122064270
Jet cross sections probing possible quark substructure at hadron colliders
We calculate the two- and three-jet angular distributions in the presence of an effective contact interaction of two flavour-diagonal left-handed quark currents. Assuming five flavours of composite quarks, present data show that the compositeness scale Λc should be above ∼ 600 GeV. Forthcoming data from the Fermilab-Tevatron may soon push this bound up to Λc ⪆ 1500 GeV.
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.
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.
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).
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.
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.
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.
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.
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.
123786004
Neutron physics of the Re/Os clock. III : Resonance analyses and stellar (n, gamma) cross sections of Os-186,Os-187,Os-188
Neutron resonance analyses have been performed for the capture cross sections of Os-186, Os-187, and Os-188 measured at the n_TOF facility at CERN. Resonance parameters have been extracted up to 5, 3, and 8 keV, respectively, using the SAMMY code for a full R-matrix fit of the capture yields. From these results average resonance parameters were derived by a statistical analysis to provide a comprehensive experimental basis for modeling of the stellar neutron capture rates of these isotopes in terms of the Hauser-Feshbach statistical model. Consistent calculations for the capture and inelastic reaction channels are crucial for the evaluation of stellar enhancement factors to correct the Maxwellian averaged cross sections obtained from experimental data for the effect of thermally populated excited states. These factors have been calculated for the full temperature range of current scenarios of s-process nucleosynthesis using the combined information of the experimental data in the region of resolved resonances and in the continuum. The consequences of this analysis for the s-process component of the Os-187 abundance and the related impact on the evaluation of the time duration of galactic nucleosynthesis via the Re/Os cosmochronometer are discussed.
54968955
Nuclear Physics for the Re/Os Clock
Dating the age of the universe by the β-decay of 187Re (t1/2 = 41.2 Gyr) 
requires the accurate assessment of the s-process reaction flow. The daughter 
nucleus 187Os as well as its immediate s-only neighbor 186Os are shielded from 
the r-process. Therefore, the radiogenic contribution to 187Os can be derived 
via the local approximation of the s-process, which is well justified in this 
mass region: ( σ Ns)187 = ( σ Ns)186. Accordingly, accurate Maxwellianaveraged 
(n, γ ) cross sections have to be known for 186Os and 187Os over the 
full range of s-process temperatures. Because 187Os has low-lying excited 
states, which are significantly populated during the s-process, neutron captures 
on these excited states have to be properly taken into account. The input 
for the corresponding Hauser–Feshbach calculations can be constrained by 
deriving the strength functions from a detailed resonance analysis of the 
measured (n, γ ) cross sections as well as by an additional measurement of 
the inelastic scattering cross section for the first exited level, which dominates 
the competition between the capture and scattering channels. This contribution 
reports on measurements of the neutron capture cross sections of 186Os, 187Os 
and 188Os from the eV region to 1MeV at the CERN/n TOF facility and of the 
inelastic scattering cross section of 187Os around 30 keV at the Karlsruhe 
3.7 MV Van de Graaff accelerator. Based on these results and on a 
detailed resonance analysis, improved Maxwellian-averaged cross sections 
were obtained for thermal energies between 5 keV and 100 keV. The 
implications of these results for the Re/Os clock are discussed.