New Technique for Barium Daughter Ion Identification in a Liquid Xe-136 Double Beta Decay Experiment

Technical Report · Wed Jun 08 00:00:00 EDT 2016

DOI:https://doi.org/10.2172/1256102· OSTI ID:1256102

Fairbank, William ^[1]

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1. Colorado State Univ., Fort Collins, CO (United States)

This work addresses long-standing issues of fundamental interest in elementary particle physics. The most important outcome of this work is a new limit on neutrinoless double beta decay. This is an extremely rare and long-sought-after type of radioactive decay. If discovered, it would require changes in the standard model of the elementary constituents of matter, and would prove that neutrinos and antineutrinos are the same, a revolutionary concept in particle physics. Neutrinos are major components of the matter in the universe that are so small and so weakly interacting with other matter that their masses have not yet been discovered. A discovery of neutrinoless double beta decay could help determine the neutrino masses. An important outcome of the work on this project was the Colorado State University role in operating the EXO-200 neutrinoless double beta decay experiment and in analysis of the data from this experiment. One type of double beta decay of the isotope ¹³⁶Xe, the two-neutrino variety, was discovered in this work. Although the other type of double beta decay, the neutrinoless variety, was not yet discovered in this work, a world’s best sensitivity of 1.9x10²⁵ year half-life was obtained. This result rules out a previous claim of a positive result in a different isotope. This work also establishes that the masses of the neutrinos are less than one millionth of that of electrons. A unique EXO-200 analysis, in which the CSU group had a leading role, has established for the first time ever in a liquid noble gas the fraction of daughter atoms from alpha and beta decay that are ionized. This result has important impact on other pending studies, including nucleon decay and barium tagging. Novel additional discoveries include multiphoton ionization of liquid xenon with UV pulsed lasers, which may find application in calibration of future noble liquid detectors, and studies of association and dissociation reactions of Ba⁺ ions in gaseous xenon. Through this project, we are substantially closer to demonstrating “barium tagging”, i.e., detection of single daughter ¹³⁶Ba atoms from ¹³⁶Xe double beta decay. Milestones achieved include obtaining spectra of small numbers of Ba atoms and cryoprobe advances toward trapping single ¹³⁶Ba atoms in solid xenon and probe extraction for detection. One of the other benefits to society is the training of six Ph.D. students in a variety of state-of-the-art technologies, half under primary support of this grant and half with partial support, with four finishing their Ph.D. degrees and two well on their way.

• Research Organization: Colorado State Univ., Fort Collins, CO (United States)
• Sponsoring Organization: USDOE Office of Science (SC), High Energy Physics (HEP)
• Contributing Organization: EXO Collaboration; nEXO Collaboration
• DOE Contract Number: FG02-03ER41255
• OSTI ID: 1256102
• Report Number(s): DOE-CSU-41255-1; TRN: US1700207
• Country of Publication: United States
• Language: English

Related Subjects

73 NUCLEAR PHYSICS AND RADIATION PHYSICS
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY
NEUTRINOLESS DOUBLE BETA DECAY
NEUTRINOS
XENON 136
BARIUM 136
XENON
CRYOGENIC FLUIDS
LIQUIDS
BARIUM
ATOMS
MASS
DETECTION
IONS
PHOTOIONIZATION
MULTI-PHOTON PROCESSES
HALF-LIFE
LASERS
PULSES
SENSITIVITY
SOLIDS
SPECTRA
TRAPPING
LIMITING VALUES
DAUGHTER PRODUCTS
ALPHA DECAY
BETA DECAY