Recursos de colección

Caltech Authors (170.931 recursos)

Repository of works by Caltech published authors.

Group = CMS@Caltech

Mostrando recursos 1 - 20 de 236

  1. Measurement of angular parameters from the decay B^0 → K^(⁎0)μ^+μ^− in proton–proton collisions at √s = 8 TeV

    Sirunyan, A. M.; Anderson, D.; 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.
    Angular distributions of the decay B^0 → K^(⁎0)μ^+μ^− are studied using a sample of proton–proton collisions at √s =8 TeV collected with the CMS detector at the LHC, corresponding to an integrated luminosity of 20.5fb^(−1). An angular analysis is performed to determine the P_1 and P_5′ parameters, where the P_5′ parameter is of particular interest because of recent measurements that indicate a potential discrepancy with the standard model predictions. Based on a sample of 1397 signal events, the P_1 and P_5′ parameters are determined as a function of the dimuon invariant mass squared. The measurements are in agreement with predictions based on...

  2. Search for excited quarks of light and heavy flavor in γ + jet final states in proton–proton collisions at √s = 13 TeV

    Sirunyan, A. M.; Anderson, D.; 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 is presented for excited quarks of light and heavy flavor that decay to γ+jet final states. The analysis is based on data corresponding to an integrated luminosity of 35.9fb^(−1) collected by the CMS experiment in proton–proton collisions at √s = 13 TeV at the LHC. A signal would appear as a resonant contribution to the invariant mass spectrum of the γ+ jet system, above the background expected from standard model processes. No resonant excess is found, and upper limits are set on the product of the excited quark cross section and its branching fraction as a function of...

  3. Bose-Einstein correlations in pp, pPb, and PbPb collisions at √s_(NN) = 0.9–7 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.
    Quantum-statistical (Bose-Einstein) two-particle correlations are measured in pp collisions at √s = 0.9, 2.76, and 7 TeV, as well as in pPb and peripheral PbPb collisions at nucleon-nucleon center-of-mass energies of 5.02 and 2.76 TeV, respectively, using the CMS detector at the Large Hadron Collider. Separate analyses are performed for same-sign unidentified charged particles as well as for same-sign pions and kaons identified via their energy loss in the silicon tracker. The characteristics of the one-, two-, and three-dimensional correlation functions are studied as functions of the pair average transverse momentum (k_T) and the charged-particle multiplicity in the event. For...

  4. Measurement of differential cross sections for the production of top quark pairs and of additional jets in lepton + jets events from pp collisions at √s = 13  TeV

    Sirunyan, A. M.; Anderson, D.; Bornheim, A.; Bunn, J.; Lawhorn, J. M.; Newman, H. B.; Nguyen, T. Q.; Pena, C.; Spiropulu, M.; Vlimant, J. R.; Wilkinson, R.; Xie, S.; Zhang, Z.; Zhu, R. Y.; Dubinin, M.
    Differential and double-differential cross sections for the production of top quark pairs in proton-proton collisions at √s = 13  TeV are measured as a function of kinematic variables of the top quarks and the top quark-antiquark (tt) system. In addition, kinematic variables and multiplicities of jets associated with the tt production are measured. This analysis is based on data collected by the CMS experiment at the LHC in 2016 corresponding to an integrated luminosity of 35.8  fb^(-1). The measurements are performed in the lepton+jets decay channels with a single muon or electron and jets in the final state. The differential cross sections...

  5. Search for single production of vector-like quarks decaying to a b quark and a Higgs boson

    Sirunyan, A. M.; Anderson, D.; Bornheim, A.; Bunn, J.; Dutta, I.; Lawhorn, J. M.; Newman, H. B.; Nguyen, T. Q.; Pena, C.; Spiropulu, M.; Vlimant, J. R.; Wilkinson, R.; Xie, S.; Zhang, Z.; Zhu, R. Y.; Dubinin, M.
    A search is presented for single production of heavy vector-like quarks (B) that decay to a Higgs boson and a b quark, with the Higgs boson decaying to a highly boosted bb pair reconstructed as a single collimated jet. The analysis is based on data collected by the CMS experiment in proton-proton collisions at √s = 13 TeV, corresponding to an integrated luminosity of 35.9 fb^(−1). The data are consistent with background expectations, and upper limits at 95% confidence level on the product of the B quark cross section and the branching fraction are obtained in the range 1.28–0.07 pb,...

  6. Search for dark matter in events with energetic, hadronically decaying top quarks and missing transverse momentum at √s = 13 TeV

    Sirunyan, A. M.; Anderson, D.; 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 dark matter is conducted in events with large missing transverse momentum and a hadronically decaying, Lorentz-boosted top quark. This study is performed using proton-proton collisions at a center-of-mass energy of 13 TeV, in data recorded by the CMS detector in 2016 at the LHC, corresponding to an integrated luminosity of 36 fb^(−1). New substructure techniques, including the novel use of energy correlation functions, are utilized to identify the decay products of the top quark. With no significant deviations observed from predictions of the standard model, limits are placed on the production of new heavy bosons coupling to...

  7. Measurement of b hadron lifetimes 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.
    Measurements are presented of the lifetimes of the B^0, B^0_ s, Λ^0_b, and B+_c hadrons using the decay channels B^0→J/ψK∗(892)^0, B^0→J/ψK^0_S, B^0_s→J/ψπ^+π^−, B^0_s→J/ψϕ(1020), Λ^0_b→J/ψΛ^0, and B+_c→J/ψπ^+. The data sample, corresponding to an integrated luminosity of 19.7fb^(-1), was collected by the CMS detector at the LHC in proton–proton collisions at √s = 8 TeV. The B^0 lifetime is measured to be 453.0 ± 1.6(stat) ± 1.8(syst) μ m in J/ψK∗(892)^0 and 457.8 ± 2.7(stat) ± 2.8(syst) μ m in J/ψK^0_S, which results in a combined measurement of cτ_(B^0) = 454.1 ± 1.4(stat) ± 1.7(syst) μ m. The effective lifetime of the...

  8. Search for Physics Beyond the Standard Model in Events with High-Momentum Higgs Bosons and Missing Transverse Momentum in Proton-Proton Collisions at 13 TeV

    Sirunyan, A. M.; Anderson, D.; Bornheim, A.; Bunn, J.; Lawhorn, J. M.; Newman, H. B.; Nguyen, T. Q.; Pena, C.; Spiropulu, M.; Vlimant, J. R.; Wilkinson, R.; Xie, S.; Zhang, Z.; Zhu, R. Y.; Dubinin, M.
    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 √s = 13  TeV. The analysis utilizes a new b quark tagging technique based on jet substructure to identify jets from H → bb. Events are categorized by the multiplicity of H-tagged jets, jet mass, and the missing transverse momentum. No significant deviation from...

  9. Observation of ttH Production

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

  10. Search for new long-lived particles 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 long-lived particles was performed with data corresponding to an integrated luminosity of 2.6 fb^(−1) collected at a center-of-mass energy of 13 TeV by the CMS experiment in 2015. The analysis exploits two customized topological trigger algorithms, and uses the multiplicity of displaced jets to search for the presence of a signal decay occurring at distances between 1 and 1000 mm. The results can be interpreted in a variety of different models. For pair-produced long-lived particles decaying to two b quarks and two leptons with equal decay rates between lepton flavors, cross sections larger than 2.5 fb are...

  11. Search for gauge-mediated supersymmetry in events with at least one photon and missing transverse momentum in pp collisions at √s = 13 TeV

    Sirunyan, A. M.; Anderson, D.; 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 gauge-mediated supersymmetry (SUSY) in final states with photons and large missing transverse momentum is presented. The data sample of pp collisions at √s = 13 TeV was collected with the CMS detector at the CERN LHC and corresponds to an integrated luminosity of 35.9 fb^(−1). Data are compared with models in which the lightest neutralino has bino- or wino-like components, resulting in decays to photons and gravitinos, where the gravitinos escape detection. The event selection is optimized for both electroweak (EWK) and strong production SUSY scenarios. The observed data are consistent with standard model predictions, and limits are...

  12. Evidence for the Higgs boson decay to a bottom quark–antiquark pair

    Sirunyan, A. M.; Anderson, D.; Bornheim, A.; Lawhorn, J. M.; Newman, H. B.; Nguyen, T. Q.; Pena, C.; Spiropulu, M.; Vlimant, J. R.; Xie, S.; Zhang, Z.; Zhu, R. Y.; Dubinin, M.
    A search for the standard model (SM) Higgs boson (H) decaying to bb when produced in association with an electroweak vector boson is reported for the following processes: Z(νν)H, W(μν)H, W(eν)H, Z(μμ)H, and Z(ee)H. The search is performed in data samples corresponding to an integrated luminosity of 35.9fb^(-1) at √s = 13 TeV recorded by the CMS experiment at the LHC during Run 2 in 2016. An excess of events is observed in data compared to the expectation in the absence of a H→bb signal. The significance of this excess is 3.3 standard deviations, where the expectation from SM Higgs...

  13. Measurement of quarkonium production cross sections 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.
    Differential production cross sections of prompt J/ψ and ψ(2S) charmonium and ϒ(nS) (n=1,2,3) bottomonium states are measured in proton–proton collisions at √s = 13 TeV, with data collected by the CMS detector at the LHC, corresponding to an integrated luminosity of 2.3 fb^(−1) for the J/ψ and 2.7 fb^(−1) for the other mesons. The five quarkonium states are reconstructed in the dimuon decay channel, for dimuon rapidity |y|<1.2. The double-differential cross sections for each state are measured as a function of y and transverse momentum, and compared to theoretical expectations. In addition, ratios are presented of cross sections for prompt...

  14. Search for supersymmetry in events with one lepton and multiple jets exploiting the angular correlation between the lepton and the missing transverse momentum 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.
    Results are presented from a search for supersymmetry in events with a single electron or muon and hadronic jets. The data correspond to a sample of proton–proton collisions at √s = 13 TeV with an integrated luminosity of 35.9fb^(-1), recorded in 2016 by the CMS experiment. A number of exclusive search regions are defined according to the number of jets, the number of b-tagged jets, the scalar sum of the transverse momenta of the jets, and the scalar sum of the missing transverse momentum and the transverse momentum of the lepton. Standard model background events are reduced significantly by requiring...

  15. Search for lepton flavour violating decays of the Higgs boson to μτ and eτ in proton-proton collisions at √s = 13 TeV

    Sirunyan, A. M.; Anderson, D.; 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 lepton flavour violating decays of the Higgs boson in the μτ and eτ decay modes is presented. The search is based on a data set corresponding to an integrated luminosity of 35.9 fb^(-1) of proton-proton collisions collected with the CMS detector in 2016, at a centre-of-mass energy of 13 TeV. No significant excess over the standard model expectation is observed. The observed (expected) upper limits on the lepton flavour violating branching fractions of the Higgs boson are ℬ(H → μτ) < 0.25% (0.25%) and ℬ(H → eτ) < 0.61% (0.37%), at 95% confidence level. These results are used to derive upper limits on the off-diagonal...

  16. Measurements of differential cross sections of top quark pair production as a function of kinematic event variables in proton-proton collisions at √s = 13 TeV

    Sirunyan, A. M.; Anderson, D.; Bornheim, A.; Bunn, J.; Lawhorn, J. M.; Newman, H. B.; Nguyen, T. Q.; Pena, C.; Spiropulu, M.; Vlimant, J. R.; Wilkinson, R.; Xie, S.; Zhang, Z.; Zhu, R. Y.; Dubinin, M.
    Measurements of differential tt production cross sections are presented in the single-lepton decay channel, as a function of a number of kinematic event variables. The measurements are performed with proton-proton collision data at √s = 13 TeV, collected by the CMS experiment at the LHC during 2016, with an integrated luminosity of 35.9 fb^(−1). The data are compared to a variety of state-of-the-art leading-order and next-to-leading-order tt simulations.

  17. Search for Heavy Neutral Leptons in Events with Three Charged Leptons in Proton-Proton Collisions at √s = 13  TeV

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

  18. Search for new physics in final states with an energetic jet or a hadronically decaying W or Z boson and transverse momentum imbalance at √s = 13  TeV

    Sirunyan, A. M.; Anderson, D.; Bornheim, A.; Bunn, J.; Lawhorn, J. M.; Newman, H. B.; Nguyen, T. Q.; Pena, C.; Spiropulu, M.; Vlimant, J. R.; Wilkinson, R.; Xie, S.; Zhang, Z.; Zhu, R. Y.; Dubinin, M.
    A search for new physics using events containing an imbalance in transverse momentum and one or more energetic jets arising from initial-state radiation or the hadronic decay of W or Z bosons is presented. 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 observed data are found to be in agreement with the expectation from standard model processes. The results are interpreted as limits on the dark matter production cross section in simplified models with vector, axial-vector, scalar, and pseudoscalar...

  19. Search for a heavy right-handed W boson and a heavy neutrino in events with two same-flavor leptons and two jets at √s = 13 TeV

    Sirunyan, A. M.; Anderson, D.; Bornheim, A.; Bunn, J.; Lawhorn, J. M.; Newman, H. B.; Nguyen, T. Q.; Pena, C.; Spiropulu, M.; Vlimant, J. R.; Wilkinson, R.; Xie, S.; Zhang, Z.; Zhu, R. Y.
    A search for a heavy right-handed W boson (W_R) decaying to a heavy right-handed neutrino and a charged lepton in events with two same-flavor leptons (e or μ) and two jets, is presented. The analysis is based on proton-proton collision data, collected by the CMS Collaboration at the LHC in 2016 and corresponding to an integrated luminosity of 35.9 fb^(−1). No significant excess above the standard model expectation is seen in the invariant mass distribution of the dilepton plus dijet system. Assuming that couplings are identical to those of the standard model, and that only one heavy neutrino flavor N_R...

  20. Search for the X(5568) State Decaying into B^0_sπ^± in Proton-Proton Collisions at √s = 8  TeV

    Sirunyan, A. M.; Anderson, D.; 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 resonancelike structures in the B^0_sπ^± invariant mass spectrum is performed using proton-proton collision data collected by the CMS experiment at the LHC at √s = 8  TeV, corresponding to an integrated luminosity of 19.7  fb^(−1). The B^0_s mesons are reconstructed in the decay chain B^0_s → J/ψϕ, with J/ψ → μ^+μ^− and ϕ → K^+K^−. The B^0_sπ^± invariant mass distribution shows no statistically significant peaks for different selection requirements on the reconstructed B^0_s and π^± candidates. Upper limits are set on the relative production rates of the X(5568) and B0s states times the branching fraction of the decay X(5568)^±...

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