On the Production of $\pi^+\pi^+$ Pairs in pp Collisions at 0.8 GeV

TL;DR

This study searched for the $pp o nn \pi^+\pi^+$ reaction at 0.793 GeV and found no events, setting a strict upper limit on its cross section, which is significantly lower than other two-pion production channels.

Contribution

The paper provides the first experimental upper limit on the $pp o nn \\pi^+\\pi^+$ reaction cross section near threshold, testing chiral dynamics predictions in pion production.

Findings

No candidate events found for the $pp o nn \\pi^+\\pi^+$ reaction.

Established an upper limit of 0.16 μb for the reaction cross section.

The upper limit is more than ten times smaller than other two-pion production channels.

Abstract

Data accumulated recently for the exclusive measurement of the $pp\to pp\pi^+\pi^-$ reaction at a beam energy of 0.793 GeV using the COSY-TOF spectrometer have been analyzed with respect to possible events from the $pp \to nn\pi^+\pi^+$ reaction channel. The latter is expected to be the only $\pi\pi$ production channel, which contains no major contributions from resonance excitation close to threshold and hence should be a good testing ground for chiral dynamics in the $\pi\pi$ production process. No single event has been found, which meets all conditions for being a candidate for the $pp \to nn \pi^+\pi^+$ reaction. This gives an upper limit for the cross section of 0.16 $\mu$b (90% C.L.), which is more than an order of magnitude smaller than the cross sections of the other two-pion production channels at the same incident energy.