Development of the S-2S spectrometer and the fiber target for high-resolution spectroscopic study of the Xi-hypernuclei

Spectroscopic study of Xi-hypernuclei provides insights into the Xi-N interaction. 
A missing mass spectroscopy of the Xi-hypernuclei was performed via the 12C (K-,K+) reaction at J-PARC K1.8 beam line in 2015.
We have achieved the missing mass resolution  5.4 MeV (FWHM) which is the best resolution in the Xi-hypernuclear missing mass studies. 

It is important to achieve a better missing mass resolution of 2MeV (FWHM) to observe the hypernuclear structure including core excitation.
We are constructing a new spectrometer S-2S(Strangeness  -2 Spectrometer) for the K+, with an improved momentum resolution. In this condition, the total missing-mass resolution would be affected mainly due to the target energy loss straggling when we use a thick target to enhance the production.
To reduce energy loss straggling in the target, we are developing an active target composed of about 1000 scintillating fibers of phi 3 mm. This active fiber-target system enables us to correct energy loss of K- and K+ event by event.
Construction of the magnets and most parts of detectors for S-2S has been completed. It will soon be ready for installation in J-PARC K1.8.