SHiP作为（后）发现机器：识别双光子信号来源
SHiP as a (post-)discovery machine: identifying the diphoton signals' origin
- Ghent University（根特大学）
- Aarhus University（奥胡斯大学）
- CERN（欧洲核子研究中心）
机构由 AI 辅助整理，请以论文原文为准。
AI总结：
SHiP实验可通过双光子衰变运动学区分ALP与U(1)_Y或SU(2)_L的耦合，仅需2-4个事件即可识别纯相互作用，混合耦合需数十至百个事件。
AI中文摘要：
即将开展的SHiP实验可能探测到衰变弱耦合粒子的相互作用强度，其灵敏度比现有极限低几个数量级。一旦发现新粒子，该实验还可能揭示其性质，这需要识别其确切的产生机制，而SHiP并不直接观测这一机制。我们探讨是否可以从其可见衰变的运动学中推断出该机制。作为基准，我们考虑一个轴子类似粒子（ALP），其主导衰变为双光子，这可能发生在与$U(1)_Y$和$SU(2)_L$规范场的耦合中。对于已知的ALP质量，观测到的能量和角分布取决于耦合的相对大小和符号以及未知的寿命，我们在每种假设下独立地对其轮廓化。我们首先确定ALP能量及其纵向和横向衰变位置如何区分这些相互作用，假设完美重建并考虑产生、传播、衰变和几何接受度。然后我们加入探测器响应，并使用SHiP电磁量能器的完整模拟来重建双光子衰变。对于质量在$0.2$到$1~\mathrm{GeV}$之间的ALP，仅需$2$--$4$个重建的双光子事件即可区分纯$U(1)_{Y}$和$SU(2)_{L}$两种相互作用。对于耦合混合的情况，假设完美重建的研究表明，在有利区域需要几十到$\mathcal{O}(10^2)$个事件。
英文摘要：
The upcoming SHiP experiment may probe interaction strengths of decaying feebly coupled particles several orders of magnitude below existing limits. In the event of a discovery, it may also reveal the nature of the new particle. This requires identifying its exact production mechanism, which SHiP does not observe directly. We explore whether this mechanism can be inferred from the kinematics of its visible decays. As a benchmark, we consider an axion-like particle (ALP) with a dominant diphoton decay, which may occur for couplings to the $U(1)_Y$ and $SU(2)_L$ gauge fields. For a known ALP mass, the observed energy and angular distributions depend on the relative magnitude and sign of the couplings and on the unknown lifetime, which we profile independently under each hypothesis. We first determine how the ALP energy and its longitudinal and transverse decay positions distinguish the interactions, assuming perfect reconstruction and accounting for production, propagation, decay, and geometric acceptance. We then include the detector response and reconstruct the diphoton decays using a full simulation of the SHiP electromagnetic calorimeter. Only $2$--$4$ reconstructed diphoton events are needed to distinguish the two pure $U(1)_{Y}$ and $SU(2)_{L}$ interactions for ALP masses between $0.2$ and $1~\mathrm{GeV}$. For coupling admixtures, the study assuming perfect reconstruction indicates requirements of several tens to $\mathcal{O}(10^2)$ events in favorable regions.
