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Small x issues in nucleon spin structure (focus: polarized gluon distribution). Abhay Deshpande Stony Brook University RIKEN BNL Research Center December 15, 16, 2006 Washington DC. One of the Key Questions. Polarized gluons and its distribution…
Stony Brook University
RIKEN BNL Research Center
December 15, 16, 2006
Polarized gluons and its distribution…
From COMPASS, PHENIX and STAR…. But…..
Similar message from E143 PRD (112003) 1998… same issue of PRD, and any other
theory or experimental effort that was concluding at the time!
RHIC pC Polarimeters
Absolute Polarimeter (H jet)
BRAHMS & PP2PP
Solenoid Partial Siberian Snake
Helical Partial Siberian Snake
200 MeV Polarimeter
AGS Internal Polarimeter
AGS pC Polarimeters
Strong AGS Snake
~60-65% beam polarizations
~2 x 1031/cm2/sec
Installed and commissioned during FY04 run
Commissioned during FY05 run
Installed and commissioned during FY05 run
(From Research Plan for Spin Physics at RHIC, February 2005)
RHIC Spin Plan 2005, Feb. 11
Note the limited x range!
RHIC will constrain DG(x) very
significantly, but with limited
Low x behavior will remain
hep-ph/0607063: clearly says….
RHIC in future
Fixed target experiments
1989 – 1999 Data
eRHIC 250 x 10 GeV
Luminosity = ~85 inv. pb/day
10 days of eRHIC run
Assume: 70% Machine Eff.
70% Detector Eff.
Studies included statistical error & detector smearing to confirm
that asymmetries are measurable. No present or future approved
experiment will be able to make this measurement
Constrain better the shape and the first moment
DG determined from the Scaling violations of g1
SMC Published 1998: First Moment of DG(x)
1.0 +/- 1.0 (stat) +/- 0.4 (exp.syst) +/- 1.5 (low x)
-- one week eRHIC reduces statistical & low-x errors by ~3-5
-- low x (~10-4 to 10-2)--> strong coupling, functional form at low -x,
renorm. & fact. scales
Goudschmidt & Ulhenbeck (1926): Atomic fine structure & electron spin magnetic moment
Stern (1933) Proton anomalous magnetic moment 2.79 mN
Kusch(1947) Electron anomalous magnetic moment 1.00119m0
Prescott & Yale-SLAC Collaboration (1978) EW interference in polarized e-d DIS, parity non-conservation
European Muon Collaboration (1989) Spin Crisis/Puzzle
Elastic e-p scattering at SLAC (1950s) Q2 ~ 1 GeV2 (Finite size of the proton)
Inelastic e-p scattering at SLAC (1960s) Q2 > 1 GeV2 (Parton structure of the proton)
Inelastic mu-p scattering off p/d/N at CERN (1980s)Q2 > 1 GeV2 (Un-polarized EMC effect, nuclear shadowing?)
Inelastic e-p scattering at HERA/DESY (1990s) Q2 > 1 GeV2 Unexpected rise of F2 at low x, diffraction in e-p, Saturation/CGC (??)Spin & Low x Surprises…..