Free and Quasi-free Production of gamma, pi,
eta, and eta' bosons
in Nucleon-Nucleon Collisions
This letter comprises suggestions for investigations of
few different physics issues by means of the measurement
of the total and differential cross sections of the
production of gamma, pi, eta, and
eta' bosons in the collisions of nucleons in various
It is proposed
- to make a systematic study of the dependence
of the meson production cross sections in nucleon-nucleon
collisions as a function of the nucleon virtuality defined
as a difference between a mass of a free nucleon and the mass
of its virtual counterpart inside eg. a deuteron.
- to study thepi andeta meson production in
neutron-neutron collisions via double quasi-free nn->nnX
A Dalitz-plot analysis of the n-n-meson system would enable
eg. to study the neutron-neutron and neutron-meson scattering
lengths, the first is still not well etablished and the second
- in case of eta -
is only roughly estimated, yet highly desired as one of the
key constants in hadron physics.
It will also allow to determine the production cross sections
in the channel of isospin equal to one without the necessity
of correcting for the Coulomb interaction.
- to investigate theeta' meson structure and the
isospin dependence of its creation in the nucleon-nucleon
interaction by comparing its production in proton-proton
and proton-neutron collisions.
The excitation function for pp->pp eta'
is already established.
In August 2004 the COSY-11 collaboration will start
measurements of the pn->pn eta' reaction in
the excess energy range between 0 and 30 MeV and these could
be extended up to the excess energy of about 150 MeV when
- to search for a signal from the eta-proton and
eta'-proton interaction, which should manifest itself as
a modification of events population on a Dalitz-plot of a
At present such investigations are carried out at COSY-11,
however, due to the need of the subtraction of the unavoidable
multi-pion background, the available statistics allows only
for the determination of one-dimensional invariant mass
distributions, yet the full information of the mutual interaction
between ejectiles is excessible from the two-dimensional spectra.
The detection of protons and an independent identification of
the produced meson via the detection of the gamma quants would
allow to determine a background free Dalitz-plot.
- to measure the nucleon-nucleon bremsstrahlung radiation.
This process is highly sensitive to the nucleon-nucleon potential,
and hence may serve as a tool to discriminate between various
Moreover, since the interaction of gamma quants with
nucleons is negligibly small in comparison to the meson-nucleon
one, a comparative study of the NNeta, NNeta', and
NNgamma systems will certainly allow to draw less model
dependend conclusions of the Neta and Neta'
interaction than those) which might follow from the study of
the meson production only.
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