Preliminary results on position reconstruction for ZEPLIN III

ZEPLIN IIIis a two-phase xenondetector for direct dark matter search that will look for rare nuclear recoils from elastic scattering of Weakly Interacting Massive Particlesoff xenonatoms. ZEPLIN IIImeasures both the scintillation and ionisation signals produced in the liquid by the interacting particle. The prompt scintillation is detected by an array of 31 photomultipliers(PM) immersed in the liquid, and a strong electric field extracts the ionisation electrons to the vapour phase. Electroluminescence photons are produced in the gas and detected by the same PM array. In this paper we describe position reconstruction methods that use both these signals to achieve a position accuracy of a few millimetres in the horizontal planeand sub-millimetre in the vertical coordinate.