109 research outputs found
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.
Spin Correlation Coefficients in pp-->pnpi+ from 325 to 400 MeV
The spin correlation coefficient combinations Axx + Ayy, Axx - Ayy and the
analyzing powers Ay(theta) were measured for pp-->pnpi+ at beam energies of
325, 350, 375 and 400 MeV. A polarized internal atomic hydrogen target and a
stored, polarized proton beam were used. These polarization observables are
sensitive to contributions of higher partial waves. A comparison with recent
theoretical calculations is provided.Comment: 8 Pages, 1 Table, 5 Figures. Accepted for publication in Phys. Lett.
Cross section of the reaction close to threshold
We have measured inclusive data on -meson production in collisions
at COSY J\"ulich close to the hyperon production threshold and determined the
hyperon-nucleon invariant mass spectra. The spectra were decomposed into three
parts: , and . The cross section for the
channel was found to be much smaller than a previous measurement in
that excess energy region. The data together with previous results at higher
energies are compatible with a phase space dependence.Comment: accepted by Phys. lett. B some typos correcte
Measurement of p + d -> 3He + eta in S(11) Resonance
We have measured the reaction p + d -> 3He + eta at a proton beam energy of
980 MeV, which is 88.5 MeV above threshold using the new ``germanium wall''
detector system. A missing--mass resolution of the detector system of 2.6% was
achieved. The angular distribution of the meson is forward peaked. We found a
total cross section of (573 +- 83(stat.) +- 69(syst.))nb. The excitation
function for the present reaction is described by a Breit Wigner form with
parameters from photoproduction.Comment: 8 pages, 2 figures, corrected typos in heade
High resolution study of the Lambda p final state interaction in the reaction p + p -> K+ + (Lambda p)
The reaction pp -> K+ + (Lambda p) was measured at Tp=1.953 GeV and Theta = 0
deg with a high missing mass resolution in order to study the Lambda p final
state interaction. The large final state enhancement near the Lambda p
threshold can be described using the standard Jost-function approach. The
singlet and triplet scattering lengths and effective ranges are deduced by
fitting simultaneously the Lambda p invariant mass spectrum and the total cross
section data of the free Lambda p scattering.Comment: submitted to Physics Letters B, 10 pages, 3 figure
Detailed comparison of the pp -> \pi^+pn and pp -> \pi^+d reactions at 951 MeV
The positively charged pions produced in proton-proton collisions at a beam
momentum of 1640 MeV/c were measured in the forward direction with a high
resolution magnetic spectrograph. The missing mass distribution shows the bound
state (deuteron) clearly separated from the continuum. Despite the very
good resolution, there is no evidence for any significant production of the
system in the spin-singlet state. However, the cross section ratio is about twice as large as
that predicted from -wave final-state-interaction theory and it is suggested
that this is due to -state effects in the system.Comment: 8 pages, 3 figure
Forward K+ production in subthreshold pA collisions at 1.0 GeV
K+ meson production in pA (A = C, Cu, Au) collisions has been studied using
the ANKE spectrometer at an internal target position of the COSY-Juelich
accelerator. The complete momentum spectrum of kaons emitted at forward angles,
theta < 12 degrees, has been measured for a beam energy of T(p)=1.0 GeV, far
below the free NN threshold of 1.58 GeV. The spectrum does not follow a thermal
distribution at low kaon momenta and the larger momenta reflect a high degree
of collectivity in the target nucleus.Comment: 4 pages, 3 figure
A precision determination of the mass of the meson
Several processes of meson production in proton-deuteron collisions have been
measured simultaneously using a calibrated magnetic spectrograph. Among these
processes, the meson is seen clearly as a sharp missing--mass peak on a
slowly varying background in the reaction. Knowing
the kinematics of the other reactions with well determined masses, it is
possible to deduce a precise mass for the meson. The final result,
,
is significantly lower than that found by the recent NA48 measurement, though
it is consistent with values obtained in earlier counter experiments.Comment: 10 pages, 6 figures, Fig. 3 change
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