Improving 3D Electric Field Map for the EXO-200 Experiment
Yi-Hsuan Lin1, Michelle Dolinski1
1Physics Department, Drexel University, Philadelphia, PA
yl654@drexel.edu
BACKGROUND
MOTIVATION
Neutrino
Beta (β) Decay
• Occurs when nuclei have
unfavored atomic mass to
atomic number ratio
• β decay creates positronneutrino or electronantineutrino pair
• ββ decay occurs
when single β decay is
forbidden
Energy
• Weakly interacting and has very small mass
• Oscillation experiments confirm 3 flavors of neutrinos,
made up of different combinations of mass states
Atomic
Number
http://www.cobra-experiment.org
RESULTS
EXO-200 fits SS and MS events
simultaneously in energy and
standoff distance
• Standoff distance ≡ smallest
distance between charge
deposit in the TPC and the
edge of the TPC
• Low standoff distance = high
radius
Discrepancies in the shapes
of the standoff distance plot
affect the background
estimation
Leads to 9.2 % systematic error
Radius
At high R, there is no improvement
from the 3D digitizer
Standoff Distance
Neutrinoless Double Beta Decay (0νββ)
EXO-200 (Enriched Xenon Observatory)
• Time projection chamber (TPC) experiment filled with 110
kg of active liquid xenon-136 operating at -100°C
• Set the most sensitive limit for 0νββ half-life in 2014 Nature
paper:
T1/20νββ(136Xe) > 1.1x1025yr (90% C.L.)
Energy Deposition Readout
• Events are classified as single-site (SS) and multi-site (MS)
according to number of detected charge deposits
• 0νββ are predominately SS and γ are predominately MS
METHOD
Incorporate full 3D drift field simulations of EXO-200 geometry in
full-scale Monte Carlo simulation
• Consider the edge effects in order to improve the shape
agreement for standoff distance in the first bin
140 cm
• Ultra-rare phenomenon
requires neutrinos to be
Majorana particles and
at least one favor to have
non-zero mass
• Finding the half-life of
0νββ is an indirect way
to find neutrino masses
Half of
EXO-200 TPC
(side view)
Slice: Electric
potential (kV)
z
z
x
Full-scale Simulation
y
y
x
• Create standard EXOSim charges
at position S5 to simulate
calibration data
• Drift the charges through the 3D
drift field simulation
(25.5cm, 0.0, 0.0)
• Run simulated data through
standard EXO-200 data analysis
processes and cuts
• Create shape agreement plots,
comparing MC simulation to
http://dx.doi.org/10.1103/PhysRevC.89.015502
data 228Th calibration data at
position S5
There is no statistically significant
improvement in the first bin of
the standoff distance plot
FUTURE WORK
Other approaches to consider to explain the
discrepancy at low standoff distance:
• Check on the source location uncertainty
• Look at the background subtracted 2νββ
• Model charge buildup in TPC plastics
REFERENCES
Albert J B et al (EXO Collab.) 2014 Phys. Rev. C 89 015502; arXiv:
1306.6106
Albert, JB (2014) Search for Majorana neutrinos with the first two years
of EXO-200 data. Nature 510: pp. 229