547 research outputs found
Extraction of proton form factors in the timelike region from unpolarized e+e- --> p pbar events
We have performed numerical simulations of the unpolarized e+e- --> p pbar
process in kinematic conditions under discussion for a possible upgrade of the
existing DAFNE facility. By fitting the cross section angular distribution with
a typical Born expression, we can extract information on the ratio |G_E/G_M| of
the proton electromagnetic form factors in the timelike region within a 5-10%
uncertainty. We have explored also non-Born contributions to the cross section
by introducing a further component in the angular fit, which is related to
two-photon exchange diagrams. We show that these corrections can be identified
if larger than 5% of the Born contribution, and if relative phases of the
complex form factors do not produce severe cancellations.Comment: 10 pages in RevTeX style; 8 figures in eps forma
Limits on the low energy antinucleon-nucleus annihilations from the Heisenberg principle
We show that the quantum uncertainty principle puts some limits on the
effectiveness of the antinucleon-nucleus annihilation at very low energies.
This is caused by the fact that the realization a very effective short-distance
reaction process implies information on the relative distance of the reacting
particles. Some quantitative predictions are possible on this ground, including
the approximate A-independence of antinucleon-nucleus annihilation rates.Comment: 10 pages, no figure
Strangeness production in antiproton-nucleus collisions
Antiproton annihilations on nuclei provide a very interesting way to study
the behaviour of strange particles in the nuclear medium. In low energy annihilations, the hyperons are produced mostly by strangeness exchange
mechanisms. Thus, hyperon production in interactions is very
sensitive to the properties of the antikaon-nucleon interaction in nuclear
medium. Within the Giessen Boltzmann-Uehling-Uhlenbeck transport model (GiBUU),
we analyse the experimental data on and production in collisions at GeV/c. A satisfactory overall agreement is
reached, except for the production in Ne collisions at
MeV/c, where we obtain substantially larger
production rate. We also study the hyperon production, important in view
of the forthcoming experiments at FAIR and J-PARC.Comment: 8 pages, 4 figures, invited talk given by A.B. Larionov at the 10th
International Conference on Low Energy Antiproton Physics (LEAP2011),
Vancouver, Canada, Apr 27 - May 1, 2011, Hyperfine Interact. in pres
Some comments on -annihilation branching ratios into -, - and -channels
We give some remarks on the -partial branching ratios in flight at
low momenta of antineutron, measured by OBELIX collaboration. The comparison is
made to the known branching ratios from the -atomic states. The
branching ratio for the reaction is found to be
suppressed in comparison to what follows from the -data. It is also
shown, that there is no so called dynamic I=0-amplitude suppression for the
process .Comment: 8 pages, LaTeX, no figure
Latest results for the antikaon-nucleon optical potential
The key question of this letter is whether the K-nucleus optical potential is
deep, as it is prefered by the phenomenological fits to kaonic atoms data, or
shallow, as it comes out from unitary chiral model calculations. The current
experimental situation is reviewed.Comment: 3 pages, 1 figure. Presented at the 21st European Conference on the
Few-Body problems in Physics (EFB21), Salamanca, Spain, August 29 - September
3, 201
Measurements of the reaction of antiproton annihilation at rest at three hydrogen target densities
The proton-antiproton annihilation at rest into the final state
was measured for three different target densities: liquid hydrogen, gaseous
hydrogen at NTP and at a low pressure of 5 mbar. The yield of this reaction in
the liquid hydrogen target is smaller than in the low-pressure gas target. The
branching ratios of the channel were calculated on the basis of
simultaneous analysis of the three data samples. The branching ratio for
annihilation into from the protonium state turns out to be
about ten times smaller as compared to the one from the state.Comment: 10 pages, 3 Postscript figures. Accepted by Physics Letters
New data on OZI rule violation in bar{p}p annihilation at rest
The results of a measurement of the ratio R = Y(phi pi+ pi-) / Y(omega pi+
pi-) for antiproton annihilation at rest in a gaseous and in a liquid hydrogen
target are presented. It was found that the value of this ratio increases with
the decreasing of the dipion mass, which demonstrates the difference in the phi
and omega production mechanisms. An indication on the momentum transfer
dependence of the apparent OZI rule violation for phi production from the 3S1
initial state was found.Comment: 11 pages, 3 PostScript figures, submitted to Physics Letter
Strangeness nuclear physics: a critical review on selected topics
Selected topics in strangeness nuclear physics are critically reviewed. This
includes production, structure and weak decay of --Hypernuclei, the
nuclear interaction and the possible existence of bound
states in nuclei. Perspectives for future studies on these issues are also
outlined.Comment: 63 pages, 51 figures, accepted for publication on European Physical
Journal
Producing Slow Antihydrogen for a Test of CPT Symmetry with ATHENA
The ATHENA experiment at the Antiproton Decelerator facility at CERN aims at testing CPT symmetry with antihydrogen. An overview of the experiment, together with preliminary results of development towards the production of slow antihydrogen are reported.The ATHENA experiment at the Antiproton Decelerator facility at CERN aims at testing CPT symmetry with antihydrogen. An overview of the experiment, together with preliminary results of development towards the production of slow antihydrogen are reported.The ATHENA experiment at the Antiproton Decelerator facility at CERN aims at testing CPT symmetry with antihydrogen. An overview of the experiment, together with preliminary results of development towards the production of slow antihydrogen are reported.The ATHENA experiment at the Antiproton Decelerator facility at CERN aims at testing CPT symmetry with antihydrogen. An overview of the experiment, together with preliminary results of development towards the production of slow antihydrogen are reported
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