120586857
The Gross-Neveu model near the critical temperature. A mechanism for quark-hadron phase transition in relativistic ion collisions
Abstract It is argued that the longitudinal, critical evolution of the quark-gluon system, formed in relativistic ion collisions, can be reliably studied within the framework of the Gross-Neveu two-dimensional field theory at finite temperature. In particular, the Ginzburg-Landau approximation, near the critical temperature reveals some remarkable and measurable inhomogeneities in the rapidity density of the hadronic phase, when appropriate boundary conditions, dictated by space-time causality, are imposed on the classical solutions of the model. The relevance of the results for the experiments with relativistic ions is briefly discussed.
38248008
Helac-Phegas: A generator for all parton level processes
Abstract The updated version of the Helac-Phegas 1 event generator is presented. The matrix elements are calculated through Dyson–Schwinger recursive equations using color connection representation. Phase-space generation is based on a multichannel approach, including optimization. Helac-Phegas generates parton level events with all necessary information, in the most recent Les Houches Accord format, for the study of any process within the Standard Model in hadron and lepton colliders. New version program summary Program title: HELAC-PHEGAS Catalogue identifier: ADMS_v2_0 Program summary URL: http://cpc.cs.qub.ac.uk/summaries/ADMS_v2_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 35 986 No. of bytes in distributed program, including test data, etc.: 380 214 Distribution format: tar.gz Programming language: Fortran Computer: All Operating system: Linux Classification: 11.1, 11.2 External routines: Optionally Les Houches Accord (LHA) PDF Interface library ( http://projects.hepforge.org/lhapdf/ ) Catalogue identifier of previous version: ADMS_v1_0 Journal reference of previous version: Comput. Phys. Comm. 132 (2000) 306 Does the new version supersede the previous version?: Yes, partly Nature of problem: One of the most striking features of final states in current and future colliders is the large number of events with several jets. Being able to predict their features is essential. To achieve this, the calculations need to describe as accurately as possible the full matrix elements for the underlying hard processes. Even at leading order, perturbation theory based on Feynman graphs runs into computational problems, since the number of graphs contributing to the amplitude grows as n !. Solution method: Recursive algorithms based on Dyson–Schwinger equations have been developed recently in order to overcome the computational obstacles. The calculation of the amplitude, using Dyson–Schwinger recursive equations, results in a computational cost growing asymptotically as 3 n , where n is the number of particles involved in the process. Off-shell subamplitudes are introduced, for which a recursion relation has been obtained allowing to express an n -particle amplitude in terms of subamplitudes, with 1-, 2-, …  up to ( n − 1 ) particles. The color connection representation is used in order to treat amplitudes involving colored particles. In the present version HELAC-PHEGAS can be used to efficiently obtain helicity amplitudes, total cross sections, parton-level event samples in LHA format, for arbitrary multiparticle processes in the Standard Model in leptonic, p p ¯ and pp collisions. Reasons for new version: Substantial improvements, major functionality upgrade. Summary of revisions: Color connection representation, efficient integration over PDF via the PARNI algorithm, interface to LHAPDF, parton level events generated in the most recent LHA format, k ⊥ reweighting for Parton Shower matching, numerical predictions for amplitudes for arbitrary processes for phase-space points provided by the user, new user interface and the possibility to run over computer clusters. Running time: Depending on the process studied. Usually from seconds to hours. References: [1] A. Kanaki, C.G. Papadopoulos, Comput. Phys. Comm. 132 (2000) 306. [2] C.G. Papadopoulos, Comput. Phys. Comm. 137 (2001) 247.
118433589
NLO QCD calculations with HELAC-NLO
Achieving a precise description of multi-parton final states is crucial for many analyses at LHC. In this contribution we review the main features of the HELAC-NLO system for NLO QCD calculations. As a case study, NLO QCD corrections for t t ¯ + 2 jet production at LHC are illustrated and discussed.
16415075
Studying trilinear gauge couplings at LEP2 using optimal observables
Abstract We study the sensitivity of the processes e + e − → l ν l q q ′ at LEP2 energies on the non-standard trilinear gauge couplings (TGC), using the optimal observables method. All relevant leading logarithmic corrections to the three-order cross section, as well as experimental resolution effects have been studied. Taking into account correlations among the different TGC parameters we show that the limits on the TGC can reach the level of 0.15 (ld) at 161 GeV with 100 pb −1 , a challenge for the first LEP2 phase. At higher energies this can be improved drastically, reaching for the level of 0.02 (1 sd).
5166537
NLO QCD corrections to tri-boson production
We present a calculation of the NLO QCD corrections for the production of three vector bosons at the LHC, namely ZZZ, W+W−Z, W+ZZ, and W+W−W+ production. The virtual corrections are computed using the recently proposed method of reduction at the integrand level (OPP reduction). Concerning the contributions coming from real emission we used the dipole subtraction to treat the soft and collinear divergences. We find that the QCD corrections for these electroweak processes are in the range between 70 and 100 percent. As such they have to be considered in experimental studies of triple vector boson production at the LHC.
122772869
Quantum dynamical aspects of two-dimensional spaces of constant negative curvature
The authors study the quantum mechanics of two-dimensional spaces of constant negative curvature. The connection between different formulations is analysed. They derive the propagator and find that in the semiclassical approximation, the time evolution of observables exhibits similar features as in the classical case.
123018842
Neutron capture on Zr-94 : Resonance parameters and Maxwellian-averaged cross sections
The neutron capture cross sections of the Zr isotopes play an important role in nucleosynthesis studies. The s-process reaction flow between the Fe seed and the heavier isotopes passes through the neutron magic nucleus {sup 90}Zr and through {sup 91,92,93,94}Zr, but only part of the flow extends to {sup 96}Zr because of the branching point at {sup 95}Zr. Apart from their effect on the s-process flow, the comparably small isotopic (n,{gamma}) cross sections make Zr also an interesting structural material for nuclear reactors. The {sup 94}Zr (n,{gamma}) cross section has been measured with high resolution at the spallation neutron source n{sub T}OF at CERN and resonance parameters are reported up to 60 keV neutron energy.
118856700
Numerical investigations of mismatch induced halos in intense charged particle beams
In this paper, we discuss the parametric resonance model of halo creation, and compare it with self consistent simulation results. In particular, we employ two different initial distribution functions, and we find agreement with the particle‐core model, within the limitations of the latter. Furthermore, using a simple particle tracking algorithm, we are able to follow the trajectories of the halo particles, noting that a large number of them go through the core and re‐emerge later.
59270303
High Accuracy 233U(n, f) Cross-Section Measurement at the White-Neutron Source n_TOF from Near-Thermal to 1 MeV Neutron Energy
The U-233(n, f) cross section has been measured at the white neutron source n_TOF in a wide energy range with a dedicated fission ionization chamber. We report here the results from similar to 30 meV to 1 MeV neutron energy. The U-233(n, f) cross section has been determined relative to a reference sample of U-235(n, f) measured simultaneously with the same detector. The very high instantaneous neutron flux and the intrinsically low background of the n_TOF installation result in an accuracy around 3 range, while the energy resolution of the neutron beam allows for an accurate description of the fission cross section by means of R-matrix analysis over a wide energy range. The results are, in general, in good agreement with the most recent high-accuracy measurement of this fission cross section, over the more limited range of the previous measurements, and indicated that even the latest evaluations underestimate the cross section in the epithermal region. The present high-quality data provide the basis for a more precise evaluation of the U-233 fission cross section and for improving the reliability of databases needed for the design of new energy systems based on the Th/U cycle.
37433006
Measurement and simulation of source-generated halos in the University Of Maryland Electron Ring (UMER)
One of the areas of fundamental beam physics that have served as the rationale for recent research on UMER is the study of the generation and evolution of beam halos. Recent experiments and simulations have identified imperfections in the source geometry, particularly in the region near the emitter edge, as a significant potential source of halo particles. The edge-generated halo particles, both in the experiments and the simulations are found to pass through the center of the beam a short distance downstream of the anode plane. Understanding the detailed evolution of these particle orbits is therefore important to designing any aperture to remove the beam halo.
37166453
Neutron Capture Cross Section of 90Zr: Bottleneck in the s-Process Reaction Flow
The neutron capture cross sections of the Zr isotopes have important implications in nuclear astrophysics and 
for reactor design. The small cross section of the neutron magic nucleus 90Zr, which accounts for more than 50% 
of natural zirconium represents one of the key isotopes for the stellar s-process, because it acts as a bottleneck 
in the neutron capture chain between the Fe seed and the heavier isotopes. The same element, Zr, also is an 
important component of the structural materials used in traditional and advanced nuclear reactors. The (n, γ ) 
cross section has been measured at CERN, using the n TOF spallation neutron source. In total, 45 resonances 
could be resolved in the neutron energy range below 70 keV, 10 being observed for the first time thanks to the 
high resolution and low backgrounds at n TOF. On average, the γ widths obtained in resonance analyses with 
the R-matrix code SAMMY were 15% smaller than reported previously. By these results, the accuracy of the 
Maxwellian averaged cross section for s-process calculations has been improved by more than a factor of 2.