Search for Neutrinoless Double-Beta Decay with the Upgraded EXO-200 Detector

Area of Science:

• Nuclear Physics
• Particle Physics
• Experimental Physics

Background:

• Neutrinoless double-beta decay (0νββ) is a hypothetical nuclear process not observed yet.
• Its observation would indicate that neutrinos are Majorana particles and violate lepton number conservation.
• The search for 0νββ is a key area in modern particle and nuclear physics.

Purpose of the Study:

• To search for 0νββ decay of ^{136}Xe using an upgraded detector.
• To improve the sensitivity and background rejection capabilities compared to previous experiments.
• To set a new lower limit on the 0νββ half-life of ^{136}Xe.

Main Methods:

• Utilized the upgraded EXO-200 detector with improved energy resolution (1.23%) and electric field.
• Implemented a radon suppression system to reduce background noise.
• Developed advanced analysis techniques for topological discrimination between signal and background events.

Main Results:

• Achieved a twofold increase in 0νββ half-life sensitivity, reaching 3.7×10^{25} yr.
• Observed no statistically significant evidence for 0νββ decay.
• Set a new 90% confidence level lower limit on the 0νββ half-life of ^{136}Xe at 1.8×10^{25} yr.

Conclusions:

• The upgraded EXO-200 detector has enhanced capabilities for searching for 0νββ decay.
• The experiment places stringent constraints on the properties of neutrinos and the nature of lepton number violation.
• Further investigation is warranted to potentially observe this rare decay process.