The Relativistic Heavy Ion Collider

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Dissecting the Proton's Spin with Polarized
Proton Collisions at
The Relativistic Heavy Ion Collider
4 km circ. Collider
J. Sowinski
Heavy ions Au-Au Lighter ions Asymmetric d-Au
PHOBOS
4 detectors STAR PHENIX PHOBOS Brahms pp2pp
(p-p only)
The first polarized p-p collider!
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Two complementary detectors continue at RHIC as
main participants in spin program
RHIC Discovery of New Form of Matter Particle su
ppression and jet quenching wrt d-Au seen in
Au-Au at 200 GeV/N
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Where does the protons spin come from?
p is made of 2 u and 1d quark
S ½ S Sq
Explains magnetic moment of baryon octet
p
BUT partons have an x distribution and there are
sea quarks and gluons
Check via electron scattering and find quarks
carry only 1/3 of the protons spin!
Sz ½ ½ DS DG Lzq Lzg
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DG via partonic scattering from a gluon
Spin dependence of partonic scattering is large!
Know from DIS
Measure

A P 3P 3a
g
part
LL
LL
pQCD
DG
Prefer

• Dominant reaction mechanism
• Experimentally clean reaction mechanism
• Large a
• But jet and p0 rates are sufficient to give
  significant DG const. in first RHIC pol. p data

LL
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Many special devices in RHIC to generate,
preserve and measure polarization
Snakes
Development runs
First devoted physics run
Lum. recordedat STAR
Est. next 2 years
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Measured Cross Sections Agree well with pQCD
Calculations
p0s
Jets
PRL 97, 252001 (2006)
hep-ex 07043599
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2005 Results
Inclusive Jets in STAR
Inclusive p0 in PHENIX
GRSV curves ?G G ?G -G ?G 0 ?G STD
Preliminary
hep-ex 07043599
Theory curves from B.Jager et. al., PRD70
(2004)034010
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Add important new constraints to Dg Need global
analysis
hep-ex 07043599
Jets
Sensitive to 0.03 moment of Dg for GRSV
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2006 Inclusive Jets and p0s
Jets
Preliminary
x dependence Dg(x) becomes important now!
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Summary

• RHIC is adding important new constraints on DG
• Expect an order of magnitude more statistics at
  200 GeV in next two years
  
• Coincident channels and direct g provide greater
  selectivity and x dependence Dg(x)
  
• 500 GeV and upgrades add complementary data for
  DG
  
• And Du and Dd measurements with W decay leptons
• see poster of S. Pate on future and upgrades

RHIC