BESⅢ上奇特强子态的寻找及研究

发布时间：2018-06-25 10:36

  本文选题：粲偶素 + 新型强子结构　； 参考：《山东大学》2017年博士论文

【摘要】：自从量子色动力学问世以来,对于微扰能区的物理量可以很完美地计算,但是对非微扰能区一向缺少精确计算及认识,对夸克受前相互作用束缚为强子时的规律更是缺少限制,由此人们一直在通过寻找新型强子结构以及高精度的测量来完善量子色动力学以对整个物质世界有更深地了解。北京正负电子对撞机上的BESⅢ探测器工作的粲夸克能区正是量子色动力学由微扰向非微扰的过渡区域,而且实验上发现的可能拥有新型强子结构的奇特强子态也多数位于该区域,所以研究该区域中相应强子的产生与衰变机制以及寻找奇特强子态对研究量子色动力学有非常重要的意义。目前国际上多个粒子物理实验已经发现存在X(3872),Y(4140),Y(4260),Y(2175)以及Ds0*(2317)等与常规强子性质截然不同的共振态,这些态均以不同寻常的衰变模式出现在不同寻常的位置上。人们普遍认为这些态极有可能拥有新型强子结构,并提出多种理论模型试图去解释它们的存在,但是实验结果的匮乏使得人们离理解这些态的内部结构还有很远的距离。本文致力于利用BESⅢ上质心系能量在3.7 GeV之上的正负电子对撞数据寻找并研究上述态,具体为寻找它们的新产生和衰变模式,以及它们之间的关联,从而为全面理解这些态提供关键的信息。利用BESⅢ探测器在质心系能量(?)=4.26 GeV附近的数据,我们首次通过e+e-→ γπ+π-(ρ)J/φ过程观测到著名的奇特强子态候选者X(3872),其信号统计显著性超过10σ,测得质量为3872.6 ± 0.5 ± 0.2 MeV/c2,其中后两项分别为统计和系统误差。测量得到的各个能量点下的截面分布显示X(3872)很可能来自于另一奇特强子态候选者Y(4260)的辐射跃迁,并且分支比与Y(4260)→ π+π-J/φ相当。该结果首次发现X(3872)与Y(4260)态相关联,表明其具有类似的本质,除目前仅知的B介子衰变以及强子对撞外,此过程发现新的X(3872)产生机制,并且为Y(4260)除了π+π-J/φ之外新的衰变模式,为理解这些态提供强有力的信息。在BESⅢ上继发现X(3872)之后,我们利用相同的数据通过e+e-→γφJ/φ过程对另一奇特强子态候选者Y(4140)进行了寻找因为Y(4140)与X(3872)可能为同一类型强子态,其中分别用K+K-,KS0欠L0和π+π-π0道重建φ然后合并分析,所有数据中均没有观测到明显的信号,我们给出相应过程在质心系能量为4.23,4.26和4.36 GeV处的截面在90%置信度下的上限分别为0.35,0.38和0.33 pb。结合之前所测量的γX(3872)产生截面,以及在分子态模型下计算的Y(4140)→φJ/φ分宽度可以得到在4.23和4.26 GeV下两个过程的截面比σ(e+e-→-γY(4140))/(e+e-→ γX(3872))处于0.1的量级或者更小。在奇异夸克偶素能区的奇特强子态候选者Y(2175),有与Y(4260)类似的性质,我们利用BESⅢ采集的质心系能量在3.7 GeV之上的数据首次观测到e+e-→ ηY(2175)过程,联合所有数据得到的统计显著性超过10σ,这是实验观测的Y(2175)新的产生机制。测得Y(2175)质量为2135±8±9 MeV/c2,宽度为104 ±24 土 12 MeV,这里两项误差分别为统计和系统误差。各个能量点上的截面中,没有发现明显的粲偶素贡献,与预期的矢量赝标量过程的分布相吻合。同时利用质心系能量为3.686 GeV包含(447.9 ± 2.9)× 106个φ(3686)事例的数据寻找φ(3686)→ηY(2175)过程,并没有发现显著信号,考虑J/φ和φ(3686)衰变的相空间差异之后的分支比比例B*(φ(3686)→ηY(2175))/B*(J/φ → η(2175))=(0.23 ± 0.29 ± 0.13)%,与 12%规则相比有非常大的压低,这也是新的不符合该规则的矢量赝标量过程。同时我们用相同的数据寻找e+e-→ η'Y(2175)过程,没有发现明显信号,联合所有数据得到的截面之比σ(e+e-→ η'Y(2175))/σ(e+e-→ ηY(2175))在90%置信度下的上限为0.43。除夸克偶素能区外,在粲介子能区也发现有常规夸克模型很难解释的态,其中人们认知最少也是最感兴趣的为Ds0*(2317)±。我们利用BESⅢ在质心系能量为4.6 GeV采集的566.93 pb-1数据首次通过Ds*(?)的反冲质量信息观测到 Ds0*(2317)±信号,测得Ds0*(2317)质量为(2318.3± 1.2±1.2)MeV/c2,统计显著性为5.8σ,并利用Ds*(?)的反冲侧信息通过部分重建Ds0*(2317)±的方法首次测量了Ds0*(2317)衰变的绝对分支比B(Ds*0(2317)±→ π0Ds±)为1.00-0.14±0.14,这里两项误差分别为统计和系统误差。该结果表明Ds0*(2317)±的衰变中π0Ds±占绝对主导部分,与常规粲介子cs模型下的预期有差异,却与分子态模型下的计算相吻合。在粲介子对阈值以上,预期所有矢量粲偶素或类粲偶素倾向于衰变到粲介子对末态,所以精确测量这些粲介子对的产生截面对理解这些(类)粲偶素有非常重要的意义。我们利用BESⅢ所采集的从Ds+Ds-阈值直到质心系能量为4.6 GeV处的超过100个能量点下的数据精确测量了 e+e-→D+Ds-过程的玻恩截面,我们分别重建一个Ds+和-并测量相应截面,之后再合并两组结果。从截面随质心系能量的分布中在4.23 GeV即Ds*+Ds*-质量阈值附近发现Ds+Ds-过程有明显的增强效应,该处的奇特结构也可能来自于Y(4260)与周围其它粲偶素之间的干涉效应。
[Abstract]:Since the advent of quantum chrodonic dynamics, the physical quantity of the perturbation energy region can be perfectly calculated, but the non perturbation energy region has always been lack of accurate calculation and understanding. The law of the quark's pre interaction as a hadron is lack of restriction, so people have been through searching for new hadronic structures and high precision measurements. To improve the quantum color dynamics to understand the whole material world, the charm quark area of the BES III detector on the Beijing positive and negative electron collider is the transition region of the quantum chromatic dynamics from the perturbation to the non perturbative, and the strange hadron states that may have the new hadron structure found in the experiment are mostly located in the region. So it is of great significance to study the generation and decay mechanism of the corresponding hadron in the region and to find the odd hadron states for the study of quantum chromo dynamics. At present, many particle physics experiments in the world have found the existence of X (3872), Y (4140), Y (4260), Y (2175), and Ds0* (2317), which are completely different from the conventional hadron properties. It is generally believed that these states are highly likely to have a new hadron structure, and a variety of theoretical models are proposed to explain their existence, but the lack of experimental results makes people far away from understanding the internal structures of these states. To find and study the above states by using the positive and negative electron collisions data of the BES III superior mass on 3.7 GeV, it is specific to find their new generation and decay patterns, and the correlation between them, so as to provide the key information for the comprehensive understanding of these states. The data near the =4.26 GeV of the mass heart (?) =4.26 GeV are used. We first observed the famous strange hadron candidate X (3872) through the process of e+e- - gamma - PI + - (rho) - (rho) - (rho) J/ phi. The statistical significance of the signal was more than 10 sigma, and the measured mass was 3872.6 + 0.5 + 0.2 MeV/c2, and the latter two items were statistical and systematic error respectively. The distribution of X (3872) at each of the measured points showed that X (3872) was likely to come from In another strange hadron candidate Y (4260), the radiative transition, and the branch ratio is equivalent to Y (4260) - PI + PI -J/. The result is first found that X (3872) is associated with Y (4260) state, indicating that it has a similar nature, except for the only known B meson decay and hadron colliding, this process finds a new X (3872) generation mechanism, and is Y (4260) except for Y (4260)). The new decay mode outside PI + PI -J/ Phi provides strong information for understanding these states. After the discovery of X (3872) on BES III, we use the same data to search for another strange hadron candidate Y (4140) through the e+e- to gamma J/ Phi process, because Y (4140) and X (3872) may be the same type of hadronic state, of which K+K-, respectively. KS0 is under L0 and PI + pi - pi 0 channel reconstruction phi and then combined analysis. No obvious signals are observed in all data. We give the cross section at the upper limit of the 90% confidence level at the 90% confidence level at the 90% confidence level in the mass of the mass of the mass, respectively, to produce the cross-section of the measured gamma X (3872) before the combination of the 0.35,0.38 and 0.33 pb., respectively, and in the molecular mode. The width of Y (4140) - J/ Phi can be calculated in the two processes of 4.23 and 4.26 GeV (e+e- to - gamma Y (4140)) / (e+e- to gamma X (3872)) at the order of 0.1 or smaller. The strange hadron candidate in the singular quarkeven energy region Y (2175) has the properties similar to Y (4260). We use the centroid system collected by BES III For the first time, the data above 3.7 GeV observed the e+e- > Y (2175) process. The statistical significance of the combined data is more than 10 sigma. This is the new generation mechanism of the experimental observation Y (2175). The mass of Y (2175) is 2135 + 8 + 9 MeV/c2, and the width is 104 + 24 soil 12 MeV, and the two errors are respectively statistical and systematic error. Each energy is respectively energy. No obvious charm contribution is found in the cross section of the point, which is consistent with the expected distribution of the pseudo scalar process. At the same time, the data of the centroid system energy is 3.686 GeV including (447.9 + 2.9) x 106 (3686) cases to find the (3686) - ETA Y (2175) process, and no significant signals are found, considering the phase space of the decay of J/ phi and (3686). The branch ratio after the difference ratio B* (3686) - ETA Y (2175)) /B* (J/ [1] (2175)) = (0.23 + 0.29 + 0.13)%, compared with the 12% rule, has a very large reduction. This is a new vector pseudo scalar process that does not conform to the rule. At the same time, we use the same data to find the e+e- to'Y (2175) process, no obvious signals are found, United ownership is found. The ratio of the ratio of the cross section of the data (e+e- to ETA'Y (2175)) / (e+e- to ETA Y (2175)) at 90% confidence level is 0.43. except quark dienergy region, and the normal quark model is also difficult to explain in the charmed meson region. In which people have the least cognition and the most interesting is Ds0* (2317). We use BES III in the mass of the heart system to be 4. The 566.93 PB-1 data collected by.6 GeV observed the Ds0* (2317) + signal for the first time through the Ds* (?) recoil quality information, and measured the Ds0* (2317) mass of (2318.3 + 1.2 + 1.2) MeV/c2, and the statistical significance was 5.8 sigma, and the absolute branch ratio of Ds0* (2317) decay was first measured by using the Ds* (?) backflash information to measure the absolute branching ratio of Ds0* (2317) decay for the first time (D). S*0 (2317) + + 0Ds +) is 1.00-0.14 + 0.14, and the two errors here are statistical and systematic errors, respectively. The results show that the absolute dominant part of the Ds0* (2317) + decay is in the absolute dominant part, which is different from the conventional charm meson CS model, but is consistent with the calculation under the molecular model. All vector charms are expected above the charmed meson to the threshold value. It is very important to accurately measure the production cross sections of these charmed meson pairs to understand these (class) charm pairs. We use the data collected by BES III to measure e+e- accurately from the data of the Ds+Ds- threshold at 4.6 GeV at the energy of the centroid system until the energy of the centroid system is at 4.6. The Born section of the D+Ds- process, we reconstruct a Ds+ and - and measure the corresponding section, and then combine the two sets of results. It is found that the Ds+Ds- process has obvious enhancement effect near the distribution of mass heart system energy in the vicinity of 4.23 GeV, that is, the Ds*+Ds*- mass threshold, and the peculiar structure of the branch may also come from Y (4260) and the surrounding other charms. The interference effect between even elements.
【学位授予单位】：山东大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：O572.243
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本文编号：2065622