Forward Meson Production and Spin Asymmetries at RHIC

众所周知，质子和中子是由称为夸克和胶子的较小成分组成的。质子是被强核力束缚的夸克集合，就像原子是被电力束缚在原子核上的电子集合一样。通过研究高能质子碰撞，我们了解到这些夸克是如何束缚在质子内部的。质子还有一种称为自旋的内在属性，它可以通过将质子想象成一个围绕其轴旋转的球体来可视化，就像地球围绕其轴自转一样。特别是，当自旋排列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。这个项目的目标是寻找胶子对质子自旋的贡献，这被核科学咨询委员会确定为一个重要的问题。这些碰撞以光子和电子的形式在恒星探测器及其称为FMS的部件中被观测到，该部件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是一种电磁量热计，覆盖了从2.6到4的伪快度区域。它探测来自中性介子、ETA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对的横向质子自旋相关性。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除以这些横截面的总和。在当前微扰量子色动力学模型不断发展的情况下，测量到的不对称性对强核力很敏感。

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.