Forward Meson Production and Spin Asymmetries at RHIC

众所周知，质子和中子是由更小的夸克和胶子组成的。 质子是由强核力束缚的夸克的集合，就像原子是由电力束缚在原子核上的电子的集合一样。通过研究高能质子碰撞，我们可以了解这些夸克是如何束缚在质子内部的。质子还有一个内在的属性，称为自旋，可以通过将质子想象为绕轴旋转的球体来可视化，就像地球绕轴旋转一样。特别是，当自旋对齐质子的高能束在布鲁克海文国家实验室的相对论重离子对撞机（RHIC）上碰撞时，产生的粒子可以揭示质子的自旋有多少是由胶子或不同类型的夸克携带的。该项目的目标是寻找胶子对质子自旋的贡献，这是核科学咨询委员会确定的一个重要问题。这些碰撞在星星探测器及其组成部分FMS中被观察到，FMS将作为该项目的一部分进行维护。该奖项将资助宾夕法尼亚州立大学的团队为即将到来的RHIC运行准备，校准和操作FMS，并分析最近收集的数据。 FMS是一个电磁量能器，覆盖了从2.6到4的赝快度区域。 它探测来自中性π介子、η介子、喷流、单光子和电子的碰撞碎片。 即将到来的极化RHIC运行将强调产生电子-正电子Drell-Yan对的横向质子自旋依赖性。这将允许测量横向单自旋不对称性，定义为质子自旋向上或向下的横截面的差异除以这些横截面的总和。 测得的不对称性是敏感的强核力的制度，目前的微扰量子色动力学模型正在发展。

It is a well-established fact that protons and neutrons are made up of smaller constituents called quarks and gluons. Protons are collections of quarks bound by the strong nuclear force much as atoms are collections of electrons bound to the nucleus by the electric force. By studying the proton collisions at high energy we learn how these quarks are bound inside the proton. The proton also has an intrinsic property called spin, which can be visualized by thinking of the proton as a sphere spinning on its axis, much like the Earth rotates on its axis. In particular, when high energy beams of spin-aligned protons collide at Brookhaven National Laboratory's Relativistic Heavy Ion Collider (RHIC) the resulting particles can reveal how much of the proton's spin is carried by its gluons or by different types of quarks. The goal of this project is search for the gluon contribution to the spin of the proton, which is identified as an important question by the Nuclear Science Advisory Committee. These collisions are observed as photons and electrons in the STAR detector and its component part, called the FMS, which will be maintained as part of this project.This award will fund the Penn State group to prepare, calibrate and operate the FMS for upcoming RHIC runs and to analyze data recently collected. The FMS is an electromagnetic calorimeter covering the pseudo-rapidity region from 2.6 to 4. It detects collision fragments from neutral pions, eta mesons, jets, single photons and electrons. The upcoming polarized RHIC run will be emphasizing the transverse proton spin dependence for production of electron-positron Drell-Yan pairs. This will allow measurement of the transverse single spin asymmetry, defined as the difference in cross section for proton spin up or down divided by the sum of those cross sections. The measured asymmetry is sensitive to the strong nuclear forces in a regime where current models of Perturbative Quantum Chromodynamics are evolving.