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arXiv 1004.2489hep-phhep-ex
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N-Jettiness：一个包含事件形状的Veto Jets

N-Jettiness: An Inclusive Event Shape to Veto Jets

Iain W. Stewart, Frank J. Tackmann, Wouter J. Waalewijn

备注：
4 pages, 1 figure, v2: typos corrected, journal version
发表信息：
Phys.Rev.Lett.105:092002,2010
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摘要：

在LHC和Tevatron的许多希格斯和新物理分析中，喷射否决是必不可少的。这些信号通常以特定数量的硬喷流、轻子或光子为特征，而背景通常有额外的喷流。在这种情况下，否决不需要的额外射流是区分信号和背景的有效方法。给定具有N个或更多个射流的包含性事件样本，仅具有N个高能射流的否决权定义了“排他性”N-射流截面。这强烈地限制了相空间的基本包容性N-喷截面，并导致大的双扰动理论，必须总结，以获得理论预测。喷射否决通常使用喷射算法来实现。这就产生了复杂的相空间限制，人们往往依赖于部分子簇射Monte Carlos，这是有限的领先对数精度。我们引入了一个全局事件形状“N-jettiness”，tau_N，它是为具有N个信号喷流的事件定义的，并且在恰好N个无限窄喷流的极限处消失。要求tau_N << 1限制了N个信号射流之间的辐射，并否决了额外的不期望的射流。这提供了一个包容性的方法来否决射流，并定义一个独特的N-射流截面，可以很好地控制理论。N-jettiness产生包含射流和梁函数的因子分解公式。

英文摘要：

Jet vetoes are essential in many Higgs and new-physics analyses at the LHC and Tevatron. The signals are typically characterized by a specific number of hard jets, leptons, or photons, while the backgrounds often have additional jets. In such cases vetoing undesired additional jets is an effective way to discriminate signals and background. Given an inclusive event sample with N or more jets, the veto to have only N energetic jets defines an "exclusive" N-jet cross section. This strongly restricts the phase space of the underlying inclusive N-jet cross section and causes large double logarithms in perturbation theory that must be summed to obtain theory predictions. Jet vetoes are typically implemented using jet algorithms. This yields complicated phase-space restrictions and one often relies on parton-shower Monte Carlos, which are limited to leading-logarithmic accuracy. We introduce a global event shape "N-jettiness", tau_N, which is defined for events with N signal jets and vanishes in the limit of exactly N infinitely narrow jets. Requiring tau_N << 1 constrains radiation between the N signal jets and vetoes additional undesired jets. This provides an inclusive method to veto jets and to define an exclusive N-jet cross section that can be well-controlled theoretically. N-jettiness yields a factorization formula with inclusive jet and beam functions.

机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。

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