Studies in Experimental Nuclear Physics at Indiana University

该提案将支持印第安纳大学实验核物理小组在基础研究的三个关键领域继续发挥领导作用：(1)了解胶子和夸克-反夸克对的内部“海洋”对质子和中子的整体自旋和磁性的贡献；(2)阐明核物质在极端温度下的性质，例如那些被认为与宇宙大爆炸起源后宇宙演化的最早时刻有关的性质；(3)测试粒子物理学标准模型精确解释低能中子和中微子的性质和相互作用的能力。第(1)类的测量将通过两种互补的技术进行：利用相对论重离子对撞机（RHIC）设施研究高能自旋极化质子束碰撞，以及印第安纳小组刚刚完成的STAR探测器的主要新添加；中微子-质子和中微子-中子散射过程的比较研究。与第(2)类相关的实验也将利用RHIC，重点关注由重夸克-反夸克对组成的介子在高能核-核碰撞中的产生，以及夸克与胶子在这些碰撞中产生的独特热物质中的相互作用之间的差异。对基本粒子相互作用的研究将包括：完成一项正在进行的实验，以证实或反驳中微子从一种类型到另一种类型振荡的有争议的信号，这种信号不容易被自然中出现的中微子状态的图像所适应；通过利用创新的概念来寻找电子自旋的禁止电相互作用，在测试自然界近乎完美的时间反转对称性方面取得了最先进的进展；通过高度敏感地暴露中子-核相互作用和核结构中完美镜像对称的偏差，改进了中子和质子之间通常被掩盖的弱相互作用的表征。拟议的研究还将涉及开发创新的新技术，用于跟踪中微子相互作用的产物，以及为基本相互作用实验产生“超冷”中子束

This proposal will support continuing leadership roles for the Indiana University experimental nuclear physics group in three critical areas of basic research: (1) understanding the contributions from the internal "sea" of gluons and quark-antiquark pairs to the overall spin and magnetism of the proton and neutron; (2) elucidating the properties of nuclear matter at extreme temperatures, such as those believed to pertain during the earliest instants of the universe's evolution following its Big Bang origin; (3) testing the ability of the Standard Model of particle physics to account precisely for the properties and interactions of low-energy neutrons and of neutrinos. Measurements in category (1) will be made via two complementary techniques: studies of spin-polarized proton beam collisions at high energy exploiting the Relativistic Heavy Ion Collider (RHIC) facility and a major new addition to the STAR detector at that facility just completed by the Indiana group; comparative studies of neutrino-proton and neutrino-neutron scattering processes. Experiments relevant to category (2) will also utilize RHIC, with focus on the production in high-energy nucleus-nucleus collisions of mesons composed from a heavy quark-antiquark pair, and on differences between the interactions of quarks vs. gluons in the unique, hot matter produced in those collisions. Studies of fundamental particle interactions will include: completion of an ongoing experiment to confirm or refute a controversial signal for the oscillation of neutrinos from one type to another, a signal that cannot be easily accommodated in the emerging picture of neutrino states in nature; dramatic advances in the state-of-the-art for tests of nature's nearly perfect time-reversal symmetry, by exploiting innovative concepts to search for forbidden electric interactions of the spin of an electron; improved characterization of the normally masked weak interaction among neutrons and protons via highly sensitive exposure of deviations from perfect mirror symmetry in neutron-nucleus interactions and in nuclear structure. The proposed research will also involve the development of innovative new technology for tracking products from neutrino interactions and for producing beams of "ultra-cold" neutrons for fundamental interaction experiments