Near-threshold charged kaon pair production in two protons collisions

Abstract

Abstract. The pp → ppK + K − reaction was measured near threshold at excess energy Q = 4.5 MeV using the COSY-11 detection system installed at the COSY-Juelich accelerator. Preliminary value of upper limit of the total cross section was determined. This limit indicates that an enhancement of the total cross section close to the threshold, caused by the final state interaction, is smaller than suggested by extrapolation of data measured at higher energies. Physics motivationThe energy dependence of the pp → ppK + K − total cross section close to threshold is very sensitive to the interactions between particles in the final state, and therefore is well suited for studies of these interactions. There are many interesting topics connected with the interactions of the final state kaons and protons. For example, the K + K − interaction is crucial for understanding the structure of the scalar mesons f 0 (980) and a 0 (980), which according Ref. [1,2] are KK molecules. In turn, the K − p interaction is interesting from the point of view of study the nature of the Λ(1405) hyperon, which is considered as a K − p molecular state [3]. There are also some astrophysical aspects of studying kaons production reactions, like description of neutron stars structure [4]. Elementary reactions of kaon pair production in pp collisions are also important for better understanding of the properties of kaons inside dense baryonic matter [5]. The existing data for the kaon pair production in pp collisions were measured for excess energies higher than Q = 6 MeV, with exception of one point at 3 MeV, for which only upper limit of the total cross section was determined. On the other hand, data very close to threshold (for Q < 6 MeV) are crucial for distinguishing between various models of the final state interaction (FSI) in the ppK + K − system. Therefore, we performed a high luminosity measurement at Q = 4.5 MeV. ExperimentThe measurement was performed with the COSY-11 detection system, described in details in Ref. [6], at the COSY-Juelich accelerator. A principle of the measurement is presented in Fig. 1. Internal proton beam of the COSY was scattered on the COSY-11 H 2 cluster target. The beam momentum