Measurement of the $^{2}$H($p,\gamma$)$^{3}$He S-factor at 265-1094keV

TL;DR

This study provides new measurements of the $^2$H($p, extgamma$)$^3$He reaction rate at energies relevant for Big Bang nucleosynthesis, which helps refine primordial deuterium abundance predictions.

Contribution

It presents the first high-energy measurements of the $^2$H($p, extgamma$)$^3$He S-factor, improving the accuracy of nuclear reaction rates used in cosmological models.

Findings

The S-factor is higher at Big Bang temperatures than previously estimated.

The new data reduces the uncertainty in primordial deuterium abundance predictions.

Results support a tighter constraint on the baryon-to-photon ratio from Big Bang nucleosynthesis.

Abstract

Recent astronomical data have provided the primordial deuterium abundance with percent precision. As a result, Big Bang nucleosynthesis may provide a constraint on the universal baryon to photon ratio that is as precise as, but independent from, analyses of the cosmic microwave background. However, such a constraint requires that the nuclear reaction rates governing the production and destruction of primordial deuterium are sufficiently well known. Here, a new measurement of the $^2$H($p,\gamma$)$^3$He cross section is reported. This nuclear reaction dominates the error on the predicted Big Bang deuterium abundance. A proton beam of 400-1650keV beam energy was incident on solid titanium deuteride targets, and the emitted $\gamma$-rays were detected in two high-purity germanium detectors at angles of 55$^\circ$ and 90$^\circ$, respectively. The deuterium content of the targets has been obtained in situ by the $^2$H($^3$He,$p$)$^4$He reaction and offline using the Elastic Recoil Detection method. The astrophysical S-factor has been determined at center of mass energies between 265 and 1094 keV, addressing the uppermost part of the relevant energy range for Big Bang nucleosynthesis and complementary to ongoing work at lower energies. The new data support a higher S-factor at Big Bang temperatures than previously assumed, reducing the predicted deuterium abundance.