Title:

Measurements of 8Be production in Au+Au collisions at √(s_NN ) = 3 GeV

PAs:

Jinhui Chen, Yugang Ma, Tianhao Shao, Zhangbu Xu, Jie Zhao

Target journal:

Physical Review Letter

Abstract:

High-energy heavy-ion collisions provide a unique environment for replicating the Big Bang nucleosynthesis toward heavy elements in our universe. We observed high yields of the three 8Be resonant states (0.1, 3, 11) MeV from their decay 8Beàalpha+alpha. The 8Be/alpha ratio is compared to measurement of d/p ratio in the same system, and also to coalescence model calculations. This result reveals the importance and similarity of alpha cluster in the formation of heavier elements in both heavy-ion collisions and Big Bang nucleosynthesis.

Conclusion:

In summary, 8Be yields are measured as a function of transverse momentum in the rapidity range of -1 < ycm < -0.2 in Au+Au collisions at sqrt{sNN} = 3 GeV. The integrated yield in differential rapidity ranges are compared to the previously reported light nuclei. In mid-rapidity, the 8Be yields are consistent with the expected mass scaling and are consistent with alpha-alpha coalescence model calculation. In high rapidity, they are higher than the expected mass scaling.  The measured 8Be/4He ratio are compared with the d/p ratio in the same pT/A window, and compared with model calculation. Our results support that 8Be are formed by thermal coalescence of alphas in mid-rapidity. The high yield of 8Be at high rapidity are consistent with Hoyle mechanism of the nucleosynthesis of heavy elements from alpha clusters.

Figures:

Figure 1. Left: invariant mass distributions of in pT region (2.3, 2.5) GeV/c and rapidity region (-1.0, -0.8) of Alpha+Alpha. Pink crosses show the pure signal obtained by substructing the mixed event background (blue crosses) from the same event pairs (red crosses). Dash lines represent the fittings for different states and the total fit (black). Right: efficiency times acceptance according to detector characteristic for 8Be shown in the rapidity versus transerve momentum plot. The red squares show the different pT-y regions uesd to extract the 8Be yields.

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