PM: Search for a Cosmologically-Relevant Boson in Antimuon Decay

在粒子加速器设施中进行的实验通常涉及在所使用的探测器中产生非常大的信号。这是被赋予加速射弹的高能量的结果，而加速射弹又在碰撞中产生非常高能量的碎片。这种实验中粒子相互作用的意想不到的产物是新物理理论的先驱。当寻找新物理学的这些特征时，传统的注意力一直是在所寻找的信号中推动越来越高的能量。该奖项将支持对这一趋势的创新背离，转而专注于观察到在一束反介子撞击专门为此目的建造的锗探测器的撞击和衰变之后可能产生的最小能量。收集的数据将使该团队能够显著扩展目前对这种衰变的奇异模式的敏感性，特别是在这种衰变中产生了一种意想不到的新粒子(玻色子)。这样的玻色子已经被粒子相互作用标准模型的许多扩展所预测，这个理论现在已知是不完整的。通过专注于低能量，该奖项支持的搜索将首次探索这样一种可能性，即这些玻色子是以足够慢的速度产生的，足以受到星系的引力约束。这将使它们能够在宇宙学场景中扮演有趣的角色，包括仍然悬而未决的暗物质问题。该奖项还将支持一名研究生完成学业。专门的锗探测器将被开发出来，其特征需要研究产生新玻色子的反微子的衰变模式和可以说明问题的单色低能正电子。然后，这些设备将被暴露在加拿大加速器中心TRIUMF的M15/M20表面µ子束中。TRIUMF是美国以外的两个来源之一，能够为这次搜索提供所需的Muon能量。在短时间(一周)束曝光后，玻色子相空间的相关区域可以被探测到小到1E-7的分支比，相对于以前的这种类型的搜索，这是一个巨大的进步。两个主要因素促成了这种出色的预期灵敏度：探测器能量分辨率比以前使用的大闪烁体热量计提高了三个数量级以上，以及将使用的微型探测器的适度本底速率。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Experiments performed at particle accelerator facilities typically involve the generation of very large signals in the detectors employed. This is the result of the high energies imparted to the accelerated projectiles, which in turn produce very energetic fragments in their collisions. Unexpected products of particle interactions in such experiments are the harbingers of new physics theories. When looking for these signatures of new physics, the traditional concentration has been to push towards higher and higher energies in the sought signals. This award will support an innovative departure from this trend, by concentrating instead on the observation of the smallest possible energies following the impact and decay of a beam of anti-muons striking germanium detectors built specifically for this purpose. The data collected will permit the team to significantly expand the present sensitivity to exotic modes of this decay, specifically one in which an unexpected new particle (a boson) is created. Such bosons have been predicted by many extensions of the Standard Model of particle interactions, a theory now known to be incomplete. By concentrating on low-energies, the search supported by this award will explore, for the first time, the possibility that these bosons are created with slow-enough speeds to be gravitationally bound to galaxies. This would enable them to play interesting roles in cosmological scenarios, including the still unresolved dark matter problem. This award will also support one graduate student towards the completion of their studies. Specialty germanium detectors will be developed with the characteristics required to investigate the mode of decay of an antimuon that generates the new boson and a tell-tale monochromatic low-energy positron. These devices will then be exposed to the M15/M20 surface muon beams at TRIUMF, the Canadian accelerator center. TRIUMF is one of two sources, both outside the US, able to provide the required muon energies for this search. Following short (one week) beam exposures, the pertinent region of boson phase space can be probed down to branching ratios as small as 1E-7, a vast advance with respect to previous searches of this type. Two main factors contribute to this excellent expected sensitivity: an improvement by more than three orders of magnitude in detector energy resolution with respect to previously employed large scintillator calorimeters, and the modest background rate expected in the tiny detectors to be used.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.