Fluctuation in energy loss measurement in allene-doped liquid argon for heavy ions

Liquid argon has good properties as particle detector medium and can be used to measure energies of heavy ions with capability of identification of charge and mass of particles. We have improved the response of the liquid argon detectors to heavy particles by using photoionization process in liquid argon. In this kind of detectors, the mass identification needs good resolution in measuring energy deposited along the particle track. We have investigated the resolution of energy loss measurement for heavy ions with several hundreds MeV/n in liquid argon doped with allene (C₃H₄) as a photoionization material. The experimentally obtained resolutions were several % in FWHM for neon to iron ions, which are not so good as expected by the theory. We will describe the measurements on energy loss fluctuation in LAr and some results of our attempt to clarify the cause of deterioration of resolution.