High Precision Measurement of the Pion Form Factor at BESIII - Improving the Hadronic Vacuum Polarization Correction to the muon g-2

BESIII 介子形状因子的高精度测量 - 改进对 μ 介子 g-2 的强子真空偏振校正

• 批准号: 455635585
• 负责人: Professor Dr. Achim Denig
• 金额: --
• 依托单位: Institut für Kernphysik
• 依托单位国家: 德国
• 项目类别: Research Grants
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/455635585?language=en
• 关键词: Precision; Measurement; Pion; Form; Factor

The goal of the current project is a measurement of the cross section sigma(e+e- -->pi+pi-), i.e. of the timelike pion form factor. The measurement will be performed over a very wide energy range from the two-pion threshold up to energies above 3 GeV by exploiting the initial state radiation (ISR) method at the BESIII experiment in Beijing. We aim for world-class accuracy in the full energy range. Two analysis methods will be pursued, which differ by the accessible energy ranges and the systematic effects to be considered. The first analysis intends a selection of ISR photons emitted at large polar angles (LA), while the second analysis focuses on small-angle ISR photons (SA). From the technological point of view, high-precision analysis methods based on machine learning algorithms need to be developed and calibrated in order to allow for an efficient separation of pion and muon tracks in the BESIII detector.1) The LA analysis will measure the pion form factor in the energy range below 1 GeV, which is completely dominated by the rho resonance. We aim for a reduction of the systematic uncertainty compared to an already existing BESIII measurement in the peak region of the rho resonance. A systematic uncertainty of 0.6% (or better) is possible. Two independent normalization methods will allow for important cross checks of the cross section measurement.2) The SA analysis will measure the pion form factor for energies above 0.8 GeV. A determination of the pion form factor with unprecedented accuracy is planned with important consequences for our understanding of the hadron spectrum in the mass range above 1 GeV. The project described in this proposal will allow for an improved determination of the hadronic vacuum polarization (HVP) contribution to the muon anomaly. It will furthermore be possible to clarify a discrepancy observed between the two leading experiments in the field so far, KLOE and BABAR. This will directly impact the Standard Model (SM) prediction of (g - 2) as this discrepancy currently limits the overall SM prediction.

当前项目的目标是测量截面σ（e+e->pi+pi-），即类时π介子形状因子。测量将在北京BESIII实验上利用初态辐射（ISR）方法在从2 π阈值到3 GeV以上的非常宽的能量范围内进行。我们的目标是在全能量范围内实现世界一流的精度。将采用两种分析方法，其不同之处在于可获得的能量范围和要考虑的系统效应。第一个分析旨在选择在大极角（LA）发射的ISR光子，而第二个分析侧重于小角度ISR光子（SA）。从技术角度来看，需要开发和校准基于机器学习算法的高精度分析方法，以便在BESIII探测器中有效分离π介子和μ介子轨道。1）LA分析将测量能量范围低于1 GeV的π介子形状因子，这完全由ρ共振主导。我们的目标是减少系统的不确定性相比，已经存在的BESIII测量的峰值区域的ρ共振。系统不确定度可能为0.6%（或更好）。两个独立的归一化方法将允许重要的交叉检查的横截面测量。2）SA分析将测量能量超过0.8 GeV的π介子形状因子。一个前所未有的精确度的π介子形状因子的测定计划与重要的后果，我们的理解强子谱在1 GeV以上的质量范围。在这个建议中描述的项目将允许改进的强子真空极化（HVP）的贡献的μ子异常的测定。此外，还有可能澄清迄今为止在该领域的两个主要实验-KLOE和BABAR-之间观察到的差异。这将直接影响（g - 2）的标准模型（SM）预测，因为这种差异目前限制了整体SM预测。