镓中微子吸收截面及其不确定性
The Gallium Neutrino Absorption Cross Section and its Uncertainty
AI总结：
本文更新镓中微子吸收截面及其不确定性，考虑电弱修正和激发态跃迁，给出51Cr和37Ar源结果，并重新评估BEST及镓反常的统计显著性。
摘要：
在最近的巴克桑惰性中微子跃迁实验（BEST）中，观测到镓靶上中微子吸收率受到抑制，这与早先SAGE和GALLEX/GNO太阳中微子实验的中微子源刻度结果一致。BEST合作组利用一个3.4 MCi的51Cr中微子源，在两个极短基线上得到的观测计数率与预期计数率之比分别为R=0.791±0.05和0.766±0.05。在近期的中微子实验中，BEST因其两方面的简单性而引人注目：一方面是中微子能谱简单，即来自电子俘获源的线中微子，其强度可被测到估计为0.23%的精度；另一方面是吸收截面简单，其中精确已知的到镓基态的电子俘获率，即71Ge(e,νe)71Ga(g.s.)，确定了一个最小值。然而，吸收截面的不确定性是BEST、SAGE和GALLEX/GNO中微子源实验中的一个共同系统误差。本文更新了该截面，考虑了多种电弱修正以及到激发态跃迁的作用，以确定其中心值和合理的不确定性，从而能够更准确地评估镓反常的统计显著性。文中给出了51Cr和37Ar源的结果。修正后的中微子俘获率被用于重新评估BEST和镓反常。
英文摘要：
In the recent Baksan Experiment on Sterile Transitions (BEST), a suppressed rate of neutrino absorption on a gallium target was observed, consistent with earlier results from neutrino source calibrations of the SAGE and GALLEX/GNO solar neutrino experiments. The BEST collaboration, utilizing a 3.4 MCi 51Cr neutrino source, found observed-to-expected counting rates at two very short baselines of R=0.791 plus/minus 0.05 and 0.766 plus/minus 0.05, respectively. Among recent neutrino experiments, BEST is notable for the simplicity of both its neutrino spectrum, line neutrinos from an electron-capture source whose intensity can be measured to a estimated precision of 0.23%, and its absorption cross section, where the precisely known rate of electron capture to the gallium ground state, 71Ge(e,nue)71Ga(g.s.), establishes a minimum value. However, the absorption cross section uncertainty is a common systematic in the BEST, SAGE, and GALLEX/GNO neutrino source experiments. Here we update that cross section, considering a variety of electroweak corrections and the role of transitions to excited states, to establish both a central value and reasonable uncertainty, thereby enabling a more accurate assessment of the statistical significance of the gallium anomalies. Results are given for 51Cr and 37Ar sources. The revised neutrino capture rates are used in a re-evaluation of the BEST and gallium anomalies.
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