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We present a precise measurement of the asymptotic normalization coefficient (ANC) for the¹⁶O ground state (GS) through the¹²C(¹¹B,⁷Li)¹⁶O transfer reaction using the Quadrupole‐3‐Dipole (Q3D) magnetic spectrograph. The present work sheds light on the existing discrepancy of more than 2 orders of magnitude between the previously reported GS ANC values. This ANC is believed to have a strong effect on the¹²C(α,γ)¹⁶O reaction rate by constraining the external capture to the¹⁶O ground state, which can interfere with the high-energy tail of the 2⁺subthreshold state. Based on the new ANC, we determine the astrophysicalS-factor and the stellar rate of the¹²C(α,γ)¹⁶O reaction. An increase of up to 21% in the total reaction rate is found within the temperature range of astrophysical relevance compared with the previous recommendation of a recent review. Finally, we evaluate the impact of our new rate on the pair-instability mass gap for black holes (BH) by evolving massive helium core stars using the MESA stellar evolution code. The updated¹²C(α,γ)¹⁶O reaction rate decreases the lower and upper edges of the BH gap about 12% and 5%, respectively.

 

Underground Nuclear Astrophysics Experiment in China (JUNA) has been commissioned by taking the advantage of the ultra-low background in Jinping underground lab. High current mA level 400 KV accelerator with an ECR source and BGO detectors were commissioned. JUNA studies directly a number of nuclear reactions important to hydrostatic stellar evolution at their relevant stellar energies. In the first quarter of 2021, JUNA performed the direct measurements of 25 Mg(p, γ ) 26 Al, 19 F(p, α ) 16 O, 13 C( α ,n) 16 O and 12 C( α , γ ) 16 O near the Gamow window. The experimental results reflect the potential of JUNA with higher statistics, precision and sensitivity of the data. The preliminary results of JUNA experiment and future plan are given.