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采用的探测器中产生非常大的信号。这是由于被加速的射弹被赋予高能量，而这又在其碰撞中产生高能碎片。在这样的实验中，粒子相互作用的意外产物是新物理学理论的先驱。在寻找新物理学的这些特征时，传统的集中是在所寻找的信号中推动越来越高的能量。该奖项将支持创新性地偏离这一趋势，而是集中精力观察一束反μ子撞击专门为此目的建造的锗探测器后的最小可能能量。收集到的数据将使研究小组能够显着扩大目前对这种衰变的奇异模式的敏感性，特别是一种意想不到的新粒子（玻色子）的产生。这种玻色子已经被粒子相互作用的标准模型的许多扩展所预测，现在已知这个理论是不完整的。通过专注于低能量，该奖项支持的搜索将首次探索这些玻色子以足够慢的速度被引力束缚到星系的可能性。这将使它们能够在宇宙学场景中扮演有趣的角色，包括尚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。特种锗探测器将被开发，其特性将用于研究产生新玻色子和单色低能正电子的反μ子的衰变模式。然后，这些设备将在加拿大加速器中心TRIUMF暴露于M15/M20表面μ子束。TRIUMF是两个来源之一，都在美国以外，能够为这项研究提供所需的μ子能量。在短时间（一周）的光束照射后，玻色子相空间的相关区域可以探测到小至1 E-7的分支比，这是相对于以前这种类型的搜索的巨大进步。两个主要因素促成了这种出色的预期灵敏度：检测器能量分辨率相对于先前采用的大闪烁体量热计提高了三个数量级以上，该奖项反映了NSF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进行评估，被认为值得支持的搜索.

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.