Neutron spectra from the in-flight $^{16}$O($K^-,n$) and $^{12}$C($K^-,n$) reactions

We carried out an experiment to study kaonic nuclei at K2 beam line of KEK 12GeV Proton Synchrotron in this spring. We employed the in-flight ($K^-,N$) reaction to excite the kaonic nuclear state since expected that almost the highest energy nucleon made background ineffective. Water, carbon, and polyethylene were used as targets. We would like to show the preliminary result of the missing mass spectra of the $^{16}$O($K^-,n$) and $^{12}$C($K^-,n)$ reaction and discuss kaonic nuclei by spectra in the bound region.