| 1. |
- Schael, S, et al.
(författare)
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Precision electroweak measurements on the Z resonance
- 2006
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Ingår i: Physics Reports. - : Elsevier BV. - 0370-1573 .- 1873-6270. ; 427:5-6, s. 257-454
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Forskningsöversikt (refereegranskat)abstract
- We report on the final electroweak measurements performed with data taken at the Z resonance by the experiments operating at the electron-positron colliders SLC and LEP. The data consist of 17 million Z decays accumulated by the ALEPH, DELPHI, L3 and OPAL experiments at LEP, and 600 thousand Z decays by the SLID experiment using a polarised beam at SLC. The measurements include cross-sections, forward-backward asymmetries and polarised asymmetries. The mass and width of the Z boson, m(Z) and Gamma(Z), and its couplings to fermions, for example the p parameter and the effective electroweak mixing angle for leptons, are precisely measured: m(Z) = 91.1875 +/- 0.0021 GeV, Gamma(Z) = 2.4952 +/- 0.0023 GeV, rho(l) = 1.0050 +/- 0.0010, sin(2)theta(eff)(lept) = 0.23153 +/- 0.00016. The number of light neutrino species is determined to be 2.9840 +/- 0.0082, in agreement with the three observed generations of fundamental fermions. The results are compared to the predictions of the Standard Model (SM). At the Z-pole, electroweak radiative corrections beyond the running of the QED and QCD coupling constants are observed with a significance of five standard deviations, and in agreement with the Standard Model. Of the many Z-pole measurements, the forward-backward asymmetry in b-quark production shows the largest difference with respect to its SM expectation, at the level of 2.8 standard deviations. Through radiative corrections evaluated in the framework of the Standard Model, the Z-pole data are also used to predict the mass of the top quark, m(t) = 173(+10)(+13) GeV, and the mass of the W boson, m(W) = 80.363 +/- 0.032 GeV. These indirect constraints are compared to the direct measurements, providing a stringent test of the SM. Using in addition the direct measurements of m(t) and m(W), the mass of the as yet unobserved SM Higgs boson is predicted with a relative uncertainty of about 50% and found to be less than 285 GeV at 95% confidence level. (c) 2006 Elsevier B.V. All rights reserved.
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| 2. |
- Aamodt, K., et al.
(författare)
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The ALICE experiment at the CERN LHC
- 2008
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Ingår i: Journal of Instrumentation. - 1748-0221. ; 3:S08002
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Forskningsöversikt (refereegranskat)abstract
- ALICE (A Large Ion Collider Experiment) is a general-purpose, heavy-ion detector at the CERN LHC which focuses on QCD, the strong-interaction sector of the Standard Model. It is designed to address the physics of strongly interacting matter and the quark-gluon plasma at extreme values of energy density and temperature in nucleus-nucleus collisions. Besides running with Pb ions, the physics programme includes collisions with lighter ions, lower energy running and dedicated proton-nucleus runs. ALICE will also take data with proton beams at the top LHC energy to collect reference data for the heavy-ion programme and to address several QCD topics for which ALICE is complementary to the other LHC detectors. The ALICE detector has been built by a collaboration including currently over 1000 physicists and engineers from 105 Institutes in 30 countries, Its overall dimensions are 16 x 16 x 26 m(3) with a total weight of approximately 10 000 t. The experiment consists of 18 different detector systems each with its own specific technology choice and design constraints, driven both by the physics requirements and the experimental conditions expected at LHC. The most stringent design constraint is to cope with the extreme particle multiplicity anticipated in central Pb-Pb collisions. The different subsystems were optimized to provide high-momentum resolution as well as excellent Particle Identification (PID) over a broad range in momentum, up to the highest multiplicities predicted for LHC. This will allow for comprehensive studies of hadrons, electrons, muons, and photons produced in the collision of heavy nuclei. Most detector systems are scheduled to be installed and ready for data taking by mid-2008 when the LHC is scheduled to start operation, with the exception of parts of the Photon Spectrometer (PHOS), Transition Radiation Detector (TRD) and Electro Magnetic Calorimeter (EMCal). These detectors will be completed for the high-luminosity ion run expected in 2010. This paper describes in detail the detector components as installed for the first data taking in the summer of 2008.
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| 3. |
- Agertz, O., et al.
(författare)
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Large-scale galactic turbulence: can self-gravity drive the observed HI velocity dispersions?
- 2009
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 392:1, s. 294-308
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Tidskriftsartikel (refereegranskat)abstract
- Observations of turbulent velocity dispersions in the HI component of galactic discs show a characteristic floor in galaxies with low star formation rates and within individual galaxies the dispersion profiles decline with radius. We carry out several high-resolution adaptive mesh simulations of gaseous discs embedded within dark matter haloes to explore the roles of cooling, star formation, feedback, shearing motions and baryon fraction in driving turbulent motions. In all simulations the disc slowly cools until gravitational and thermal instabilities give rise to a multiphase medium in which a large population of dense self-gravitating cold clouds are embedded within a warm gaseous phase that forms through shock heating. The diffuse gas is highly turbulent and is an outcome of large-scale driving of global non-axisymmetric modes as well as cloud-cloud tidal interactions and merging. At low star formation rates these processes alone can explain the observed HI velocity dispersion profiles and the characteristic value of similar to 10 km s(-1) observed within a wide range of disc galaxies. Supernovae feedback creates a significant hot gaseous phase and is an important driver of turbulence in galaxies with a star formation rate per unit area greater than or similar to 10(-3) M(circle dot) yr(-1) kpc(-2).
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| 4. |
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| 5. |
- Birgisson, Björn, et al.
(författare)
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Determination and Prediction of Crack Patterns in Asphalt Mixture under Static Loading
- 2006
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Ingår i: International Conference on CRACK PATHS (CP 2006).
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Konferensbidrag (refereegranskat)abstract
- This paper presents a comparison between predicted and measured crack patterns developing in asphalt mixtures during static loading. Two different state configuration were investigated performing the Indirect Tensile Test (IDT) and the Semi-Circular Bending Test (SCB). A Digital Image Correlation System was applied to obtain a dense and accurate displacement/strain field of asphalt mixtures and for describing the cracking behavior. The resulting fracture behavior in the tests was predicted using a displacement discontinuity boundary element method to explicitly model the microstructure of asphalt mixtures. The predicted crack initiation and crack propagation patterns are consistent with observed cracking behavior. The results also imply that fracture in mixtures can be modeled effectively using a micromechanical approach that allows for crack growth both along aggregate surfaces, as well as through aggregates.
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| 6. |
- Birgisson, Björn, et al.
(författare)
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Determination and prediction of crack patterns in hot mix asphalt (HMA) mixtures
- 2008
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Ingår i: Engineering Fracture Mechanics. - : Elsevier BV. - 0013-7944 .- 1873-7315. ; 75:3-4, s. 664-673
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a comparison between predicted and measured crack patterns developing in hot mix asphalt (HMA) mixtures during common fracture tests. A digital image correlation (DIC) System was applied to obtain displacement/strain fields and for detecting crack patterns. The resulting cracking behavior was predicted using a displacement discontinuity boundary element method to explicitly model the microstructure of HMA. The predicted fracture initiation and crack propagation patterns are consistent with observed cracking behavior. The results imply that fracture in mixtures can be modeled effectively using a micro-mechanical approach and that crack propagation patterns can be captured using the DIC System.
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| 7. |
- Birgisson, Björn, et al.
(författare)
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Determination of fundamental tensile failure limits of mixtures
- 2007
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Ingår i: Asphalt Paving Technology: Association of Asphalt Paving Technologists-Proceedings of the Technical Sessions. ; , s. 303-344
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Konferensbidrag (refereegranskat)abstract
- Cracking is one of the most influential distresses that governs the service life of asphalt concrete pavements. Acquiring more insight into the fracture behavior of asphalt mixtures is essential to improve the cracking resistance of asphalt pavements. Recent work at University of Florida (1,2) has focused on the development of a new visco-elastic fracture mechanics-based crack growth law which identified the fracture energy density of mixtures as a fundamental crack growth threshold. The work that led to the development of the HMA fracture mechanics framework was based solely on Superpave IDT test results, therefore, it is of considerable interest to evaluate the existence of a fundamental fracture threshold for other laboratory test configurations. The work presented in this paper focuses on the identification and evaluation of fundamental tensile failure limits of hot mix asphalt mixtures (HMA) from multiple laboratory test configurations. Fracture energy densities and tensile strengths were evaluated for three different mixtures, including unmodified and heavily polymer modified mixtures, from the Superpave IDT, the Semi-Circular Bending Test (SCB) and the Three Point Bending Beam Test (3PB). Experimental analyses were complemented by a Digital Image Correlation System capable of providing dense and accurate full field strain estimations and thus suitable for describing the cracking behavior of the material at crack initiation. Tensile failure limits and the resulting fracture behavior in the three test configurations were predicted using a displacement discontinuity boundary element method with tessellations. Both experimental and numerical results indicate that fundamental HMA tensile failure properties can be determined from different test methods when appropriate analysis and interpretation methods are used. It was found that significant damage and first fracture occur locally in specimens associated with all test methods prior to peak loading, while analysis based on peak load and approximate analysis may lead to erroneous results.
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| 8. |
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| 9. |
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| 10. |
- Birgisson, Björn, et al.
(författare)
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The displacement discontinuity method for modeling fracture in the semi-circular bending test
- 2005
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Ingår i: 3rd M.I.T. Conference on Computational Fluid and Solid Mechanics. - : Elsevier Science Ltd., Boston. - 9780080444819 ; , s. 79-82
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Konferensbidrag (refereegranskat)abstract
- This paper investigates the capability of a displacement discontinuity boundary element method, which was already used to assess the mechanics of fracture in the SuperPave™ Indirect Tension Test, to model the microstructure of asphalt mixtures. The paper presents a semicircular bending test simulation in order to verify the independence of the method from the testing setup application. The predicted stress-strain curves were shown to compare well to the experimental results, as well as the cracking behaviour. The results imply that the method is able to characterize asphalt mixtures properties regardless of the particular testing setup used in the investigation. It has also shown promise as a tool for studying the mechanism of crack growth and propagation in hot mix asphalt (HMA) during every kind of testing setup.
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