Phenomenological study of the pp→π+pn reaction

Abstract

Fully constrained bubble chamber data on the pp → π + pn and pp → π + d reactions are used to investigate the ratio of the counting rates for the two processes as function of the pn excitation energy Q. Though it is important to include effects associated with the p-wave nature of pion production, the data are insufficient to establish unambiguously the dependence on Q. The angular distributions show the presence of higher partial waves which seem to be anomalously large at small Q. The dispersion relation method to determine scattering lengths is extended to encompass cases where, as for the pp → π + pn reaction, there is a bound state and, in a test example, it is shown that the values deduced for the low energy neutron-proton scattering parameters are significantly influenced by the pion p-wave behavior.

An introduction to mesic nuclei

“…Since the Coulomb repulsion has here been neglected, there is some ambiguity in the value to take for the pole position ε. The best fit to the analogous η ′ production data [2,3,4,5,6,7] was achieved with ε = 0.75 +0.20 −0.15 MeV [7], which is quite consistent with the original theoretical assumptions [1]. The resulting curves for η and η ′ production are compared to experimental data in Fig.…”

“…If one only includes the S-wave and its final state interaction (FSI) in the pp system in the simplest possible approximation [1], one expects the pp → ppη total cross section to vary as…”

The d ⁎ (2380) dibaryon resonance width and decay branching ratios

“…For Γ d * dπ + π − we multiplied Γ d * dπ 0 π 0 by 1.83 [10], close to the pure isospin limit of 2, and followed the latter work also to obtain Γ d * pnπ 0 π 0 , Γ d * pnπ 0 π 0 = 1.04 × Γ d * dπ 0 π 0 in rough agreement with Refs. [22,23]. The obtained value of Γ d * pnπ 0 π 0 was then multiplied by the same factor 1.83 as above to get the isoscalar part of Γ NN /Γ D 12 tot ≈ 0.18, taken from the Argand diagram of the NN 1 D 2 partial wave in the SAID SP07 fit [16].…”

The legacy of the experimental hadron physics programme at COSY

“…This predicts about 100 µb for the I = 1 np → npπ 0 π 0 cross section at the d * (2380) peak but is is impossible to quantify the associated theoretical uncertainty. Nevertheless, if we accept this value, it means that σ(np → {np} I=0 π 0 π 0 )/σ(np → dπ 0 π 0 ) ≈ 0.7 compared to the 0.8-0.9 predicted in the simplest FSI model [189]. Though this does not prove the dibaryon assertion, it clearly does not invalidate it.…”

“…4.1 a method was presented to make simple estimates of the cross section for the production of Swave isoscalar np states in the reaction pp → {pn}π + in terms of that for pp → dπ + . This can be extended to estimate the rate for pn → {pn}ππ in terms of that for pn → dππ [189,190]. Due to the different kinematic factors, these estimates have to be made separately for the two spin hypotheses but, when this is done for the J P = 1 + case, it is seen that the sums of the dππ and {pn}ππ productions significantly exceeds the total inelastic cross section in the SAID SP07 solution [65] in the combined 3 D 1 + 3 S 1 states.…”