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.
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.
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.
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.
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).
16812499
Path integrals in polar field variables in QFT
We show how to transform a d-dimensional Euclidean path integral in terms of two (Cartesian) fields to a path integral in terms of polar field variables. First we present a conjecture that states how this transformation should be done. Then we show that this conjecture is correct in the case of two toy models. Finally the conjecture will be proven for a general QFT model with two fields.
109430895
Rotational Mismatches and Emittance Growth for the UMER Beam
This is a numerical study of the effects of a rotational mismatch of a beam at injection. A closely related type of mismatch is the presence of a skew quadrupole at some place in the transporting channel. In both cases, the initial mismatch implies that the emittance of the beam will increase as the beam is transported through an alternating focusing channel. In our simulations, we used the WARP computer code to simulate the University of Maryland Electron Ring (UMER) beam and we have indeed seen a substantial emittance growth (by a factor of 2–3) for mismatches of 10 degrees.
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.
121849618
Electromagnetic properties of states in Cu-63 through the inelastic scattering of protons
23902126
The University of Maryland Electron Ring (UMER) enters a new regime of high-tune-shift rings
Beams with a high phase space density are useful for many modern applications such as free electron lasers, pulsed neutron sources, high-energy-density physics, and high-luminosity colliders. Production of such beams requires understanding the complex space charge dynamics at the low-energy end of the accelerator. The University of Maryland Electron Ring (UMER) has been designed and built with the purpose of investigating space charge effects using scaled low-energy electron experiments. We have recently circulated the highest- space-charge beam in a ring to date, achieving a breakthrough both in the number of turns and in the amount of current propagated. We have propagated a beam with an integer tune shift for over 100 turns, and other, even higher-current beams, for 5-50 turns albeit with some beam loss. One beam had a tune shift at injection of 5.0, which is several factors higher than anything propagated in the past. We report here as well on other interesting aspects of the UMER work.
118327429
Au-197(n,gamma) cross section in the resonance region
The (n,gamma) cross section of Au-197 has been measured at n_TOF in the resolved resonance region, up to 5 keV, with the aim of improving the accuracy in an energy range where it is not yet considered standard. The measurements were performed with two different experimental setup and detection techniques, the total energy method based on C6D6 detectors, and the total absorption calorimetry based on a 4 pi BaF2 array. By comparing the data collected with the two techniques, two accurate sets of neutron-capture yields have been obtained, which could be the basis for a new evaluation leading to an extended cross-section standard. Overall good agreement is found between the n_TOF results and evaluated cross sections, with some significant exceptions for small resonances. A few resonances not included in the existing databases have also been observed.