Measuring the spin structure of the proton with the STAR Detector at RHIC Page: 1 of 5
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The submitted manuscript has been authored
by a contractor of the U. S. Government ANL-HEP-CP-96-67
under contract No. W-31-109-ENG-38. lLi
Accordingly, the U.S. Government retains a For the Proceedings of the 1996 Divisional
nonexclusive. royalty-free license to publishofue17 .vson
or reproduce the published form of this E V Meeting of the Division of Particles and Fields
coriu*"s r alowoer to do sD, for American Physical Society, University of M innesota
U. S. Government purposes.
SFP 19 1996 Minneapolis, Minnesota, 10-15 August 1996
O S T I CoNF- %0? --
MEASURING THE SPIN STRUCTURE OF THE PROTON
WITH THE STAR DETECTOR AT RHIC
THOMAS J. LeCOMPTE
High Energy Physics Division, Argonne National Laboratory, 9700 S. Cass Avenue,
Argonne, IL 60439
For the STAR Collaboration
A unique aspect of RHIC is the ability to collide beams of polarized protons at
' = 200 and 500 GeV. The STAR experiment will measure the spin structure
functions for the sea quarks and gluons by measuring spin asymetries in W, Z,
direct photon and jet production. Sensitivity expectations are presented.
1 Introduction and Motivation
A long standing puzzle in high energy physics is "what carries the spin of
the proton?" Deep inelastic scattering experiments suggest less than half of
the proton's spin is carried by the valence quarks (perhaps this should not
be too surprising, considering that only half of the linear momentum of the
proton is carried by the quarks); it is therefore highly desirable to measure the
fraction of the proton's spin in the sea and gluons. It is important to make
these measurements in a kinematic region where perturbative QCD is valid.
Polarized pp collisions at RHIC collider energies satisfy both requirements.
2 The RHIC Collider and STAR Detector
The Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Labora-
tory, when completed in 1999, will collide heavy ions (up to Au79+) at collision
energies expected to be high enough to create a hot, dense plasma of quarks
and gluons. To clearly identify a phase transition to this Quark-Gluon Plasma,
it is necessary to compare heavy ion collisions with pp collisions. A unique as-
pect of RHIC is that a polarization of 70-80% is expected for each proton beam
for these collisions. Peak luminosities of 2 x 1032cm-2/s for Vs = 500 GeV
collisions and 8 x 101cm-2/s for ' = 200 GeV are anticipated, resulting
in data sets of 800 and 320 pb- respectively over two 100 day runs at 50%
efficiency. Because pp running is not the primary focus of RHIC, these data
sets will be collected over approximately three years.
The heart of the STAR Detector is a Time Projection Chamber covering
the region 17 < 1.0, although tracks out to about 17 < 1.8 can be recon-
structed. Inside of the TPC is a three layered Silicon Vertex Tracker, for
Di'3TRIBUT1CN OF ThWS DOCUMENT IS UNUMITED
* Work supported in part by the U. S. Department of Energy, Division of High Energy Physics,
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LeCompte, T.J. Measuring the spin structure of the proton with the STAR Detector at RHIC, article, October 1, 1996; Illinois. (digital.library.unt.edu/ark:/67531/metadc675172/m1/1/: accessed January 23, 2019), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.