利用大亚湾中微子探测器进行惰性中微子实验的可行性研究

发布时间：2018-05-21 09:24

本文选题：大亚湾中微子探测器 + 惰性中微子　；参考：《山东大学》2016年博士论文

【摘要】：中微子物理作为粒子物理、天体物理和宇宙学的交叉前沿学科,是当今理论及实验研究的热点。在粒子物理标准模型中,中微子是自旋为1/2的Dirac粒子,不带电,只参与弱相互作用,最初被认为是没有质量的。但是,近几十年来一系列实验乙证实,中微子有很小的质量,并且其质量本征态与弱相互作用的味道本征态不简并,因此在传播过程中可以在不同的味道之间转化,发生中微子振荡。在标准三代中微子振荡模型中,中微子的每个味道本征态(ve,vμ,vτ)都可以写成三个质量本征态(v1,v2,v3)的线性叠加。参数化后,三代中微子的振荡模型就可以通过三个混合角θ12、θ1a、θ23,两个独立的质量平方差△m212、Δm322和一个CP相角δCP来描述。在精确测量中微子振荡参数的过程中,LSND实验由于设计时两个质量平方差还未知,并且当时有暗物质模型假设存在质量大于1 eV的中微子,因此LSND将物理目标定为测量较大的质量平方差,并最终观测到了振荡现象。然而,现在我们已经知道两个质量平方差分别为△m212～10-5 eV2、|△m312|10-3 eV2,所以LSND观测到的振荡现象超出了标准三代中微子模型,这一异常首次引起了人们对质量约为1 eV的中微子的注意。之后出现的一系列实验异常,包括为了验证LSND结果设计的MiniBooNE加速器实验异常,还有不同类型的反应堆中微子异常、Gallium异常,甚至宇宙学数据分析显示的异常迹象,都不能通过标准三代中微子振荡模型解释。由于加速器上的Zo衰变实验已经证明只存在三种参与弱作用的轻中微子,所以只能假设存在一种甚至多种不直接参与弱作用、但是可以通过中微子振荡与三代“活跃”中微子混合的“惰性中微子”。惰性中微子的引入无论从理论还是从实验的角度看,都是非常自然的处理方法,但是考虑到也有一些实验并没有观测到可能存在惰性中微子振荡的迹象,因此目前我们还不能确定惰性中微子是否存在。综合一系列实验的全局拟合结果显示,如果存在惰性中微子,那么惰性中微子与活跃中微子之间的质量平方差可能在1 eV2量级。显然,仅有一两个统计量不是很高的实验表明存在惰性中微子,是不足以让人信服的。我们需要有一系列不依赖于模型、使用不同原理或探测手段的实验来提供确凿的证据。这就使得利用大亚湾的实验装置进行惰性中微子的研究成为一种可能。大亚湾实验的主要物理目标是测量三个混合角中最后一个未知的混合角θ13至sin22θ130.01的精度。大亚湾实验于2012年3月首次以5.2σ公布了θ13不为零的结果,给出sin22θ913=0.092±0.016(stat.)+0.005(syst.),被美国权威学术杂志《科学》评选为当年的十大科学突破,并在2015年获得“基础物理学突破奖”。大亚湾实验完成之后,如果各种实验装置到时候就那么废弃,未免太过可惜。因此我们提议：结合当前惰性中微子研究的热点,在大亚湾停止取数后,利用大亚湾实验的探测器和反应堆,升级建造一个短基线(100 m)中微子振荡实验,以探测△m412～1 eV.的惰性中微子为主要物理目标,同时可以开展关于反应堆中微子能谱的精确测量、以及探测器技术应用相关的研究。本论文就是围绕这个提议展开,探讨了利用大亚湾中微子探测器进行惰性中微子实验的可行性。为了得到实验的灵敏度,我们采取了一些假设,构造了χ2函数,讨论了尺寸效应和探测器位置布局对灵敏度的影响。研究发现：利用大亚湾中微子探测器进行惰性中微子研究的提议在10-2eV2(?)△m412(?)1 eV2的参数空间灵敏度较高,而在△m412(?)1 eV2的参数空间,由于大亚湾反应堆为商业用反应堆,堆芯尺寸太大,因此提升测量灵敏度的可能性有限。如果我们侧重于探索Δm412～1eV2区域,那么推荐非对称的探测器布局,其中近点探测器与相近反应堆之间的距离最好小于30 m,探测器之间的距离最好在m的量级；如果我们侧重于探索△m412～several×0.1 eV2区域,则推荐对称的探测器布局,以减少反应堆之间的干涉、避免可能的人为因素导致的对某些Δm412值探索能力的丧失。为了估算探测器移到地表时的宇宙线缪子通量及相应的本底水平,我们开发了一套Geant4模拟程序,并模仿大亚湾实验与其它一些实验的设计,构造了一个中心探测器外有水池、铅和混凝土屏蔽材料的探测器模型。通过研究发现,在这种探测器设计方案下,缪子反符合探测器和中心探测器液闪区域中的宇宙线缪子事例率分别高达约15 kHz和2 kHz。通过取20μs的缪子反符合时间窗口,并对模拟数据添加要求从快信号前20μs到慢信号后20μs的时间范围内没有大于0.7 MeV信号的多重度挑选条件,我们估计出了缪子引起的关联本底事例率约为0.2 Hz的保守结果。这里的0.2 Hz关联本底,与大亚湾实验中缪子引起的关联本底主要来自9Li/8He和快中子不同,主要是来自于未被反符合掉的子事例。参考大亚湾实验的经验,我们知道想要模拟得到足够统计量的9Li/8He和快中子本底不可行,因此只好利用其产额对缪子能量的power law依赖关系,估算了这两类本底大小的量级,分别为O(10-3)Hz和0(10-2)Hz。使用模拟给出的11 Hz缪子致快信号事例率,加上大亚湾设计报告给出的50 Hz放射性本底事例率,近似作为总的快信号事例率,同时使用模拟给出的3 Hz缪子致慢信号事例率近似作为总的慢信号事例率,我们计算给出非常保守的0.04 Hz偶然符合本底事例率。关于对宇宙线中子本底的额外讨论,我们发现选取的“水池-铅-混凝土”的屏蔽层结构具有非常强的中子屏蔽能力,导致宇宙线中子引起的本底事例率不会超过0.001 Hz。总之,以探测器位于大亚湾两个反应堆中点时IBD事例率约为0.6Hz为例,这样的本底水平完全有可能使实验的信噪比好于1。综合灵敏度和本底水平的研究结果,本文最后我们基于大亚湾核电站反应堆附近的实际情况,选取了两个可能摆放探测器的位置,然后通过研究灵敏度随一些参数的变化趋势,提出了利用大亚湾中微子探测器进行惰性中微子实验的需求。发现以大亚湾反应堆和探测器的现有条件,只要能使bin-to-bin误差σdb(?)(1)％,本底事例率Rbkg(?)(10)Hz,就可能在10-2 eV2(?)△m412(?)3eV2参数空间具有较强的排除能力。Bin-to-bin误差σdb(?)(1)％这一需求根据以往的实验经验,应该比较容易满足。本底事例率Rbkg(?)(10)Hz的需求,通过研究“闪烁体-聚乙烯-铁”屏蔽层设计方案下的本底水平,发现即便不使用很厚的屏蔽材料也可以满足。因此我们认为,利用大亚湾中微子探测器进行惰性中微子实验的提议,在探测10-2 eV2(?)△m412(?)3 eV2的参数空间时具有可行性。
[Abstract]:Neutrino physics, a cross frontier subject in particle physics, astrophysics and cosmology, is a hot spot in theoretical and experimental research. In the standard model of particle physics, neutrino is a Dirac particle with a spin of 1/2, which is not charged, only participates in weak interaction and is initially considered to have no mass. However, a series of experimental B in recent decades has been considered. It is proved that the neutrino has a small mass, and its mass eigenstate and the taste eigenstate of the weak interaction are not simple. Therefore, the neutrino oscillation can be converted between different flavors during the propagation process. In the standard three generation neutrino oscillation model, each flavor eigenstate (VE, V, V tau) of the neutrino can be written as three substances. The linear superposition of the eigenstate (V1, V2, V3). After the parameterization, the oscillation model of the three generation neutrino can be described by three mixed angles, theta 12, theta 1a, theta 23, two independent mass squared Delta m212, Delta m322 and a CP angle Delta CP. In the process of accurate measurement of the neutrino oscillation parameters, the LSND experiment is due to two mass squared differences in the design. Unknown, and at that time there was a dark matter model that assumed a neutrino with a mass greater than 1 eV, so LSND set the physical target as a measured mass squared difference, and finally observed the oscillation. However, now we have known that two mass squared differences are Delta m212 to 10-5 eV2, Delta m312|10-3 eV2, so LSND observed vibration. The phenomenon is beyond the standard three generation neutrino model, which first caused attention to the neutrinos with a mass of about 1 eV. A series of experimental anomalies followed, including the MiniBooNE accelerator experimental anomalies designed to verify the LSND results, and the different types of counter Reactor Neutrino anomalies, Gallium anomalies, and even the universe. The abnormal signs in the analysis of the data analysis can not be explained by the standard three generation neutrino oscillation model. Since the Zo decay experiment on the accelerator has proved that only three light neutrinos involved in the weak action have been proved, it can only assume that there is one or more non direct participation in the weak action, but it can pass the neutrino oscillation and the three generation. The introduction of inert neutrinos in the mixture of neutrinos. The introduction of inert neutrinos, both theoretically and experimentally, is a very natural treatment. However, there are some experiments that have not observed signs that the inert neutrino oscillations are likely to exist, so we are not yet able to determine whether inert neutrinos are available. The global fitting results of a series of experiments show that the mass squared difference between inert neutrinos and active neutrinos may be in the order of 1 eV2 if there are inert neutrinos. Obviously, only one or two statistics are not very high, and the existence of inert neutrinos is not sufficient to convince people. We need to have a line. It is not dependent on the model to provide solid evidence using experiments with different principles or detection methods. This makes it possible to use the experimental device in Dayawan to study inert neutrinos. The main physical object of the Dayawan experiment is to measure the last unknown mixture angle of the mixed angle of three mixed angles, theta 13 to sin22 theta 130.01. Degree. In March 2012, the Dayawan experiment published the results of theta 13 not zero for the first time with 5.2 sigma, giving sin22 theta 913=0.092 + 0.016 (stat.) +0.005 (syst.), being selected as the ten major scientific breakthrough by the American authoritative academic magazine "Science >" and winning the "basic physics burst Award" in 2015. After the experiment was completed, if various experiments were completed. It is a pity that the device is so abandoned, so we propose that, with the current hot spot of inert neutrino research, after stopping in Dayawan, we use the detector and reactor in the Dayawan experiment to upgrade the construction of a short baseline (100 m) neutrino oscillation experiment to detect the inert neutrinos of delta M412 to 1 eV. as the main object. In this paper, the feasibility of the inert neutrino experiment using the Dayawan neutrino detector is discussed around this proposal. In order to obtain the sensitivity of the experiment, we have taken some assumptions. The x 2 function is constructed, and the effect of the size effect and the location of the detector on the sensitivity is discussed. It is found that the proposal of the inert neutrino study using the Dayawan neutrino detector is more sensitive in the parameter space of the 10-2eV2 (?) Delta M412 (?) 1 eV2, and the parameter space of the delta M412 (?) 1 eV2, because the Dayawan reactor is commercial In the reactor, the core size is too large, so the possibility of improving the sensitivity of the measurement is limited. If we focus on the exploration of the delta M412 ~ 1eV2 region, then the asymmetric detector layout is recommended, in which the distance between the near point detector and the similar reactor is best less than 30 m, and the distance between the detectors is best at the order of M; if we side Rather than exploring the delta M412 ~ several x 0.1 eV2 region, a symmetrical detector layout is recommended to reduce interference between the reactors and avoid the loss of potential exploration capabilities for some Delta M412 values caused by possible human factors. In order to estimate the cosmic ray Muse flux and the corresponding background levels when the detector moves to the surface, a set of Gean is developed. The T4 simulation program, and imitates the design of the Dayawan experiment and other experiments, constructs a detector model of a pool, lead and concrete shielding materials outside the central detector. Through the study, it is found that the cosmic ray Samuel case rate in the Muse counter conforming detector and the central detector's liquid flash area under the design of this detector is found. Do not get up to about 15 kHz and 2 kHz. by taking a 20 mu s Muse counter coincidence time window, and adding a multi severe selection condition that requires no more than 0.7 MeV signals in the time range of the analog data from 20 mu before the fast signal to the slow signal 20 mu s, and we estimate the conservative result of the incidence of the underlying case rate of about 0.2 Hz caused by the muse. The background of the 0.2 Hz Association, which is mainly derived from the 9Li/8He and fast neutrons in the Dayawan experiment, mainly comes from the sub cases that have not been inverse conformed. Referring to the experience of the Dayawan experiment, we know that the 9Li/8He and the fast neutron background are not feasible to simulate sufficient statistics, so we have to use their production. For the power law dependence of the Muse energy, the magnitude of these two kinds of background sizes are estimated, respectively, the rate of fast signal cases caused by 11 Hz Muse by simulation of O (10-3) Hz and 0 (10-2) Hz., plus the rate of 50 Hz radioactive background events given in the Dayawan design report, approximately as the total fast signal case rate, and using the 3 Hz given by the simulation. The rate of the slow signal case rate of the Muse is approximated as the total slow signal case rate. We calculate a very conservative 0.04 Hz coincidence case rate. With regard to the extra discussion of the neutron background of the cosmic ray, we find that the selected "pool lead concrete" shielding structure has a very strong neutron shielding ability, which leads to the cosmic ray. The bottom case rate will not exceed 0.001 Hz., and the IBD incident rate is about 0.6Hz when the detector is located at the middle point of the two reactor in Dayawan. This background level can make the experimental signal-to-noise ratio better than the 1. comprehensive sensitivity and the background level. Finally, we are based on the reactor of the Dayawan nuclear power plant. In the vicinity of the actual situation, the location of two possible detectors is selected, and then the demand of the inert neutrino experiment using the Dayawan neutrino detector is proposed by studying the variation trend of the sensitivity with some parameters. It is found that the existing conditions of the Dayawan reactor and the detector can make the bin-to-bin error DB (?) (?) (?) (?) (1). %, the background case rate is Rbkg (?) (?) (10) Hz, it is possible to have a strong exclusion.Bin-to-bin error of.Bin-to-bin error dB (?) (1)% (?) (1)% in the 10-2 eV2 (?) Delta M412 (?) 3eV2 parameter space. According to the previous experimental experience, it should be easier to meet the requirement of the background case rate Rbkg (?) (?) (10) Hz, by studying the design of "scintillation PE iron" shielding layer The background level under the scheme is found to be satisfied even without the use of very thick shielding materials. Therefore, we think that the proposal of using the Dayawan neutrino detector for inert neutrino experiments is feasible in detecting the parameter space of 10-2 eV2 (?) Delta M412 (?) 3 eV2.
【学位授予单位】：山东大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：O572.321

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