Prospects for Spin Physics at RHIC

TL;DR

RHIC-Spin aims to resolve how proton spin arises from quarks, antiquarks, and gluons by colliding polarized protons at √s up to 500 GeV. The paper outlines a QCD-based spin-physics program using factorization, spin-dependent PDFs, and various hard probes (prompt photons, jets, W/Z, Drell-Yan) to measure Δg and flavor-separated quark helicities, plus exploration of transversity and spin effects in fragmentation. It also discusses potential new-physics sensitivity through parity violation in jet production and small-angle elastic scattering, and describes detector capabilities, polarimetry, and expected precision. The work presents a roadmap for testing fundamental QCD spin dynamics and potentially uncovering beyond-Standard-Model phenomena.

Abstract

Colliding beams of 70% polarized protons at up to $\sqrt{s}$=500 GeV, with high luminosity, L=2$\times10^{\rm 32}$ cm$^{-2}$sec$^{-1}$, will represent a new and unique laboratory for studying the proton. RHIC-Spin will be the first polarized-proton collider and will be capable of copious production of jets, directly produced photons, and $W$ and $Z$ bosons. Features will include direct and precise measurements of the polarization of the gluons and of $\bar{u}$, $\bar{d}$, $u$, and $d$ quarks in a polarized proton. Parity violation searches for physics beyond the standard model will be competitive with unpolarized searches at the Fermilab Tevatron. Transverse spin will explore transversity for the first time, as well as quark-gluon correlations in the proton. Spin dependence of the total cross section and in the Coulomb nuclear interference region will be measured at collider energies for the first time. These qualitatively new measurements can be expected to deepen our understanding of the structure of matter and of the strong interaction.

Figures (22)

• Figure 1: Schematic layout of the RHIC accelerator complex. Only relevant devices for polarized $pp$ collisions are shown.
• Figure 2: Production of a large-$p_T$ pion in a hard $pp$ collision.
• Figure 3: Lowest-order analyzing powers for various reactions relevant for RHIC, as functions of the partonic center-of-mass system (cms) scattering angle craigie83jaffe96. Left: longitudinal polarization, right: transverse polarization (a factor $\cos(2 \phi)$ has been taken out, where $\phi$ is the azimuthal angle of one produced particle).
• Figure 4: Bunch filling pattern with respect to the spin states of polarized protons.
• Figure 5: The Phenix detector system.