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RHIC handles its first polarized protons

1 December 2000

Soon after commissioning with high-energy beams of heavy
nuclei (see October
News
), Brookhaven’s Relativistic Heavy Ion Collider
(RHIC) tested the second string to its bow when it underwent
its first two-week test of transferring, storing, measuring and
accelerating polarized (spin-oriented) protons. The run
culminated in the acceleration of polarized protons to 32
GeV.

Spin is an intrinsic angular momentum of
elementary particles and nuclei. To collect and then accelerate
protons where most of the spins are in the same direction
requires a special source. Special equipment is also required to
keep the protons spinning in the same direction as they are
accelerated.

A new polarized proton source was
installed for the RHIC experiments, a new device was installed
to measure the proton degree of polarization, and a special
string of magnets was installed to maintain the polarization
through acceleration.

The type of magnet string to
control polarization was invented at Novosibirsk, Russia, and
therefore dubbed a “Siberian Snake” in the trade. In the
Brookhaven test, polarized protons from the new source were
accelerated in the Alternating Gradient Synchrotron before
being transferred to RHIC.

The new polarimeter
measured stable polarization in RHIC at injection and after
acceleration. When the Siberian Snake was turned off, no
polarization was seen after acceleration.

The ultimate
goal is to collide spin-polarized proton beams together next
year to yield insight into the spin structure inside the proton.
RHIC is the first machine in the world capable of colliding
such beams.

In 1995, the Japanese Institute of Physical
and Chemical Research, RIKEN, first agreed to provide
funding to equip RHIC for work with high-energy
spin-polarized protons. This led to the establishment of the
RIKEN Research Centre at Brookhaven, a major partner in
this work, along with groups from Brookhaven and across
the world, including RIKEN and KEK in Japan, ITEP
Moscow, Argonne, the Universities of New Mexico and
Indiana, and members of the STAR and PHENIX
experimental collaborations at RHIC. RIKEN also provided
funds for the Siberian Snake and polarimeter.

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