82 research outputs found
SEARCH FOR NARROW ISOVECTOR DIBARYONS CLOSE TO LOW MASSES THRESHOLD
For masses larger than 2 MN + Mπ, narrow peaks in two proton invariant (missing) masses spectra : Mpp (Mx) are now well established. The existence of such narrow peaks is not so unquestionable below 2 MN + Mπ. Tensor analyzing power T20 of the invariant mass Mpp has been studied using the p ([MATH], pp) reaction. Depending on the assumption done for background substraction -a hole or an oscillation may appear at Mpp = 1941 MeV. Additional data are under analysis and will improve the statistics
Comparison of the Near-Threshold Production of eta- and K-Mesons in Proton-Proton Collisions
The pp -> pp eta and pp -> pLambda K^+ reactions near threshold are dominated
by the first and second S_11 resonance respectively. It is shown that a
one-pion-exchange model exciting these isobars reproduces well the ratio of the
production cross sections. The consequences for this and other channels are
discussed.Comment: 10 pages, LaTeX2e, 1 eps-figur
Near-Threshold Production of omega Mesons in the pp -> pp omega Reaction
The total cross section for omega production in the pp -> pp omega reaction
has been measured at five c.m. excess energies from 3.8 to 30 MeV. The energy
dependence is easily understood in terms of a strong proton-proton final state
interaction combined with a smearing over the width of the state. The ratio of
near-threshold phi and omega production is consistent with the predictions of a
one-pion-exchange model and the degree of violation of the OZI rule is similar
to that found in the pi-p -> n omega/phi reactions.Comment: Report in LaTeX2e. 12 pages with 2 eps figure
Dilepton production in heavy ion collisions at intermediate energies
We present a unified description of the vector meson and dilepton production
in elementary and in heavy ion reactions. The production of vector mesons
() is described via the excitation of nuclear resonances ().
The theoretical framework is an extended vector meson dominance model (eVMD).
The treatment of the resonance decays with arbitrary spin is
covariant and kinematically complete. The eVMD includes thereby excited vector
meson states in the transition form factors. This ensures correct asymptotics
and provides a unified description of photonic and mesonic decays. The
resonance model is successfully applied to the production in
reactions. The same model is applied to the dilepton production in elementary
reactions (). Corresponding data are well reproduced. However, when
the model is applied to heavy ion reactions in the BEVALAC/SIS energy range the
experimental dilepton spectra measured by the DLS Collaboration are
significantly underestimated at small invariant masses. As a possible solution
of this problem the destruction of quantum interference in a dense medium is
discussed. A decoherent emission through vector mesons decays enhances the
corresponding dilepton yield in heavy ion reactions. In the vicinity of the
-peak the reproduction of the data requires further a substantial
collisional broadening of the and in particular of the meson.Comment: 32 pages revtex, 19 figures, to appear in PR
Eta-N Final State Interaction in incoherent Photoproduction of Eta-mesons from the Deuteron near Threshold
An analysis of incoherent photoproduction of mesons off the deuteron
for photon energies from threshold to 800 MeV is presented. The dominant
contribution, the N-N amplitude, is described within an isobar
model. Effects of the final state interactions in the as well as the
systems are included employing models derived within the
meson-exchange approach. It is found that their consideration is important.
Specifically, due to an interference effect the influence of the final
state interaction is enhanced in the reaction close to
threshold.Comment: 11 pages (LaTeX), 7 postscript figure
Invariant mass distributions for the pp to p p eta reaction at Q=10 MeV
Proton-proton and proton-eta invariant mass distributions and the total cross
section for the pp to pp eta reaction have been determined near the threshold
at an excess energy of Q=10 MeV. The experiment has been conducted using the
COSY-11 detector setup and the cooler synchrotron COSY. The determined
invariant mass spectra reveal significant enhancements in the region of low
proton-proton relative momenta, similarly as observed previously at higher
excess energies of Q=15.5 MeV and Q= 40MeV.Comment: 6 pages, 3 figures, submitted to Eur.Phys. J.
CMS Forward-Backward MSGC milestone
The CMS MF1 milestone was set in order to evaluate system aspects of the CMS forward-backward MSGC tracker, to check the design and feasibility of mass production and to set up assembly and test procedures. We describe the construction and the experience gained with the operation of a system of 38 MSGC detectors assembled in six multi-substrate detector modules corresponding to the geometry of the forward-backward MSGC tracker in CMS. These modules were equipped with MSGCs mounted side by side, forming a continuous detector surface of about 0.2 m2. Different designs were tried for these modules. The problems encountered are presented with the proposed solutions. Operation conditions for the 38 MSGCs are reported from an exposure to a muon beam at the CERN SPS. Gain uniformity along the wedge-shaped strip pattern and across the detector modules are shown together with the detection efficiency, the spatial resolution, alignment and edge studies
Anatomy of life and well-being: A framework for the contributions of phenomenology and complexity theory
This paper proposes an anatomy of the phenomena of life and of correlate qualitative modes of empirical research, theory, and professional practice concerned with health and well-being. I explicate the qualitative dynamic operative at every level of order, from the biological realm of cells and organisms, through distinctively human lifeworld experiences and practices, to communities of organisms in ecosystems and bio-cultural regions. This paper clarifies the unity of the dimensions of life and aligns these with demonstrated and emerging contributions of hermeneutical phenomenology and current complexity–autopoietic theory (including disciplinary and professional interpretations of empirical findings). The intent is begin to delineate a common framework upon which we could build—facilitating better understanding of the distinctive contributions of each specialization as well as the integration of diverse qualitative approaches with each other (and with quantitative complements)
Evidence for a backward peak in the gamma+d->pi^0+d cross section near the eta threshold
High-quality cross sections for the reaction gamma+d->pi^0+d have been
measured using the CLAS at Jefferson Lab over a wide energy range near and
above the eta-meson photoproduction threshold. At backward c.m. angles for the
outgoing pions, we observe a resonance-like structure near E_gamma=700 MeV. Our
model analysis shows that it can be explained by eta excitation in the
intermediate state. The effect is the result of the contribution of the
N(1535)S_11 resonance to the amplitudes of the subprocesses occurring between
the two nucleons and of a two-step process in which the excitation of an
intermediate eta meson dominates.Comment: slightly modified title, additional paragraph and a table (Table 2)
added on p. 5; to be submitted to EPJA, 6 pages, 3 figure
CMS physics technical design report : Addendum on high density QCD with heavy ions
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