Extended Data Fig. 1: Typical γ-ray spectrum obtained underground with the high-purity germanium detector at proton beam energy Ep = 50 keV.
From: The baryon density of the Universe from an improved rate of deuterium burning
Typical γ-ray spectrum (blue) obtained with the deuterium gas target at P = 0.3 mbar, clearly showing the full-energy, single-escape and double-escape peaks from the D(p,γ)3He reaction. The continuum is mainly due to Compton scattering events in which photons deposit only part of their energy in the detector. In grey is the beam-induced background spectrum acquired in the control run under the same experimental conditions but with an inert 4He gas target. Both spectra are normalized to the integrated beam current. The region of interest (Eγ ≈ 4.5−5.8 MeV) is essentially background free owing to the million-fold shielding8 from cosmic-ray muons attained at the LUNA underground laboratory.
