Fig. 2: The STJ array of the BeEST experiment and precision energy measurement.
From: Direct experimental constraints on the spatial extent of a neutrino wavepacket
The measured 7Li recoil spectrum with the four peaks described in the text for 20 h of data from the single STJ pixel shown in the inset. The L-ES peak is barely visible because of its weak population probability. The measured uncertainty of the K-GS peak is shown, and is conservatively extracted as the upper limit on the inherent energy width of the recoil, σN,E ≤ 2.9 eV, through the procedure described in the text. The comb of the peaks from the calibration laser spectrum (violet) is also shown for comparison. The small bump in the spectrum at 4 eV results from a non-prompt, decay-induced process, the source of which is still under investigation. Scale bar, 1 mm.
