New experimental data on the pd -> 3He pi+ pi- reaction obtained with the COSY-MOMO detector below the three-pion threshold are presented. The reaction was also studied in inverse kinematics with a deuteron beam and the higher counting rates achieved were especially important at low excess energies. The comparison of these data with inclusive pd -> 3He+X rates allowed estimates also to be made of pi0 pi0 production. The results confirm our earlier findings that close to threshold there is no enhancement at low excitation energies in the pi+ pi- system, where the data seem largely suppressed compared to phase space. Possible explanations for this behavior, such as strong p- waves in the pi+pi- -system or the influence of two-step processes, are explored.

New experimental data on the pd → 3 He π+π− reaction obtained with the COSY-MOMO detector below the three-pion threshold are presented. The reaction was also studied in inverse kinematics with a deuteron beam and the higher counting rates achieved were especially important at low excess energies. The comparison of these data with inclusive pd → 3 He X0 rates allowed estimates also to be made of π0π0 production. The results confirm our earlier findings that, close to threshold, there is no enhancement at low excitation energies in the π+π− system, where the data seem largely suppressed compared with phase space. Possible explanations for this behavior, such as strong p waves in the π+π− system or the influence of two-step processes, are explored.

The cross section for the pd → He ππ reaction has been measured at the MOMO facility in a kinematically complete experiment at a c.m. excess energy of Q = 70 MeV. The energy and angular distributions show that the reaction is dominated by p-wave ππ pairs. This is in complete contrast to the results of inclusive measurements at somewhat higher beam energies which show a strong s-wave ABC enhancement at low ππ masses. There are however indications of p-wave pion pairs from other experiments at low Q.

Two-kaon production in proton-deuteron collisions has been studied at three energies close to threshold using a calibrated magnetic spectrograph to measure the final He-3 and a vertex detector to measure the K+K- pair. Differential and total cross sections are presented for the production of phi-mesons, decaying through phi -> K+K-, as well as for prompt K+K- production. The prompt production seems to follow phase space in both its differential distributions and in its energy dependence. The amplitude for the pd -> He-3 phi reaction varies little for excess energies below 22 MeV and the value is consistent with that obtained from a threshold measurement. The angular distribution of the K+K- decay pair shows that near threshold the phi-mesons are dominantly produced with polarization m=0 along the initial proton direction. No conclusive evidence for f(0)(980) production is found in the data.

Wear threshold two meson production via the reactions pd --> He-3 pi(+)pi(-) and pd --> He-3 K+K- was measured kinematically complete with the MOMO experiment at COSY. The obtained two pion invariant mass spectra and angular distributions depict a remarkable deviation from phase space. The two kaon data are consistent with phase space topped by a clear signal of the phi meson.

~COSY-MOMO Collaboration ! Institut für Strahlenund Kernphysik, Universita ̈t Bonn, Bonn, Germany Institute of Physics, Jagellonian University, Cracow, Poland Institute of Nuclear Physics, Cracow, Poland Institut für Kernphysik, Forschungszentrum Ju ̈lich, Jülich, Germany Institut für Kernphysik, Technische Universita ̈t Darmstadt, Darmstadt, Germany Department of Physics and Astronomy, University College London, London WC1E 6BT, United Kingdom ~Received 24 December 1998; published 2 November 1999 !

The cross section for the pd-->He-3 pi(+)pi(-) reaction has been measured in a kinematically complete experiment at a c.m. excess energy of Q = 70 MeV. The striking energy and angular distributions are reproduced in a simple model calculation when it is assumed that the reaction is dominated by p-wave pi(+)pi(-) pairs. This is in complete contrast to the results of inclusive measurements at somewhat higher beam energies which show a strong s-wave ABC enhancement at low pi pi masses. [S0556-2813(99)51111-4].

Near threshold two pion production via the reaction pd → 3Heπ+π− was measured kinematically complete with the MOMO experiment at COSY. A remarkable deviation of the obtained two pion invariant mass spectra from phase space as well as a predominant back to back and sidewise emission of the two pions was observed.

The cross section of the pd -> 3He pi+ pi - reaction has been measured at the MOMO facility in a kinematically complete experiment at a c. m. excess energy of Q = 70 MeV. The energy and angular distributions show that the reaction is dominated by p-wave pi+ pi- pairs. This is in complete contrast to the results of inclusive measurements at somewhat higher energies which show a strong s-wave ABC enhancement at low pi pi masses. There are however indications of p-wave pion pairs from other experiments at low Q.

The reaction pd-->He-3 pi(+)pi(-) was measured at 1150 MeV/c proton beam momentum using MOMO instalation at COSY.