Performance of the silicon vertex tracker used in the ⁸He(p,pα)⁴n experiment at SAMURAI

An experiment at the SAMURAI setup at RIKEN was performed to study the existence of a resonant state of four neutrons in a quasi-free α-knockout reaction in inverse kinematics from ⁸He. For this the missing-mass method will be used, which requires to know precisely the reaction vertex inside the 5 cm thick liquid hydrogen target. The channel of interest is selected by the detection of a fast proton and a slow α, i.e., low and high deposited energies, respectively, with a very small angle. Therefore a silicon strip detector system, consisting of 6 planes (3 horizontal and 3 vertical) with 100 μm pitch size, was built. Additionaly this detector allows, amongst others, backgroundsubtraction and transverse momentum reconstruction. The design and performance of this detector during the experiment are presented.