【作者】 王雄飞；

【导师】 鲁公儒； 王至勇；

【作者基本信息】 河南师范大学 ， 理论物理， 2012， 硕士

【摘要】 粲偶素(Charmonium)是由一对cc夸克通过强相互作用组成的束缚态。自从1974年实验上发现了粲偶素家族的第一个粒子J//ψ以来,许多粲偶素家族成员被相继发现,如ψ(2S),ψ(3S)和ψ(4S)等,其中ψ(2S)是DD质量阂以下的质量最重的粲偶素态,它可以辐射衰变到电荷共轭宇称为正的ηc(1S),ηc(2S),χc0,1,2等粲偶素态。作为粲偶素家族成员之一的XcJ介子,对研究螺旋度(HSR)破坏和色八重态(COM)理论有着重要的意义。根据早期的量子色动力学(QCD)理论可知,螺旋度规则禁止Xc0介子衰变到重子对(pp,AA,Σ0Σ0,Σ-Σ-,(?)0(?)0,(?)-(?)+),但是目前的测量结果证明了它们的衰变分支比并没有消失。然而由于这些测量结果统计量的不足,导致了对X。0介子衰变到重子对分支比测量的精确度不是太高,甚至许多的衰变道还没被观测到。所以为了很好的理解螺旋度规则破缺理论和色八重态理论,本文利用工作在BEPCII上的BESIII收集的106M的ψ(2S)事例样本,大约是CLEO-c的4倍左右,详细地研究了XcJ(J=0,1,2)介子到BB(B=A,∑0,∑+)的衰变,测得它们的分支比分别为Br(Xe0→AA)=(33.3土2.0土2.6)×10-5, Br(Xe1→AA)=(12.2土1.1土1.1)×10-5, Br(Xe2→AA)=(20.8土1.6土2.2)×10-5, Br(Xe0→∑0Σ0)=(47.8土3.4土3.8)×10-5, Br(Xe1→∑0Σ0)=(3.8土1.0土0.5)×10-5, Br(Xe2→∑0Σ0)=(4.0土1.1土0.4)×10-5, Br(Xe0→∑十∑-)=(45.4土4.2土2.5)×10-5, Br(Xe1→∑+∑-)=(5.4土1.5土0.4)×10-5, Br(Xe2→∑+∑-)=(4.9土1.9土0.6)×10-5.与以前的测量结果相比较,BESIII的测量精度有显著的提高,并且第一次提供了χc1,2到∑0Σ0,Σ+Σ-衰变的证据,它们的信号显著性分别为4.3σ,4.6σ,4.4σ和3.0σ,而且我们也利用Bayesian方法估计了它们在90%置信度下的上限,分别为Br(Xe1→∑0Σ0)<6.1×10-5, Br(Xe2→∑0Σ0)<6.4×10-5, Br(Xe1→∑-∑-)<8.5×10-5, Br(Xe2→∑-∑-)<8.6×10-5。更多还原

【Abstract】 Charmonium is the Pairs of cc quark bound state formed by strong interaction.The first mem-ber of charmonium family,J/(?) particle,was discovered in1974.Subsequently,so many charmo-nium states were discovered,such as (?)(2S),(?)(3S),(?)(4S),etc,where,(?)(2S)state is the heaviest charmonium state under the DD mass threshold,and it can radiatively decay to positive charge-conjugation parity charmonium state,such as ηc(1s), ηc(2s),XcJ(J=0,1,2).As one important member of charmonium states,XcJ(J=0,1,2)meson,it is essential and important to study the Violation of Helicity Selection Rule(HSR)and the Color Octet Mechanism (COM).According to the earlier theories of QCD,HSR prohibits XcO meson from decaying into the pairs of baryon-antibaryon(pp,AA,∑0∑0.,∑+∑-,Ξ0Ξ0,Ξ-Ξ+),but the observation of XcJ,decaying into baryon anti-baryon pairs indicates that those branching ratios did not vanish.However,the statistic of previous measurements are very low so that the precision of measured branching ratios for XcJ,decays in the previous measurements by other collaborations is not high and even so far many decay channels haven’t been observed.Therefore,using the106×106(?)(2s)events collected by BESIII detector at BEPCII,which is about4times of the CLEO-c data sample,the XcJ(J0,1,2)meson decaying into BB(B=A,∑0,∑+)in this article have been studied in detail to further understand and test HSR and COM.And the corresponding branching ratios are measured to be Br(Xc0→AA)=(33.3土2.0土2.6)×105, Br(Xc1→AA)=(12.2土1.1土1.1)×105, Br(Xc2→AA)=(20.8土1.6土2.2)×10-5, Br(Xc0→∑0∑0)=(47.8土3.4土3.8)×105, Br(Xc1→∑0∑0)=(3.8土1.0土0.5)×10-5, Br(Xc2→∑0∑0)=(4.0土1.1土0.4)×105, Br(Xc0→∑-∑+)=(45.4土4.2土2.5)×10-5, Br(Xc1→∑-∑+)=(5.4土1.5土0.4)×10-5, Br(Xc3→∑∑1)=(4.9土1.9土0.6)×105.The BESIII’s measurements further improve the Precision of the those decays by comparing with the previous works,and meanwhile we firstly provide the evidence for Xcl,2decays into∑0∑0,∑-∑-with the significance of4.3σ,4.6σ,4.4σand3.0σ.For the decays with more than3σ, we also present their upper limits at90%confidence level by using Bayesian method to be Br(Xc1→Σ0Σ0)<6.1×10-5, Br(Xc2→Σ0Σ0)<6.4×105, Br(Xc1→Σ-Σ+)<8.5×10-5, Br(Xc1→Σ-Σ+)<8.6×10-5.更多还原