Experimental search of strange tribaryons in the 4He(K stop − , n) reaction

Abstract

Recent prediction of Akaishi and Yamazaki on the strongly bound kaonic nuclear states with remarkably narrow widths have generated a lot of physics interests and the states have been studied and discussed intensively [1]. The fundamental motivation behind such intense study was that on one hand they could give us the excellent opportunities to investigate dense and cold hadronic systems in which quarks may be deconfined and the partial restoration of the chiral symmetry is expected to occur in a large scale [2], on the other hand the existence itself with such narrow width is extremely peculiar and interesting. Since then, the states have been studied in a series of experiments at BNL [3], KEK [4,5], GSI [6] and LNF [7]. We have recently reported an indication of a strange tribaryon state, S+, with a width Γ < 23 MeV/c 2, in the neutron time of flight (TOF) spectrum of the 4He(K stop − , n) reaction in the KEK-PS E471 which was the first experiment at KEK-PS to search for the deeply bound narrow K − ppn (T=0) state [4]. In order to confirm the state, S+, and search for other possible total isospin T=0/1 tribaryonic states, we have re-measured the neutron energy spectrum from 4He(K stop − , n) reaction in the KEK-PS E549 experiment with the upgraded setup with which TOF resolution was improved 1.5 times and the statistics was increased 6 times. However, in the neutron spectra, we find such a smooth momentum distribution that we conclude the state either not so strong to stick out of the inclusive background or too broad to form a peak. It is now necessary to analyze the data for further details such as the hyperon motion correlation.