Study of neutrino oscillations with a low energy conventional neutrino superbeam
Study of neutrino oscillations with a low energy conventional neutrino superbeam
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用低能常规中微子超级光束研究中微子振荡
DOI：
10.18429/jacow-ipac2016-thpmb055
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发表时间：
2000
影响因子：
1.4
通讯作者：
M. Donega
中科院分区：
文献类型：
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作者：
M. Donega
宇宙线相互作用产生的中微子通量的测量和太阳中微子相对于太阳标准模型的不足表明我们对中微子基本性质的理解有了重大的重新考虑，指出中微子振荡是可能的解释，并且在任何情况下都是中微子质量。已经进行了许多实验，未来几年将有许多其他实验研究这种可能性。一种特殊的中微子实验使用质子加速器来产生中微子，这一领域最雄心勃勃的项目是中微子工厂。在中微子工厂中，一个兆瓦级的质子加速器被用来产生π介子束。介子衰变产生的μ子，用磁喇叭收集，加速到50 GeV，最后储存在一个积累环中，在那里它们衰变，将中微子发送到不同距离的探测器。目前基于加速器的实验通常从功率在40 kW范围内的高能质子产生的π介子和K介子的衰变产生中微子。这些实验可以分为两类：探测器靠近生产点的短基线实验和探测器距离生产点数百公里的长基线实验。在目前基于加速器的实验和中微子工厂之间的中间步骤是所谓的中微子超束。这些超束是由π介子衰变产生的传统中微子束，但使用非常强烈的兆瓦级质子源。一个新的低能直线加速器在兆瓦级，SPL（超导质子直线加速器），已在欧洲核子研究中心设计，并可用于超级束和作为第一级的中微子工厂。欧洲核子研究中心已经成立了一个工作组来研究这种低能中微子超束的可行性和物理范围。在本研究中进行的可能的SPL为基础的超束的潜力的分析。该实验旨在观察初始νμ束中νe的出现，并改进现有的一些振荡参数的测量方法。利用目前的中微子探测器技术，高水平的背景抑制是可能的，因此在外观实验中，主要的背景是由初始束的νe污染给出的。本研究的主要部分是优化的初始中微子超束流的SPL为基础的配置纯度。第一章将讨论振荡参数和对它们的实验研究，报告测量参数的当前值。vi中微子振荡形式主义是在第二章中开发的，公式推导出将被用来计算振荡概率估计振荡中微子的数量在考虑的超束。第三章分析了基于SPL的中微子超束的描述。从加速器的简要说明开始，注意力将集中在π介子的生产和聚焦与磁喇叭。确定中微子束初始成分的唯一工具是π衰变隧道。研究了νe污染与衰变隧道参数的关系。用解析方法研究了π介子衰变和随后的μ介子衰变产生的中微子，并编制了计算中微子通量的FORTRAN程序。第四章是对衰变分析的详细说明。所用程序见附录。本研究的主要工作是优化π介子衰变隧道，并对所有可能的组态进行了系统的分析。研究了用这种中微子超束进行实验的灵敏度。为了获得显著的信号，选择了130 km处的40 kton探测器作为合理的配置。研究的探测器是水切伦科夫超级神冈和液体闪烁体MiniBooNE样。闪烁体探测器的分析已经使用MiniBooNE提案中报告的探测器性能数据进行，而对于水Cerenkov，可以利用Super Kamiokande合作并使用完整的探测器模拟软件。第五章对比较分析的结果进行了讨论。对振荡参数的分析主要集中在$\theta_{13}$上。第六章介绍了中微子振荡研究中常用的两种方法：李克图法和不相容图。与所研究的超束进行分析的结果报告和比较，在显着的参数范围内，与CHOOZ给出的$\theta_{13}$目前的限制。目前的研究表明，相对于这些已发表的数据，灵敏度几乎提高了一个数量级。由于“米兰大学”物理系和“热内夫”在伊拉斯谟项目框架内的合作，这项研究得以进行。我要感谢：CERN让我能够与PS部门合作; Dave Casper负责Super Kamiokande模拟和探测器物理学的重要解释; Mauro Mezzetto负责MiniBooNE的重要讨论; Simone Gilardoni负责中微子工厂喇叭的MARS模拟和整个中微子工厂振荡工作组。
Measurement of neutrino fluxes produced by cosmic rays interactions and the deficit of solar neutrino compared with the Solar Standard Model suggest a major reconsideration of our understanding of the fundamental neutrino properties, pointing to neutrino oscillations as possible explanation and in any case to neutrinos masses. Many experiments have been performed and many other will investigate this possibility in the coming years. A particular kind of neutrino experiment use a proton accelerator to produce neutrinos, the most ambitious project in this field being the Neutrino Factory. In a Neutrino Factory a MW-scale proton accelerator is used to produce a pion beam. Muons from pion decays, collected with a magnetic horn are accelerated up to 50 GeV and finally stored in an accumulation ring where they decay, sending neutrinos to detectors at different distances. The present accelerator based experiments generally produce neutrinos from the decay of pions and kaons generated from high energy protons with a power in the 40 kW range. These experiments can be divided into two classes: short baseline experiments where the detector is close to the production point and long baseline experiments where the detector is at hundreds of kilometers away from the production point. An intermediate step between the present accelerator based experiments and the Neutrino Factory, are the so called neutrino superbeams. These superbeams are conventional neutrino beams generated by pion decay but using a very intense MW-scale proton source. A new low energy linear accelerator in the MW-scale, the SPL (Superconducting Proton Linac), has been designed at CERN, and could be used for both superbeam and as first stage for the Neutrino Factory. A working group has been created at CERN to investigate the feasibility and the physics reach of this low energy neutrino superbeam. The analysis of the potential of the possible SPL-based superbeam is performed in the present study. The experiment would aim at observe the appearance of νe in a initial νμ beam and improve some of the existing mea- surements on the oscillation parameters. With the technology of present neutrino detectors, a high level of background rejection is possible, hence in appearance experiments the dominant background is given by the νe contamination of the initial beam. The leading part of the presented study is the optimization of the initial neutrino superbeam purity in the SPL based configuration. The oscillation parameters and the experiments investigating on them will be considered in the first chapter, reporting the present values of the measured parameters. vi Neutrino oscillations formalism is developed in the second chapter; formulas derived there will be used to calculate oscillations probabilities to estimate the number of oscillated neutrinos in the considered superbeam. The description of the SPL-based neutrino superbeam is analyzed in the third chapter. Starting from a brief description of the accelerator the attention will concentrate on the pion production and focalization with a magnetic horn. The only tool to define the initial composition of the neutrino beam is the pion decay tunnel. The relation between νe contamination and decay tunnel parameters has been investigated. Neutrino from pion decay and subsequent muon decay have been studied analytically and a FORTRAN program has been implemented to calculate neutrino fluxes. The detailed explanation of the decay analysis is the subject of the fourth chapter. The program used is reported in appendix. The do- minant effort in this study is the optimization of the pion decay tunnel and it is performed with a systematic analysis of all the possible configurations. The sensibility of the experiment using this neutrino superbeam has been investigated. In order to have significant signal, a 40 kton detector at 130 km has been chosen as a reasonable configuration. The detectors studied are a water Cerenkov Super Kamiokande-like and a liquid scintillator MiniBooNE- like. The analysis of the scintillator detector has been performed using the data on detector performance reported in the MiniBooNE proposal, while for the water Cerenkov it has been possible to take advantage of the Super Kamiokande collaboration and use the full detector simulation software. Results of the compared analysis are discussed in the fifth chapter. The analysis on the oscillation parameters has been focalized on $\theta_{13}$. Likelihood method and exclusion plots as general tools used in neutrino oscillation studies are described in the sixth chapter. Results of the analysis performed with the studied superbeam are reported and compared, in the significant parameters range, with the present limits on $\theta_{13}$ given by CHOOZ. The present study has shown an improvement of almost an order of magnitude in sensi- tivity with respect to these published data. This study has been possible thanks to the collaboration between the physics department of “Universta` degli studi di Milano” and the “Universite de Geneve” in the frame of the Erasmus project. I wish to thank: CERN that allowed me to collaborate with the PS-division; Dave Casper for Super Kamiokande simulations and the important explanations on detector physics; Mauro Mezzetto for the important discussion on MiniBooNE; Simone Gilardoni for MARS simulations of the neutrino factory horn and the whole Neutrino Factory Oscillations Working Group.