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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…

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Small x issues in nucleon spin structure (focus: polarized gluon distribution)

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  1. 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

  2. One of the Key Questions Polarized gluons and its distribution… • What was known before today’s premier facilities existed? • What will we know using today’s premier facilities? • What needs to be done to address the remaining questions in future? • Summary/Conclusion/Message: • Need precise data at low x • Require high CM and Q2 • As wide a range in Q2 as possible Abhay.Deshpande@Stonybrook.Edu

  3. Summary/Conclusion PRD (112002) 1998Spin Muon Collaboration’s NA47 Experiment at CERN 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! Abhay.Deshpande@Stonybrook.Edu

  4. RHIC >> gg collider @ high energy RHIC pC Polarimeters Absolute Polarimeter (H jet) BRAHMS & PP2PP PHOBOS Siberian Snakes Siberian Snakes PHENIX STAR Spin Rotators (longitudinal polarization) Spin flipper Spin Rotators (longitudinal polarization) Solenoid Partial Siberian Snake LINAC BOOSTER Helical Partial Siberian Snake AGS 200 MeV Polarimeter AGS Internal Polarimeter Rf Dipole AGS pC Polarimeters Strong AGS Snake Run6: ~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 Abhay.Deshpande@Stonybrook.Edu

  5. RHIC Spin: inclusive p0 and jet Spin2006 Abhay.Deshpande@Stonybrook.Edu

  6. DG Prospects: 2009-2012 • Left: ALL (p0) prospects by 2009 (65 pb-1 luminosity intregrated by PHENX using p0 double spin asymmetries • Right: ALL (jets) prospects by 2012 by STAR with 500 GeV in Center of Mass data (From Research Plan for Spin Physics at RHIC, February 2005) Abhay.Deshpande@Stonybrook.Edu

  7. Now in the x space… how does this look? • Spin plan: • 65 pb-1 at √s=200GeV & 70% pol • 309 pb-1 at √s=500GeV & 70% pol RHIC Spin Plan 2005, Feb. 11 Note the limited x range! RHIC will constrain DG(x) very significantly, but with limited x reach. Low x behavior will remain unconstrained Abhay.Deshpande@Stonybrook.Edu

  8. One “recent” attempt of global analysis.... • Asymmetry analysis collaboration (AAC) • Hirai, Kumano, Saito • Pre-print: hep-ph/0603213 • Recent:hep-ph/0607063 hep-ph/0607063: clearly says…. Abhay.Deshpande@Stonybrook.Edu

  9. This should not be surprising…. pQCD “questionable” pQCD works For sure RHIC now DIS now W. Vogelsang RHIC in future Abhay.Deshpande@Stonybrook.Edu

  10. eRHIC vs. Other DIS Facilities • New kinematic region • Ee = 10 GeV (~5-12 GeV variable) • Ep = 250 GeV (~50-250 GeV variable) • EA= 100 GeV • Sqrt[Sep] = 30-100 GeV • Kinematic reach of eRHIC: • X = 10-4 --> 0.7 (Q2 > 1 GeV2) • Q2 = 0 --> 104 GeV2 • Polarization of e,p and light ion beams at least ~ 70% or better • Heavy ions of ALL species at RHIC • High gluonic densities • Luminosity Goal: • L(ep) ~1033cm-2 sec-1 eRHIC DIS Abhay.Deshpande@Stonybrook.Edu

  11. Low x Proton Spin Structure 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 Abhay.Deshpande@Stonybrook.Edu

  12. An Exercise: DG from fits to eRHIC g1(x,Q2) 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 Abhay.Deshpande@Stonybrook.Edu

  13. Summary • Importance of low x, high Q2 and wide Q2 range demonstrated for polarized gluons, but there are other important measurements which also suffer due to lack of low x data • Understanding the nucleon spin depends crucially on exploring the low x spin structure • A high luminosity polarized electron proton collider is required. • Historically, low x and spin have been variables of high return in terms of major discoveries that fundamentally changed our understanding of nature. Both together in an EIC certainly show high promise….. Abhay.Deshpande@Stonybrook.Edu

  14. Stern & Gehrlach (1921) Space quantization associated with direction 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….. Abhay.Deshpande@Stonybrook.Edu

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