Lightest elements were produced in the first few minutes of the Universe through a sequence of
nuclear reactions known as Big Bang nucleosynthesis (BBN). Although astronomical observations
of primordial deuterium abundance have reached percent accuracy, theoretical predictions based
on BBN are affected by the large uncertainty on the cross-section of the D(p, 𝛾)3He deuterium
burning reaction. Here I am reporting on a new measurement of the D(p, 𝛾)3He cross section
performed by the LUNA collaboration to an unprecedented precision of better than 3%. This result
settles the most uncertain nuclear physics input to BBN calculations and substantially improve the
use of primordial abundances as probes of the physics of the early Universe.