相对论重离子碰撞中超氚核的实验研究

发布时间：2018-03-22 16:55

本文选题：超氚　切入点：超核　出处：《中国科学院研究生院(上海应用物理研究所)》2017年博士论文　论文类型：学位论文

【摘要】：量子色动力学(QCD)是描述强相互作用的规范场理论。这一理论有两个基本特征,即夸克禁闭和渐进自由。根据格点QCD计算,在高温、低重子数密度的条件下,被禁闭在强子中的夸克会解禁闭,形成一种新的物质形态,即夸克胶子等离子体(QGP)。为了研究这种新物质形态,科学家们研制了大型相对论重离子对撞机。位于美国长岛的布鲁克海文国家实验室的相对论重离子对撞机(RHIC)上包括了两个主要的实验装置,即螺线管径迹探测器实验组(STAR)和高能核作用实验组(PHENIX)。其中STAR实验组已经积累了大量的实验证据,证明在对撞之初的极短时间内(若干fm/c),确实产生了一种高温、高密、存在强相互作用的新物质,被称为强耦合夸克胶子等离子体(Strong-coupling Quark Gluon Plasma,s QGP)。从20世纪中期开始,随着奇异夸克以及一系列奇异粒子的发现,超子-核子(YN)相互作用及其性质成为了一个重要的研究方向。一方面,对YN相互作用的研究能帮助我们进一步理解重子-重子(BB)相互作用,另一方面,YN相互作用也被认为在中子星内部起重要的作用,对YN相互作用的研究在天文学上也有重要的意义。相对论重离子对撞机的出现为YN相互作用的研究带来了很大的便利:作为最轻的超核,超氚3是RHIC上产额最大的超核,也是YN相互作用最好的研究对象。超氚有两个主要的衰变模式,即π介子衰变模式和非π介子衰变模式。其中π介子衰变模式的衰变分支比大于98%,是主要的衰变模式。在本文中,主要讨论两个衰变道,即含有π的两体和三体衰变道。我们使用了STAR在2010年和2011年采集的对撞质心系能量为和200Ge V的最小偏差(Minimum Biased)数据,通过以上两个衰变道,重构出了超氚的信号。在进行了探测器重构效率、接收度、事件数的修正之后,一方面计算得到了的寿命,即,另一方面也计算了两体衰变道分支比与两体、三体衰变道分支比之和的比值,即。理论上一般认为,超氚核是由一个氘核和一个∧超子组成的弱束缚态。这样一来,的寿命将会比较接近非束缚态的∧的寿命,即263ps。早期的实验结果大都含有较大的误差,在误差范围内大都较接近∧的寿命。2000年之后,使用时间投影室(TPC)技术,RHIC-STAR、LHC-Alice以及GSI-Hyp HI的若干实验结果,以及本文的结果,都支持这样一个结论,即的寿命明显的小于非束缚态∧的寿命。这意味我们之前对的结构的理解需要进一步的修正。STAR的零度量能器(ZDC)在工作了近10年后,由于辐照损伤等原因,已经无法维持合适的工作状态。考虑到BRAHMS上的ZDC已经于2006年停止使用并一直闲置,我们将其安装到了STAR并替换了旧的ZDC。在安装到STAR之前,我们对其进行了刻度。刻度之后的ZDC在RHIC上经历了若干不同能量和种类的束流。我们使用相应的数据计算了ZDC的能量分辨率。结果显示,目前对于200Ge V的金-金束流来说,两侧ZDC模块的能量分辨率大约为27%,这比ZDC设计之初使用实验束流得到的20%的能量分辨率略高,但仍然处在良好的范围内。重味探测器(HFT)已经于2014年开始了数据采集。为了将HFT的信号加入到STAR目前的高阶触发系统(HLT)中,我们使用相关程序对HFT进行了径迹重构测试。测试的结果显示,当初始顶点的位置可以较准确的确定时,径迹的重构效率可以得到保证。但是目前程序的CPU时间消耗过高,需要进一步的改进和优化。
[Abstract]:Quantum chromodynamics (QCD) is to describe the strong interaction of the gauge field theory. This theory has two basic characteristics, namely quark confinement and asymptotic freedom. Based on the lattice QCD calculations, in high temperature, low density conditions, is confined in hadrons quark will form a solution. The new form of matter, namely the quark gluon plasma (QGP). In order to study the new matter, scientists developed large Relativistic Heavy Ion Collider. The Relativistic Heavy Ion Collider in Long Island Brook Brookhaven National Laboratory (RHIC) comprising two main experimental device, namely solenoid track detector experimental group (STAR) and high energy nuclear interactions in experimental group (PHENIX). The STAR group has accumulated a large amount of experimental evidence that, in a very short period of time at the beginning (several fm/c), had a high temperature, high density, strong The new material interaction, known as the strong coupling of quark gluon plasma (Strong-coupling Quark Gluon Plasma, s QGP). From the middle of twentieth Century, with a series of strange quark and the discovery of strange particles, hyperon nucleon (YN) interaction and its properties has become an important research direction. On the one hand, the research on the interaction of YN can help us to further understand the baryon baryon interaction (BB), on the other hand, YN interaction is considered to play an important role in the study of neutron stars, YN interaction has important significance in astronomy. The relativistic heavy ion collider has brought great the convenience for the study of the interaction of YN: as the lightest hypernucleus, super 3 super yield nuclear tritium is the largest RHIC, but also YN interaction research object. The best super tritium has two main decay modes, namely pion decay mode And the pion decay mode. The pion decay pattern of branching ratio is greater than 98%, is the main mode of decay. In this paper, mainly discusses two decay, which contains two PI and three body decays. We use the minimum deviation of the STAR in 2010 and 2011 at the center of mass energy collection for 200Ge and V (Minimum Biased) data, through the above two channels, to reconstruct the signal. In the super tritium reconstruction efficiency, detector, fixed number of events, on the one hand, to calculate the life, namely, on the other hand also calculated the two body decay branching ratio with the two body, three body decay ratio of branch road, and the general theory. That is a weakly bound state of super Triton consists of a deuteron and a hyperon. As a result, the life will be relatively close to the non bound states of a life, namely the early 263ps. The experimental results have large errors in the error range is close to the life of a mostly.2000 years after the use of a time projection chamber (TPC) technology, RHIC-STAR, LHC-Alice and GSI-Hyp HI some experimental results, and the results support such a conclusion, that is the life of significantly less than the non bound lambda the life. This is our measure means zero prior to the understanding of the structure of the modified.STAR need further (ZDC) at work after nearly 10 years, due to radiation damage and other reasons, have been unable to maintain the proper working condition. Taking into account the BRAHMS ZDC ended in 2006 and has been idle, we will install it to STAR and replace the old ZDC. before installing STAR, we carried out the calibration. Calibration after ZDC in RHIC through a number of different type and energy of the beam. We use the corresponding data The energy resolution of the ZDC was calculated. The results show that the 200Ge V gold gold beam, both sides of the ZDC module of the energy resolution is about 27%, the ratio of ZDC at the beginning of design experiment using beam obtained 20% energy resolution is slightly higher, but still in the range of heavy flavor (HFT detector.) has been started in 2014. The data acquisition for HFT signal is added to the STAR current high order trigger system (HLT), we use the relevant procedures carried out on the HFT Track Reconstruction test. The test results show that, when the initial vertex position can be accurately determined, the track reconstruction efficiency can be obtained to ensure the program. But at present CPU time consumption is too high, need further improvement and optimization.

【学位授予单位】：中国科学院研究生院(上海应用物理研究所)
【学位级别】：博士
【学位授予年份】：2017
【分类号】：O571.6

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