Production Rate Measurement of Tritium and Other Cosmogenic Isotopes in Germanium with CDMSlite

TL;DR

This study measures the production rates of tritium and other cosmogenic isotopes in germanium detectors, crucial for background estimation in low-mass dark matter searches, using data from the CDMSlite experiment.

Contribution

It provides experimental estimates of cosmogenic isotope production rates in germanium, improving upon limited existing data and constraining theoretical models.

Findings

Measured production rate of tritium: 74±9 atoms/(kg·day)

Estimated production rates for other isotopes like Fe-55, Zn-65, Ge-68

Analysis helps refine background models for dark matter detection

Abstract

Future direct searches for low-mass dark matter particles with germanium detectors, such as SuperCDMS SNOLAB, are expected to be limited by backgrounds from radioactive isotopes activated by cosmogenic radiation inside the germanium. There are limited experimental data available to constrain production rates and a large spread of theoretical predictions. We examine the calculation of expected production rates, and analyze data from the second run of the CDMS low ionization threshold experiment (CDMSlite) to estimate the rates for several isotopes. We model the measured CDMSlite spectrum and fit for contributions from tritium and other isotopes. Using the knowledge of the detector history, these results are converted to cosmogenic production rates at sea level. The production rates in atoms/(kg$\cdot$day) are 74$\pm$9 for $^3$H, 1.5$\pm$0.7 for $^{55}$Fe, 17$\pm$5 for $^{65}$Zn, and 30$\pm$18 for $^{68}$Ge.