Experimental study of the 7Be destruction reaction relevant to Big Bang nucleosynthesis and future prospects

Abstract: The Cosmological Lithium Problem (CLP) is a well-known issue in astrophysics. It refers to an overestimation of the primordial 7Li abundance in the standard Big Bang nucleosynthesis (BBN) model predictions relative to astrophysical observations. Our research focuses on experimental nuclear physics to address the CLP. In particular, we aim to constrain the reaction rate of the 7Be(d, p)8Be reaction by measuring its cross section. The majority of 7Li nuclei were produced by the electron capture decay (T1/2= 53.22 days = 4.6 × 106 seconds) of 7Be. 7Be nuclei were produced in several hundred seconds during the BBN, leading to a timescale difference of more than 104 between the production time of 7Li and 7Be. This significant timescale difference implies that if more 7Be nuclei were destroyed during the BBN, it could result in a lower abundance of 7Li, potentially resolving the discrepancy.

Our study focuses on the 7Be(d, p)8Be reaction based on a theoretical suggestion that this reaction played a significant role in the destruction of 7Be nuclei during the BBN [1]. The measurement of the absolute cross section in the Big Bang energy region (Ec.m.=0.1−0.4 MeV) was crucial for understanding the nuclear reactions in the primordial universe. We produced a radioactive 7Be target and measured the 7Be(d, p)8Be reaction cross section at the tandem facility of Kobe University in Japan. A distinctive feature of this experiment was the production of an unstable nucleus 7Be as a target. The thick-target analysis method was applied to determine the cross sections. The cross section at the lowest energy of Ec.m.=0.12 MeV was measured with the highest sensitivity compared to the available data [2, 3, 4]. We confirmed that the measured 7Be(d, p)8Be cross sections have a limited impact on resolving the CLP.

This talk will outline the key details and discuss future perspectives, including a new project aimed at addressing the CLP.

References

[1] S. Q. Hou et al., Phys. Rev. C 91, 055802 (2015).

[2] R. Kavanagh, Nucl. Phys. 18, 492-501 (1960).

[3] C. Angulo et al., ApJ 630, L105 (2005).

[4] N. Rijal et al., PRL 122, 182701 (2019).