Refine
Year of publication
Document Type
- Article (1902) (remove)
Has Fulltext
- yes (1902) (remove)
Is part of the Bibliography
- no (1902) (remove)
Keywords
- Heavy Ion Experiments (20)
- heavy ion collisions (16)
- BESIII (15)
- LHC (15)
- Kollisionen schwerer Ionen (14)
- Hadron-Hadron Scattering (11)
- Hadron-Hadron scattering (experiments) (11)
- e +-e − Experiments (11)
- Relativistic heavy-ion collisions (10)
- Branching fraction (9)
Institute
- Physik (1902) (remove)
A new SPS programme
(2006)
A new experiemntal program to study hadron production in hadron-nucleus and nucleus-nucleus collisions at the CERN SPS has been recently proposed by the NA49-future collaboration. The physics goals of the program are: (i) search for the critical point of strongly interacting matter and a study of the properties of the onset of deconfinemnt in nucleus-nucleus collisions, (ii) measurements of correlations, fluctuations and hadron spectra at high transverse momentum in proton-nucleus collisions needed as for better understanding of nucleus-nucleus results, (iii) measurements of hadron production in hadron-nucleus interactions needed for neutrino (T2K) and cosmic-ray (Pierre Auger Observatory and KASCADE) expriments. The physics of the nucleus-nucleus program is reviewed in this presentation.
The J/psi-hadron interaction is a key ingredient in analyzing the J/psi suppression in hot hadronic matter as well as the propagation of J/psi in nuclei. As a first step to clarify the J/psi-hadron interactions at low energies, we have calculated J/psi-pi, J/psi-rho and J/psi-nucleon scattering lengths by the quenched lattice QCD simulations with Wilson fermions for beta=6.2 on 24^3*48 and 32^3*48 lattices. Using the Luscher's method to extract the scattering length from the simulations in a finite box, we find an attractive interaction in the S-wave channel for all three systems: Among others, the J/psi-nucleon interaction is most attractive. Possibility of the J/psi-nucleon bound state is also discussed.
The energy dependence of various hadronic observables is reviewed. The study of their evolution from AGS over SPS to the highest RHIC energy reveals interesting features, which might locate a possible onset of deconfinement. These observables include transverse spectra of different particle types and their total multiplicities, as well as elliptic flow. In this context especially the observation of a maximum of the strangeness to pion ratio is of particular interest, since on one hand it has been predicted as a signal for the onset of deconfinement but on the other hand also statistical model calculations exhibit qualitatively similar structures. The sharpness of these features is however not reproduced by hadronic scenarios. The significance of these structures will be discussed in this contribution. Other observables, such as radius parameters from Bose-Einstein correlations, on the other hand do not exhibit any structure in their energy dependence.
We present quantitative and qualitative arguments in favor of the claim that, within the present cosmological epoch, the U(1)gamma factor in the Standard Model is an effective manifestation of SU(2) pure gauge dynamics of Yang-Mills scale Lambda ~ 10^-4 eV. Results for the pressure and the energy density in the deconfining phase of this theory, obtained in a nonperturbative and analytical way, support this connection in view of large-angle features inherent in the map of the CMB temperature fluctuations and temperature-polarization cross correlations.
Obstacle detection is an important part of Video Processing because it is indispensable for a collision prevention of autonomously navigating moving objects. For example, vehicles driving without human guidance need a robust prediction of potential obstacles, like other vehicles or pedestrians. Most of the common approaches of obstacle detection so far use analytical and statistical methods like motion estimation or generation of maps. In the first part of this contribution a statistical algorithm for obstacle detection in monocular video sequences is presented. The proposed procedure is based on a motion estimation and a planar world model which is appropriate to traffic scenes. The different processing steps of the statistical procedure are a feature extraction, a subsequent displacement vector estimation and a robust estimation of the motion parameters. Since the proposed procedure is composed of several processing steps, the error propagation of the successive steps often leads to inaccurate results. In the second part of this contribution it is demonstrated, that the above mentioned problems can be efficiently overcome by using Cellular Neural Networks (CNN). It will be shown, that a direct obstacle detection algorithm can be easily performed, based only on CNN processing of the input images. Beside the enormous computing power of programmable CNN based devices, the proposed method is also very robust in comparison to the statistical method, because is shows much less sensibility to noisy inputs. Using the proposed approach of obstacle detection in planar worlds, a real time processing of large input images has been made possible.
The interaction of T cells and antigen-presenting cells is central to adaptive immunity and involves the formation of immunological synapses in many cases. The surface molecules of the cells form a characteristic spatial pattern whose formation mechanisms and function are largely unknown. We perform computer simulations of recent experiments on geometrically repatterned immunological synapses and explain the emerging structure as well as the formation dynamics. Only the combination of in vitro experiments and computer simulations has the potential to pinpoint the kind of interactions involved. The presented simulations make clear predictions for the structure of the immunological synapse and elucidate the role of a self-organizing attraction between complexes of T cell receptor and peptide–MHC molecule, versus a centrally directed motion of these complexes.
An alternative theoretical description of axial electron channeling in the multi-GeV region has been developed. We solve a kinetic equation to evaluate an electron distribution function in axially oriented single crystals. Based on the single-string model, the required matrix elements for radiation and scattering by lattice vibrations are calculated employing solutions of the Dirac equation in cylindrical coordinates. Results obtained for 150-GeV electrons propagating along the <110> axis of germanium are in good agreement with experimental observations.
The experimental cold-fission yields for the system 233U(nth, f) are analyzed as function of the effective total excitation energy (TXE). The nuclear level density effect is taken into account at higher TXE, in order to benefit by the lower experimental data uncertainty as well as to avoid the quantitative account of the level densities close to fragment ground states. In this way the odd-even staggering which appears in the yields extrapolated at zero excitation energy by using the level densities, vanishes. We conclude that the cold nuclear fragmentation theory including the dynamical model describes well the experimental data.
The components of the nuclear inertia tensor, functions of the separation distance R and of the radius of the light fragment R2, BRR(R,R2), BRR2(R,R2), and BR2R2(R,R2) are calculated within the Werner-Wheeler approximation, by using the parametrization of two intersected symmetric or asymmetric spheres. Analytical relationships are derived. When projected to a path R2=R2(R), the reduced mass is obtained at the touching point. The two one-dimensional parametrizations with R2=const, and the volume V2=const previously studied, are found to be particular cases of the present more general approach. Illustrations for the cold fission, cluster radioactivity, and α decay of 252Cf are given.
We have investigated the channeling process of charged particles in a bent crystal. Invoking simple assumptions we derive a criterion, which determines whether channeling occurs or not. We obtain the same criterion using the Dirac equation. It is shown that the centrifugal force acting on the particle in the bent crystal significantly alters the effective transverse potential. The cases of axial and planar channeling are considered. The channeling probability and the dechanneling probability due to tunneling of the particle under the barrier in the effective transverse potential are estimated. These probabilities depend on the specific scaling parameter characterizing the process. Using the quasiclassical theory of synchrotron radiation we have calculated the contribution to the radiation spectrum, which arises due to the curvature of the channel. This contribution becomes significant to TeV electrons or positrons. Some practical consequences of our results are briefly discussed.