arXiv 1303.52992013-03-21hep-ph

强子对撞机不稳定粒子产生中的束宽效应

Finite-width effects in unstable-particle production at hadron colliders

P. Falgari, A. S. Papanastasiou, A. Signer

备注：: 41 pages, 18 figures, 2 tables
DOI：: 10.1007/JHEP05(2013)156

摘要：

本文给出了强子对撞机上有限宽度对不稳定粒子微分产生截面贡献的一般计算方法。在这种形式主义，它采用了有效的理论描述的不稳定粒子的生产和衰变，矩阵元素的计算被组织为规范不变的扩展的权力$Γ_X/m_X$，与$Γ_X$和$m_X$的宽度和质量的不稳定粒子。该框架允许系统地包含离壳效应和不可因式分解效应，同时与复质量方案中的完整计算相比，保持计算工作量最小。作为一个概念验证的例子，我们给出了结果的非线性光学计算的顶-反顶生产的$q \bar{q}$部分通道。正如在类似的单炉顶生产计算中已经发现的那样，有限宽度对总截面的影响很小，正如从原始计算$\sim Γ_t/m_t \sim 1%$中所预期的那样。然而，它们可以是相当大的，超过10%，接近某些运动学分布的边缘。依赖的质量重整化方案的结果，其含义精确提取的顶夸克质量，也进行了讨论。

英文摘要：

We present a general formalism for the calculation of finite-width contributions to the differential production cross sections of unstable particles at hadron colliders. In this formalism, which employs an effective-theory description of unstable-particle production and decay, the matrix element computation is organized as a gauge-invariant expansion in powers of $Γ_X/m_X$, with $Γ_X$ and $m_X$ the width and mass of the unstable particle. This framework allows for a systematic inclusion of off-shell and non-factorizable effects whilst at the same time keeping the computational effort minimal compared to a full calculation in the complex-mass scheme. As a proof-of-concept example, we give results for an NLO calculation of top-antitop production in the $q \bar{q}$ partonic channel. As already found in a similar calculation of single-top production, the finite-width effects are small for the total cross section, as expected from the na\" ive counting $\sim Γ_t/m_t \sim 1%$. However, they can be sizeable, in excess of 10%, close to edges of certain kinematical distributions. The dependence of the results on the mass renormalization scheme, and its implication for a precise extraction of the top-quark mass, is also discussed.

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