857 research outputs found
On Quasibound N* Nuclei
The possibility for the existence of unstable bound states of the S11 nucleon
resonance N(1535) and nuclei is investigated. These quasibound states are
speculated to be closely related to the existence of the quasibound states of
the eta mesons and nuclei. Within a simple model for the N N interaction
involving a pion and eta meson exchange, N-nucleus potentials for N*-He
and N*-Mg are evaluated and found to be of a Woods-Saxon like form which
supports two to three bound states. In case of N*-He, one state bound by
only a few keV and another by 4 MeV is found. The results are however quite
sensitive to the N N and N N vertex parameters. A rough
estimate of the width of these states, based on the mean free path of the
exchanged mesons in the nuclei leads to very broad states with 80
and 110 MeV for N*-He and N*-Mg respectively.Comment: Presented at the Jagiellonian Symposium on Fundamental and Applied
Subatomic Physics, Cracow, Poland, June 2015; to be published in Acta Physica
Polonica B (2016
Eta physics at threshold
The production of eta and eta-prime mesons in elementary nucleon-nucleon
collisions has been investigated at the synchrotrons CELSIUS, COSY and SATURNE.
The magnitude and energy dependence of the total cross section as well as the
occupation distribution of the phase space serve as observables for
investigating the mechanisms underlying the production processes and the
interaction of mesons with nucleons. The precise data on the eta and eta-prime
creation via the pp --> pp eta(eta-prime) reactions allowed to settle the
general features of the eta and eta-prime meson production and revealed the
sensitivity of the mentioned observables to the nucleon-nucleon-meson final
state interaction. The particular production properties, like for example the
determination of the dominating exchange processes which lead to the excitation
of the S_11 nucleon isobar in the case of eta creation, must be established by
confrontation with other observables. The present status of this investigation
with an emphasis on the results of the COSY-11 collaboration is briefly
presented. The available data are interpreted in view of the production
mechanism and the meson-nucleon interaction.Comment: 3 pages, 3 figures, Presented at Conference on Quarks and Nuclear
Physics (QNP 2002), Julich, Germany, 9-14 Jun 200
On the close to threshold meson production in neutron-neutron collisions
A method of measuring the close to threshold meson production in
neutron-neutron collisions is described where the momenta of the colliding
neutrons can be determined with the accuracy obtainable for the proton-proton
reaction. The technique is based on the double quasi-free nn --> nn X^0
reaction, where deuterons are used as a source of neutronsComment: 6 pages, 2 figures, to be published in Phys. Lett.
Drift chamber with a c-shaped frame
We present the construction of a planar drift chamber with wires stretched
between two arms of a c-shaped aluminium frame. The special shape of the frame
allows to extendthe momentum acceptance of the COSY-11 detection system towards
lower momenta without suppressing the high momentum particles. The proposed
design allows for construction of tracking detectors covering small angles with
respect to the beam, which can be installed and removed without dismounting the
beam-pipe. For a three-dimensional track reconstruction a computer code was
developed using a simple algorithm of hit preselection.Comment: submitted to Nucl. Instr. & Meth
A method to disentangle single- and multi-meson production in missing mass spectra from quasi-free pn --> pn X reactions
The separation of contributions from multi- and single-meson production in
the missing mass spectrum of the quasi-free pn --> pnX reaction constitutes
a~challenging task when the reaction is studied close to threshold. This is
especially true if the resolution of the mass determination is comparable with
the excess energy and if the investigated signal appears close to the
kinematical limit. In this article we outline a method which permits the
extraction of the signal originating from the creation of a single meson
without the necessity of conducting model-dependent simulations. For the pd -->
pnXp(spectator) reactions, the method allows one to combine events
corresponding to multi-meson production at various excess energies with respect
to the pn --> pn meson process, and hence leads to an increase of the
statistics needed for the determination of the shape of the multi-meson
background.
As an example of the application of the method, we demonstrate that the
evaluation of the data from the pd --> pnXp(sp) process according to the
described technique enables one to extract a signal of the pn --> pn eta
reaction whose shape is consistent with expectations, supporting the
correctness and usefulness of the method introduced.Comment: 14 pages, 10 figure
Determination of the map of efficiency of the J-PET detector with the GATE package
A novel PET detector consisting of strips of polymer scintillators is being
developed by the J-PET Collaboration. The map of efficiency and the map of
geometrical acceptance of the 2-strip J-PET scanner are presented. Map of
efficiency was determined using the Monte Carlo simulation software GATE based
on GEANT4. Both maps were compared using method based on the chi2 test.Comment: 14 pages, 9 figures, proceeding from conference Symposium on Positron
Emission Tomography: http://koza.if.uj.edu.pl/pet-symposium-2013
Test of a single module of the J-PET scanner based on plastic scintillators
Time of Flight Positron Emission Tomography scanner based on plastic
scintillators is being developed at the Jagiellonian University by the J-PET
collaboration. The main challenge of the conducted research lies in the
elaboration of a method allowing application of plastic scintillators for the
detection of low energy gamma quanta. In this article we report on tests of a
single detection module built out from BC-420 plastic scintillator strip (with
dimensions of 5x19x300mm^3) read out at two ends by Hamamatsu R5320
photomultipliers. The measurements were performed using collimated beam of
annihilation quanta from the 68Ge isotope and applying the Serial Data Analyzer
(Lecroy SDA6000A) which enabled sampling of signals with 50ps intervals. The
time resolution of the prototype module was established to be better than 80ps
(sigma) for a single level discrimination. The spatial resolution of the
determination of the hit position along the strip was determined to be about
0.93cm (sigma) for the annihilation quanta. The fractional energy resolution
for the energy E deposited by the annihilation quanta via the Compton
scattering amounts to sigma(E)/E = 0.044/sqrt(E[MeV]) and corresponds to the
sigma(E)/E of 7.5% at the Compton edge.Comment: 12 pages, 6 figures; Updated with editorial corrections related to
publication in NIM
Beam profile investigation of the new collimator system for the J-PET detector
Jagiellonian Positron Emission Tomograph (J-PET) is a multi-purpose detector
which will be used for search for discrete symmetries violations in the decays
of positronium atoms and for investigations with positronium atoms in
life-sciences and medical diagnostics. In this article we present three methods
for determination of the beam profile of collimated annihilation gamma quanta.
Precise monitoring of this profile is essential for time and energy calibration
of the J-PET detector and for the determination of the library of model signals
used in the hit-time and hit-position reconstruction. We have we have shown
that usage of two lead bricks with dimensions of 5x10x20 cm^3 enables to form a
beam of annihilation quanta with Gaussian profile characterized by 1 mm FWHM.
Determination of this characteristic is essential for designing and
construction the collimator system for the 24-module J-PET prototype.
Simulations of the beam profile for different collimator dimensions were
performed. This allowed us to choose optimal collimation system in terms of the
beam profile parameters, dimensions and weight of the collimator taking into
account the design of the 24 module J-PET detector.Comment: 14 pages, 9 figure
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