79 research outputs found
Physics at COSY
The COSY accelerator in J\'ulich is presented together with its internal and
external detectors. The physics programme performed recently is discussed with
emphasis on strangeness physics.Comment: Invited talk given at the "10th International Symposium on
Meson-Nucleon Physics and the Structure of the Nucleon (MENU04)," IHEP,
Beijing, China, 30/Aug.-4/Sept./0
Study of the and reactions close to threshold
Two--kaon production in proton--deuteron collisions has been studied at three
energies close to threshold using a calibrated magnetic spectrograph to measure
the final He and a vertex detector to measure the pair.
Differential and total cross sections are presented for the production of
--mesons, decaying through , as well as for prompt
production. The prompt production seems to follow phase space in both
its differential distributions and in its energy dependence. The amplitude for
the {He} reaction varies little for excess energies below 22
MeV and the value is consistent with that obtained from a threshold
measurement. The angular distribution of the decay pair shows that
near threshold the --mesons are dominantly produced with polarization
along the initial proton direction. No conclusive evidence for
production is found in the data.Comment: 13 figure
Specific CT 3D rendering of the treatment zone after Irreversible Electroporation (IRE) in a pig liver model: the âChebyshev Center Conceptâ to define the maximum treatable tumor size
Background: Size and shape of the treatment zone after Irreversible electroporation (IRE) can be difficult to depict due to the use of multiple applicators with complex spatial configuration. Exact geometrical definition of the treatment zone, however, is mandatory for acute treatment control since incomplete tumor coverage results in limited oncological outcome. In this study, the âChebyshev Center Conceptâ was introduced for CT 3d rendering to assess size and position of the maximum treatable tumor at a specific safety margin. Methods: In seven pig livers, three different IRE protocols were applied to create treatment zones of different size and shape: Protocol 1 (nâ=â5 IREs), Protocol 2 (nâ=â5 IREs), and Protocol 3 (nâ=â5 IREs). Contrast-enhanced CT was used to assess the treatment zones. Technique A consisted of a semi-automated software prototype for CT 3d rendering with the âChebyshev Center Conceptâ implemented (the âChebyshev Centerâ is the center of the largest inscribed sphere within the treatment zone) with automated definition of parameters for size, shape and position. Technique B consisted of standard CT 3d analysis with manual definition of the same parameters but position. Results: For Protocol 1 and 2, short diameter of the treatment zone and diameter of the largest inscribed sphere within the treatment zone were not significantly different between Technique A and B. For Protocol 3, short diameter of the treatment zone and diameter of the largest inscribed sphere within the treatment zone were significantly smaller for Technique A compared with Technique B (41.1 ± 13.1 mm versus 53.8 ± 1.1 mm and 39.0 ± 8.4 mm versus 53.8 ± 1.1 mm; p < 0.05 and p < 0.01). For Protocol 1, 2 and 3, sphericity of the treatment zone was significantly larger for Technique A compared with B. Conclusions: Regarding size and shape of the treatment zone after IRE, CT 3d rendering with the âChebyshev Center Conceptâ implemented provides significantly different results compared with standard CT 3d analysis. Since the latter overestimates the size of the treatment zone, the âChebyshev Center Conceptâ could be used for a more objective acute treatment control
Experimental study of the pd(d p) â 3 He ÏÏ reactions close to threshold
New experimental data on the pd â 3
He Ï+Ïâ reaction obtained with the COSY-MOMO detector below
the three-pion threshold are presented. The reaction was also studied in inverse kinematics with a deuteron beam
and the higher counting rates achieved were especially important at low excess energies. The comparison of
these data with inclusive pd â 3
He X0 rates allowed estimates also to be made of Ï0Ï0 production. The results
confirm our earlier findings that, close to threshold, there is no enhancement at low excitation energies in the
Ï+Ïâ system, where the data seem largely suppressed compared with phase space. Possible explanations for
this behavior, such as strong p waves in the Ï+Ïâ system or the influence of two-step processes, are explored
Exclusive Measurements of : the Effect Revisited
Exclusive measurements of the reactions and
have been carried out at GeV at the
CELSIUS storage ring using the WASA detector. The channel
evidences a pronounced enhancement at low invariant masses - as
anticipated from previous inclusive measurements of the ABC effect. This
enhancement is seen to be even much larger in the isoscalar
channel. The differential distributions prove this enhancement to be of
scalar-isoscalar nature. calculations give a good description of
the data, if a boundstate condition is imposed for the intermediate
system.Comment: extended version, 8 pages, 7 figures, theoretical model calculations
adde
Polarisation of the omega meson in the pd-->3He+omega reaction at 1360 and 1450 MeV
The tensor polarisation of omega mesons produced in the pd-->3He+omega
reaction has been studied at two energies near threshold. The 3He nuclei were
detected in coincidence with the pi0pi+pi- or pi0gamma decay products of the
omega. In contrast to the case of phi meson production, the omega mesons are
found to be unpolarised. This brings into question the applicability of the
Okubo-Zweig-Iizuka rule when comparing the production of vector mesons in low
energy hadronic reactions.Comment: 11 pages, 4 figure
The pd --> ^3He eta pi0 reaction at T_p = 1450 MeV
The cross section for the pd --> ^3He eta pi0 reaction has been measured at a
beam energy of 1450 MeV using the WASA detector at the CELSIUS storage ring and
detecting one ^3He and four photons from the decays of the two photons. The
data indicate that the production mechanism involves the formation of the
Delta(1232) isobar. Although the beam energy does not allow the full peak of
this resonance to be seen, the invariant masses of all three pairs of final
state particles are well reproduced by a phase space Monte Carlo simulation
weighted with the p-wave factor of the square of the pi^0 momentum in the
^3Hepi^0 system.Comment: 10 pages, 5 figure
Strangeness Production in Hadron Reactions
The paper gives an overview of strangeness-production experiments at the
Cooler Synchrotron COSY. Results on kaon-pair and meson production in
, and collisions, hyperon-production experiments and
final-state interaction studies are presented as well as a search for a
strangeness resonance in the system.Comment: Talk presented at Erice 201
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