1. Kst*Charged triggered, hence reaction vertex is determined by BLC-PDC
2. One neutral particle on 1 PA/PB/NT arm, and 1 charged particle on the other PA/PB/NT arm.
3. Neutron detection threshold is set to 3 MeVee. This is also imposed to counter-detected neutron, hence even if a neutral particle is counter-detected, the event is neglected if the light output is less than 3 MeVee.
4. Set physical 1/&beta region for counter-detected neutron, to be 1.6 < 1/&beta < 9.0 . Otherwise, the event is accidental (or &gamma coincidence), and neglected.
5. TC/VDC selection is applied optionally, hence no explicit requirement unless especially mentioned.
6. VDC/PDC VETO is neglected. This situation is kept in E570 also if we select events from Kst*Charged events.
First, the global shape of p/n spectra is presented. The proton spectra is clearly different from that for pp back-to-back events.
As is done for nn/pp back-to-back spectra, we now apply cos(pn) and counter-detected-particle-momentum slections.
The correlation of p-n momenta is shown below.
pn invariant mass spectra are shown below. At around 2130 MeV/c^2, a peak structure is found. If the pn pair is interpreted as &Sigma N, then 2130 MeV/c^2 is roughly corresponds to Kbar NN threshold value.
