EXO-200 Phase-II Results Announced

August 7, 2017

The new neutrinoless double beta decay search results from EXO-200 was announced at the TAUP meeting after one year of Phase-II operation.   In Phase-II, the detector energy resolution at the decay energy region is improved to 1.23%.    External radon background between the cryostat and lead shield has been suppressed with radon free air.   In addition, new analysis techniques for discriminating the gamma background has been implemented.    Incorporating both hardware and software upgrades, the combined sensitivity for Phase-I and Phase-II data improved 2-fold to 3.7 x 10^25 years.   No statistically significant signal was observed, leading to a lower limit on the 0νββ half-life of 1.8 x 10^25 yr at the 90% confidence level.   The UIUC group led the front end electronics upgrade for Phase-II and contributed substantially to the analysis.  Graduate student Shaolei Li studied the wire gain calibration and checked the grid correction for Phase-II.   Graduate student Matthew Coon presented the new results at the 2017 Meeting of APD Division of Particle & Fields.