19,009 research outputs found
Factorisation, Parton Entanglement and the Drell-Yan Process
We discuss the angular distribution of the lepton pair in the Drell-Yan
process, hadron+hadron -> \gamma^* X -> l^+ l^- X. This process gives
information on the spin-density matrix \rho^{(q,\bar{q})} of the annihilating
quark-antiquark pair in q+\bar{q} -> l^+ l^-. There is strong experimental
evidence that even for unpolarised initial hadrons \rho^{(q,\bar{q})} is
nontrivial, and therefore the quark-antiquark system is polarised. We discuss
the possibilities of a general \rho^{(q,\bar{q})} -which could be entangled-
and a factorising \rho^{(q,\bar{q})}. We argue that instantons may lead to a
nontrivial \rho^{(q,\bar{q})} of the type indicated by experiments.Comment: 14 pages, 2 figures, comments and references added; to appear in EPJ
Spin asymmetries in jet-hyperon production at LHC
We consider polarized Lambda hyperon production in proton-proton scattering,
p p -> (\Lambda^\uparrow jet) jet X, in the kinematical region of the LHC
experiments, in particular the ALICE experiment. We present a new Lambda
polarization observable that arises from the Sivers effect in the fragmentation
process. It can be large even at midrapidity and therefore, is of interest for
high energy hadron collider experiments. Apart from its potential to shed light
on the mechanisms behind the phenomenon of Lambda polarization arising in
unpolarized hadronic collisions, the new observable in principle also allows to
test the possible color flow dependence of single spin asymmetries and the
(non)universality of transverse momentum dependent fragmentation functions.Comment: 11 pages, 10 eps figures; minor modifications, conclusions unchanged,
version to be publishe
Distributed multilevel optimization for complex structures
Optimization problems concerning complex structures with many design variables may entail an unacceptable computational cost. This problem can be reduced considerably with a multilevel approach: A structure consisting of several components is optimized as a whole (global) as well as on the component level. In this paper, an optimization method is discussed with applications in the assessment of the impact of new design considerations in the development of a structure. A strategy based on fully stressed design is applied for optimization problems in linear statics. A global model is used to calculate the interactions (e.g., loads) for each of the components. These components are then optimized using the prescribed interactions, followed by a new global calculation to update the interactions. Mixed discrete and continuous design variables as well as different design configurations are possible. An application of this strategy is presented in the form of the full optimization of a vertical tail plane center box of a generic large passenger aircraft. In linear dynamics, the parametrization of the component interactions is problematic due to the frequency dependence. Hence, a modified method is presented in which the speed of component mode synthesis is used to avoid this parametrization. This method is applied to a simple test case that originates from noise control. \u
Can we discover a light singlet-like NMSSM Higgs boson at the LHC?
In the next-to minimal supersymmetric standard model (NMSSM) one additional
singlet-like Higgs boson with small couplings to standard model (SM) particles
is introduced. Although the mass can be well below the discovered 125 GeV Higgs
boson mass its small couplings may make a discovery at the LHC difficult. We
use a novel scanning technique to efficiently scan the whole parameter space
and determine the range of cross sections and branching ratios for the light
singlet-like Higgs boson below 125 GeV. This allows to determine the
perspectives for the future discovery potential at the LHC. Specific LHC
benchmark points are selected representing the salient NMSSM features.Comment: 22 pages, 5 figures, this version is accepted by PLB after minor
modification
Single spin asymmetries in the Drell-Yan process
We discuss single transverse spin asymmetries in the Drell-Yan process
originating from so-called gluonic poles in twist-three hadronic matrix
elements, as first considered by Qiu and Sterman. Even though time-reversal
invariance is not broken, the effects of such poles cannot be distinguished
from those of time-reversal odd distribution functions. We show the connection
between gluonic poles and large distance gluon fields, in particular we focus
on boundary conditions. We identify the possible single spin asymmetries in the
Drell-Yan process.Comment: 10 pages, Latex, 4 Postscript figure, uses epsfig.sty. Invited talk
presented at the workshop 'Deep inelastic scattering off polarized targets:
theory meets experiment', DESY-Zeuthen, September 1-5, 199
A Hybrid Design Optimization Method using Enriched Craig-Bampton Approach
A hybrid design optimization method is presented which combines a number of techniques such as Component Mode Synthesis (CMS), Design of Computer Experiments and Neural Networks for surrogate modeling with Genetic Algorithms and Sequential Quadratic Programming for optimization. In the method, the FE analysis is decomposed and reduced by a well-known CMS technique called the Craig-Bampton method. Since the optimization method requires CMS calculations of the updated model at each of its iterations due to the changes in the design variables, one can either reuse the reduction basis of the initial components or compute new reduction basis for the condensation of the system matrices. The first option usually leads to inaccurate results and the last one increases the omputation time. In the method, instead of using one of these options, the Enriched Craig-Bampton method, proposed by Masson et al., is employed for efficient optimization. New basis for the modified components are generated by extending the corresponding initial reduction basis with a set of static residual vectors which are calculated using prior knowledge of the initial component designs. Thus, time consuming complete component analyzes are prevented. A theoretical test problem is used for the demonstration of the method
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