  In the atmospheric Cerenkov technique gamma rays are detected against the
abundant background produced by hadronic showers. In order to improve the
signal to noise ratio of the experiment, it is necessary to reject a
significant fraction of hadronic showers. Traditional background rejection
methods based on image shape parameters have been extensively used for the data
from imaging telescopes. However, non-imaging Cerenkov telescopes have to
develop very different means of statistically identifying and removing cosmic
ray events. Some of the parameters which could be potentially important for
non-imaging arrays are the temporal and spectral differences, the lateral
distributions and density fluctuations of Cerenkov photons generated by gamma
ray and hadron primaries. Here we study the differences in fluctuations of
Cerenkov photon density in the light pool at the observation level from showers
initiated by photons and those initiated by protons or heavier nuclei. The
database of simulated events for the PACT array has been used to evaluate the
efficiency of the new technique. Various types of density fluctuations like the
short range and medium range fluctuations as well as flatness parameter are
studied. The estimated quality factors reflect the efficiencies with which the
hadrons can be rejected from the data. Since some of these parameters are
independent, the cuts may be applied in tandem and we demonstrate that the
proton rejection efficiency of about 90% can be achieved. Use of density
fluctuations is particularly suited for wavefront sampling observations and it
seems to be a good technique to improve the signal to noise ratio.
