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，例如 ILC 或 FCC-ee，为挑战标准模型的高精度测量提供了绝佳的可能性。例如，通过扫描总 WW 产生截面超过其能量阈值，可以分别以 3MeV (ILC) 甚至 0.5-1MeV (FCC-ee) 的精度确定 W 玻色子质量。该研究项目旨在为 e+e- -> WW -> 4费米子 (ee4f) 过程的截面提供所需的高精度预测，以实现预期的实验精度，特别是在 WW 阈值区域，其中需要总横截面的亚千分精度。对于 LEP2 的 WW 分析，阈值处 ~2% 的精度和之上 ~0.5% 的精度就足够了，因此仅在 W 共振区域中需要次前导阶 (NLO) 的辐射校正，从而产生了“双极近似”的概念。 LEP2 之后的几年，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环振幅评估问题后，计算了 ee4f 过程的 NLO 校正。其次，在设计用于描述 WW 阈值区域的有效场论 (EFT) 内计算完整的 NLO 校正和一些主要高阶项。为了达到 WW 阈值区域最终所需的精度，必须合并和扩展 ee4f 和 EFT 预测。 ee4f 计算为横截面的离壳尾部提供了必要的精度，而 EFT 则提供了在 W 共振区域超越 NLO 的可能性。任一方向都需要进行重大改进。在 ee4f 分支中，所有四费米子最终状态都必须以完全 NLO 精度进行处理，包括所有特定于过程的干扰，并且必须包括 NLO 之外的初始状态辐射的影响。自动非线性光学计算的最新进展对于实现这一目标至关重要。 EFT 计算必须扩展到完整的次次次领先阶 (NNLO) 级别，这带来了概念和技术挑战。 NNLO 的 EFT 概念进展将提供一些在类似计算中有用的衍生结果，例如用于重夸克对的产生。由于近年来多环计算的巨大进步，硬二环校正的技术挑战才能得到解决。计划项目的最终成果将是一个蒙特卡洛计划，将 WW 阈值区域中经过改进的 NLO ee4f 和 NNLO EFT 部分合并，并在中能和高能下平稳过渡到 NLO ee4f 预测。