Search Constraints
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Search Results
- Creator:
- Gao, Yongsheng and ATLAS Collaboration
- Description:
- The ratio of production cross sections of the W and Z bosons with exactly one associated jet is presented as a function of jet transverse momentum threshold. The measurement has been designed to maximise cancellation of experimental and theoretical uncertainties, and is reported both within a particle-level kinematic range corresponding to the detector acceptance and as a total cross-section ratio. Results are obtained with the ATLAS detector at the LHC in pp collisions at a centre-of-mass energy of 7 TeV using an integrated luminosity of 33 pb−1. The results are compared with perturbative leading-order, leading-log, and next-to-leading-order QCD predictions, and are found to agree within experimental and theoretical uncertainties. The ratio is measured for events with a single jet with pT > 30 GeV to be 8.73 ± 0.30(stat) ± 0.40(syst) in the electron channel, and 8.49 ± 0.23(stat) ± 0.33(syst) in the muon channel.
- Resource Type:
- Article
- Identifier:
- doi: 10.1016/j.physletb.2012.01.042
- Campus Tesim:
- Fresno
- Creator:
- Ovchinnikova, Olga, Ng, Kin C., and Meyer, Kent A.
- Description:
- We report on the development of a versatile scanning apparatus for nanoscale surface sampling that utilizes the interaction of laser radiation at a sharp probe tip to effect desorption/ablation on opaque substrates. The process, which currently yields surface craters as small as similar to 50 nm diameterx5 nm deep, has been demonstrated with both metal-coated and bare silicon tips. Desorption/ablation under the tip occurs at illumination intensities below the corresponding optical far-field threshold, suggesting that the latter process should not degrade the spatial resolution attainable for proposed chemical imaging methods based on the scanning surface probe.
- Resource Type:
- Article
- Identifier:
- dx.doi.org/10.1063/1.3053200
- Campus Tesim:
- Fresno
- Creator:
- Gao, Yongsheng and ATLAS Collaboration
- Description:
- Measurements of normalized differential cross sections for top-quark pair production are presented as a function of the top-quark transverse momentum, and of the mass, transverse momentum, and rapidity of the t (t) over bar system, in proton proton collisions at a center-of-mass energy of root s = 7 TeV. The data set corresponds to an integrated luminosity of 4.6 fb(-1), recorded in 2011 with the ATLAS detector at the CERN Large Hadron Collider. Events are selected in the lepton jets channel, requiring exactly one lepton and at least four jets with at least one of the jets tagged as originating from a b-quark. The measured spectra are corrected for detector efficiency and resolution effects and are compared to several Monte Carlo simulations and theory calculations. The results are in fair agreement with the predictions in a wide kinematic range. Nevertheless, data distributions are softer than predicted for higher values of the mass of the t (t) over bar system and of the top-quark transverse momentum. The measurements can also discriminate among different sets of parton distribution functions.
- Resource Type:
- Article
- Identifier:
- Publisher version: dx.doi.org/10.1103/PhysRevD.90.072004
- Campus Tesim:
- Fresno
- Creator:
- Hall, Raymond E. and D0 Collaboration
- Description:
- We present a search for direct CP violation in B-+/- -> J/psi K-+/- (pi(+/-)) decays. The event sample is selected from 2: 8 fb(-1) of p (p) over bar collisions recorded by D0 experiment in run II of the Fermilab Tevatron Collider. The charge asymmetry A(CP)(B+ -> J/psi K+) = +0: 0075 +/- 0: 0061(stat) +/- 0: 0030 (syst) is obtained using a sample of approximately 40 000 B-+/- -> J/psi K-+/- decays. The achieved precision is of the same level as the expected deviation predicted by some extensions of the standard model. We also measured the charge asymmetry A(CP) (B+ -> J/psi pi(+)) = - 0: 09 +/- 0: 08(stat) +/- 0: 03(syst).
- Resource Type:
- Article
- Identifier:
- Publisher version: dx.doi.org/10.1103/PhysRevLett.100.211802
- Campus Tesim:
- Fresno
- Creator:
- Gao, Yongsheng and ATLAS Collaboration
- Description:
- Multi-particle cumulants and corresponding Fourier harmonics are measured for azimuthal angle distributions of charged particles in pp collisions at root S = 5.02 and 13 TeV and in p + Pb collisions at root S-NN = 5.02 TeV, and compared to the results obtained for low-multiplicity Pb + Pb collisions at root S-NN = 2.76 TeV. These measurements aim to assess the collective nature of particle production. The measurements of multi-particle cumulants confirm the evidence for collective phenomena in p + Pb and low-multiplicity Pb + Pb collisions. On the other hand, the pp results for four-particle cumulants do not demonstrate collective behaviour, indicating that they may be biased by contributions from non-flow correlations. A comparison of multi-particle cumulants and derived Fourier harmonics across different collision systems is presented as a function of the charged-particle multiplicity. For a given multiplicity, the measured Fourier harmonics are largest in Pb + Pb, smaller in p + Pb and smallest in pp collisions. The pp results show no dependence on the collision energy, nor on the multiplicity.
- Resource Type:
- Article
- Identifier:
- Publisher version: https://doi.org/10.1140/epjc/s10052-017-4988-1
- Campus Tesim:
- Fresno