Forward Meson Production and Spin Asymmetries at RHIC

质子和中子是由叫做夸克和胶子的更小的成分组成的，这是一个公认的事实。质子是受强核力束缚的夸克集合，就像原子是受电作用力束缚在原子核上的电子集合一样。通过研究高能的质子碰撞，我们了解了这些夸克是如何被束缚在质子内部的。质子还有一种叫做自旋的固有特性，可以把质子想象成一个绕着自己的轴旋转的球体，就像地球绕着自己的轴旋转一样。特别是，当高能自旋质子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STAR探测器及其组成部分FMS中以光子和电子的形式被观察到，FMS将作为该项目的一部分进行维护。该合同将资助宾夕法尼亚州立大学小组为即将到来的RHIC运行准备、校准和操作FMS，并分析最近收集的数据。FMS是一种覆盖2.6 ~ 4伪快度区的电磁量热计。它可以探测来自中性介子、介子、喷流、单光子和电子的碰撞碎片。即将到来的极化RHIC运行将强调横向质子自旋依赖于电子-正电子Drell-Yan对的产生。这将允许测量横向单自旋不对称性，定义为质子向上或向下自旋的横截面差除以这些横截面的总和。在当前微扰量子色动力学模型正在演化的状态下，测量的不对称性对强核力敏感。

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.