W-pair production at future lepton colliders

未来轻子对撞机的 W 对生产

• 批准号: 493103835
• 负责人: Professor Dr. Stefan Dittmaier
• 金额: --
• 依托单位: Physikalisches Institut
• 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/493103835?language=en
• 关键词: pair; production; future; lepton; colliders

Future e+e- colliders, such as the ILC or FCC-ee, offer fantastic possibilities for high-precision measurements to challenge the Standard Model. For instance, from a scan of the total WW production cross section over its energy threshold, the W-boson mass could be determined with a precision of 3MeV (ILC) and even 0.5-1MeV (FCC-ee), respectively.This research project aims at providing the needed highly precise predictions for the cross section of the process e+e- -> WW -> 4fermions (ee4f) to account for the great expected experimental accuracy, in particular in the WW threshold region where sub-permille precision of the total cross section is required.For WW analyses at LEP2, a precision of ~2% at threshold and of ~0.5% above was sufficient, so that radiative corrections of next-to-leading order (NLO) were needed only in the W resonance regions, leading to the concept of the "double-pole approximation". Some years after LEP2, the state-of-the-art predictions were improved in two ways: Firstly, the NLO corrections for the ee4f process were calculated, after solving problems with the gauge-invariant treatment of the W resonances and in the evaluation of multi-leg one-loopamplitudes. Secondly, the complete NLO corrections and some leading higher-order terms were calculated within an Effective Field Theory (EFT) designed to describe the WW threshold region.To reach the ultimately required precision in the WW threshold region, the ee4f and EFT predictions have to be merged and extended. The ee4f calculation provides the necessary precision in the off-shell tails of the cross section, while the EFT offers the possibility to go beyond NLO in the W resonance regions. Significant improvements are needed in either direction. In the ee4f branch all four-fermion final states have to be treated in full NLO precision, including all process-specific interferences, and effects from initial-state radiation have to be included beyond NLO. The recent progress in automated NLO calculations is vital to achieve this. The EFT calculation has to be extended to the complete next-to-next-to-leading order (NNLO) level, posing conceptual and technical challenges. The conceptual progress in the EFT at NNLO will provide several spin-off results that are useful in similar calculations, e.g. for heavy-quark pair production. The technical challenges in the hard two-loop corrections can only be mastered owing to the dramatic progress in multi-loop calculations of recent years. The final outcome of the planned project will be a Monte Carlo program merging the refinedNLO ee4f and NNLO EFT parts in the WW threshold region with a smooth transition to NLO ee4f predictions at intermediate and high energies.

未来的e+e对撞机，如ILC或FCC-ee，为高精度测量提供了极好的可能性，以挑战标准模型。例如，通过在其能量阈值上扫描总WW产生截面，W玻色子质量可以以3 MeV（ILC）甚至0.5- 1 MeV（FCC-ee）的精度确定，本研究项目的目的是提供所需的高精度预测的截面的过程e+e-> WW -> 4费米子（ee 4f）考虑到很高的预期实验精度，特别是在WW阈值区域，其中总截面的亚千分之一精度是必需的。对于LEP 2的WW分析，阈值处~2%的精度和阈值以上~0.5%的精度是足够的，因此，仅在W共振区需要次领先阶（NLO）的辐射校正，从而产生了“双极近似”的概念。在LEP 2之后的几年里，最先进的预测在两个方面得到了改进：首先，在解决了W共振的规范不变处理和多腿单回路振幅评估的问题之后，计算了ee 4f过程的NLO修正。其次，在有效场理论（Effective Field Theory，EFT）的框架内计算了完整的非线性光学修正和一些高阶项，并将ee 4f和EFT的预测进行了合并和扩展，以达到最终在WW阈值区所需的精度。ee 4f计算在横截面的离壳尾翼中提供了必要的精度，而EFT提供了在W谐振区中超过NLO的可能性。在这两个方面都需要作出重大改进。在ee 4f分支中，所有的四费米子末态都必须在完全的NLO精度下处理，包括所有的过程特定的干扰，并且来自初态辐射的影响必须包括在NLO之外。最近在自动NLO计算方面取得的进展对于实现这一目标至关重要。EFT的计算必须扩展到完整的次领先订单（NNLO）水平，这带来了概念和技术上的挑战。NNLO在EFT中的概念进展将提供几个在类似计算中有用的分拆结果，例如重夸克对的产生。由于近年来多回路计算的巨大进步，硬双回路校正中的技术挑战只能被掌握。计划中的项目的最终结果将是一个蒙特卡罗程序合并的refinedNLO ee 4f和NNLO EFT部分在WW阈值区域与一个平稳过渡到NLO ee 4f预测在中，高能量。