7,078 research outputs found
Predictions of striking energy and angular dependence in pp --> (pp)_S-wave pi^0 production
A phenomenological calculation from threshold to 800 MeV of the initial
proton beam energy is presented to describe recent data on the reaction pp -->
(pp)_S-wave pi^0 with a low energy cut on the final state diproton excitation
energy. A strong forward dip is obtained in the differential cross section as
in the data from COSY at 800 MeV, although the absolute value of the forward
cross section is too low. Earlier low energy data from CELSIUS are reasonably
well reproduced. In the unexplored energy interval between these two
experiments the model predicts a spectacular energy dependence both in the
forward direction and in the angle-integrated cross section.Comment: 9 pages, 4 figure
Comment on "Role of heavy meson exchange in near threshold N N --> d pi"
In a recent paper by C. J. Horowitz (Phys. Rev. C {\bf 48}, 2920 (1993)) a
heavy meson exchange is incorporated into threshold NN --> d pi to enhance the
grossly underestimated cross section. However, that calculation uses an
unjustified assumption on the initial and final momenta, which causes an
overestimate of this effect by a factor of 3--4. I point out that the inclusion
of the Delta(1232) isobar increases the cross section significantly even at
threshold.Comment: 7 pages, figures by fax or mail from [email protected]
Isospin breaking in the reaction np --> dpi^0 at threshold
The model for charge symmetry breaking in the reaction np --> dpi^0 applied
earlier around the Delta region is used to calculate the integrated
forward-backward asymmetry of the cross section close to threshold. The mixing
of the pi and eta mesons appears as strongly dominant at these energies. This
contrasts elastic np scattering experiments, where the np mass difference in
OPE dominates, or np --> d\pi^0 closer to the Delta region.Comment: 10 pages, LaTeX, submitted to Few-Body System
Quasifree photoabsorption on neutron-proton pairs in 3He
Three-body photodisintegration of 3He is calculated in the photon energy
range 200 - 400 MeV assuming quasifree absorption on np pairs both in initial
quasideuteron and singlet configurations. The model includes the normal
nucleonic current, explicit meson exchange currents and the Delta(1232)-isobar
excitation. The total cross section is increased by a factor of about 1.5
compared with free deuteron photodisintegration. Well below and above the Delta
region also some spin observables differ significantly from the ones of free
deuteron disintegration due to the more compressed wave function of the
correlated np pairs in 3He compared to the deuteron. The initial singlet state
causes a significant change in the analyzing power Ay. These differences could
presumably be seen at the conjugate angles where two-body effects are maximized
and where photoreactions could complement similar pion absorption experiments.
Figures by fax or post from [email protected]: 23 pages, report MKPH-T-94-10/HU-TFT-94-1
Undecidability of Two-dimensional Robot Games
Robot game is a two-player vector addition game played on the integer lattice
. Both players have sets of vectors and in each turn the vector
chosen by a player is added to the current configuration vector of the game.
One of the players, called Eve, tries to play the game from the initial
configuration to the origin while the other player, Adam, tries to avoid the
origin. The problem is to decide whether or not Eve has a winning strategy. In
this paper we prove undecidability of the robot game in dimension two answering
the question formulated by Doyen and Rabinovich in 2011 and closing the gap
between undecidable and decidable cases
Charge dependence of
We calculate the isospin symmetry violating effects to the reactions
and arising from the different
hadron masses and from the Coulomb interaction between the positive pion and
the deuteron. These effects are large enough in the cross section and analyzing
power that they should be taken into account in comparisons of accurate
experiments in different charge channels.Comment: 10 pages plus 2 figures, submitted to Phys. Lett.
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