Small x issues in nucleon Small x issues in nucleon spin structure spin structure (focus: polarized gluon (focus: polarized gluon distribution) distribution) Abhay Deshpande Abhay Deshpande Stony Brook University Stony Brook University RIKEN BNL Research Center RIKEN BNL Research Center December 15, 16, 2006 December 15, 16, 2006 Washington DC Washington DC
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Small x issues in nucleon spin structure (focus: polarized gluon distribution)
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… - PowerPoint PPT Presentation
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Small x issues in nucleon spin Small x issues in nucleon spin structurestructure
One of the Key QuestionsOne of the Key QuestionsPolarized gluons and its distribution…Polarized gluons and its distribution…• What was known before today’s premier facilities What was known before today’s premier facilities
existed?existed?• What will we know using today’s premier facilities?What will we know using today’s premier facilities?• What needs to be done to address the remaining What needs to be done to address the remaining
questions in future?questions in future?
Summary/Conclusion/MessageSummary/Conclusion/Message::•Need precise data at Need precise data at low xlow x•Require Require high CM and Qhigh CM and Q22
•As wide a As wide a range in Qrange in Q22 as possible as possible
Summary/Conclusion PRD (112002) 1998Summary/Conclusion PRD (112002) 1998Spin Muon Collaboration’s NA47 Experiment at CERNSpin Muon Collaboration’s NA47 Experiment at CERN
From COMPASS, PHENIX and STAR…. But…..From COMPASS, PHENIX and STAR…. But…..
Similar message from E143 PRD (112003) 1998… same issue of PRD, and any other Similar message from E143 PRD (112003) 1998… same issue of PRD, and any other theory or experimental effort that was concluding at the time!theory or experimental effort that was concluding at the time!
• Left:Left: A ALLLL ( (00) prospects by 2009 (65 pb-1 luminosity ) prospects by 2009 (65 pb-1 luminosity intregrated by intregrated by PHENXPHENX using using 00 double spin asymmetries double spin asymmetries
• Right:Right: A ALL LL (jets) prospects by 2012 by (jets) prospects by 2012 by STARSTAR with 500 GeV in with 500 GeV in Center of Mass dataCenter of Mass data
(From Research Plan for Spin Physics at RHIC, February 2005)(From Research Plan for Spin Physics at RHIC, February 2005)
An Exercise:An Exercise:G from fits to eRHIC G from fits to eRHIC gg11(x,Q(x,Q22) )
Constrain better the shape and the first moment
G determined from the Scaling violations of g1
SMC Published 1998: First Moment of G(x) 1.0 +/- 1.0 (stat) +/- 0.4 (exp.syst) +/- 1.5 (low x)
-- one week eRHIC reduces statistical & low-x errors by ~3-5~3-5-- low x (~10-4 to 10-2)--> strong coupling, functional form at low -x, renorm. & fact. scales
SummarySummary• Importance of low x, high QImportance of low x, high Q22 and wide Q and wide Q22 range range
demonstrated for polarized gluons,demonstrated for polarized gluons, but there are other but there are other important measurements which also suffer due to lack important measurements which also suffer due to lack of low x dataof low x data
• Understanding the nucleon spin depends crucially on Understanding the nucleon spin depends crucially on exploring the low x spin structureexploring the low x spin structure
• A high luminosity polarized electron proton collider is A high luminosity polarized electron proton collider is required. required.
• Historically, low x and spin have been variables of high Historically, low x and spin have been variables of high return in terms of major discoveries that fundamentally return in terms of major discoveries that fundamentally changed our understanding of nature. Both together in changed our understanding of nature. Both together in an EIC certainly show high promise…..an EIC certainly show high promise…..
Spin & Low x Surprises…..Spin & Low x Surprises…..• Stern & Gehrlach (1921) Stern & Gehrlach (1921) Space Space
quantization associated with quantization associated with directiondirection
• Goudschmidt & Ulhenbeck Goudschmidt & Ulhenbeck (1926): (1926): Atomic fine structure & Atomic fine structure & electron spin magnetic electron spin magnetic momentmoment
• Stern (1933) Stern (1933) Proton anomalous Proton anomalous magnetic moment 2.79 magnetic moment 2.79 NN
• Kusch(1947) Kusch(1947) Electron Electron anomalous magnetic moment anomalous magnetic moment 1.001191.0011900
• Prescott & Yale-SLAC Prescott & Yale-SLAC Collaboration (1978) Collaboration (1978) EW EW interference in polarized e-dinterference in polarized e-d DIS, parity non-conservationDIS, parity non-conservation
• European Muon Collaboration European Muon Collaboration (1989) (1989) Spin Crisis/PuzzleSpin Crisis/Puzzle
• Elastic e-p scattering at SLAC Elastic e-p scattering at SLAC (1950s) (1950s) Q2 ~ 1 GeV2 Q2 ~ 1 GeV2 (Finite (Finite size of the proton)size of the proton)
• Inelastic e-p scattering at SLAC Inelastic e-p scattering at SLAC (1960s) (1960s) Q2 > 1 GeV2 Q2 > 1 GeV2 (Parton structure of the proton)(Parton structure of the proton)
• Inelastic mu-p scattering off Inelastic mu-p scattering off p/d/N at CERN (1980s)p/d/N at CERN (1980s) Q2 > Q2 > 1 GeV2 1 GeV2 (Un-polarized EMC (Un-polarized EMC effect, nuclear shadowing?)effect, nuclear shadowing?)
• Inelastic e-p scattering at Inelastic e-p scattering at HERA/DESY (1990s)HERA/DESY (1990s) Q2 > 1 Q2 > 1 GeV2 GeV2 Unexpected rise of F2 at Unexpected rise of F2 at low x, diffraction in e-p, low x, diffraction in e-p, Saturation/CGC (??)Saturation/CGC (??)