Final results of Borexino Phase-I on low-energy solar neutrino spectroscopy
Final results of Borexino Phase-I on low-energy solar neutrino spectroscopy
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DOI：
10.1103/physrevd.89.112007
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发表时间：
2014-06-25
影响因子：
5
通讯作者：
Zuzel, G.
中科院分区：
文献类型：
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作者：
Bellini, G.;Benziger, J.;Zuzel, G.
博雷西诺（Borexino）自2007年5月起在意大利格兰萨索国家实验室（Laboratori Nazionali del Gran Sasso laboratory）运行，其主要目标是探测太阳中微子。该探测器是一个大型无分段液体闪烁体量热计，具有前所未有的低本底放射性水平，针对光谱的低能部分研究进行了优化。在第一阶段（2007 - 2010年），博雷西诺首先探测到，然后精确测量了铍 - 7太阳中微子的通量，排除了其相互作用率存在任何显著的昼夜不对称性，首次直接观测到了质子 - 电子 - 质子（pep）中微子，并对碳氮氧（CNO）循环中产生的太阳中微子通量设定了最严格的上限，在该循环中碳、氮和氧在聚变过程中起催化剂作用。在本文中，我们讨论了信号特征，对本底进行了全面描述，量化了它们的事件率，描述了识别、选择或扣除本底的方法，并介绍了数据分析。关键特征包括使用放射源进行广泛的原位校准程序、探测器响应的详细建模、能够通过软件切割定义一个具有极低本底的最内层基准体积，以及闪烁体出色的脉冲形状甄别能力，从而实现粒子识别。我们报告了对铍 - 7中微子相互作用率年调制的测量结果。观测到的调制的周期、幅度和相位与这些事件的太阳起源相符，并且以高于99%的置信水平否定了其年调制不存在的情况。文中还介绍了第一阶段结果在中微子振荡物理和太阳模型背景下的物理意义。
Borexino has been running since May 2007 at the Laboratori Nazionali del Gran Sasso laboratory in Italy with the primary goal of detecting solar neutrinos. The detector a large unsegmented liquid scintillator calorimeter characterized by unprecedented low levels of intrinsic radioactivity is optimized for the study of the lower energy part of the spectrum. During Phase-I (2007-2010) Borexino first detected and then precisely measured the flux of the Be-7 solar neutrinos ruled out any significant day-night asymmetry of their interaction rate made the first direct observation of the pep neutrinos and set the tightest upper limit on the flux of solar neutrinos produced in the CNO cycle (carbon nitrogen oxigen) where carbon nitrogen and oxygen serve as catalysts in the fusion process. In this paper we discuss the signal signature and provide a comprehensive description of the backgrounds quantify their event rates describe the methods for their identification selection or subtraction and describe data analysis. Key features are an extensive in situ calibration program using radioactive sources the detailed modeling of the detector response the ability to define an innermost fiducial volume with extremely low background via software cuts and the excellent pulse-shape discrimination capability of the scintillator that allows particle identification. We report a measurement of the annual modulation of the Be-7 neutrino interaction rate. The period the amplitude and the phase of the observed modulation are consistent with the solar origin of these events and the absence of their annual modulation is rejected with higher than 99% C.L. The physics implications of Phase-I results in the context of the neutrino oscillation physics and solar models are presented.