References - Bogoliubov Laboratory of Theoretical Physics - JINR

HIGH ENERGY SPIN PHYSICS WITH THE PHENIX DETECTOR AT
RHIC
D. Kawall 1 † on behalf of the PHENIX Collaboration
(1) RIKEN-BNL Research Center and University of Massachusetts, Amherst, USA
† E-mail: kawall@bnl.gov
Abstract
The Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory
has demonstrated the unique ability to collide beams of polarized protons at center
of mass energies from √ s= 62.4 to 500 GeV. Such collisions have been analyzed
by members of the PHENIX collaboration to shed light on the size and shape of
the spin-dependent distribution function of the gluon Δg(x), and on the origin of
large asymmetries in inclusive hadron production from collisions involving transversely
polarized protons. After a brief review of RHIC and the PHENIX detector,
our recent results in spin physics will be presented, along with our prospects for
determining quark flavor-separated spin-dependent distribution functions extracted
using parity violation in the production and decay of W bosons at RHIC.
1 Introduction
From polarized deep-inelastic scattering experiments at SLAC, CERN, and DESY, we
have learned that quark and antiquarks carry perhaps 25% of the spin of the proton [1].
This fraction was unexpectedly small, and understanding the remainder, which must come
from the intrinsic spin of the gluons Δg(x), and orbital angular momentum of the quarks
Lq, and gluons Lg, presents an outstanding challenge to theorists and experimentalists.
The Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory has
the unique ability to collide beams of highly polarized protons. This has provided experimentalists
with a new tool to measure, with leading order sensitivity, the gluon contribution
to the spin of the proton [2]. In addition, RHIC has reached pp center of mass
energies of 500 GeV, where measurements of Δu, Δū, Δd, and Δ ¯ d are possible by exploiting
parity-violation in the process pp → W ± + X [2].
2 RHIC : The Polarized Proton Collider
RHIC has two rings, each of which can contain 120 bunches of polarized protons. In the
interaction regions, a bunch from one ring collides with a bunch from the other ring, then
these same bunches circulate in opposite directions 3833 m around the RHIC rings and
collide again about 13 μs later [3].
The spin is preserved during acceleration and store through the use of a pair of Siberian
snakes. The spins can be rotated from transverse to longitudinal at the interaction region
by spin rotators. In the most recent run in 2009, RHIC was run at √ s=500 GeV for 30
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