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تسجيل مستخدم جديدCross Section and Tensor Analysing Power of the $vec{d}dto etaalpha$ Reaction Near Threshold
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The angular distributions of the unpolarised differential cross section and tensor analysing power $A_{xx}$ of the $vec{d}dtoalpha eta$ reaction have been measured at an excess energy of 16.6 MeV. The ambiguities in the partial-wave description of these data are made explicit by using the invariant amplitude decomposition. This allows the magnitude of the s-wave amplitude to be extracted and compared with results published at lower energies. In this way, firmer bounds could be obtained on the scattering length of the $eta alpha$ system. The results do not, however, unambiguously prove the existence of a quasi-bound $eta alpha$ state.
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In order to establish links between p-wave pion production in nucleon-nucleon collisions and low energy three-nucleon scattering, an extensive programme of experiments on pion production is currently underway at COSY-ANKE. The final proton pair is de
tected at very low excitation energy, leading to an S-wave diproton, denoted here as {pp}_s. We now report on measurements of the differential cross section and analysing power of the pol{p}p->{pp}_s pi^0$ reaction at 353 MeV. Both observables can be described in terms of s- and d-wave pion production and, by using the phase information from elastic pp scattering, unique solutions can be obtained for the corresponding amplitudes. This information is vital for the partial wave decomposition of the corresponding pn->{pp}_s pi^- reaction and hence for the extraction of the p-wave terms.
A first measurement of the analysing power in the reaction p(pol)p --> pp eta near the production threshold has been performed at the internal facility COSY-11 at the COoler SYnchrotron COSY.
In order to establish links between p-wave pion production in nucleon-nucleon collisions and low energy three-nucleon scattering, an extensive programme of experiments on pion production is currently underway at COSY-ANKE. The final proton pair is me
asured at very low excitation energy, leading to an S-wave diproton, denoted here as {pp}_s. By using a deuterium target we have obtained data on the differential cross section and analysing power of the quasi-free pol{p}n -> {pp}_s pi^- reaction at 353 MeV. The spectator proton p_sp was either measured directly in silicon tracking telescopes or reconstructed using the momentum of a detected pi^-. Both observables can be described in terms of s-, p-, and d-wave pion production amplitudes. Taken together with the analogous data on the pol{p}p -> {pp}_s pi^0 reaction, full partial wave decompositions of both processes were carried out.
Total cross sections for the pp --> pp eta reaction have been measured in the excess energy range from Q = 1.53 MeV to Q = 23.64 MeV. The experiment has been performed at the internal installation COSY-11 using a stochastically cooled proton beam of
the COoler SYnchrotron COSY and a hydrogen cluster target. The determined energy dependence of the total cross section weakens the hypothesis of the S-wave repulsive interaction between the eta meson and the proton. New data agree well with predictions based on the phase-space distribution modified by the proton-proton final-state-interaction (FSI) only.
The differential cross section and analyzing power $A_y$ of the ${vec p}p{to}pp{pi}^0$ reaction have been measured at RCNP in coplanar geometry at a beam energy of 390 MeV and the dependence on both the pion emission angle and the relative momentum o
f the final protons have been extracted. The angular variation of Ay for the large values of the relative momentum studied here shows that this is primarily an effect of the interference of pion s- and p-waves and this interference can also explain the momentum dependence. Within the framework of a very simple model, these results would suggest that the pion-production operator has a significant long-range component.
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