Energy functional for the three-level Lipkin model

We compute the energy functional of a three-level Lipkin model via a Legrendre transform and compare exact numerical results with analytical solutions obtained from the random phase approximation (RPA). Except for the region of the phase transition, the RPA solutions perform very well. We also study the case of three non-degenerate levels and again find that the RPA solution agrees well with the exact numerical result. For this case, the analytical results give us insight into the form of the energy functional in the presence of symmetry-breaking one-body potentials.Comment: 6 pages, 5 figure

Pairing in Many-Fermion Systems: An Exact Renormalisation Group Treatment

We study the application of the exact renormalisation group to a many-fermion system with a short-range attractive force. We introduce a boson field to describe pairing effects, and take a simple ansatz for the effective action. We derive a set of approximate flow equations for the effective coupling including boson and fermionic fluctuations. The initial conditions are obtained by renormalising the interaction to fit the scattering length in vacuum. At some critical value of the running scale, the numerical solutions show a phase transition to a gapped phase. Standard results are recovered if we omit the boson loops. When boson fluctuations are included, we find that their contributions are significant only in the small-gap regime.Comment: 12 pages (RevTeX), 2 figures (eps

Identification of a plastid response element that acts as an enhancer within the Chlamydomonas HSP70A promoter

Chloroplast-derived signals control a subset of nuclear genes in higher plants and eukaryotic algae. Among the types of signals identified are intermediates of chlorophyll biosynthesis such as Mg-protoporphyrin IX (MgProto). In Chlamydomonas reinhardtii, it was suggested that this tetrapyrrole mediates the light induction of chaperone gene HSP70A. Here we have analyzed cis elements involved in the regulation of HSP70A by MgProto and light. We identified two promoters and between their transcription start sites two regulatory regions that each may confer inducibility by MgProto and light to both HSP70A promoters. These regulatory regions, when cloned in front of basal non-light inducible heterologous promoters, conferred inducibility by MgProto and light. The orientation and distance independent function of these cis-regulatory sequences qualifies them as enhancers that mediate the response of nuclear genes to a chloroplast signal. Mutational analysis of one of these regulatory regions and an alignment with promoters of other MgProto-inducible genes revealed the sequence motif (G/C)CGA(C/T)N(A/G)N(15) (T/C/A)(A/T/G) which, as shown for HSP70A, may confer MgProto responsiveness. This cis-acting sequence element is employed for induction of HSP70A by both MgProto and light, lending support to the model that light induction of this gene is mediated via MgProto

Investigations on the tensor analyzing power

The reaction dp →3He η has been investigated at the COSY-ANKE experiment with both an unpolarised and a vector/tensor polarised deuteron beam in an excess energy range of Q = 0 MeV up to Q = 10 MeV. The determination of the tensor analysing power t20 along with the unpolarised cross section allows for the investigation of the s-wave production amplitudes near threshold. The weak energy dependence of t20 supports a strong final state interaction of the η 3He system which might lead to a quasi-bound η-mesic state. Furthermore, the angular dependence of the t20 might reveal further insight into the production amplitude

Antihyperon-Hyperon production in antiproton-proton annihilations with PANDA at FAIR

Hyperon production is an excellent probe of QCD in the confinement domain, and spin observables are a powerful tool in understanding the underlying physics. For the Omega hyperon, seven polarisation parameters can be extracted from the angular distributions of its decay products with the future PANDA experiment at FAIR. Simulation studies reveal great prospects for strange and single charmed hyperon channels with PANDA. Software tools supporting these investigations are currently under development

DyTER - Dynamic Track and Event Reconstruction

The future PANDA experiment at FAIR experiment aims to cover a wide range of processes in antiproton-proton collisions at event rates of up to 20 MHz. Such event rates make reconstruction a challenging task for the purely software -based event filter. Investigating complex event topologies with displaced vertices increases the difficulty even further. Here we present two attempts to meet these future challenges: an algorithm for track reconstruction based on pattern matching with pre-determined look-up tables, and as a continuation of this approach a system of neural networks for identifying specific particle track candidates and predicting their momentum

Spin observables in antihyperon-hyperon production at PANDA at FAIR

Hyperon production is an excellent probe of QCD in the confinement domain, and spin observables are a powerful tool in understanding the underlying physics. For the Q hyperon, seven polarisation parameters can be extracted from the angular distributions of its decay products with the future PANDA experiment at FAIR. Simulation studies reveal great prospects for strange and single charmed hyperon channels with PANDA. Software tools supporting these investigations are currently under development

Track Reconstruction with PANDA at FAIR

The future PANDA experiment at FAIR aims to investigate a wide range of physics processes in antiproton-proton collisions at rates of up to 20 MHz, while employing a purely software-based event filter. To educate the trigger decisions, a full event reconstruction has to be carried out in real time. This challenge is amplified when considering tracks from particles with long lifetimes and displaced decay vertices, which add to the complexity of the reconstruction algorithms. Here, we present modifications to a cellular automatonbased track finder taking detector time-stamps into account in addition to spatial information, as well as several pattern recognition methods for longitudinal track reconstrucion with PANDA’s Straw Tube Tracker

Track Reconstruction with PANDA at FAIR

The future PANDA experiment at FAIR aims to investigate a wide range of physics processes in antiproton-proton collisions at rates of up to 20 MHz, while employing a purely software-based event filter. To educate the trigger decisions, a full event reconstruction has to be carried out in real time. This challenge is amplified when considering tracks from particles with long lifetimes and displaced decay vertices, which add to the complexity of the reconstruction algorithms. Here, we present modifications to a cellular automatonbased track finder taking detector time-stamps into account in addition to spatial information, as well as several pattern recognition methods for longitudinal track reconstrucion with PANDA’s Straw Tube Tracker