119117898
CutTools: a program implementing the OPP reduction method to compute one-loop amplitudes
We present a program that implements the OPP reduction method to extract the coefficients of the one-loop scalar integrals from a user defined (sub)-amplitude or Feynman Diagram, as well as the rational terms coming from the 4-dimensional part of the numerator. The rational pieces coming from the -dimensional part of the numerator are treated as an external input, and can be computed with the help of dedicated tree-level like Feynman rules. Possible numerical instabilities are dealt with the help of arbitrary precision routines, that activate only when needed.
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.
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).
14317912
Polarizing the dipoles
We extend the massless dipole formalism of Catani and Seymour, as well as its massive version as developed by Catani, Dittmaier, Seymour and Trocsanyi, to arbitrary helicity eigenstates of the external partons. We modify the real radiation subtraction terms only, the primary aim being an improved efficiency of the numerical Monte Carlo integration of this contribution as part of a complete next-to-leading order calculation. In consequence, our extension is only applicable to unpolarized scattering. Upon summation over the helicities of the emitter pairs, our formulae trivially reduce to their original form. We implement our extension within the framework of \textsc{Helac-Phegas}, and give some examples of results pertinent to recent studies of backgrounds for the LHC. The code is publicly available. Since the integrated dipole contributions do not require any modifications, we do not discuss them, but they are implemented in the software.
17496843
Multi-parton cross sections at hadron colliders
We present an alternative method to calculate cross sections for multi-parton scattering processes in the standard model at leading order. The helicity amplitudes are computed using recursion relations in the number of particles, based on the Dyson–Schwinger equations, whereas the summation over colour and helicity configurations is performed by Monte Carlo methods. The computational cost of our algorithm grows asymptotically as 3n, where n is the number of particles involved in the process, as opposed to the n!-growth of the Feynman diagram approach. Typical results for the total cross section, the differential distributions of the invariant masses and the transverse momenta of the partons are presented and cross checked by explicit summation over colours.
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.
34083016
The n_TOF Total Absorption Calorimeter for neutron capture measurements at CERN
The n_TOF Collaboration has built and commissioned a high-performance detector for (n, gamma) measurements called the Total Absorption Calorimeter (TAC). The TAC was especially designed for measuring neutron capture cross-sections of low-mass and/or radioactive samples with the accuracy required for nuclear technology and stellar nucleosynthesis. We present a detailed description of the TAC and discuss its overall performance in terms of energy and time resolution, background discrimination, detection efficiency and neutron sensitivity.
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.
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.
2491688
Modeling skew quadruple effects on the UMER beam
This is a numerical and experimental study of the effects of skew quadrupoles on the beam used in University of Maryland Electron Ring (UMER). As this beam is space- charge dominated, we expect new phenomena to be present compared to the emittance-dominated case. In our studies we find that skew quadrupoles can severely affect the halo of the beam and cause emittance growth, even in the first turn of the beam. For our simulations we use the WARP particle-in-cell code and we compare the results with the experimental study of skew quadrupole effects.
121284029
The measurement of the Pb-206 (n, gamma) cross section and stellar implications
The neutron capture cross section of 206Pb has been measured at the CERN n\TOF spectrometer using a setup of two C6D6 detectors. In the energy interval from 1 eV to 600 keV the cross section is dominated by resonances, which were analyzed via the R-matrix analysis code SAMMY. In the relevant energy ranges for stellar nucleosynthesis, i.e., at thermal energies of kT = 8 keV and kT = 23 keV, the present Maxwellian average cross section differs by 20% and 9% from the recommended values of Bao et al respectively. From the new cross section the s-abundance of 206Pb could be reliably determined as 70(4)%. This result is of importance in order to test and constrain r-process abundance calculations in the actinide region, because the r-process portion of 206Pb is dominated by α-back decays of short-lived transbismuth isotopes.