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

本提案致力于在有效理论框架内研究独占夸克衰变。近年来，CLEO、BABAR、BELLE、BES和LHCb等合作项目获得了许多新的、精确的和声和底铵态衰变数据。目前，BES III、BELLE II和LHCb实验仍在继续收集数据。在不久的将来，许多精确的测量也有望从PANDA@FAIR实验中得到。虽然目前人们对低洼夸克子的光谱已经有了相当的了解，但它的许多衰变还没有得到很好的了解，或者令人困惑。对排他性衰变的成功描述将揭示涉及不同尺度的复杂潜在QCD动力学。在项目的第一部分，我计划研究$S$ -和$P$ -波谐音的重子-反重子衰变。对于许多不同的最终态，包括$p, n, \Lambda, \Sigma$和$\Xi$介子，这些衰变都可以很好地测量出来。对这些衰变的描述取决于调和子和重子的波函数。长期以来，人们认为与重子波函数相关的$3$ -夸克超前扭转分布振幅（DA）可以合理地估计衰变宽度。然而，在QCD求和规则和晶格上对各种重子DAs进行的新计算表明，高扭转DAs的影响可以足够大。这强烈地影响了现有的谐音衰变的描述。这一点也得到了各种螺旋抑制衰变的分支比的大值的支持。后者甚至没有被系统地考虑过。这个项目的目标是研究$S$ -和$P$ -谐波衰变，考虑到重子的高扭DAs。该项目的第二部分致力于研究颜色八元体在$^3S_1$ charmonia到$PV$最终状态的衰变中的贡献，其中$PV=\rho\pi, K^*\bar K, \dots$。测量到的$\Psi(2S)$和$J/\Psi$分支比率的比值比从先导级描述中预期的要小两个数量级。在许多其他双体强子通道中也观察到类似的效应。色八元体的作用通常被认为是对这种效应的一种解释。然而，还没有人建议系统地描述这种对排他性衰变的贡献。本项目的目的是利用有效场论框架系统地研究$PV$ -衰变中的色八元体机制。计划定义相关的色八元算符，研究其性质及其与色单重态算符的混合，研究色八元矩阵元素及其在描述衰变宽度中的作用。

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.