Likelihood of the combined D1 and D2 analysis (solid line) as a function of ﹩\delta T^{2}_{l}﹩. The null tests: quadrature (signal with chopper sweeping one direction minus that with the chopper sweeping the other direction; dotted line), fast and slow dither (differences of subsequent 0.5 and 10 s averages, dashed and dash‐doted lines, respectively), and first half minus second half (triple‐dot–dashed line) are also shown. The vertical lines indicate the maximum, ±1 σ, or 95% confidence upper bound.