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挑战标准模型的绝佳可能性。例如，通过扫描w -玻色子总产生截面超过其能量阈值，可以分别以3MeV （ILC）和0.5-1MeV （FCC-ee）的精度确定w -玻色子的质量。本研究项目旨在为过程e+e- -> WW -> 4费米子（ee4f）的横截面提供所需的高精度预测，以满足极高的期望实验精度，特别是在WW阈值区域，该区域要求总横截面的亚许可精度。对于LEP2的WW分析，阈值精度为~2%，高于阈值精度为~0.5%就足够了，因此仅在W共振区域需要次领先级的辐射校正（NLO），从而产生了“双极近似”的概念。在LEP2之后的几年中，最先进的预测在两个方面得到了改进：首先，在解决了W共振的量规不变处理和多腿单环振幅评估问题之后，计算了ee4f过程的NLO修正。其次，在描述WW阈值区域的有效场论（EFT）中计算了NLO的全部修正和一些主要的高阶项。为了在WW阈值区域达到最终需要的精度，必须对ee4f和EFT预测进行合并和扩展。ee4f计算提供了截面离壳尾部的必要精度，而EFT提供了在W共振区域超越NLO的可能性。在任何一个方向上都需要重大的改进。在ee4f分支中，所有四费米子的最终态都必须以完全的NLO精度处理，包括所有特定过程的干扰，并且初始态辐射的影响必须包括在NLO之外。自动化NLO计算的最新进展对实现这一目标至关重要。EFT的计算必须扩展到完整的次对次领先订单（NNLO）级别，这带来了概念和技术上的挑战。NNLO在EFT概念上的进展将提供一些衍生结果，这些结果在类似的计算中很有用，例如重夸克对的产生。由于近年来在多环计算方面取得了巨大的进步，硬双环校正中的技术挑战才得以掌握。计划项目的最终结果将是蒙特卡罗程序，将WW阈值区域的精炼NLO ee4f和NNLO EFT部分合并，并顺利过渡到中高能的NLO ee4f预测。