电磁三体衰变过程J/ψ→e+e-π0的研究以及在J/ψ→ω/φη的衰变道中寻找 ω和φ介子到不可探测粒子的衰变

We propose to perform the study of the electromagnetic (EM) Dalitz decay of J/psi-->e+e-pi0 and search for invisible decays of omega and phi mesons in J/psi --> V eta (V=omega, phi) decays using 1.31 billion J/psi events collected by BESIII experiment during 2009 and 2012. The J/psi-->e+e-pi0 decay can be described by the quantum electrodynamics (QED) via J/psi --> gamma* pi0, with the virtual photon (gamma*) decaying to the lepton pair. The conversion decay of a squared invariant mass of the electron pair is not equal to zero as usual for radiative decays of J/psi --> gamma pi0. The squared di-electron invariant mass dependent decay rate of J/psi --> e+e- pi0 is strongly modified by a dynamics of the EM structure arising at the vertex and formally described by the transition form factor. The form factor is mainly governed by the resonance interaction between photons and hadrons in the time-like region within the Vector Meson.Dominance (VMD) model. A large discrepancy in this decay between previous BESIII measurement and VMD prediction was seen due to computing the branching fraction of J/psi --> e+e- pi0 for the di-electric invariant mass to be less than 0.4 GeV/c^2. This study will be performed once again in the full di-electric invariant mass range to get a good agreement between theoretical and experimental.results as suggested by several theory papers. The Standard Model (SM) does not allow the invisible decays except the neutrino-pair decaying to the quarkonium. The branching fractions of neutrino-pair decays of omega and phi mesons are expected to be up to the level of 10^{-14} and 10^{-12}, respectively. But, the contribution of the new physics, assuming the dark matter annihilation in the.early universe occurs either s wave or p-wave, may enhance the branching fractions of invisible decays of omega and phi mesons up to the level of 10^{-8}. Besides the study of EM Dalitz decays of J/psi --> e+e- pi0, we also plan to perform the invisible decays of omega and phi mesons in J/psi --> omega/phi decays. The invisible decays of omega and phi mesons have not yet explored by any collider experiments. Any evidence of signal in these invisible decay modes would be an indication of new physics beyond the SM。

利用BESIII实验的13.1亿个J/ψ事例，我们计划研究电磁三体衰变过程J/ψ->e+e-π0并 首次在J/ψ→Vη(V为ω或φ介子)的衰变道中寻找ω和φ介子衰变到不可探测粒子。量子电动 力学(QED)理论可以用来很好的解释J/ψ->e+e-π0过程，该过程的衰变率强烈依赖于顶点上的电磁转换形状因子。BESIII实验曾对该过程的衰变分支比在Mee<0.4GeV的区域进行过测量，但与VMD理论有较大偏离。我们计划在电子对不变质量全区间上再次对该课题进行研究，以期能 够消除测量与理论的偏差。标准模型理论禁止夸克偶素衰变到不可测粒子（中微子除外）。ω/φ介子衰变到中微子对的分支比预期只有10-14和10-12量级。考虑到可能的新物理贡献，ω/φ介子衰变到不可探测粒子的分支比可能会增强到10-8量级，所以我们也计划在J/ψ→ω/φη的衰变道中寻找ω和φ介子到不可探测粒子的衰变。

该项目的目的是研究J / psi的电磁（EM）Dalitz衰变-> e + e- P（= pi0，eta）并寻找J中V（= omega，phi）介子的无形衰变/ psi-> V eta）使用BESIII检测器收集的13亿个J / pis事件衰减。这些测量对于提高μon异常磁矩的精确度和限制新物理参数超出标准模型非常重要。我们的测量比以前的测量将J / psi-> e + e-eta的支化分数提高了1.5倍，并报告了J / psi-> e + e的双电子不变质量依赖性过渡形状因子-第一次eta（发表于Phys。Rev.D 99，012006（2019））。 J / psi-> e + e-pi0的分支分数的精度比以前的测量结果提高了1.6倍（记录在BESIII Analysis Memo＃0325中），其结果将很快更新为100亿BESIII检测器收集的J / psi数据。没有发现Ω和phi介子无形衰变的证据。 ω和phi介子的不可见衰变的分支分数的90％CL上限也设置为小于7 .2 \乘以10 ^ {− 5}和1 .7 \乘以10 ^ {− 4}，分别是第一次（发表于Phys。Rev.D 98，032001（2018））。除了这些拟议的工作之外，我们还测量了由Cabibbo抑制的D-> omega pipi（（在Phys。Rev.D 102，052003（2020）中发布）和D0-> omega phi（在BAM-404），并使用在psi（3770）和J / psi共振下收集的BESIII数据搜索J / psi辐射衰变中轻CP奇数希格斯玻色子的μ介子衰变（在BAM-0481中进行了记录），对这些衰变进行实验测量对于提高μ子异常磁矩，B-> D tau nu_ {tau}的半轻子衰变和CKM角γ的精度是理想的。

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