UHM High Energy Physics Seminar

Detailed Characterization of Nuclear Recoil Pulse Shape Discrimination in the DarkSide-50 Direct Dark Matter Experiment(Thesis Defense)

by Erin Edkins (University of Hawaii)

Wednesday, 5 April 2017 from to (Pacific/Honolulu)
at WAT ( 417A )
While evidence of non-baryonic dark matter has been accumulating
for decades, its exact nature remains a mystery.  Weakly Interacting
Massive Particles (WIMPs) are a well motivated dark matter candidate which
appear in certain extensions of the Standard Model.  If such particles
exist, they should occasionally interact with particles of normal matter,
producing a signal which may be detected.  The DarkSide-50 direct dark
matter experiment aims to detect the energy of recoiling argon atoms due to
the elastic scattering of postulated WIMPs.
    As nuclear recoils produced by WIMPs are indistinguishable from those
produced by neutrons, radiogenic neutrons are both the most dangerous class
of background and a vital calibration source for the study of the potential
WIMP signal.  Unfortunately, radioactive sources used for the calibration
of DarkSide-50 are universally accompanied by gamma decays, which obscure
the low energy region where most WIMP interactions are expected to occur.
Prior to this work, this problem was circumvented by determining the dark
matter acceptance region in a separate, dedicated experiment, ScENE.
However, this work presents a novel method of nuclear recoilcalibration
employing event selection, unique to the design of DarkSide-50, which
produces a nearly pure sample of nuclear recoils, allowing for the
definition of the acceptance region independent of ScENE values. 
Two analytical models defining the signal region are described and their results compared. 
Finally, a detailed study of integrated noise in nuclear and electron recoil events is presented,
which demonstrates a difference between these classes of events for the first time.