Electron emission from liquid into gaseous xenon is a cornerstone of dark matter search detectors such as ZEPLIN , XENON , LUX and LZ .
The probability of emission is a function of the applied electric field E , and electrons which fail to pass from the liquid into the gas have been previously hypothesized to become thermalized and trapped .
This article shows , for the first time , quantitative agreement between an electron emission model and existing data .
The model predicts that electrons in the liquid must surmount a typical potential barrier \phi _ { b } = 0.34 \pm 0.01 eV in order to escape into the gas .
This value is a factor of about \times 2 smaller than has previously been calculated or inferred .
Knowledge of \phi _ { b } allows calculation of the lifetime of thermalized , trapped electrons .
The value is \mathcal { O } ( 10 ) ms , which appears to be compatible with XENON10 observations of electron train backgrounds .
As these backgrounds limit the sensitivity of dark sector dark matter searches , possible mitigations are discussed .