Collaborative Research: The MuLAN Project -- Development of Instrumentation for a New High-Precision Determination of the Fermi Coupling Constant

合作研究：MuLAN 项目——开发用于新的高精度测定费米耦合常数的仪器

• 批准号: 0079449
• 负责人: Robert Carey
• 金额: $ 22.97万
• 依托单位: Trustees of Boston University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2000
• 资助国家: 美国
• 起止时间: 2000-08-15 至 2005-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0079449&HistoricalAwards=false
• 关键词: Collaborative; Research; MuLAN; Project; Development

0079449Carey The MuLan Project will develop the instrumentation needed tomeasure the lifetime of the positive muon to unprecedentedprecision, namely, a factor of 20 better than the current worldaverage. The muon lifetime fixes the value of the Fermi constant,which governs the strength of all weak-interaction processes, justas the fine structure constant governs the strength of allelectromagnetic-interaction processes. The Fermi constant is oneof the fundamental parameters of the Standard Model of particlephysics. A low-energy, continuous-wave muon beam at the Paul Scherrer Institute (PSI) in Switzerland will be modified by a newbeam chopper system in order to create intense, short bursts ofmuons, which will stop in thin targets. A positive muon stopped inappropriate materials decays as if it were in vacuum. Such targetswill be surrounded by a nearly hermetic set of 180 fast-scintillatortiming detectors, each coupled to a state-of-the-art waveformdigitizer, and all readout by a high-speed data acquisition system. Online analysis of the nearly 100 terabytes of data will take placewith a small array of fast microprocessors. A second use of the instrumentation is in conjunction with anongoing effort at PSI to measure the negative muon lifetime inhydrogen gas. The negative muon can decay exactly in the samemanner as the positive muon, or in hydrogen it can interact with aproton by the weak-interaction process known as "capture." Thecapture rate is predicted very accurately by theory; however,current experiments, which have various interpretation problems, arein disagreement with theory by a very significant amount. If thisdisagreement is confirmed, this difference raises the excitingpossibility of pointing to new and unaccounted-for physics. Bymeasuring the difference between the positive and negative muonlifetimes, we will determine the muon capture rate reliably and at aprecision more than four times better than current measurements. The MuLan timing detectors, beamline and custom electronics areexpected to play a major role in this effort.

0079449凯里穆兰项目将开发测量正μ子寿命所需的仪器，以达到前所未有的精度，即比目前世界平均水平高出20倍。 μ子寿命决定了费米常数的值，费米常数决定了所有弱相互作用过程的强度，正如精细结构常数决定了所有电磁相互作用过程的强度一样。 费米常数是粒子物理学标准模型的基本参数之一。 瑞士保罗谢勒研究所（PSI）的一个低能量连续波μ子束将被一个新的束流斩波器系统修改，以产生强烈的短μ子脉冲，它将在薄目标中停止。 一个正的μ介子阻止了不合适的物质的衰变，就好像它在真空中一样。 这样的目标将被一组几乎密封的180个快速振荡器定时探测器包围，每个探测器都连接到一个最先进的波形数字化仪，所有的数据都由一个高速数据采集系统读出。在线分析近100兆字节的数据将发生与一个小阵列的快速微处理器。 仪器的第二个用途是与PSI正在进行的测量氢气中负μ子寿命的工作结合起来。 负μ子可以在与正μ子完全相同的环境中衰变，或者在氢中它可以通过被称为“俘获”的弱相互作用过程与质子相互作用。“理论非常准确地预测了捕获率;然而，目前的实验存在各种解释问题，与理论存在非常大的分歧。 如果这种分歧得到证实，那么这种差异就有可能指向新的、未知的物理学。 通过测量正负μ子寿命之间的差异，我们将可靠地确定μ子的捕获率，其精确度比目前的测量结果高出四倍以上。穆兰定时探测器、光束线和定制电子设备预计将在这项工作中发挥重要作用。