157 research outputs found
Resonant behaviour in double charge exchange reaction of \pi^+ mesons on the nuclear photoemulsion
The invariant mass spectra of the and systems produced in the
double charge exchange (DCX) of positively charged pions on photoemulsion are
analysed. A pronounced peak is observed in the invariant mass
spectrum, while the spectrum exhibits a strong Migdal-Watson effect of
the proton-proton final state interaction. These findings are in favor of the
-decoupled pseudoscalar resonance with T=0 called .Comment: 13 pages, 5 figures, revised versio
The pi N -> pi pi N reaction around the N(1440) energy
We study the pi N -> pi pi N reaction around the N(1440) mass-shell energy.
Considering the total cross sections and invariant mass distributions, we
discuss the role of N(1440) and its decay processes. The calculation is
performed by extending our previous approach [Phys. Rev. C 69, 025206 (2004)]
to this reaction, in which only the nucleon and Delta(1232) were considered as
intermediate baryon states. The characteristics observed in the recent data for
the pi- p -> pi0 pi0 n reaction obtained by Crystal Ball Collaboration (CBC),
can be understood as a strong interference between the two decay processes:
N(1440) -> pi Delta(1232) and N(1440) -> N(pi pi)_S. It is also found that the
scalar-isoscalar pi pi rescattering effect in the NN*(pi pi)_S vertex, which
corresponds to the propagation of sigma meson, seems to be necessary for
explain ing the several observables of the pi N -> pi pi N reaction: the large
asymmetric shape in the pi0-pi0 invariant mass distributions of the pi- p ->
pi0 pi0 n reaction and the pi+ p -> pi+ pi+ n total cross section.Comment: 28 pages, 13 figures. Version to appear in Phys. Rev.
Antiproton scattering off and nuclei at low and intermediate energies
Antiproton scattering off ^3\He and ^4\He targets is considered at beam
energies below 300 MeV within the Glauber-Sitenko approach, utilizing the amplitudes of the J\"ulich model as input. A good agreement with available
data on differential \bar p ^4\He cross sections and on \bar p ^3\He and
\pbar ^4\He reaction cross sections is obtained. Predictions for polarized
total He cross sections are presented, calculated within the
single-scattering approximation and including Coulomb-nuclear interference
effects. The kinetics of the polarization buildup is discussed.Comment: 11 pages, 6 figure
On the muon neutrino mass
During the runs of the PS 179 experiment at LEAR of CERN, we photographed an
event of antiproton-Ne absorption, with a complete pi+ -> mu+ ->e+ chain. From
the vertex of the reaction a very slow energy pi+ was emitted. The pi+ decays
into a mu+ and subsequently the mu+ decays into a positron. At the first decay
vertex a muon neutrino was emitted and at the second decay vertex an electron
neutrino and a muon antineutrino. Measuring the pion and muon tracks and
applying the momentum and energy conservation and using a classical statistical
interval estimator, we obtained an experimental upper limit for the muon
neutrino mass: m_nu < 2.2 MeV at a 90% confidence level. A statistical analysis
has been performed of the factors contributing to the square value of the
neutrino mass limit.Comment: 18 pages, 5 eps figure
Proposal of the Experiment on Study of Meson-Nuclear Interactions and Search of Rare Meson Decays at the "Hyperon-M"-Setup
Constraining Antimatter Domains in the Early Universe with Big Bang Nucleosynthesis
We consider the effect of a small-scale matter-antimatter domain structure on
big bang nucleosynthesis and place upper limits on the amount of antimatter in
the early universe. For small domains, which annihilate before nucleosynthesis,
this limit comes from underproduction of He-4. For larger domains, the limit
comes from He-3 overproduction. Most of the He-3 from antiproton-helium
annihilation is annihilated also. The main source of He-3 is
photodisintegration of He-4 by the electromagnetic cascades initiated by the
annihilation.Comment: 4 pages, 2 figures, revtex, (slightly shortened
Spin physics with antiprotons
New possibilities arising from the availability at GSI of antiproton beams,
possibly polarised, are discussed. The investigation of the nucleon structure
can be boosted by accessing in Drell-Yan processes experimental asymmetries
related to cross-sections in which the parton distribution functions (PDF) only
appear, without any contribution from fragmentation functions; such processes
are not affected by the chiral suppression of the transversity function
. Spin asymmetries in hyperon production and Single Spin Asymmetries
are discussed as well, together with further items like electric and magnetic
nucleonic form factors and open charm production. Counting rates estimations
are provided for each physical case. The sketch of a possible experimental
apparatus is proposed.Comment: Presented for the proceedings of ASI "Spin and Symmetry", Prague,
July 5-10, 2004, to be published in Czech. J. Phys. 55 (2005
Big Bang Nucleosynthesis with Matter--Antimatter Domains
We investigate Big Bang nucleosynthesis (hereafter, BBN) in a cosmic
environment characterized by a distribution of small-scale matter/antimatter
domains. Production of antimatter domains in a baryo-asymmetric universe is
predicted in some electroweak baryogenesis scenarios. We find that cosmic
antimatter domains of size exceeding the neutron-diffusion length at
temperature T approx. 1 MeV significantly affect the light-element production.
Annihilation of antimatter preferentially occurs on neutrons such that
antimatter domains may yield a reduction of the He-4 abundance relative to a
standard BBN scenario. In the limiting case, all neutrons will be removed
before the onset of light-element production, and a universe with net baryon
number but without production of light elements results. In general, antimatter
domains spoil agreement between BBN abundance yields and observationally
inferred primordial abundances limits which allows us to derive limits on their
presence in the early universe. However, if only small amounts of antimatter
are present, BBN with low deuterium and low He-4, as seemingly favored by
current observational data, is possible.Comment: revised version, conclusions slightly modified 5 pages, 3 ps-figures
included, revtex, also available at
http://www.mpa-garching.mpg.de/~jan/bbn/bbn.htm
About the first experiment at JINR nuclotron deuteron beam with energy 2.52 gev on investigation of transmutation of I-129, NP-237, PU-238 and PU-239 in the field of neutrons generated in pbtarget with U-blanket
The experiment described in this communication is a part of the scientific program âInvestigations of physical aspects of electronuclear method of energy production and transmutation of radioactive waste of atomic energetic using relativistic beams from the JINR Synchrophasotron/Nuclotronâ - the project âEnergy plus Transmutationâ. The performing of the first experiment at deuteron beam with energy 2.52 GeV at the electronuclear setup which consists of Pb-target with U-blanket (206.4 kg of natural uranium) and transmutation samples and its preliminary results are described. The hermetic samples of isotopes of I-129, Np-237, Pu-238 and Pu-239 which are produced in atomic reactors and industry setups which use nuclear materials and nuclear technologies were irradiated in the field of electronuclear neutrons produced in the Pbtarget surrounded with the U-blanket setup âEnergy plus transmutationâ. The estimations of its transmutations (radioecological aspect) were obtained in result of measurements of gamma activities of these samples. The information about space-energy distribution of neutrons in the volume of the Pb-target and the U-blanket was obtained with help of sets of activation threshold detectors (Al, V, Cu, Co, Y, In, I, Ta, Au, W, Bi and other), solid state nuclear track detectors, He-3 neutron detectors and nuclear emulsions
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