MATHUSLA: A Detector Proposal to Explore the Lifetime Frontier at the HL-LHC

MATHUSLA：一个用于最大化 HL-LHC 发现潜力的外部长寿命粒子探测器

MATHUSLA: An External Long-Lived Particle Detector to Maximize the Discovery Potential of the HL-LHC

本文介绍了位于 HL-LHC 的 MATHUSLA 长寿命粒子探测器的设计、制造与安装现状，指出其能将 LLP 探测范围提升一至两个数量级，为解决等级问题等提供独特灵敏度，是 CERN 探索新物理的关键。

MATHUSLA长寿命粒子探测器（位于CMS附近）的概念设计报告

Conceptual Design Report for the MATHUSLA Long-Lived Particle Detector near CMS

本报告介绍MATHUSLA长寿命粒子探测器概念设计，其位于CMS附近，利用大体积闪烁体跟踪和岩石屏蔽，探测HL-LHC主探测器灵敏度之外一至两个数量级的LLP信号，并展示高信号效率与极低本底。

Braneworld Cosmological Effect on Freeze-in Dark Matter Density and Lifetime Frontier

In the 5-dimensional braneworld cosmology, the Friedmann equation of our 4-dimensional universe on a brane is modified at high temperatures while the standard Big Bang cosmology is reproduced at low temperatures. Based on two well-known scenarios, the Randall-Sundrum and Gauss-Bonnet braneworld cosmologies, we investigate the braneworld cosmological effect on the relic density of a non-thermal dark matter particle whose interactions with the Standard Model particles are so weak that its relic density is determined by the freeze-in mechanism. For dark matter production processes in the early un…

LHCb 发现寿命超过 100 ps 的长寿命新物理粒子的潜力

LHCb potential to discover long-lived new physics particles with lifetimes above 100 ps

本文提出利用 LHCb 的新型 Downstream 算法重建无顶点探测器击中信息的径迹，证明其可成为寿命前沿实验，并在多种长寿命粒子模型中达到与主 LHC 外拟建实验相当的灵敏度。

在CiADS的束流倾倒实验中探索寿命前沿

Exploring the lifetime frontier with a beam-dump experiment at CiADS

提出在CiADS设施上开展束流倾倒实验（CiADS-BDE），利用强前向增强和低本底环境，通过暗光子模型研究长寿命粒子，在5年运行时间内可探测O(100) MeV暗光子质量和O(10^{-9}–10^{-8})动力学混合的未排除参数空间。

Displaced vertex signature of type-I seesaw

A certain class of new physics models includes long-lived particles which are singlet under the Standard Model (SM) gauge group.A displaced vertex is a spectacular signature to probe such particles productions at the high energy colliders, with a negligible SM background. In the context of the minimal gauged $B-L$ extended SM, we consider a pair creation of Majorana right-handed neutrinos (RHNs) at the high energy colliders through the production of the SM and the $B-L$ Higgs bosons and their subsequent decays into RHNs. With parameters reproducing the neutrino oscillation data, we show that t…

Long-lived TeV-scale right-handed neutrino production at the LHC in gauged $U(1)_X$ model

A gauged $U(1)_X$ extension of the Standard Model is a simple and consistent framework to naturally incorporate three right-handed neutrinos (RHNs) for generating the observed light neutrino masses and mixing by the type-I seesaw mechanism. We examine the collider testability of the $U(1)_X$ model, both in its minimal form with the conventional charges, as well as with an alternative charge assignment, via the resonant production of the $U(1)_X$ gauge boson ($Z^\prime$) and its subsequent decay into a pair of RHNs. We first derive an updated upper limit on the new gauge coupling $g_X$ as a fun…

The High-Energy Frontier of the Intensity Frontier: Closing the Dark Photon, Inelastic Dark Matter, and Muon g-2 Windows

We study hidden sector and long-lived particles at past (CHARM and NuCal), present (NA62 and SeaQuest/DarkQuest), and future (LongQuest) experiments that are at the high-energy frontier of the intensity frontier. We focus on exploring the minimal vector portal and variere-lifetime particles (VLP). VLP models have mostly been devised to explain experimental anomalies while avoiding existing constraints, and we demonstrate that proton fixed-target experiments provide one of the most powerful probes for the sub-GeV to few GeV mass range of the VLP models, using inelastic dark matter (iDM) as an e…

SHIFT@LHC：在大型强子对撞机上利用固定靶移位相互作用寻找新物理

SHIFT@LHC: Searches for New Physics with Shifted Interaction on a Fixed Target at the Large Hadron Collider

本研究提出在LHC的CMS相互作用点附近安装SHIFT气态固定靶，无需新建探测器即可拓展新物理参数空间探索范围，在暗光子和隐谷模型下物理可达性较现有方案最高提升千倍。

制冷演示实验的研制

Development of a Frictional Cooling Demonstration experiment

μ子对撞机将开辟高能粒子物理研究的新领域，允许在TeV能量前沿进行精确测量。建造μ子对撞机的最大挑战之一是在与μ子寿命相当的时间尺度上制备μ子束。制冷是解决这一问题的一个潜在方案。在本文中，我们简要介绍了摩擦冷却和详细的摩擦冷却演示（FCD）实验在马克斯普朗克物理研究所，慕尼黑。FCD实验旨在验证摩擦冷却背后的工作原理，目前已进入调试阶段，并将很快开始数据采集。

Searching for long-lived particles beyond the Standard Model at the Large Hadron Collider

Particles beyond the Standard Model (SM) can generically have lifetimes that are long compared to SM particles at the weak scale. When produced at experiments such as the Large Hadron Collider (LHC) at CERN, these long-lived particles (LLPs) can decay far from the interaction vertex of the primary proton-proton collision. Such LLP signatures are distinct from those of promptly decaying particles that are targeted by the majority of searches for new physics at the LHC, often requiring customized techniques to identify, for example, significantly displaced decay vertices, tracks with atypical pr…

Muon Collider进展：加速器

Muon Collider Progress: Accelerators

μ子对撞机将是探索轻子能量前沿的有力工具，并将补充大型强子对撞机目前正在进行的研究。这种装置将提供几个重要的好处。μ子和电子一样，都是点粒子，所以所有的质心能量都可以用来产生粒子。此外，由于它们的质量较高，μ子产生的同步辐射非常少，产生的束辐射也非常少。第一个特点允许使用一个圆形对撞机，它可以有效地利用昂贵的射频系统，并且它的占地面积与现有的实验室场地兼容。第二个特征导致在碰撞点处的相对窄的能量扩散。为μ子对撞机设计加速器复合体是一项具有挑战性的任务。首先，μ子是作为第三束产生的，因此需要高功率质子束和能够承受它的靶，以提供所需的~1 \times 10 ^34 cm^-2 s ^-1的亮度。其次，束最初产生具有大的6D相空间，这需要用于减小μ子束流发射度（“冷却”）的方案。最后，μ子的寿命很短，所以所有的束操纵都必须非常迅速地完成。μ子加速器计划由费米实验室领导，包括一些美国国家实验室和大学，已经开展了旨在最终建造μ子对撞机的设计和研发活动。这种设施的设计特点和配套的R&D计划进行了说明。