  Weakly Interacting Massive Particles (WIMPs) are one of the leading
candidates for Dark Matter. We developed a model-independent method for
determining the WIMP mass by using data (i.e., measured recoil energies) of
direct detection experiments. Our method is independent of the as yet unknown
WIMP density near the Earth, of the form of the WIMP velocity distribution, as
well as of the WIMP-nucleus cross section. It requires however positive signals
from at least two detectors with different target nuclei. At the first phase of
this work we found a systematic deviation of the reconstructed WIMP mass from
the real one for heavy WIMPs. Now we improved this method so that this
deviation can be strongly reduced for even very high WIMP mass. The statistical
error of the reconstructed mass has also been reduced. In a background-free
evironment, a WIMP mass of ~ 50 GeV could in principle be determined with an
error of ~ 35% with only 2 times 50 events.
