993 research outputs found
Instrumentation for calibration and control of a continuous-flow cryogenic tunnel
Those aspects of selection and application of calibration and control instrumentation that are influenced by the extremes in the temperature environment to be found in cryogenic tunnels are described with emphasis on the instrumentation and data acquisition system used in the Langley 0.3 m transonic cryogenic tunnel. Typical calibration results obtained in a 20 by 60 cm two dimensional test section are included
Two-Loop Virtual Corrections to Drell-Yan Production at order alpha_s alpha^3
The Drell-Yan mechanism for the production of lepton pairs is one of the most
basic processes for physics studies at hadron colliders. It is therefore
important to have accurate theoretical predictions. In this work we compute the
two-loop virtual mixed QCD x QED corrections to Drell-Yan production. We
evaluate the Feynman diagrams by decomposing the amplitudes into a set of known
master integrals and their coefficients, which allows us to derive an
analytical result. We also perform a detailed study of the ultraviolet and
infrared structure of the two-loop amplitude and the corresponding poles in
epsilon.Comment: 20 pages, 3 figure
Higgs + 2 jets via gluon fusion
Real emission corrections to gg -> H, which lead to H+2 jet events, are
calculated at order alpha_s^4. Contributions include top-quark triangles, boxes
and pentagon diagrams and are evaluated analytically for arbitrary top mass
m_t. This new source of H+2 jet events is compared to the weak-boson fusion
cross section for a range of Higgs boson masses. The heavy top-mass
approximation appears to work well for intermediate Higgs-boson masses,
provided that the transverse momenta of the final-state partons are smaller
than the top-quark mass.Comment: 8 pages, 3 figure
Application of Computer Axial Tomography (CAT) to measuring crop canopy geometry
The feasibility of using the principles of computer axial topography (CAT) to quantify the structure of crop canopies was investigated because six variables are needed to describe the position-orientation with time of a small piece of canopy foliage. Several cross sections were cut through the foliage of healthy, green corn and soybean canopies in the dent and full pod development stages, respectively. A photograph of each cross section representing the intersection of a plane with the foliage was enlarged and the air-foliage boundaries delineated by the plane were digitized. A computer program was written and used to reconstruct the cross section of the canopy. The approach used in applying optical computer axial tomography to measuring crop canopy geometry shows promise of being able to provide needed geometric information for input data to canopy reflectance models. The difficulty of using the CAT scanner to measure large canopies of crops like corn is discussed and a solution is proposed involving the measurement of plants one at a time
Production of a pseudo-scalar Higgs boson at hadron colliders at next-to-next-to leading order
The production cross section for pseudo-scalar Higgs bosons at hadron
colliders is computed at next-to-next-to-leading order (NNLO) in QCD. The
pseudo-scalar Higgs is assumed to couple only to top quarks. The NNLO effects
are evaluated using an effective lagrangian where the top quarks are integrated
out. The NNLO corrections are similar in size to those found for scalar Higgs
boson production.Comment: 20 pages, 6 figures, JHEP style, Minor changes, Journal reference
adde
- …