  In a dedicated test setup at the Kamioka Observatory we studied pulse shape
discrimination (PSD) in liquid xenon (LXe) for dark matter searches. PSD in LXe
was based on the observation that scintillation light from electron events was
emitted over a longer period of time than that of nuclear recoil events, and
our method used a simple ratio of early to total scintillation light emission
in a single scintillation event. Requiring an efficiency of 50% for nuclear
recoil retention we reduced the electron background to 7.7\pm1.1(stat)\pm1.2
0.6(sys)\times10-2 at energies between 4.8 and 7.2 keVee and to
7.7\pm2.8(stat)\pm2.5 2.8(sys)\times10-3 at energies between 9.6 and 12 keVee
for a scintillation light yield of 20.9 p.e./keV. Further study was done by
masking some of that light to reduce this yield to 4.6 p.e./keV, the same
method results in an electron event reduction of 2.4\pm0.2(stat)\pm0.3
0.2(sys)\times10-1 for the lower of the energy regions above. We also observe
that in contrast to nuclear recoils the fluctuations in our early to total
ratio for electron events are larger than expected from statistical
fluctuations.
