Physics with diproton final states at ANKE-COSY

Abstract

The study of processes with production of proton pairs with small excitation energy (diprotons) pro- vides a new approach to hadron interactions at intermediate energies. It is especially instructive due to compari- son with processes where a deuteron is produced in the same kinematics. Provided that the momentum transfer is high enough the diprotons are found presumably in the 1 S 0 state, and this simplifies the theoretical analysis. The ANKE spectrometer provides the possibility to select the diprotons with suffi ciently high excitation energy resolution. A number of processes including pd→ {pp}sn, production of one and two pions in pN collisions, and the pp→{pp}s process, have been investigated. 1 Experiments with diproton final states at ANKE Few nucleon systems have long been a subject of intensive theoretical and experimental study. A particularly impor- tant role in this study is played by processes with produc- tion of the deuteron, a bound state of proton and neutron. In this respect, a particular interest arises for the investigation of the diproton, an unbound system of two protons with small excitation energy. The diproton, being the isospin partner of the deuteron, possesses different quantum num- bers. Selection of the excitation energy of the proton pair Epp < 3 MeV ensures the dominance of the 1 S 0 state of the diproton, which simplifies significantly the theoretical in- terpretation. The reactions with formation of a diproton in- volve transitions in the NN system, different from the case of the deuteron, and, in particular, the role of theisobar is expected to be much suppressed because the S-waveN intermediate state is forbidden. Detection of the proton pair with Epp < 3 MeV in an experiment requires an excellent excitation energy resolu- tion and the ability to resolve the two spatially close trajec- tories of the protons. The ANKE spectometer (1) provides a resolution of �(Epp) = 0.2− 0.6 MeV in the Epp = 0− 3 MeV range and is particularly well suited for this purpose. The diproton program at ANKE involves several ex- periments: