氚俘获探测非相对论宇宙中微子：唯象学和物理势
Detecting non-relativistic cosmic neutrinos by capture on tritium: phenomenology and physics potential
摘要：
本文以PIMMY实验为例，研究了利用中微子俘获氚探测宇宙中微子背景的物理潜力。由于$Δ\sim$的投影能量分辨率为0.15 eV，实验将对简并谱为$m_1 \simeq m_2 \simeq m_3 = m_ν\gtrsim 0.1$ eV的中微子质量敏感。这些中微子在今天是非相对论性的;探测它们将是探索这种未探索的运动学机制的独特机会。中微子俘获的特征是电子光谱中的一个峰，它在β衰变终点之上被$2 m_ν$取代。如果能量分辨率为$Δ\lesssim 0.7 m_ν$，则信号将超过β衰变的背景。有趣的是，总的俘获率取决于中微子质量的来源，分别是每年的$Γ^{\rm D} \simeq 4$和$Γ^{\rm M} \simeq 8$事件（对于100 g氚靶）。由于引力聚集，预计$\mathcal{O}(1)$的速率会提高，具有探测中微子局部过密度的独特潜力。转向更奇特的中微子物理学，PINEMY可能对轻子不对称性敏感，并揭示了短基线振荡搜索所青睐的eV尺度的无菌中微子。该实验还将对宇宙年龄量级的中微子寿命敏感，并打破影响现有界限的中微子质量和寿命之间的简并性。
英文摘要：
We study the physics potential of the detection of the Cosmic Neutrino Background via neutrino capture on tritium, taking the proposed PTOLEMY experiment as a case study. With the projected energy resolution of $Δ\sim$ 0.15 eV, the experiment will be sensitive to neutrino masses with degenerate spectrum, $m_1 \simeq m_2 \simeq m_3 = m_ν\gtrsim 0.1$ eV. These neutrinos are non-relativistic today; detecting them would be a unique opportunity to probe this unexplored kinematical regime. The signature of neutrino capture is a peak in the electron spectrum that is displaced by $2 m_ν$ above the beta decay endpoint. The signal would exceed the background from beta decay if the energy resolution is $Δ\lesssim 0.7 m_ν$. Interestingly, the total capture rate depends on the origin of the neutrino mass, being $Γ^{\rm D} \simeq 4$ and $Γ^{\rm M} \simeq 8$ events per year (for a 100 g tritium target) for unclustered Dirac and Majorana neutrinos, respectively. An enhancement of the rate of up to $\mathcal{O}(1)$ is expected due to gravitational clustering, with the unique potential to probe the local overdensity of neutrinos. Turning to more exotic neutrino physics, PTOLEMY could be sensitive to a lepton asymmetry, and reveal the eV-scale sterile neutrino that is favored by short baseline oscillation searches. The experiment would also be sensitive to a neutrino lifetime on the order of the age of the universe and break the degeneracy between neutrino mass and lifetime which affects existing bounds.
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