Polarized Proton Beams from Laser-induced Plasmas

We report on the concept of an innovative source to produce polarized proton/deuteron beams of a kinetic energy up to several GeV from a laser-driven plasma accelerator. Spin effects have been implemented into the PIC simulation code VLPL to make theoretical predictions about the behavior of proton spins in laser-induced plasmas. Simulations of spin-polarized targets show that the polarization is conserved during the acceleration process. For the experimental realization, a polarized HCl gas-jet target is under construction using the fundamental wavelength of a Nd:YAG laser system to align the HCl bonds and simultaneously circular polarized light of the fifth harmonic to photo-dissociate, yielding nuclear polarized H atoms. Subsequently, their degree of polarization is measured with a Lamb-shift polarimeter. The final experiments, aiming at the first observation of a polarized particle beam from laser-generated plasmas, will be carried out at the 10 PW laser system SULF at SIOM/Shanghai.Comment: 7 pages, 7 figure

Silizium-basierte Lichtemitter : Neue Möglichkeiten für Lab-on-Chip Systeme?

Die Realisierung von Lichtemittern in herkömmlicher Siliziumtechnologie ist ein großer Traum der Mikroelektronik. Aufgrund seines indirekten Bandgaps ist Silizium prinzipiell schlecht als Lichtemitter geeignet. Teure und aufwendige andere Verfahren und Werkstoffe (z.B. Verbindungshalbleiter wie GaAs, GaN, SiC usw.) fanden Verwendung für Leuchtdioden und werden heute kommerziell eingesetzt. Diese sind jedoch nicht in herkömmliche Silizium-Chipstrukturen integrierbar. Die Integration in die Silizium – Technologie ist jedoch von eminenter Bedeutung für die kostengünstige Herstellung von Emitterarrays, die neben der Nutzung für integrierte Systeme der Mikrosystemtechnik und der optischen Informationsübertragung auf und zwischen Chips auch zur Lumineszenzanregung von Farbstoffmolekülen in Lab-on-Chip Systemen dienen können. Seit Anfang der 90er Jahre kann durch modifizierte Schichten und Strukturen im Nanometerbereich die bisherige Beschränkung des Siliziums überwunden werden. So können in Siliziumdioxid eingebettete Nanostrukturen aufgrund ihrer speziellen Eigenschaften zur Lumineszenz angeregt werden. In den hier beschriebenen Untersuchungen werden Nanostrukturen durch Ionenimplantation in thermisch auf einen Siliziumwafer (100, n-Typ) aufgewachsene SiO2 – Schichten erzeugt. Im Anschluß an die Ionenimplantation werden durch eine Temperung Strahlenschäden ausgeheilt und die Clusterbildung angeregt. Die so erhaltenen Nanocluster weisen Größen von 4 ... 6 nm auf. Als Frontkontakt der Lumineszenzstrukturen wird eine aufgesputterte transparente Indium-Zinnoxid (ITO) - Schicht lithographisch in kreisrunde Flächen von 0.2mm2 strukturiert. Der Rückseitenkontakt wird durch Al - Beschichtung der Wafersrückseite hergestellt

New determination of the mass of the eta meson at COSY-ANKE

A value for the mass of the eta meson has been determined at the COSY-ANKE facility through the measurement of a set of deuteron laboratory beam momenta and associated 3He center-of-mass momenta in the d+p -> 3He+X reaction. The eta was then identified by the missing-mass peak and the production threshold determined. The individual beam momenta were fixed with a relative precision of 3 x 10^-5 for values around 3 GeV/c by using a polarized deuteron beam and inducing an artificial depolarizing spin resonance, which occurs at a well-defined frequency. The final-state momenta in the two-body d+p -> 3He+eta reaction were investigated in detail by studying the size of the 3He momentum ellipse with the forward detection system of the ANKE spectrometer. Final alignment of the spectrometer for this high precision experiment was achieved through a comprehensive study of the 3He final-state momenta as a function of the center-of-mass angles, taking advantage of the full geometrical acceptance. The value obtained for the mass, m(eta)=(547.873 +- 0.005(stat) +- 0.027(syst)) MeV/c^2, is consistent and competitive with other recent measurements, in which the meson was detected through its decay products.Comment: 11 pages, 11 figures, 3 tables, published versio

Absence of spin dependence in the final state interaction of the d(pol) p --> 3He eta reaction

The deuteron tensor analysing power t_{20} of the d(pol) p --> 3He eta reaction has been measured at the COSY-ANKE facility in small steps in excess energy Q up to Q = 11 MeV. Despite the square of the production amplitude varying by over a factor of five through this range, t_{20} shows little or no energy dependence. This is evidence that the final state interaction causing the energy variation is not influenced by the spin configuration in the entrance channel. The weak angular dependence observed for t_{20} provides useful insight into the amplitude structure near threshold.Comment: 5 pages, 4 figure

Kaon pair production in proton-nucleus collisions at 2.83 GeV kinetic energy

The production of non-phi K+K- pairs by protons of 2.83 GeV kinetic energy on C, Cu, Ag, and Au targets has been investigated using the COSY-ANKE magnetic spectrometer. The K- momentum dependence of the differential cross section has been measured at small angles over the 0.2--0.9 GeV/c range. The comparison of the data with detailed model calculations indicates an attractive K- -nucleus potential of about -60 MeV at normal nuclear matter density at a mean momentum of 0.5 GeV/c. However, this approach has difficulty in reproducing the smallness of the observed cross sections at low K- momenta.Comment: 7 pages, 5 figures, 1 tabl

Isolation and characterization of a cDNA encoding rat liver cytosolic epoxide hydrolase and its functional expression in Escherichia coli

A cDNA of 1992 base pairs encoding the complete rat liver cytosolic epoxide hydrolase has been isolated using a polymerase chain reaction-derived DNA fragment (Arand, M., Knehr, M., Thomas, H., Zeller, H. D., and Oesch, F. (1991) FEBS Lett. 294, 19-22) known to represent the 3'-end of the cytosolic epoxide hydrolase mRNA. Sequence analysis revealed an open reading frame of 1662 nucleotides corresponding to 554 amino acids (M(r) = 62,268). The DNA sequence obtained did not display significant homology to the sequences of microsomal epoxide hydrolase or leukotriene A4 hydrolase or to any other DNA included in the EMBL Data Bank (release 32). On Northern blotting of rat liver RNA, a single mRNA species was detected that was strongly induced on treatment of the animal with fenofibrate, a potent peroxisome proliferator. The most significant structure of the deduced protein is a modified peroxisomal targeting signal (Ser-Lys-Ile) at the carboxyl terminus that is regarded to be responsible for the unusual dual localization of the cytosolic epoxide hydrolase in peroxisomes as well as in the cytosol. In addition, a leucine zipper-like motif was identified at the amino terminus. Its possible implication for the observed dimeric structure of cytosolic epoxide hydrolase is discussed. The isolated cDNA was expressed in bacteria to yield a catalytically active enzyme. Specific activity of the crude lysate obtained exceeded that of rat liver cytosols from maximally induced animals by a factor of 8

Resonance-like coherent production of a pion pair in the reaction pd→pdππpd \rightarrow pd\pi\pi in the GeV region

The reaction $p + d \rightarrow p + d + X$ was studied at 0.8-2.0 GeV proton beam energies with the ANKE magnetic spectrometer at the COSY synchrotron storage ring. The proton-deuteron pairs emerging with high momenta, 0.6-1.8 GeV/$c$, were detected at small angles with respect to the proton beam. Distribution over the reaction missing mass $M_x$ reveals a local enhancement near the threshold of the pion pair production specific for the so-called ABC effect. The enhancement has a structure of a narrow bump placed above a smooth continuum. The invariant mass of the $d\pi\pi$ system in this enhancement region exhibits a resonance-like peak at $M_{d\pi\pi} \approx 2.36$ GeV/$c^2$ with the width $\Gamma \approx 0.10$ GeV/$c^2$. A possible interpretation of these features is discussed.Comment: 14 pages, 16 figures, submitted to Eur. Phys. J. A. v2: Added references [42,43] in section IV.A. v3: revised version according to referee remarks v4: revised version according to referee remark

The production of K+K- pairs in proton-proton collisions at 2.83 GeV

Differential and total cross sections for the pp -> ppK+K- reaction have been measured at a proton beam energy of 2.83 GeV using the COSY-ANKE magnetic spectrometer. Detailed model descriptions fitted to a variety of one-dimensional distributions permit the separation of the pp -> pp phi cross section from that of non-phi production. The differential spectra show that higher partial waves represent the majority of the pp -> pp phi total cross section at an excess energy of 76 MeV, whose energy dependence would then seem to require some s-wave phi-p enhancement near threshold. The non-phi data can be described in terms of the combined effects of two-body final state interactions using the same effective scattering parameters determined from lower energy data.Comment: 12 pages, 12 figures, 3 table