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RHIC Serves as World’s First & Only Collider
of Polarized Protons for ‘Spin’ Physics

Accelerating & Colliding High-Energy Polarized Protons at RHIC

As a collider of high-energy, high-luminosity polarized protons, the Relativistic Heavy Ion Collider (RHIC) is uniquely enabling physicists to study the spin structure of the proton, with the goal of understanding the contribution of gluons and antiquarks to proton spin, and verifying spin effects in perturbative Quantum Chromodynamics and parity violation in W and Z particle production.

To do all this, certain RHIC accelerator physics challenges had to be met in the production, acceleration, storage, and collision of polarized protons (), while maintaining and being able to measure the percentage of beam polarization. These were no easy tasks, as spinning protons act like tiny magnets, which must be bent and focused by the magnets making up the four accelerators within the RHIC complex.

In the control room is the staff of accelerator physicists who are responsible for the successful collision of polarized protons at the Relativistic Heavy Ion Collider.

“The level of beam polarization is extremely important, since the accuracy of spin related asymmetry measurements made by the polarized proton experiments goes proportionally with polarization or the square of polarization, so every percent of polarization is significant,” explains Thomas Roser, who heads the accelerator division of Broookhaven’s Collider- Accelerator Department, which is responsible for RHIC operations.

The proof that these challenges were met are in the records of RHIC’s first two runs as the world’s first and only collider: During RHIC’s first run, from November 2000 through January 2001, approximately 25 percent polarization was maintained at a beam energy of 100 billion electron volts (GeV). During RHIC’s second p≠p≠ run, from April through May 2003, spin polarization was increased to about 40 percent at the same beam energy. 

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