2,377 research outputs found
Next-to-leading order QCD corrections to top quark spin correlations at hadron colliders: the reactions and
We have computed the cross section for production by gluon-gluon
fusion at next-to-leading order (NLO) in the QCD coupling, keeping the full
dependence on the spins. Furthermore we have determined to the same
order the spin dependent cross sections for the processes . Together with our previous results for these results allow for predictions, at NLO QCD, of the
hadronic production of pairs in a general spin configuration. As an
application we have determined the degree of correlation of the and spins at NLO, using various spin quantisation axes.Comment: 10 pages, 8 figure
Mixed QCD and weak corrections to top quark pair production at hadron colliders
The order mixed QCD and weak corrections to top quark
pair production by quark antiquark annihilation are computed, keeping the full
dependence on the and spins. We determine the contributions to the
cross section and to single and double top spin asymmetries at the parton
level. These results are necessary ingredients for precise standard model
predictions of top quark observables, in particular of top spin-induced
parity-violating angular correlations and asymmetries at hadron colliders.Comment: 12 pages, 9 figure
QCD corrections to top quark spin correlations at hadron colliders
Future hadron collider experiments will allow for a detailed investigation of
spin correlation effects. In this talk, recent progress in the
theoretical description of these effects is reported. In particular,
next-to-leading order results for the spin correlations in
are presented, using various spin quantization axes.Comment: 5 pages, 5 figures. Talk presented at the conference `QCD 00',
Montpellier, 6-13th July 2000, to appear in the proceeding
Recommended from our members
Effect of dead materials on calorimeter response and Monte Carlo simulation
The D0 calorimeter system, cylindrical central calorimeter and two end calorimeters, is constructed with minimal cracks and dead regions in order to provide essentially hermetic coverage over the full solid angle. The effect of the existing few construction features which could perturb the uniformity of the calorimeter is studied in detail with beam tests. The results with the correction algorithms are presented. A comparison with the Monte Carlo simulation is made
Transverse Polarization of Top Quarks Produced at a Photon-Photon Collider
At future colliders copious production of pairs
is possible. This would allow a detailed investigation of the interactions
involving the top quark. We propose some orrelations which are sensitive to final state interactions and we compute the QCD and standard model
Higgs boson contributions to these correlations. QCD induced transverse
polarization of top quarks is found to be sizeable and measurable at a
high-energy collider with an integrated luminosity of 10 which is converted into a photon collider by backscattering of laser
photons.Comment: 8 pages. No fig. Preprint UM-P-94/25 and PITHA 94/1
Next-to-leading order QCD corrections to top quark spin correlations at hadron colliders: the reactions
Future hadron collider experiments are expected to record large to huge
samples of events. The analysis of these data with respect to spin-spin correlations requires precise predictions of the production of
these quark pairs in a general spin configuration. Therefore we have computed,
at next-to-leading order (NLO) in the QCD coupling, the spin density matrices
describing production by quark antiquark annihilation, which is the
dominant production process at the Tevatron. Moreover we have computed the
strength of the spin correlation at NLO, using various spin
quantization axes.Comment: 14 pages, 5 figure
AN INVESTIGATION OF THE NOISE ABSORPTION POTENTIAL OF A SIX SELECTED GRASS SPECIES
Grass has a high leaf density and requires minimum space to grow. This experiment was designed to determine the sound absorption behaviour of six grass species (Zoysia matrella (L) Merr., Stenotaphrum dimidiatum(L.) Brongn, Panicum repens (L.), Eleusine indica (L.) Gaertn., Axonopus compressus (Sw) P. Beauv, and Ischaemum sp.) for their possible use as noise screens. The sound absorption of each morphological leaf structure was studied. For Sound Absorption Coefficients (SAC) (α) studies, the reverberation room method under ISO 345:2003 standards was followed. A B&K dodecahedron Omni-directional speaker, power amplifier, and 2250L handheld analyser were used for reverberation time and RT60 measurements. Microscopic images of grass leaves were analysed using ImageJ software. This study revealed that grasses with the highest and lowest SAC for higher noise frequencies (> 1500 Hz) are S. dimidiatum Brongn and A. compressus, respectively. The SAC of S. dimidiatum Brongn positively correlated with noise frequency. In general, the correlation of SAC (α) with noise frequency (f) is in the form of log10α = a1log10f + b1 where a1 and b1 are grass type-dependent constants. The morphological parameters like total leaf area, total sample area, plant height, and sample dry weight strongly correlated with the SAC. But leaf thickness, length, width, surface area, and the weight of the sample poorly correlated with SAC in the frequency range
Top quark pair production and decay at hadron colliders
In ongoing and upcoming hadron collider experiments, top quark physics will
play an important role in testing the Standard Model and its possible
extensions. In this work we present analytic results for the differential cross
sections of top quark pair production in hadronic collisions at next-to-leading
order in the QCD coupling, keeping the full dependence on the spins of the top
quarks. These results are combined with the corresponding next-to-leading order
results for the decay of polarized top quarks into dilepton, lepton plus jets,
and all jets final states. As an application we predict double differential
angular distributions which are due to the QCD-induced top quark spin
correlations in the intermediate state. In addition to the analytic results, we
give numerical results in terms of fit functions that can easily be used in an
experimental analysis.Comment: 58 pages, 12 figure
Transverse polarization in inclusive quasi-real photoproduction at the current fragmentation
It is shown that the recent HERMES data on the transverse
polarization in the inclusive quasi-real photoproduction at can be
accommodated by the strange quark scattering model. Relations with the quark
recombination approach are discussed.Comment: 5 pages, 3 figures, accepted by Eur. Phys. J.
Proton-Antiproton Annihilation into a Lambda_c-Antilambda_c Pair
The process p-pbar -> Lambda_c-Antilambda_c is investigated within the
handbag approach. It is shown that the dominant dynamical mechanism,
characterized by the partonic subprocess u-ubar -> c-cbar factorizes in the
sense that only the subprocess contains highly virtual partons, a gluon to
lowest order of perturbative QCD, while the hadronic matrix elements embody
only soft scales and can be parameterized in terms of helicity flip and
non-flip generalized parton distributions. Modelling these parton distributions
by overlaps of light-cone wave functions for the involved baryons we are able
to predict cross sections and spin correlation parameters for the process of
interest.Comment: 39 pages, 7 figures, problems with printout of figures resolved, Ref.
33 and referring sentences in section 4 change
- …