Minimization of spin tune spread for preservation of spin polarization at RHIC

Abstract

The spin structure of the proton is one of the unsolved problems in physics. The Relativistic Heavy Ion Collider (RHIC) Spin Physics Program has been conducting research to investigate the spin structure by colliding high energy polarized proton beams. Maintaining high spin polarization while achieving high luminosity is critical for this program. Two of the challenges related to the program are to maintain spin polarization during spin flipping, a process designed to reduce systematic errors in spin asymmetry measurements, and during beam acceleration from the low energy source to the high energy collision experiment. Recently, a modification of the accelerator's magnet configuration (optics) was developed for reducing the spin tune spread. With the new optics implemented, higher spin flipping efficiency was achieved at both injection and top beam energies. The spin tune spread was also minimized during beam acceleration and the transmission efficiency of spin polarization was evaluated. In this report the modifications needed for minimizing the spin tune spread and their impact on the global beam optics are described.

Polarization Preservation and Spin Manipulation

“…The drive tune needs to be close to the spin tune, which requires a small spin tune spread. In RHIC, where a pair of Siberian snakes are used, the small spin tune spread was achieved by the reduction of the dispersion slope difference at the two Siberian snakes [32,33]. These experimental results prove that it is possible to routinely measure the spin tune of polarized proton beams-the most important polarized beam parameter.…”

Siberian Snakes, Figure-8 and Spin Transparency Techniques for High Precision Experiments with Polarized Hadron Beams in Colliders

“…After a polarized beam is generated by a polarized source, the first challenge is to preserve the beam polarization in the process of its acceleration to the final energy. The main difficulties with preserving the polarization are associated with crossing of numerous spin resonances [17][18][19][20][21][22][23][24][25][26][27][28].…”