SNOElectroweak Interaction Research at the University of Washington
Neutral Current Detectors Pulse Shape Analysis
When an ionizing event occurs in a Neutral Current Detector (NCD)
the current pulse is read in to be recorded and analyzed. These current
pulses have been observed to display varying topologies based on the
particle type and the direction in which the particle track is oriented
with respect to the anode wire. It can be seen that this pulse
topology can be broken down into an energy contribution, a geometrical
contribution, a drift velocity contribution, and a normalization factor.
The current is defined to be the rate with which charge is collected from
the ionizing electrons in the gas, i(t)=dq/dt.
Our current efforts are to show that for both alpha and neutron pulses,
a total of 3 variables are sufficient to describe the fundamental pulse shape.
This fundamental pulse shape excludes the treatment of the ion tail, straggling,
white noise, etc. Additionally, a fitting routine using Least Squares fitting and
the Marquardt Search Method are being developed to determine each of the three
variables for individual NCD pulses. The c2 goodness of fit parameter resulting
from the pulse fitting routine will be used to distinguish between neutron
events and alpha events. Sample pulses, generated by a Monte Carlo routine
that utilizes the fundamental pulse shape formula, will be used to test the
performance of the fitting routine. An example alpha pulse generated by
this Monte Carlo routine and a real alpha pulse obtained from NCD data are shown below.
