[论文解读] Combined analyses of the antiproton production from cosmic-ray interactions and its possible dark matter origin

Pedro De la Torre Luque|arXiv (Cornell University)|Jul 14, 2021

Dark Matter and Cosmic Phenomena参考文献 110被引用 36

一句话总结

本研究结合了二级宇宙射线比值（B/C、Be/B、Li/Be）与反质子/质子比值（¯p/p）的马尔可夫链蒙特卡洛（MCMC）分析，以约束宇宙射线传播参数及截面不确定性。结果表明，AMS-02测量的¯p/p谱的能量依赖性可由纯二级起源良好解释，而约10%的恒定过剩最可能由反质子产生截面的10%重标度解释，而非暗物质WIMP信号。

ABSTRACT

Recent cosmic-ray (CR) studies have claimed the possibility of an excess on the antiproton flux over the predicted models at around $10$ GeV, which can be the signature of dark matter annihilating into hadronic final states that subsequently form antiprotons. However, this excess is subject to many uncertainties related to the evaluation of the antiproton spectrum produced from spallation interactions of CRs. In this work, we implement a combined Markov-Chain Monte Carlo analysis of the secondary ratios of B, Be and Li and the antiproton-to-proton ratio ($\bar{p}/p$), while also including nuisance parameters to consider the uncertainties related to the spallation cross sections. This study allows us to constrain the Galactic halo height and the rest of propagation parameters, evaluate the impact of cross sections uncertainties in the determination of the antiproton spectrum and test the origin of the excess of antiprotons. In this way, we provide a set of propagation parameters and scale factors for renormalizing the cross sections parametrizations that allow us to reproduce all the ratios of B, Be, Li and $\bar{p}$ simultaneously. We show that the energy dependence of the $\bar{p}/p$ ratio is compatible with a pure secondary origin. We find that the energy dependence of the evaluated $\bar{p}/p$ spectrum matches the AMS-02 data at energies above $\sim3$GeV, although there is still a nearly constant $\sim10\%$ excess of $\bar{p}$ over our prediction. We discuss that this discrepancy is more likely explained from a $\sim10\%$ scaling in the cross sections of antiproton production, rather than a component of dark matter leading to antiprotons. In particular, we find that the best-fit WIMP mass ($\sim 300$ GeV) needed to explain the discrepancy lies above the constraints from most indirect searches of dark matter and the resultant fit is poorer than with a cross sections scaling.

研究动机与目标

• 解决约10 GeV处预测与观测反质子通量之间长期存在的差异。
• 检验观测到的反质子过剩是否源于暗物质湮灭，或源于次级反应截面中的系统性不确定性。
• 通过多个二级宇宙射线比值，同时约束传播参数（扩散、银晕高度等）与截面标度因子。
• 评估截面不确定性对反质子谱预测的影响，以及过剩显著性的意义。

提出的方法

• 利用AMS-02数据，对B/C、Be/B、Li/Be比值与¯p/p比值进行联合MCMC分析。
• 引入多余参数以对B、Be和Li生成的次级反应截面进行重标度。
• 使用DRAGON2代码模拟银河系内宇宙射线传播与反质子生成。
• 通过WIMP湮灭至强子终态来建模暗物质贡献，参数化为质量与⟨σv⟩。
• 比较包含与不包含WIMP成分的拟合结果，以评估其显著性及与间接探测约束的一致性。
• 利用新的AMS-02 ¯p/p数据集以改进约束，并评估残差的形状。

实验结果

研究问题

• RQ1 观测到的约10 GeV处反质子过剩是否与二级起源一致，还是需要引入暗物质组分？
• RQ2 次级反应截面的不确定性如何影响反质子谱的预测？
• RQ3 对B、Be、Li与¯p/p比值进行联合拟合，能否更稳健地约束传播参数与截面标度因子？
• RQ4 为解释过剩，最优拟合的WIMP质量与湮灭截面是多少？其是否与其他间接搜寻结果一致？
• RQ5 ¯p/p谱中的残差形状更类似于WIMP信号，还是系统性偏移？

主要发现

• ¯p/p谱的能量依赖性可由纯二级起源良好再现，10 GeV处残差低于12%。
• 在约3 GeV以上观测到反质子通量相对于预测存在约10%的恒定过剩，该现象最可能由反质子产生截面的10%重标度解释。
• 为解释该过剩所需的最佳拟合WIMP质量约为300 GeV，该值高于大多数间接暗物质搜寻的约束范围，且其拟合效果劣于截面重标度方案。
• 采用10%截面重标度的拟合的χ²值比包含WIMP成分的拟合低近两倍，表明统计拟合显著更优。
• 使用新的AMS-02 ¯p/p数据集后，残差更平坦，减弱了明显的峰状结构，从而削弱了WIMP信号的证据。
• 该分析提供了一组一致的传播参数与截面标度因子，可在1σ不确定性范围内同时准确再现B、Be、Li与¯p/p比值。