Theory Division T-2, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA.
Phys Rev Lett. 2013 Sep 20;111(12):121802. doi: 10.1103/PhysRevLett.111.121802. Epub 2013 Sep 18.
We point out that, in the irreducible natural supersymmetric spectrum, top squarks have comparable branching fractions to chargino-bottom and neutralino-top final states in the vast bulk of parameter space, provided only that both decay modes are kinematically accessible. The total top squark pair branching fractions into tt + MET (MET=missing transverse energy) can therefore be reduced to O(50%), whereas bb + X branching fractions are typically much smaller, O(10%), thus limiting the reach of traditional top squark searches. We propose a new top squark search targeting the asymmetric final state t[over˜]t[over˜]* → t(χ)(0)b(χ)(-) +H.c., which can restore sensitivity to natural top squarks in the 7 and 8 TeV LHC runs. In addition, we present a new variable, topness, which efficiently suppresses the dominant top backgrounds to semileptonic top partner searches. We demonstrate the utility of topness in both our asymmetric search channel and traditional t[over˜]tover ˜ →tt[over¯]+MET searches and show that it matches or outperforms existing variables.
我们指出，在不可约自然超对称能谱中，只要两种衰变模式在动力学上是可达到的，顶夸克的分支比就可与中微子- Bottom 和中性微子- Top 的终态相当，在绝大多数参数空间中。因此，顶夸克对的总分支分数可以减少到 O(50%)，而 bb + X 的分支分数通常要小得多，O(10%)，从而限制了传统顶夸克搜索的范围。我们提出了一种新的针对非对称终态 t[over˜]t[over˜]* → t(χ)(0)b(χ)(-) +H.c.的顶夸克搜索，这可以恢复在 7 TeV 和 8 TeV LHC 运行中对自然顶夸克的灵敏度。此外，我们还提出了一个新的变量——topness，它可以有效地抑制半轻子顶伙伴搜索中的主要顶背景。我们在我们的非对称搜索通道和传统的 t[over˜]tover ˜ →tt[over¯]+MET 搜索中展示了 topness 的有效性，并表明它与现有的变量相匹配或表现更好。
