Simulation for determining position and size of laser shots to identify double beta decay daughter in liquid xenon ionization drift chamber

In order to identify a daughter ion of Ba+ with laser-induced fluorescence just after a candidate event of double beta decay of 136Xe is found in a liquid xenon ionization drift chamber, the size of the laser beam directed to the vertex position is determined to be 1.6 mm in diameter by simulating the signal amplitudes of scintillation and ionization due to two beta rays with the EGS4 simulation code. The detection efficiencies of the apparatus and the trigger threshold of scintillation signals, which are obtained with the simulation, are also discussed in detail.