Search results for "3106"
showing 10 items of 44 documents
The translationally-invariant coupled cluster method in coordinate space
2000
We study a formulation of the translationally-invariant coupled cluster method in coordinate space. Previous calculations in configuration space showed poor convergence, a problem that the new formulation is expected to remedy. This question is investigated for a system of bosons interacting through the Wigner part of the Afnan-Tang S3 interaction, where previous results exist.
Translationally invariant treatment of pair correlations in nuclei - II. Tensor correlations
1998
We study the extension of our translationally invariant treatment of few-body nuclear systems to include tensor forces and correlations. It is shown that a direct application of our method is not as successful for realistic V6 interactions as our previous results for V4 potentials suggested. We investigate the cause in detail for the case of $^4$He, and show that a combination of our method with that of Jastrow-correlated wave functions seems to be a lot more powerful, thereby suggesting that for mildly to strongly repulsive forces such a hybrid procedure may be an appropriate description.
Calculation of the two-loop heavy-flavor contribution to Bhabha scattering
2008
We describe in detail the calculation of the two-loop corrections to the QED Bhabha scattering cross section due to the vacuum polarization by heavy fermions. Our approach eliminates one mass scale from the most challenging part of the calculation and allows us to obtain the corrections in a closed analytical form. The result is valid for arbitrary values of the heavy fermion mass and the Mandelstam invariants, as long as s,t,u >> m_e^2.
Production and characterization of a custom-made 228Th source with reduced neutron source strength for the Borexino experiment
2012
A custom-made 228Th source of several MBq activity was produced for the Borexino experiment for studying the external background of the detector. The aim was to reduce the unwanted neutron emission produced via (alpha,n) reactions in ceramics used typically for commercial 228Th sources. For this purpose a ThCl4 solution was converted chemically into ThO2 and embedded into a gold foil. The paper describes the production and the characterization of the custom-made source by means of gamma-activity, dose rate and neutron source strength measurements. From gamma-spectroscopic measurements it was deduced that the activity transfer from the initial solution to the final source was >91% (at 68%…
Coulomb and nuclear excitations of narrow resonances in 17Ne
2016
Physics letters / B 759, 200 - 205 (2016). doi:10.1016/j.physletb.2016.05.073
ZZ production at hadron colliders in NNLO QCD
2014
We report on the first calculation of next-to-next-to-leading order (NNLO) QCD corrections to the inclusive production of ZZ pairs at hadron colliders. Numerical results are presented for pp collisions with centre-of-mass energy ($\sqrt{s}$) ranging from 7 to 14 TeV. The NNLO corrections increase the NLO result by an amount varying from $11\%$ to $17\%$ as $\sqrt{s}$ goes from 7 to 14 TeV. The loop-induced gluon fusion contribution provides about $60\%$ of the total NNLO effect. When going from NLO to NNLO the scale uncertainties do not decrease and remain at the $\pm 3\%$ level.
The Two Loop Crossed Ladder Vertex Diagram with Two Massive Exchanges
2008
We compute the (three) master integrals for the crossed ladder diagram with two exchanged quanta of equal mass. The differential equations obeyed by the master integrals are used to generate power series expansions centered around all the singular (plus some regular) points, which are then matched numerically with high accuracy. The expansions allow a fast and precise numerical calculation of the three master integrals (better than 15 digits with less than 30 terms in the whole real axis). A conspicuous relation with the equal-mass sunrise in two dimensions is found. Comparison with a previous large momentum expansion is made finding complete agreement.
Top-pair forward-backward asymmetry beyond next-to-leading order
2011
We make use of recent results in effective theory and higher-order perturbative calculations to improve the theoretical predictions of the QCD contribution to the top-quark pair production forward-backward asymmetry at the Tevatron. In particular, we supplement the fixed-order next-to-leading order calculation with higher-order corrections from soft-gluon resummation at next-to next-to-leading order accuracy performed in two different kinematic schemes, which allows us to make improved predictions for the asymmetry in the $p\overline{p}$ and $t\overline{t}$ rest frames as a function of the rapidity and invariant mass of the $t\overline{t}$ pair. Furthermore, we provide binned results which …
Transverse-momentum resummation for vector-boson pair production at NNLL+NNLO
2015
We consider the transverse-momentum ($p_T$) distribution of $ZZ$ and $W^+W^-$ boson pairs produced in hadron collisions. At small $p_T$, the logarithmically enhanced contributions due to multiple soft-gluon emission are resummed to all orders in QCD perturbation theory. At intermediate and large values of $p_T$, we consistently combine resummation with the known fixed-order results. We exploit the most advanced perturbative information that is available at present: next-to-next-to-leading logarithmic resummation combined with the next-to-next-to-leading fixed-order calculation. After integration over $p_T$, we recover the known next-to-next-to-leading order result for the inclusive cross se…
Two-Loop Planar Corrections to Heavy-Quark Pair Production in the Quark-Antiquark Channel
2009
We evaluate the planar two-loop QCD diagrams contributing to the leading color coefficient of the heavy-quark pair production cross section, in the quark-antiquark annihilation channel. We obtain the leading color coefficient in an analytic form, in terms of one- and two-dimensional harmonic polylogarithms of maximal weight 4. The result is valid for arbitrary values of the Mandelstam invariants s and t, and of the heavy-quark mass m. Our findings agree with previous analytic results in the small-mass limit and numerical results for the exact amplitude.