A study of exclusive quarkonium decays within the effective field theory framework

有效场论框架内专有夸克素衰变的研究

• 批准号: 445769443
• 负责人: Dr. Nikolay Kivel, Ph.D.
• 金额: --
• 依托单位: Arbeitsgruppe Theoretische Teilchen und Kernphysik
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2020
• 资助国家: 德国
• 起止时间: 2019-12-31 至 2022-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/445769443?language=en
• 关键词: study; exclusive; quarkonium; decays; within

This proposal is dedicated to investigation of exclusive quarkonium decays within the effective theory frameworks. Many new precise data about various exclusive decays of charmonium and bottomonium states have been obtained during the last years by the CLEO, BABAR, BELLE, BES and LHCb collaborations. At present, the BES III, BELLE II and LHCb experiments continue to collect the data. Many accurate measurements are also expected in the near future from the PANDA@FAIR experiments. Although the spectrum of low-lying quarkonia is at present reasonably well understood, many of it decays are not yet well understood or are puzzling. A successful description of exclusive decays will shed light on the complicated underlying QCD dynamics involving different scales.In the first part of the project I plan to study the baryon-antibaryon decays of $S$- and $P$-wave charmonia. These decays are sufficiently well measured for many various final states and include $p, n, \Lambda, \Sigma$ and $\Xi$ mesons. A description of these decays depends on the wave functions of charmonium and baryons. For a long time is was accepted that the $3$-quark leading-twist distribution amplitude (DA), which is associated with the baryon wave functions, provides a reasonable estimate of the decay widths. However, the new calculations of various baryon DAs, which were made in QCD sum rules and on the lattice, indicate that the effect from higher twist DAs can be sufficiently large. This strongly affect the existing description of charmonia decays. This point is also supported by the large values of the branching ratios for various helicity suppressed decays. The latter have not been even systematically considered. The goal of this project is to study the $S$- and $P$- charmonia decays taking into account the higher twist DAs of the baryons. The second part of the project is devoted to a study of the colour-octet contributions in decays of $^3S_1$ charmonia into $PV$ final states, with $PV=\rho\pi, K^*\bar K, \dots$. The measured ratio of the $\Psi(2S)$ and $J/\Psi$ branching ratios is about two order of magnitude smaller than one expected from the leading-order description. A similar effect is also observed for many other two-body hadronic channels. The colour-octet contribution is often proposed to be responsible for an explanation of this effect. However, a systematic description of such a contribution for exclusive decays have not yet been suggested. The goal of this project is to study the colour-octet mechanism in the $PV$-decays in a systematic way using the effective field theory framework. It is planned to define the relevant colour-octet operators, to study their properties and the mixing with the colour-singlet operators, to study colour-octet matrix elements and their role in the description of the decay width.

这项建议致力于在有效的理论框架内研究独占性夸克衰变。在过去的几年里，通过CLEO、BABA、BELE、BES和LHCB的合作，已经获得了许多关于Charmonium和Bottomonim态的各种专有衰变的新的精确数据。目前，BES III、Belle II和LHCb实验仍在继续收集数据。预计在不久的将来，熊猫公平实验还将进行许多准确的测量。尽管目前人们已经相当清楚地了解了低洼夸克尼亚的光谱，但它的许多衰变还没有被很好地理解，或者令人费解。对独占衰变的成功描述将有助于揭示涉及不同标度的复杂的QCD动力学。在项目的第一部分，我计划研究$S$和$P$波的重子-反重子衰变。这些衰变足够好地测量了许多不同的终态，包括$p，n，\Lambda，\Sigma$和$\xi$介子。对这些衰变的描述取决于碳素和重子的波函数。很长一段时间以来，人们一直认为，与重子波函数有关的3美元夸克的领先扭度分布幅度(DA)提供了对衰变宽度的合理估计。然而，在QCD求和规则和晶格上对各种重子Das的新计算表明，高扭度Das的影响可以足够大。这强烈地影响了现有的对轮藻腐烂的描述。这一点也得到了各种螺旋度抑制衰减的分支比的较大值的支持。后者甚至还没有得到系统的考虑。这个项目的目标是研究$S$-和$P$-查莫尼亚的衰变，同时考虑到重子的更高扭曲das。该项目的第二部分致力于研究$3S_1$木炭在衰变到$PV$终态时的颜色八重态的贡献，其中$PV=\Rho\pi，K^*\bar K，\dots$。测得的$\Psi(2S)$和$J/\Psi$分支比比从前级描述中预计的一个数量级小了大约两个数量级。在其他许多两体强子通道上也观察到了类似的效果。颜色-八位组的贡献通常被认为是对这种效应的解释。然而，对排他性衰变的这种贡献的系统描述还没有被提出。本项目的目标是利用有效场论框架系统地研究光伏衰变中的色八重态机制。计划定义相关的色八重态算符，研究它们的性质以及与色单态算符的混合，研究色八重态矩阵元素及其在描述衰变宽度中的作用。