1,068 research outputs found
Hadron Production in Proton-Proton Collisions
No full textOnTEAM metadata: GDSID: DOC-2008-Sep-154; Attribute ID: LIBRARY-thesis_ma-2008-001; Title: [GSI Master 2008-01] Hadron Production in Proton-Proton Collisions [30.7.2008]; Author(s): Fasel, Markus; Corporate author(s): ; Publication date: 20080929; Creator: manton; Creation date: 29.09.2008 15:09:47; Change date: 30.09.2010 16:05:30; Access: Welt; Attribute type: Text.Thesis.MA; Directory path: ['GSI Publications', 'GSI as Publisher']; Attribute path: ['Infrastructure', 'Library and Documentation', 'thesis_ma', 'Added in 2008']; File name(s): ['DOC-2008-Sep-154-1.pdf']; File title(s): ['']; File access: ['GSI-intern'
Naturschutz und Landschaftspflege im Kreis Siegen-Wittgenstein, Sommertagung des Naturhistorischen Vereins der Rheinlande und Westfalens am 25. und 26. Juni 1994 in Erndtebrück
No full textAlbrecht Belz, Peter Fasel, Markus Fuhrmann, Heidrun Düssel-Siebert, Wilhelm Meyer, Sabine Porti
Simulation strategies for complex turbulent flows
No full textComputational fluid dynamics in conjunction with the Reynolds-Averaged Navier-Stokes approach is nowadays routinely employed in a large variety of engineering andindustrial applications despite some well-known reliability issues in more complex flows. In this study, the performance of a state-of-the-art Explicit-Algebraic-StressModel (EASM) and a promising elliptic-blending approach is assessed on a range of test cases to predict complex turbulent flows. In an attempt to improve the quality of the predictions, near-wall-anisotropy modifications are introduced to the EASM, which provide better predictions for the Reynolds-stress and anisotropy tensor close to solid walls. In addition, a novel elliptic-blending RANS model is presented, which is based on the inverse turbulence time scale w, and which is equipped with a non-linear constitutive stress-strain relationship. The coefficients of the non-linear stress-strain relationship are obtained from the explicit solution of a Second-Moment Closure in the limit of weak equilibrium, and by imposing an internal consistency constraint and near-wall-anisotropy modifications, such that the highly anisotropic state of turbulence and the limiting two-component state is correctly reproduced at solid boundaries. The performance of the modified EASM and the novel elliptic-blending model are illustrated and assessed for a range of complex turbulent flows. It is expected that, due to ever increasing computational resources, unified or hybrid RANS/LES approaches will slowly penetrate into engineering applications where improved accuracy and reliability is needed. For this reason, a unified RANS/LES/DNS framework is presented, which is expected to provide the required amount of turbulence modelling for any mesh resolution and seamlessly operates between RANS and DNS mode. This is achieved by a revised Flow Simulation Methodology where the turbulence modelling contribution of a RANS model is rescaled using a damping function. The Flow Simulation Methodology is operating in conjunction with a newly developed damping function and a tailored convection discretisation scheme. In addition, a thorough calibration study is performed, which ensures proper turbulence resolving capabilities. It is conjectured that a sophisticated RANS model will also improve the overall quality of the predictions of any hybrid RANS/LES model. For this reason, the new elliptic-blending RANS model is incorporated, together with two successively simpler turbulence models, into the unified RANS/LES/DNS framework and the performance are assessed on a range of test cases, and compared to other widely used hybrid RANS/LES methods
Damage detection using frequency domain ARX models and extreme value statistics
No full textThe author acknowledges Tim Johnson and Seth Gregg
and the Los Alamos Dynamic Summer School for providing
the test structure as well as helping with the set-up,
instrumentation and acquisition of data from the test
structure. Funding for the summer school was provided by
the Engineering Sciences and Application Division at Los
Alamos National Laboratory and the Department of
Energy’s Education Program Office
Application of frequency domain ARX models and extreme value statistics to impedance-based damage detection
No full textFunding for this project was provided by the Department of Energy through the internal funding program at Los Alamos National Laboratory known as Laboratory Directed Research and Development. The author acknowledges Tim Johnson and Seth Gregg and the Los Alamos Dynamic Summer School for providing the test structure as well as helping with the set-up, instrumentation and acquisition of data from the test structure. Funding for the summer school was provided by the Engineering Sciences and Application Division at Los Alamos National Laboratory and the Department of Energy’s Education Program Office
Heavy-flavour measurements in proton-proton collisions with ALICE at the LHC
No full textThe measurement of heavy-flavour production in proton-proton collisions serves as a precise test for perturbative QCD. Furthermore it provides the reference for the corresponding studies in heavy-ion collisions. The measurements are performed by ALICE in hadronic channels as well as in the semi-electronic decay channel at midrapidity, profiting from the excellent particle identification capabilities and the good impact parameter resolution, and in the semi-muonic channel at forward rapidity. In particular, electrons from beauty hadron decays can be measured at low pT by selecting electrons with a large distance to the primary vertex or by using electron-hadron correlations. Furthermore ALICE provides the unique opportunity to study the D meson yields as function of the multiplicity. We present heavy- flavour measurements in the various channels in pp collisions at √s = 7 TeV and √s = 2.76 TeV, and discuss the results by comparing them to perturbative QCD calculations
Measurements of jet fragmentation and jet substructure with ALICE
No full textWe discuss the latest results from jet fragmentation and jet substructure measurements performed with the ALICE experiment in proton-proton and heavy-ion collisions in a wide range of jet transverse momentum. The jet production cross sections and cross section ratios for different jet resolution parameters will be shown in a wide range of . Results will be compared to next-to-leading order pQCD calculations.We discuss the latest results from jet fragmentation and jet substructure measurements performed with the ALICE experiment inproton-proton and heavy-ion collisions in a wide range of jet transverse momentum. The jet production cross sections and cross section ratios for different jet resolution parameters will be shown in a wide range of . Results will be compared to next-to-leading order pQCD calculations
Measurement of the nuclear modification factor of electrons from heavy-flavour hadron decays in Pb-Pb collisions at \sqrt{^{S}NN = 2.76 TeV with ALICE at the LHC
No full textWe present a measurement of the nuclear modification factor of electrons from heavy- flavour hadron decays at midrapidity in Pb-Pb collisions at {\surd}sNN = 2.76 TeV. Electrons are identified in the pt range 1.5 GeV/c < pt < 6 GeV/c. A suppression is seen for pt larger than 3.5 GeV/c in the most central collisions.We present a measurement of the nuclear modification factor of electrons from heavyflavour hadron decays at midrapidity in Pb-Pb collisions at SNN = 2.76 TeV. Electrons are identified in the pt range 1.5 GeV/c < pt < 6 GeV/c. A suppression is seen for pt larger than 3.5 GeV/c in the most central collisions.We present a measurement of the nuclear modification factor of electrons from heavy- flavour hadron decays at midrapidity in Pb-Pb collisions at {\surd}sNN = 2.76 TeV. Electrons are identified in the pt range 1.5 GeV/c < pt < 6 GeV/c. A suppression is seen for pt larger than 3.5 GeV/c in the most central collisions
Jet substructure measurements in pp collisions at = 13 TeV with ALICE
No full textWe present a variety of jet substructure measurements performed in pp collisions at = 13 TeV with the focus on the groomed jet momentum fraction in a wide range of between 20 and 200 GeV/ and jet resolution . Thanks to the capabilities of the ALICE apparatus jet substructure measurement are possible with an infrared constituent cutoff at 0.3 GeV. Furthermore, the angular resolution of the ALICE detectors allows the measurement of jet substructure observables with a high precision. The measurements are compared to pQCD calculations and MC generators. Furthermore, the measurement of track-based jets at the same centre-of-mass energy and its dependence on the event activity are presented for different jet resolutions.We present a variety of jet substructure measurements performed in pp collisions at = 13 TeV with the focus on the groomed jet momentum fraction in a wide range of between 20 and 200 GeV/ and jet resolution . Thanks to the capabilities of the ALICE apparatus jet substructure measurement are possible with an infrared constituent cutoff at 0.3 GeV. Furthermore, the angular resolution of the ALICE detectors allows the measurement of jet substructure observables with a high precision. The measurements are compared to pQCD calculations and MC generators. Furthermore, the measurement of track-based jets at the same centre-of-mass energy and its dependence on the event activity are presented for different jet resolutions
Single-electron analysis and open charm cross section in proton-proton collisions at √s = 7 TeV
No full textThe Large Hadron Collider (LHC) at CERN is the world’s highest energy hadron collider, providing proton- proton collisions currently at a centre-of-mass energy √s = 8 TeV and Pb-Pb collisions at √sNN = 2.76 TeV. This opens a new energy regime, which allows the study of QCD in elementary pp-collisions and in the extreme environment of Pb-Pb collisions, as well as providing a discovery potential for rare and exotic particles. ALICE is the dedicated heavy-ion experiment at the LHC. The experiment is optimised to provide excellent tracking and particle identification capabilities, in particular at low-pt, where the bulk of the particles is produced in heavy-ion collisions as well as in proton-proton collisions.
The production of heavy quarks is described in proton-proton collisions by next-to-leading order per- turbative QCD (pQCD) calculations. Thus, the measurement of heavy-quark production in proton-proton collisions serves as a test of pQCD. Measurements performed at SPS, RHIC, and Tevatron experiments showed a good agreement with pQCD, where the data were usually at the upper limit of the prediction. In addition, measurements in proton-proton collisions serve as reference for heavy-ion collisions, in which heavy quarks are essential probes for parton energy loss in a deconfined medium. Heavy-quark produc- tion can be studied either with hadronic or in semi-leptonic decay channels. The analysis presented in this thesis is performed in the semi-electronic decay channel with the ALICE apparatus.
A crucial device for the electron selection is the Transition Radiation Detector (TRD), which provides an important contribution to the electron-pion separation for momenta larger than 1 GeV/c. In November 2010, the first data were recorded with the experiment. The electron selection performance was studied for the first time on real data using data-driven methods. A pion-rejection factor of 23 at a momentum of 2 GeV/c was obtained using a likelihood method on the total charge deposit in the detector for tracks with the maximum amount of charge deposit measurements.
The inclusive electron pt-spectrum, which contains contributions from heavy-flavour hadrons as well as from various background sources, was measured for 0.5 GeV/c < pt < 8 GeV/c in proton-proton collisions at √s = 7 TeV at midrapidity (|y| < 0.5). The contribution of background electrons was quantified using a cocktail method, and it was subtracted from the inclusive spectrum. For the resulting spectrum of electrons from heavy-flavour hadron decays a signal-to-background ratio of 1 was observed at pt = 2 GeV/c. This ratio grows with increasing electron pt up to ≈5 at pt = 8 GeV/c. The pt-differential cross section of electrons from heavy-flavour hadron decays obtained by this method is in good agreement with fixed-order plus next-to-leading logarithm pQCD (FONLL) predictions. The total charm cross section in proton-proton collisions obtained from this analysis is σc = 7.6 ± 0.3(stat) ± 2.9(sys) -2.5 +3.2(extr) ± 0.3(norm) ± 0.3(br) mb
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