Kaon Two-Nucleon Absorption at Rest with FINUDA

The FINUDA experiment is originally dedicated to hypernuclear physics, using the (K− stop, π−) reaction to produce Λ-hypernuclei. Almost monochromatic K− is supplied by the φ-factory DAΦNE, as a decay particle of a φ(1020) meson (φ → K+K−) with a very small momentum (∼ 127MeV/c from φ at rest). It can be easily stopped in a thin target (0.2–0.3 g/cm2). In the first data-taking (2003-2004), we put five kinds of targets (6Li, 7Li, 12C, 27Al and 51V) surrounding the beam pipe of DAΦNE. Thanks to the large acceptance (> 2π sr) of the spectrometer and the ability to detect both the charged and neutral particles with good particle identification and good momentum resolution for charged particles, we can study various topics related to the stopped K− reaction. When a kaon is absorbed into a nucleus from its atomic orbit, the kaon mainly interacts with one nucleon and emits a hyperon and a pion. According to old experiments,1) in the fraction of 15–20% per stopped K−, the kaon interacts with multi nucleons and the final state does not include pions. It is not known how much three or more nucleons absorption contributes in case of kaon absorption, but by selecting back-to-back hyperon-nucleon pairs, we can select two-nucleon absorption process.