J.; Lawhorn, J. M.; Mott, A.; Newman, H. B.; Pena, C.; Spiropulu, M.; Vlimant, J. R.; Xie, S.; Zhu, R. Y.; Dubinin, M.
    Jet charge is an estimator of the electric charge of a quark, antiquark, or gluon initiating a jet. It is based on the momentum-weighted sum of the electric charges of the jet constituents. Measurements of three charge observables of the leading jet in transverse momentum p_T are performed with dijet events. The analysis is carried out with ata collected by the CMS experiment at the CERN LHC in proton-proton collisions at √s = 8 TeV corresponding to an integrated luminosity of 19.7fb^(−1). The results are presented as a function of the p_T of the leading jet and compared to predictions...

  11. Search for light bosons in decays of the 125 GeV Higgs boson in proton-proton collisions at √s = 8 TeV

    Khachatryan, V.; Anderson, D.; Apresyan, A.; Bendavid, J.; Bornheim, A.; Bunn, J.; Chen, Y.; Duarte, J.; Lawhorn, J. M.; Mott, A.; Newman, H. B.; Pena, C.; Spiropulu, M.; Vlimant, J. R.; Xie, S.; Zhu, R. Y.; Dubinin, M.
    A search is presented for decays beyond the standard model of the 125 GeV Higgs bosons to a pair of light bosons, based on models with extended scalar sectors. Light boson masses between 5 and 62.5 GeV are probed in final states containing four τ leptons, two muons and two b quarks, or two muons and two τ leptons. The results are from data in proton-proton collisions corresponding to an integrated luminosity of 19.7 fb^(−1), accumulated by the CMS experiment at the LHC at a center-of-mass energy of 8 TeV. No evidence for such exotic decays is found in the...

  12. Search for leptophobic Z′ bosons decaying into four-lepton final states in proton–proton collisions at √s = 8 TeV

    Khachatryan, V.; Anderson, D.; Apresyan, A.; Bendavid, J.; Bornheim, A.; Bunn, J.; Chen, Y.; Duarte, J.; Lawhorn, J. M.; Mott, A.; Newman, H. B.; Pena, C.; Spiropulu, M.; Vlimant, J. R.; Xie, S.; Zhu, R. Y.; Dubinin, M.
    A search for heavy narrow resonances decaying into four-lepton final states has been performed using proton–proton collision data at √s = 8 TeV collected by the CMS experiment, corresponding to an integrated luminosity of 19.7fb^(−1). No excess of events over the standard model background expectation is observed. Upper limits for a benchmark model on the product of cross section and branching fraction for the production of these heavy narrow resonances are presented. The limit excludes leptophobic Z′ bosons with masses below 2.5 TeV within the benchmark model. This is the first result to constrain a leptophobic Z′ resonance in the...

  13. Search for Supersymmetry in pp Collisions at √s = 13  TeV in the Single-Lepton Final State Using the Sum of Masses of Large-Radius Jets

    Sirunyan, A. M.; Anderson, D.; Bendavid, J.; Bornheim, A.; Lawhorn, J. M.; Newman, H. B.; Nguyen, T.; Pena, C.; Spiropulu, M.; Vlimant, J. R.; Xie, S.; Zhang, Z.; Zhu, R. Y.; Dubinin, M.
    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 √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-...

  14. Search for high-mass Zγ resonances in proton-proton collisions at √s = 8 and 13 TeV using jet substructure techniques

    Sirunyan, A. M.; Anderson, D.; Bendavid, J.; Bornheim, A.; Bunn, J.; Duarte, J.; Lawhorn, J. M.; Mott, A.; Newman, H. B.; Pena, C.; Spiropulu, M.; Vlimant, J. R.; Xie, S.; Zhu, R. Y.; Dubinin, M.
    A search for massive resonances decaying to a Z boson and a photon is performed in events with a hadronically decaying Z boson candidate, separately in light-quark and b quark decay modes, identified using jet substructure and advanced b tagging techniques. Results are based on samples of proton-proton collisions collected with the CMS detector at the LHC at center-of-mass energies of 8 and 13 TeV, corresponding to integrated luminosities of 19.7 and 2.7 fb^(−1), respectively. The results of the search are combined with those of a similar search in the leptonic decay modes of the Z boson, based on the...

  15. Measurements of the charm jet cross section and nuclear modification factor in pPb collisions at √S_(NN) = 5.02 TeV

    Sirunyan, A. M.; Anderson, D.; Bendavid, J.; Bornheim, A.; Bunn, J.; Chen, Y.; Duarte, J.; Lawhorn, J. M.; Mott, A.; Newman, H. B.; Pena, C.; Spiropulu, M.; Vlimant, J. R.; Xie, S.; Zhu, R. Y.
    The CMS Collaboration presents the first measurement of the differential cross section of jets from charm quarks produced in proton–lead (pPb) collisions at a nucleon–nucleon center-of-mass energy of √s_(NN) = 5.02 TeV, as well as results from charm quark jets in proton–proton (pp) collisions at √s =2 .76 and 5.02 TeV. By comparing the yields of the pPb and pp collision systems at the same energy, a nuclear modification factor for charm jets from 55 to 400 GeV/c in pPb collisions at √s_(NN) = 5.02 TeV of R _(pA) = 0.92 ± 0.07(stat) ± 0.11(syst) is obtained. This is consistent...

  16. Search for standard model production of four top quarks in proton–proton collisions at √s = 13 TeV

    Sirunyan, A. M.; Anderson, D.; Bendavid, J.; Bornheim, A.; Bunn, J.; Duarte, J.; Lawhorn, J. M.; Mott, A.; Newman, H. B.; Pena, C.; Spiropulu, M.; Vlimant, J. R.; Xie, S.; Zhu, R. Y.; Dubinin, M.
    A search for events containing four top quarks (tt-bar tt-bar) is reported from proton–proton collisions recorded by the CMS experiment at √s = 13 TeV and corresponding to an integrated luminosity of 2.6 fb^(−1). The analysis considers the single-lepton (e or μ)+jets and the opposite-sign dilepton (μ^+ μ^−, μ^± e^∓, or e^+ e^−)+jets channels. It uses boosted decision trees to combine information on the global event and jet properties to distinguish between tt-bar tt-bar and tt-bar production. The number of events observed after all selection requirements is consistent with expectations from background and standard model signal predictions, and an upper...

  17. Coherent J/ψ photoproduction in ultra-peripheral PbPb collisions at √s_NN = 2.76 TeV with the CMS experiment

    Khachatryan, V.; Anderson, D.; Apresyan, A.; Bendavid, J.; Bornheim, A.; Bunn, J.; Chen, Y.; Duarte, J.; Mott, A.; Newman, H. B.; Pena, C.; Spiropulu, M.; Vlimant, J. R.; Xie, S.; Zhu, R. Y.
    The cross section for coherent J/ψ photoproduction accompanied by at least one neutron on one side of the interaction point and no neutron activity on the other side, X_(n)0_(n), is measured with the CMS experiment in ultra-peripheral PbPb collisions at √s_NN = 2.76 TeV. The analysis is based on a data sample corresponding to an integrated luminosity of 159 μb^(−1), collected during the 2011 PbPb run. The J/ψ mesons are reconstructed in the dimuon decay channel, while neutrons are detected using zero degree calorimeters. The measured cross section is dσ^(coh)_(X_(n)0_(n))/dy(J/ψ) = 0.36 ± 0.04 (stat) ± 0.04 (syst) mb in...

  18. Search for single production of vector-like quarks decaying into a b quark and a W boson in proton–proton collisions at √s = 13 TeV

    Sirunyan, A. M.; Anderson, D.; Bendavid, J.; Bornheim, A.; Bunn, J.; Duarte, J.; Lawhorn, J. M.; Mott, A.; Newman, H. B.; Pena, C.; Spiropulu, M.; Vlimant, J. R.; Xie, S.; Zhu, R. Y.; Dubinin, M.
    A search is presented for a heavy vector-like quark, decaying into a b quark and a W boson, which is produced singly in association with a light flavor quark and a b quark. The analysis is performed using a data sample of proton–proton collisions at a center-of-mass energy of √s = 13 TeV collected at the LHC in 2015. The data set used in the analysis corresponds to an integrated luminosity of 2.3 fb^(−1). The search is carried out using events containing one electron or muon, at least one b-tagged jet with large transverse momentum, at least one jet in...

  19. Cross section measurement of t-channel single top quark production in pp collisions at √s = 13 TeV

    Sirunyan, A. M.; Anderson, D.; Bendavid, J.; Bornheim, A.; Bunn, J.; Chen, Y.; Duarte, J.; Lawhorn, J. M.; Mott, A.; Newman, H. B.; Pena, C.; Spiropulu, M.; Vlimant, J. R.; Xie, S.; Zhu, R. Y.; Dubinin, M.
    The cross section for the production of single top quarks in the t channel is measured in proton-proton collisions at 13 TeV with the CMS detector at the LHC. The analyzed data correspond to an integrated luminosity of 2.2 fb^(−1). The event selection requires one muon and two jets where one of the jets is identified as originating from a bottom quark. Several kinematic variables are then combined into a multivariate discriminator to distinguish signal from background events. A fit to the distribution of the discriminating variable yields a total cross section of 238 ± 13 (stat) ± 29 (syst)...

  20. Cross section measurement of t-channel single top quark production in pp collisions at √s = 13 TeV

    Sirunyan, A. M.; Anderson, D.; Bendavid, J.; Bornheim, A.; Bunn, J.; Chen, Y.; Duarte, J.; Lawhorn, J. M.; Mott, A.; Newman, H. B.; Pena, C.; Spiropulu, M.; Vlimant, J. R.; Xie, S.; Zhu, R. Y.; Dubinin, M.
    The cross section for the production of single top quarks in the t channel is measured in proton-proton collisions at 13 TeV with the CMS detector at the LHC. The analyzed data correspond to an integrated luminosity of 2.2 fb^(−1). The event selection requires one muon and two jets where one of the jets is identified as originating from a bottom quark. Several kinematic variables are then combined into a multivariate discriminator to distinguish signal from background events. A fit to the distribution of the discriminating variable yields a total cross section of 238 ± 13 (stat) ± 29 (syst)...

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