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。这是由于加速的抛射体被赋予了高能量，而这些抛射体在碰撞中又产生了高能碎片。在这样的实验中，粒子相互作用的意想不到的产物是新的物理理论的先兆。在寻找这些新物理特征时，传统的注意力一直是在寻找的信号中向越来越高的能量推进。这一奖项将支持一种创新的背离这一趋势的方法，将重点放在观察一束反介子撞击锗探测器的撞击和衰变后尽可能小的能量上。收集到的数据将使研究小组大大提高目前对这种衰变的奇异模式的灵敏度，特别是在一种意想不到的新粒子（玻色子）产生的模式中。这些玻色子已经被粒子相互作用标准模型的许多扩展所预测，这个理论现在被认为是不完整的。通过专注于低能，该奖项支持的研究将首次探索这些玻色子以足够慢的速度产生的可能性，从而与星系引力相结合。这将使它们在宇宙学场景中扮演有趣的角色，包括仍未解决的暗物质问题。该奖项还将支持一名研究生完成学业。特制的锗探测器将被开发出来，以研究产生新玻色子和单色低能量正电子的反子的衰变模式。然后，这些装置将暴露在加拿大加速器中心TRIUMF的M15/M20表面介子束中。TRIUMF是两个来源之一，都在美国之外，能够为这次搜索提供所需的μ子能量。在短时间（一周）的光束照射下，玻色子相空间的相关区域可以被探测到分支比低至1E-7，这与之前的搜索相比是一个巨大的进步。有两个主要因素促成了这种优异的预期灵敏度：与以前使用的大型闪烁体量热计相比，探测器能量分辨率提高了三个数量级以上，以及期望使用的微型探测器具有适度的背景速率。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值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.