在高亮度大型强子对撞机（HL-LHC）上寻找长寿命双重带电标量粒子
Hunting long-lived doubly charged scalars at the HL-LHC
AI总结：
本研究在HL-LHC提出 displaced-vertex 搜寻，针对两种场景下的长寿命双重带电标量粒子，通过不变质量截断压低本底，可覆盖传统搜寻未及的参数空间，给出了预期的产生截面限制。
AI中文摘要：
本研究探讨长寿命双重带电标量粒子的对撞机现象学。在综述了现有的针对双重带电标量粒子的即时产生和长寿命 regime 的搜寻后，我们发现了一个中间固有衰变长度范围，即 $\boldsymbol{\tau}$ 对应的 $c\tau$ 满足 $\boldsymbol{\tau}$ 量级为0.1毫米 ≤ $c\tau$ ≤ $\boldsymbol{\tau}$ 量级为100毫米，在此范围内传统搜寻方法会失去灵敏度。我们研究了在存在和不存在 $SU(2)_L$ 复三重态的 $\boldsymbol{\tau}$ 轻子数破坏（$\boldsymbol{\tau}$）杨耦合两种情况下，探测双重带电标量粒子的前景。在存在该耦合时，双重带电标量粒子 $H^{\boldsymbol{\tau}}$ 仅在质量为100-150 GeV的范围内才能保持长寿命；而在费米ophobic场景（即不存在 $\boldsymbol{\tau}$ 耦合）中，该范围可扩展至TeV量级。我们针对HL-LHC提出了一项针对双重带电标量粒子的 displaced-vertex（ displaced 顶点）搜寻，在费米ophobic场景下可探测质量高达约1 TeV、$c\tau$ 为10-100毫米的双重带电标量粒子；当复三重态标量与轻子耦合时，我们选取了一个基准点，其双重带电标量粒子质量为120 GeV，$c\tau$ 为5毫米。我们证明，对从相关径迹重建的 displaced 顶点的不变质量进行截断，可大幅压低标准模型本底。我们给出了在质心系能量 $\boldsymbol{\tau}$ =14 TeV、积分亮度为3000 $\boldsymbol{\tau}$ 的条件下，针对双重带电标量粒子的 Drell-Yan 对产生截面的预期限制，同时考虑了两种残余本底的说明性假设。因此，displaced-vertex 搜寻可覆盖即时产生搜寻和重稳定带电粒子搜寻未覆盖的互补区域。
英文摘要：
This work studies the collider phenomenology of long-lived doubly charged scalars. After reviewing the existing searches for the doubly charged scalar in both the prompt and the long-lived regimes, we identify an intermediate range of proper decay length, namely, $\mathcal{O}(0.1~\mathrm{mm}) \lesssim cτ\lesssim \mathcal{O}(100~\mathrm{mm})$, where conventional searches lose sensitivity. We investigate the prospects for probing the doubly charged scalar both in the presence and in the absence of the $ΔL=2$ Yukawa coupling of the $SU(2)_{L}$ complex triplet. In the presence of this coupling, $H^{\pm\pm}$ can be long-lived only for masses in the range $100$-$150~\mathrm{GeV}$, whereas in the fermiophobic scenario (i.e., in the absence of the $ΔL=2$ coupling), the range extends to $\mathrm{TeV}$ scale. We propose a displaced-vertex search at the HL-LHC for doubly charged scalars with masses up to $\approx 1~\mathrm{TeV}$ and $cτ=10$-$100~\mathrm{mm}$ in the fermiophobic scenario, while a benchmark point with a doubly charged scalar of mass $120~\mathrm{GeV}$ and $cτ= 5~\mathrm{mm}$ is considered when the complex triplet scalar couples to leptons. We show that a cut on the invariant mass of the displaced vertex as reconstructed from the associated tracks can strongly suppress Standard Model backgrounds. We present projected limits on the Drell-Yan pair-production cross section for the doubly charged scalar at $\sqrt{s}=14~\mathrm{TeV}$ with an integrated luminosity of $3000~\mathrm{fb}^{-1}$, considering two illustrative assumptions for the residual background. Displaced-vertex searches thus probe a region complementary to those covered by prompt and heavy stable charged-particle searches.
