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arXiv 0810.5576hep-phhep-ex
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利用子系统MT2在强子对撞机上测定能量缺失衰变链的完全质量

Using Subsystem MT2 for Complete Mass Determinations in Decay Chains with Missing Energy at Hadron Colliders

Michael Burns, Kyoungchul Kong, Konstantin T. Matchev, Myeonghun Park

摘要:

我们建议使用MT 2的概念来测量所有粒子的质量在超对称事件与两个不可观测的,相同的粒子。为此,我们推广了通常的MT 2的概念,并定义了一个新的MT 2(n,p,c)变量,它可以应用于各种子系统拓扑,以及完整的事件拓扑。我们推导出其端点MT 2 {max}(n,p,c)作为未知的测试质量Mc的子链中的最后一个粒子和横向动量pT由于从初始状态的辐射的函数的解析公式。我们证明了端点函数MT 2 {max}(n,p,c)(Mc,pT)可能表现出三种不同类型的扭结,并讨论了每种类型的起源。我们证明,子系统MT 2(n,p,c)变量本身已经产生了足够数量的测量的质谱(包括整体质量尺度)的完整测定。作为一个例子,我们考虑一个简单的情况下,衰变链多达三个重粒子,X2 -> X1 -> X 0,这是相当有问题的所有其他质量测量方法。我们提出了三种不同的基于MT 2的方法,每种方法都可以完全确定粒子X 0,X1和X2的质量。第一种方法仅使用测试质量Mc的单个固定值处的MT 2(n,p,c)端点测量。在第二种方法中,将未知质谱拟合到表现出扭结的一个或多个端点函数MT 2 {max}(n,p,c)(Mc,pT)。第三种方法是混合的,将MT 2端点与不变质量分布中的运动学边缘的测量相结合。作为我们的方法的一个实际应用,我们表明,双轻子W+W-和TT-巴样品在Tevatron可以用于独立的顶夸克,W玻色子和中微子的质量的测定,没有任何事先的假设。

英文摘要:

We propose to use the MT2 concept to measure the masses of all particles in SUSY-like events with two unobservable, identical particles. To this end we generalize the usual notion of MT2 and define a new MT2(n,p,c) variable, which can be applied to various subsystem topologies, as well as the full event topology. We derive analytic formulas for its endpoint MT2{max}(n,p,c) as a function of the unknown test mass Mc of the final particle in the subchain and the transverse momentum pT due to radiation from the initial state. We show that the endpoint functions MT2{max}(n,p,c)(Mc,pT) may exhibit three different types of kinks and discuss the origin of each type. We prove that the subsystem MT2(n,p,c) variables by themselves already yield a sufficient number of measurements for a complete determination of the mass spectrum (including the overall mass scale). As an illustration, we consider the simple case of a decay chain with up to three heavy particles, X2 -> X1 -> X0, which is rather problematic for all other mass measurement methods. We propose three different MT2-based methods, each of which allows a complete determination of the masses of particles X0, X1 and X2. The first method only uses MT2(n,p,c) endpoint measurements at a single fixed value of the test mass Mc. In the second method the unknown mass spectrum is fitted to one or more endpoint functions MT2{max}(n,p,c)(Mc,pT) exhibiting a kink. The third method is hybrid, combining MT2 endpoints with measurements of kinematic edges in invariant mass distributions. As a practical application of our methods, we show that the dilepton W+W- and tt-bar samples at the Tevatron can be used for an independent determination of the masses of the top quark, the W boson and the neutrino, without any prior assumptions.

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