在LHC上用高粒度量热计提高对长寿命粒子的灵敏度
Enhancing Sensitivities to Long-lived Particles with High Granularity Calorimeters at the LHC
摘要：
寻找长寿命粒子（LLP）是大型强子对撞机即将运行的一个令人兴奋的物理学机会。在本文中，我们专注于一个新的搜索策略，使用高粒度量热仪（HGCAL），CMS检测器的升级的一部分，在这样的搜索。特别是，我们证明了这种升级的量热计的高粒度，这使我们能够看到“淋浴轨道”的量热计，可以在识别信号和抑制背景中发挥至关重要的作用。我们研究的HGCAL使用的信号模型，其中标准模型希格斯玻色子衰变成一对LLP，$h \to XX$的潜在影响。在仔细估计了标准模型QCD和错误重构的假轨道背景后，我们给出了一个更保守的矢量玻色子融合触发器和一个新的基于位移轨道的触发器的投影范围。我们的结果表明，在矢量玻色子融合通道中，Higgs衰变分支比BR $(h \to XX)$的最佳范围约为$\mathcal{O}(10^{-4})$，寿命为$cτ_X \sim 0.1$- $1$米，而对于胶子胶子融合通道，它约为$\mathcal{O}(10^{-5}\text{--}10^{-6})$，寿命相似。或者，对于具有$cτ_X \sim 10^3$仪表的LLP，基于HGCAL的搜索应该能够分别探测胶子胶子融合（矢量玻色子融合）通道中的BR $(h\to XX)$到几个$\times 10^{-4}$（$10^{-2}$）。与之前的搜索相比，我们的新搜索显示出LLP参数空间互补区域的灵敏度增强。
英文摘要：
The search for long-lived particles (LLP) is an exciting physics opportunity in the upcoming runs of the Large Hadron Collider. In this paper, we focus on a new search strategy of using the High Granularity Calorimeter (HGCAL), part of the upgrade of the CMS detector, in such searches. In particular, we demonstrate that the high granularity of the calorimeter with this upgrade, which allows us to see "shower tracks" in the calorimeter, can play a crucial role in identifying the signal and suppressing the background. We study the potential reach of the HGCAL using a signal model in which the Standard Model Higgs boson decays into a pair of LLPs, $h \to XX$. After carefully estimating the Standard Model QCD and the misreconstructed fake-track backgrounds, we give the projected reach for both a more conservative vector boson fusion trigger and a novel displaced-track-based trigger. Our results show that the best reach for the Higgs decay branching ratio, BR$(h \to XX)$, in the vector boson fusion channel is about $\mathcal{O}(10^{-4})$ with lifetime $cτ_X \sim 0.1$--$1$ meters, while for the gluon gluon fusion channel it is about $\mathcal{O}(10^{-5}\text{--}10^{-6})$ for similar lifetimes. Alternatively, for an LLP with $cτ_X \sim 10^3$ meters, the HGCAL based search should be able to probe BR$(h\to XX)$ down to a few $\times 10^{-4}$($10^{-2}$) in the gluon gluon fusion (vector boson fusion) channels, respectively. In comparison with these previous searches, our new search shows enhanced sensitivity in complementary regions of the LLP parameter space.
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