847 research outputs found
Planar Two-Loop Five-Parton Amplitudes from Numerical Unitarity
We compute a complete set of independent leading-color two-loop five-parton
amplitudes in QCD. These constitute a fundamental ingredient for the
next-to-next-to-leading order QCD corrections to three-jet production at hadron
colliders. We show how to consistently consider helicity amplitudes with
external fermions in dimensional regularization, allowing the application of a
numerical variant of the unitarity approach. Amplitudes are computed by
exploiting a decomposition of the integrand into master and surface terms that
is independent of the parton type. Master integral coefficients are numerically
computed in either finite-field or floating-point arithmetic and combined with
known analytic master integrals. We recompute two-loop leading-color
four-parton amplitudes as a check of our implementation. Results are presented
for all independent four- and five-parton processes including contributions
with massless closed fermion loops.Comment: v3: corrected wrong signs for five-gluon amplitudes with
vanishing tree
About a contactless transmission of 10 keV electrons through tapering microchannels
The possibility of increasing the current density of a beam of fast electrons passes through glass cone-shaped channels was demonstrated in. But the fraction of the electrons that passed through the conical channels without loss of the initial energy was not cleared up. Measurements of X-ray spectra generated by transmitted electrons in copper target mounted in vicinity of capillary output were performed for a detailed study of the contactless passage of 10 keV electrons through conical capillarie
Leading-Color Two-Loop QCD Corrections for Three-Jet Production at Hadron Colliders
We present the complete set of leading-color two-loop contributions required
to obtain next-to-next-to-leading-order (NNLO) QCD corrections to three-jet
production at hadron colliders. We obtain analytic expressions for a generating
set of finite remainders, valid in the physical region for three-jet
production. The analytic continuation of the known Euclidean-region results is
determined from a small set of numerical evaluations of the amplitudes. We
obtain analytic expressions that are suitable for phenomenological applications
and we present a C++ library for their efficient and stable numerical
evaluation.Comment: Analytic results in ancillary files; link for numerical code in
references. v3: matches the published versio
Leading-color two-loop amplitudes for four partons and a W boson in QCD
We present the leading-color two-loop QCD corrections for the scattering of four partons and a W boson, including its leptonic decay. The amplitudes are assembled from the planar two-loop helicity amplitudes for four partons and a vector boson decaying to a lepton pair, which are also used to determine the planar two-loop amplitudes for four partons and a Z/γ∗ boson with a leptonic decay. The analytic expressions are obtained by setting up a dedicated Ansatz and constraining the free parameters from numerical samples obtained within the framework of numerical unitarity. The large linear systems that must be solved to determine the analytic expressions are constructed to be in Vandermonde form. Such systems can be very efficiently solved, bypassing the bottleneck of Gaussian elimination. Our results are expressed in a basis of one-mass pentagon functions, which opens the possibility of their efficient numerical evaluation
Leading-Color Two-Loop Amplitudes for Four Partons and a W Boson in QCD
We present the leading-color two-loop QCD corrections for the scattering of
four partons and a boson, including its leptonic decay. The amplitudes are
assembled from the planar two-loop helicity amplitudes for four partons and a
vector boson decaying to a lepton pair, which are also used to determine the
planar two-loop amplitudes for four partons and a boson with a
leptonic decay. The analytic expressions are obtained by setting up a dedicated
Ansatz and constraining the free parameters from numerical samples obtained
within the framework of numerical unitarity. The large linear systems that must
be solved to determine the analytic expressions are constructed to be in
Vandermonde form. Such systems can be very efficiently solved, bypassing the
bottleneck of Gaussian elimination. Our results are expressed in a basis of
one-mass pentagon functions, which opens the possibility of their efficient
numerical evaluation.Comment: 31 pages, 5 figures; v3: matches the published version; analytic
expressions at http://www.hep.fsu.edu/~ffebres/W4parton
New insights from old cosmic rays: A novel analysis of archival KASCADE data
Cosmic ray data collected by the KASCADE air shower experiment are
competitive in terms of quality and statistics with those of modern
observatories. We present a novel mass composition analysis based on archival
data acquired from 1998 to 2013 provided by the KASCADE Cosmic ray Data Center
(KCDC). The analysis is based on modern machine learning techniques trained on
simulation data provided by KCDC. We present spectra for individual groups of
primary nuclei, the results of a search for anisotropies in the event arrival
directions taking mass composition into account, and search for gamma-ray
candidates in the PeV energy domain.Comment: Proceedings of the 37th International Cosmic Ray Conference
(ICRC2021), 12-23 July 2021, Berlin, Germany - Onlin
Frustrated magnet Li2ZrCuO4 - Paramagnetism meets paraelectricity
By measuring 7Li nuclear magnetic resonance, Cu2+ electron spin resonance and a complex dielectric constant in the frustrated spin-1/2 chain compound γ-Li2ZrCuO4 we find that the electric sublattice of mobile Li+ ions orders glass-like at T g ∼ 100 K. This yields the emergence of non-equivalent spin sites in the spin-1/2 CuO2 chains. We suggest that such a remarkable interplay between electrical and spin degrees of freedom may influence the properties of the spiral spin state in Li2ZrCuO4 which develops in this material at low temperatures. © 2010 IOP Publishing Ltd
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