Measurement of the anti pp → π+π- and anti pp → K+K- cross sections between 360 and 760 MeV/c

An experiment is executed to search for structure in the σsub(anti pp → π+π-) and σsub(anti pp → k+k-). In the experiment, σsub(anti pp → π+π-) and σsub(anti pp → k+k-) are measured at 15 incident beam momenta between 360 and 760 MeV/c with better statistics than any of previous experiments. The measured quantity is the folded differential cross section, dσ/dΩ (θ*) + dσ/dΩ (π-θ*). The trigger condition is the existence of an incident antiproton and two or more outgoing charged particles with no veto-counter hit. The π+π- and K+K- events are selected from huge background by requiring coplanarity and by inspecting the opening angle between the two outgoing particles. A variable Rπk is defined in order to separate the π+π- and K+K- events. It is shown that K+K- events clustering around Rπk = 0 are clearly separated from the π+π- events around Rπk = 1. Various normalization corrections are applied to the data, and additional systematic errors are taken into account. The folded differential cross sections obtained in this experiment are fitted with a Legendre polynomial series Σsub(n=0)sup(n-max) anPn (cosθ*) (n even), and σsub(anti pp →π+π-) and σ are given by 2πa0. A satisfactory fit is obtained with n-max = 4 (for the π+π- channel, the terms up to n-max = 6 are used). No significant structure is observed both in σ and in σ. The 90 % cinfidence-level upper limits for posible resonances determined from the present results are -70 μb for pp → π+π- and -40 μb for pp → K+K-. (Nogami, K.)