1,106 research outputs found
Open charm contribution to dilepton spectra produced in nuclear collisions at SPS energies
Measurements of open charm hadro-production from CERN and Fermilab
experiments are reviewed, with particular emphasis on the absolute cross
sections and on their A and sqrt(s) dependences. Differential pt and xf cross
sections calculated with the Pythia event generator are found to be in
reasonable agreement with recent data. The calculations are scaled to
nucleus-nucleus collisions and the expected lepton pair yield is deduced. The
charm contribution to the low mass dilepton continuum observed by the CERES
experiment is found to be negligible. In particular, it is shown that the
observed low mass dilepton excess in S-Au collisions cannot be explained by
charm enhancement.Comment: 19 pages, 12 eps figures included. To be published in Z.Phys.
Alternative Size and Lifetime Measurements for High-Energy Heavy-Ion Collisions
Two-Particle correlations based on the interference of identical particles
has provided the chief means for determining the shape and lifetime of sources
in relativistic heavy ion collisions. Here, Strong and Coulomb induced
correlations are shown to provide equivalent information.Comment: Two confusing typographical errors were correcte
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Pion-pion correlations in Au+Au collisions at AGS energy
Pion-pion correlation functions have been measured in Au+Au collisions at 10.8 GeV/c per nucleon by the E877 collaboration. The width of the peak in the correlation function for identical pions, which is related to the source size, shows a dependence on pion momenta and on the orientation of the reaction plane
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Azimuthal HBT and Transverse Momentum Fluctuations from CERES.
CERES is a dilepton experiment at the CERN SPS, known for its observation of enhanced production of low mass efe- pairs in collisions between heavy nuclei [1]. The upgrade of CERES in 1997-1998 by a radial Time Projection Chamber (TPC) [2] allowed to improve the momentum resolution and the particle identification capability while retaining the cylindrical symmetry. The upgraded experiment is shown in Fig. 1. The upgrade also extended the sensitivity of CERES to hadrons and made possible results like those described below. The measurement of central Pb+Au collisions at the maximum SPS energy of 158 GeV per nucleon in the fall of 2000 was the first run of the fully upgraded CERES and at the same time the last run of this experiment. About 30 million Pb+Au collision events at 158 GeV per nucleon were collected, most of them with centrality within the top 7% of the geometrical cross section {sigma}{sub G} = 6.94 b. Small samples of the 20% and the minimum bias collisions, as well as a short run at 80 AGeV, were recorded in addition. The dilepton mass spectra from this experiment were published in [3]. In this talk I present two particular results of hadron analysis, the azimuthal dependence of two-pion correlations and a differential p{sub t} fluctuation study
Multiplicity dependence of the average transverse momentum in pp, p-Pb, and Pb-Pb collisions at the LHC
Multiplicity dependence of the average transverse momentum in pp, p-Pb, and Pb-Pb collisions at the LHC
Cyanobacteria, a group of photosynthetic prokaryotes, oscillate between day and night time metabolisms with concomitant oscillations in gene expression in response to light/dark cycles (LD). The oscillations in gene expression have been shown to sustain in constant light (LL) with a free running period of 24 h in a model cyanobacterium Synechococcus elongatus PCC 7942. However, equivalent oscillations in metabolism are not reported under LL in this non-nitrogen fixing cyanobacterium. Here we focus on Cyanothece sp. ATCC 51142, a unicellular, nitrogen-fixing cyanobacterium known to temporally separate the processes of oxygenic photosynthesis and oxygen-sensitive nitrogen fixation. In a recent report, metabolism of Cyanothece 51142 has been shown to oscillate between photosynthetic and respiratory phases under LL with free running periods that are temperature dependent but significantly shorter than the circadian period. Further, the oscillations shift to circadian pattern at moderate cell densities that are concomitant with slower growth rates. Here we take this understanding forward and demonstrate that the utradian rhythm under LL sustains at much higher cell densities when grown under turbulent regimes that simulate flashing light effect. Our results suggest that the ultradian rhythm in metabolism may be needed to support higher carbon and nitrogen requirements of rapidly growing cells under LL. With a comprehensive Real time PCR based gene expression analysis we account for key regulatory interactions and demonstrate the interplay between clock genes and the genes of key metabolic pathways. Further, we observe that several genes that peak at dusk in Synechococcus peak at dawn in Cyanothece and vice versa. The circadian rhythm of this organism appears to be more robust with peaking of genes in anticipation of the ensuing photosynthetic and respiratory metabolic phases
Enhanced Out-of-plane Emission of K+ Mesons observed in Au+Au Collisions at 1 AGeV
The azimuthal angular distribution of K+ mesons has been measured in Au + Au
collisions at 1 AGeV. In peripheral and semi-central collisions, K+ mesons
preferentially are emitted perpendicular to the reaction plane. The strength of
the azimuthal anisotropy of K+ emission is comparable to the one of pions. No
in-plane flow was found for K+ mesons near projectile and target rapidity.Comment: Accepted for publication in Phys. Rev.Let
Fluoroscopy usage in contemporary interventional electrophysiology: Insights from a European registry
Background: Fluoroscopy has been an essential part of every electrophysiological procedure since its inception. However, till now no clear standards regarding acceptable x-ray exposure nor recommendation how to achieve them have been proposed. Hypothesis: Current norms and quality markers required for optimal clinical routine can be identified. Methods: Centers participating in this Europe-wide multicenter, prospective registry were requested to provide characteristics of the center, operators, technical equipment as well as procedural settings of consecutive cases. Results: Twenty-five centers (72% university clinics, with a mean volume of 526 ± 348 procedures yearly) from 14 European countries provided data on 1788 cases [9% diagnostic procedures (DP), 38% atrial fibrillation (AF) ablations, 44% other supraventricular (SVT) ablations, and 9% ventricular ablations (VT)] conducted by 95 operators (89% male, 41 ± 7 years old). Mean dose area product (DAP) and time was 304 ± 608 cGy*cm2, 3.6 ± 4.8 minutes, 1937 ± 608 cGy*cm2, 15.3 ± 15.5 minutes, 805 ± 1442 cGy*cm2, 10.6 ± 10.7 minutes, and 1277 ± 1931 cGy*cm2, 10.4 ± 12.3 minutes for DP, AF, SVT, and VT ablations, respectively. Seven percent of all procedures were conducted without any use of fluoroscopy. Procedures in the lower quartile of DAP were performed more frequently by female operators (OR 1.707, 95%CI 1.257-2.318, P =.001), in higher-volume center (OR 1.001 per one additional procedure, 95%CI 1.000-1.001, P =.002), with the use of 3D-mapping system (OR 2.622, 95%CI 2.053-3.347, P <.001) and monoplane x-ray system (OR 2.945, 95%CI 2.149-4.037, P <.001). Conclusion: Exposure to ionizing radiation varies widely in daily practice for all procedure. Significant opportunities for harmonization of exposure toward the lower range has been identified
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