The Relativistic Heavy Ion Collider

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Dissecting the Proton's Spin with Polarized
Proton Collisions at
The Relativistic Heavy Ion Collider
2.4 mile circ. Collider

• 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
suppression 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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Why is RHIC the 1st Polarized Collider?
Overcoming Depolarizing Resonances

• Spin is vertical in RHIC
• In-plane components precess rapidly at spin tune
  (turns/orbit) Gg (180 at 100GeV)
• Resonances from repetitive perturbations
• Stray in-plane fields can rotate spin into plane,
  resonance when Gginteger
• Focusing fields can also do this, resonance when
  Gginteger betatron tune
• Huge number of these in RHIC
• Solution Siberian Snakes
• Idea from Novosibirsk
• First proof in tests at IUCF Cooler ring

Siberian Snake
Res. Strength

• Siberian Snake
• Helical dipole magnet
• Rotates spin 180o no net beam defl.
• 2 in RHIC
• 100 spin transmission to 100 GeV
• Same technology for spin rotators

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Many special devices in RHIC to generate,
preserve and measure polarization
Snakes
Development runs
First devoted physics run
Lum. recorded.at 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 lt xgluon lt 0.3 about ½ the 1st
moment of Dg for GRSV
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Jet,p0 and p0 data are consistent
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2006 Inclusive Jets and p0s
Jets
Preliminary
Projections?
x dependence Dg(x) becomes important now!
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Charged p results promise of Dg sign sensitivity
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Direct g dominated by qg subprocess
Di-Jets and g-jet
200GeV pp direct photon
Access to parton kinematics to get Dg(x)

• g-jet offers
• Greater qg selectivity
• More precise pT (x resolution)

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Status of DIS and SIDIS Results

• Important new data
• Compass g1d(x) at low x
• CLAS g1p,d(x) large x
• low Q2

Compass Analysis J. Pretz DIS2007

• Compass Analysis
• DG 0.2-0.3

• LSS Analysis
• Higher twist important
• Positive, negative and zero-crossing shapes
  allowed
• DG lt 0.3

There are many others And some will include pp
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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