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Using the NA49 main TPC, the central production of hyperons has been measured in CERN SPS Pb - Pb collisions at 158 GeV c-1. The preliminary ratio, studied at 2.0 < y < 2.6 and 1 < pT < 3 GeV c-1, equals ~ (13 ± 4)% (systematic error only). It is compatible, within errors, with the previously obtained ratios for central S + S [1], S + W [2], and S + Au [3] collisions. The fit to the transverse momentum distribution resulted in an inverse slope parameter T of 297 MeV. At this level of statistics we do not see any noticeable enhancement of hyperon production with the increased volume (and, possibly, degree of equilibration) of the system from S + S to Pb + Pb. This result is unexpected and counterintuitive, and should be further investigated. If confirmed, it will have a significant impact on our understanding of mechanisms leading to the enhanced strangeness production in heavy-ion collisions.
Preliminary data on phi production in central Pb + Pb collisions at 158 GeV per nucleon are presented, measured by the NA49 experiment in the hadronic decay channel phi - K+K-. At mid-rapidity, the kaons were separated from pions and protons by combining dE/dx and time-of-flight information; in the forward rapidity range only dE/dx identification was used to obtain the rapidity distribution and a rapidity-integrated mt-spectrum. The mid-rapidity yield obtained was dN/dy = 1.85 ± 0.3 per event; the total phi multiplicity was estimated to be 5.0 ± 0.7 per event. Comparison with published pp data shows a slight, but not very significant strangeness enhancement.
The large acceptance TPCs of the NA49 spectrometer allow for a systematic multidimensional study of two-particle correlations in different part of phase space. Results from Bertsch-Pratt and Yano-Koonin-Podgoretskii parametrizations are presented differentially in transverse pair momentum and pair rapidity. These studies give an insight into the dynamical space-time evolution of relativistic Pb+Pb collisions, which is dominated by longitudinal expansion.
Lambda and Antilambda reconstruction in central Pb+Pb collisions using a time projection chamber
(1997)
The large acceptance time projection chambers of the NA49 experiment are used to record the trajectory of charged particles from Pb + Pb collisions at 158 GeV per nucleon. Neutral strange hadrons have been reconstructed from their charged decay products. To obtain distributions of Λ, and Ks0 in discrete bins of rapidity, y, and transverse momentum, pT, calculations have been performed to determine the acceptance of the detector and the efficiency of the reconstruction software as a function of both variables. The lifetime distributions obtained give values of cτ = 7.8 ± 0.6 cm for Λ and cτ = 2.5 ± 0.3 cm for Ks0, consistent with data book values.
Elliptic flow from nuclear collisions is a hadronic observable sensitive to the early stages of system evolution. We report first results on elliptic flow of charged particles at midrapidity in Au+Au collisions at sqrt(s_NN)=130 GeV using the STAR TPC at RHIC. The elliptic flow signal, v_2, averaged over transverse momentum, reaches values of about 6% for relatively peripheral collisions and decreases for the more central collisions. This can be interpreted as the observation of a higher degree of thermalization than at lower collision energies. Pseudorapidity and transverse momentum dependence of elliptic flow are also presented.
Only a few Methyl-[11C]-l-methionine (MET) positron emission tomography (PET) studies have focused on children and young adults with brain neoplasm. Due to radiation exposure, long scan acquisition time, and the need for sedation in young children MET-PET studies should be restricted to this group of patients when a decision for further therapy is not possible from routine diagnostic procedures alone, e.g., structural imaging. We investigated the diagnostic accuracy of MET-PET for the differentiation between tumorous and non-tumorous lesions in this group of patients. Forty eight MET-PET scans from 39 patients aged from 2 to 21 years (mean 15 ± 5.0 years) were analyzed. The MET tumor-uptake relative to a corresponding control region was calculated. A receiver operating characteristic (ROC) was performed to determine the MET-uptake value that best distinguishes tumorous from non-tumorous brain lesions. A differentiation between tumorous (n = 39) and non-tumorous brain lesions (n = 9) was possible at a threshold of 1.48 of relative MET-uptake with a sensitivity of 83% and a specificity of 92%, respectively. A differentiation between high grade malignant lesions (mean MET-uptake = 2.00 ± 0.46) and low grade tumors (mean MET-uptake = 1.84 ± 0.31) was not possible. There was a significant difference in MET-uptake between the histologically homogeneous subgroups of astrocytoma WHO grade II and anaplastic astrocytoma WHO grade III (P = 0.02). MET-PET might be a useful tool to differentiate tumorous from non-tumorous lesions in children and young adults when a decision for further therapy is difficult or impossible from routine structural imaging procedures alone. Keywords Brain tumor - Children - PET - Methionine - Molecular imaging
We present the first measurement of fluctuations from event to event in the production of strange particles in collisions of heavy nuclei. The ratio of charged kaons to charged pions is determined for individual central Pb+Pb collisions. After accounting for the fluctuations due to detector resolution and finite number statistics we derive an upper limit on genuine non-statistical fluctuations, perhaps related to a first or second order QCD phase transition. Such fluctuations are shown to be very small.
Zu verwilderten Vorkommen von Taxa der Gattung Cotoneaster in Deutschland gibt es nur wenige Untersuchungen. Oft basieren diese aufgrund taxonomischer und nomenklatorischer Unsicherheiten und wegen Problemen bei der Einschätzung des floristischen Status bisher nur auf sporadischen Beobachtungen. In der Dölauer Heide, einem Stadtwald von Halle (Saale), wurden subspontane Vorkommen von Cotoneaster bullatus BOIS, C. cornifolius (REHDER et H. E. WILSON) FLINCK et B. HYLMÖ, C. dielsianus E. PRITZ. ex DIELS, C. divaricatus REHDER et H. E. WILSON, C. lucidus SCHLTDL., C. aff. multiflorus, C. villosulus (REHDER et H. E. WILSON) FLINCK et B. HYLMÖ und C. zabelii C. K. SCHNEID. festgestellt. In der weiteren Umgebung von Halle wurde auch subspontanes Auftreten von C. horizontalis DECNE. und C. nitens REHDER et H. E. WILSON ermittelt. Insbesondere C. villosulus und C. divaricatus werden als invasive Arten eingeschätzt. Cotoneaster cornifolius und C. lucidus sind fest eingebürgert und haben das Potenzial, invasiv werden zu können. Die synanthropen Vorkommen mehrerer Cotoneaster- Arten haben überwiegend auffallend höheren Wuchs sowie größere Blätter und Früchte als in den Originalbeschreibungen angegeben.
Der Band 1 „Familien und Gattungen“ führt in einleitenden Kapiteln in Fragen der botanischen Nomenklatur und der Nomenklatur von Kulturpflanzen ein und gibt eine systematische Übersicht über das Pflanzenreich (i. d. R. nach CRONQUIST 1988). Kernstück des 1. Bandes ist das Kapitel „Familien und Gattungen“ mit über 1.100 Seiten. In einleitenden Unterkapiteln werden botanische Fachbegriffe kurz erläutert und mit zahlreichen schematischen Abbildungen sehr anschaulich illustriert. Kurze Bestimmungsschlüssel erlauben eine schnelle Zuordnung systematisch wichtiger Merkmale zu Familien bzw. Gattungen.