在RHIC进行绝对旋光测定
Absolute polarimetry at RHIC
摘要：
精确和绝对的束流偏振测量是RHIC自旋物理计划的关键。由于所有的实验自旋相关的结果是由光束偏振归一化，归一化的不确定性直接贡献最终的物理不确定性。我们的目标是进行光束偏振测量的精度为$ΔP_{beam}/P_{beam} < 5%$。绝对偏振计由偏振原子氢气射流靶和左右成对的硅条探测器组成，于2004年安装在RHIC环上。该系统的特点是在库仑核干涉（CNI）区域的\textit{proton-proton}弹性散射。对这一过程的分析能力$A_N$的精确测量使我们能够在2005年实现$ΔP_{beam}/P_{beam} =4.2%$，这是第一次长时间的自旋物理运行。在本报告中，我们描述了整个系统的设置和性能。介绍了2004-2005年的光束偏振测量过程和分析结果。本文还讨论了CNI区四动量平方转移$A_N$的物理问题。我们指出了目前的问题和期望在2006年和未来的最佳精度。
英文摘要：
Precise and absolute beam polarization measurements are critical for the RHIC spin physics program. Because all experimental spin-dependent results are normalized by beam polarization, the normalization uncertainty contributes directly to final physics uncertainties. We aimed to perform the beam polarization measurement to an accuracy of $ΔP_{beam}/P_{beam} < 5%$. The absolute polarimeter consists of Polarized Atomic Hydrogen Gas Jet Target and left-right pairs of silicon strip detectors and was installed in the RHIC-ring in 2004. This system features \textit{proton-proton} elastic scattering in the Coulomb nuclear interference (CNI) region. Precise measurements of the analyzing power $A_N$ of this process has allowed us to achieve $ΔP_{beam}/P_{beam} =4.2%$ in 2005 for the first long spin-physics run. In this report, we describe the entire set up and performance of the system. The procedure of beam polarization measurement and analysis results from 2004-2005 are described. Physics topics of $A_N$ in the CNI region (four-momentum transfer squared $0.001 < -t < 0.032 ~ ({\rm GeV}/c)^2$) are also discussed. We point out the current issues and expected optimum accuracy in 2006 and the future.
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