Comparison of the pp → π + pn and pp → π + d production rates

Phenomenological study of the pp→π+pn reaction

“…On general grounds one expects that close to threshold the C 2 parameter should vary like Q and C 4 like Q 2 . The obvious deviation from this rule seen in Fig 5 is in the value of C 2 in the lowest Q-bin, which shows that higher pn partial waves are important for Q even below 20 MeV [6] and this might be connected with the strong tensor force in the spin-triplet pn system.…”

“…The angular distribution shown in Fig. 4 proves that this is not a valid assumption for Q < 20 MeV in the pp → pnπ + case [6] and there are similar doubts for pp → ΛpK + when Q < 40 MeV [15].…”

“…The final state interaction (FSI) theorem [5] links the production of S-wave spin-triplet pn pairs in the pp → π + pn reaction to the cross section for pp → π + d. The failure of the theorem to describe the bubble chamber data was ascribed to the production of higher partial waves in the recoiling proton-neutron system at even low pn excitation energy Q [6]. By studying the ratio of the pp → π + pn and pp → π + d cross sections as a function of Q, as well as the angular distribution of the produced pn pairs, it is shown in Sec.…”

“…Using bubble chamber data on single pion production in proton-proton collisions at three energies between 900 to 1000 MeV [1][2][3], it is clear that the excess of F (x) over unity for low Q is primarily due to higher partial waves in the final proton-neutron system [6]. This conclusion was based upon a study of the angular distribution of the pn relative momentum in the rest frame of the two nucleons.…”

“…It was already pointed out [6] that, even for Q < 20 MeV, the distributions of the bubble chamber events [1][2][3] were not isotropic. In order to increase the statistics, in Fig.…”