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The Future of Spin Physics at RHIC

The Future of Spin Physics at RHIC. Present status and plans to improve luminosity & polarization Spin performance milestones & 6-year run plan to achieve them Recent highlights and future projections from RHIC Spin eRHIC and possible staging Precision experiments with stored polarized beams.

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The Future of Spin Physics at RHIC

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  1. The Future of Spin Physics at RHIC • Present status and plans to improve luminosity & polarization • Spin performance milestones & 6-year run plan to achieve them • Recent highlights and future projections from RHIC Spin • eRHIC and possible staging • Precision experiments with stored polarized beams Steve Vigdor for Sam Aronson SPIN2008, Charlottesville October 10, 2008

  2. Nucleon Spin Structure at RHIC and an Electron-Ion Collider p-p at RHIC addresses: 1) What does the share of p spin carried by gluons and sea quarks/ antiquarks reveal about effective degrees of freedom? 2) How is parton orbital motion (on the light front) in p manifested in transverse spin asymmetries? e-N at EIC would exploit scaling viola-tions & exclusive reactions to extend study to completely gluon-dominated region at low momentum fraction.

  3. Polarized atomic H jet RHIC Polarimeters BRAHMS & PP2PP PHOBOS RIKEN/RBRC Siberian Snakes Siberian Snakes DOE/RIKEN/RBRC muon detector PHENIX STAR Spin Rotators Spin flipper Spin Rotators Solenoid Partial Siberian Snake Pol. H- Source LINAC BOOSTER Warm AGS Snake AGS 200 MeV Polarimeter AGS Internal Polarimeter Rf Dipole AGS pC Polarimeter Siberian snakes: Strong AGS Snake built into design from the start ! RHIC: World’s Only Polarized Hadron Collider No snakes  ~1000 depolarizing resonances With snakes  no first order resonances Two partial AGS snakes (11 and 27 spin rotators)

  4. Absolute beam polarization calibration to better than 5% design goal achieved! Polarized Collision Performance at RHIC P L(pb^-1) Results 2002 15% 0.15 first pol. pp collisions! 200330% 1.6 pi^0, photon cross section, A_LL(pi^0) 2004 40% 3.0 absolute beam polarization with polarized H jet 2005 50% 13 large gluon pol. ruled out (P^4 x L = 0.8) 2006 60% 46 first long spin run * (P^4 x L = 6) 2007 no spin running 200850% (short) run * support for 2006 run from Renaissance Tech. crucial for program 2006, P=60% Delivered luminosity at s = 200 GeV 2008, P=45% 2005, P=46% 2003, P=34% Further development ( long runs!) needed to reach “enhanced” design goals: P=70%, L = 6  1031 cm2s1 (or  15 pb1/week) at s = 200 GeV

  5. Polarized proton acceleration to 250 GeV demon-strated. First collision run anticipated 2009. 45 % polarization on first acceleration to 250 GeV! Loss at strong intrinsic resonance (136 GeV); correctable by adjusting betatron tunes. injection 250 GeV

  6. RHIC Spin Luminosity and Polarization Goals • Planned luminosity improvements: • reduce * from 1.0 to 0.5 m • mitigate 10 Hz quad triplet vibration • near-integer working point • non-linear chromaticity correction • transfer line and booster mods. • 9 MHz and 56 MHz RF upgrades • Planned polarization improvements: • horizontal tune jumps in AGS • improved orbit control in RHIC snakes ** without vertex cuts

  7. Further p Beam Improvements Under Development: Electron Lenses • p-p luminosity limited by head-on beam-beam tune spread • Low energy (~5 keV) e beam interacting with proton beam can compensate head-on beam-beam tune spread ( 2 luminosity?) • Single and multi-particle simulation underway • Possible implementation in RHIC by 2014 w/o beam-beam compensation with half and full beam-beam compensation Large tune spread  luminosity loss See T. Roser talk, 10/11/08.

  8. Kicker: attraction to e-beam density peak re-duces ion-beam E spread. Wiggler: FEL amplification (x 102-3) of e-beam modulations, while chicane adds dispersion to h beam Modulator: hadron beam structure intro-duces density modu-lation in e-beam Uses 20 MeV R&D ERL already under develop-ment at BNL Further p Beam Improvements Under Development: Coherent Electron Cooling CeC of high-energy hadron beams: high-gain FEL based on high-brightness ERL (V. Litvinenko & Y. Derbenev)  boost LHC and EIC luminosities? Plan proof-of-principle test @ RHIC by 2014 with Au beam. Does not address beam-beam limit on RHIC p+p luminosity.

  9. Characterize high-momentum components induced by correlations in the few-body nuclear wave functions via (e,e'N) and (e,e'NN) knock-out processes in nuclei and compare free proton and bound proton properties via measurement of polarization transfer in the Near-Term RHIC Spin Program Addresses Three Specific DOE Hadron Physics Performance Milestones A few brief comments on the physics goals to follow…

  10. Tentative RHIC Run Plan Following 2008 PAC Recommendations (assumes 6-month FY09 CR, 2-species runs in FY10-14 & best info on detector upgrade schedules)

  11. w/ Run 6 RHIC data w/ projected Run 9 RHIC data Present and Future Constraints on Gluon Polarization in the Proton: • 1st NLO pQCD analysis incorporating RHIC spin inclusive jet and 0 ALL (2006) data (arXiv:0804.0422) by de Florian, Sassot, Stratmann & Vogelsang • DIS and RHIC spin impose comparable constraints to date on shape & magnitude of gluon polarization vs. x; RHIC spin data should dominate after next long 200 GeV p+p run, with new jet+jet coincidence data significantly constraining x-dependence.

  12. Future Constraints on Sea Anti-quark Polarization W + + X (u+d  W + e + or  + ) W + X (d+u  W  e  or   )  s = 500 GeV p + p  Measure 1-spin PV helicity asymmetry AL for 2 beams  2 charge states  u/u, d/d in valence region ( “self-calibration” of technique)  d/d, u/u for x ~ 0.02 - 0.2  check prediction of many nucleon structure models that |u  d |> |d  u | (sizable from FNAL E866) 0.8 STAR projections for mid-rapidity e+ from W+ STAR projec-tions for mid-rapidity e from W AL 0.2 0.6 AL 0 0.4 0.2 0.2 0.4 0 300 pb1, P=0.7, 70% efficiency 0.6 0.2 0.8 20 30 40 50 20 30 40 50 Lepton ET (GeV) Anticipate: 1st 500 GeV collision run in 2009 ~100 pb1 by 2012 ~300 pb1 by 2013 Similar sensitivity for PHENIX Program relies on ongoing upgrades to PHENIX  trigger, STAR forward tracking

  13. Constraining Origin of Transverse Spin Asymmetries: • Large AN observed for pp  forward hadron inclusive can arise from entrance- (Sivers) or exit-channel (Collins jet fragmentation) transverse spin-momentum correlations. • Sivers asyms. sensitive to quark and gluon orbital ang. mom. on light front  same frame where G,  measured  frame for Ji sum rule • ANSivers(SIDIS, FSI among outgoing partons) =  ANSivers(DY, ISI) prediction sensitive to all aspects of pQCD treatment HERMES Sivers Results RHIC II Drell-Yan Projections Test predicted sign change first in inclusive p+p  +X  in time for 2015 DOE milestone. 0 0 0.1 0.2 0.3 x

  14. Add ERL injector with polarized e source to enable e+p,3He and e+A (up to Uranium) to study matter in gluon-dominated regime e-ion detector Possible locations for additional e-ion detectors • 10 GeV electron design energy.Possible upgrade to 20 GeV by doubling main linac length. • 5 recirculation passes ( 4 in RHIC tunnel) • Multiple electron-hadron interaction points (IPs) permit multiple detectors; • Full polarization transparency at all energies for the electron beam; • Ability to take full advantage of transverse cooling of the hadron beams; • Possible options to include polarized positrons at lower luminosity: compact storage ring or ILC-type e+ source • R&D already under way on various accelerator issues; more to come. eRHIC PHENIX Four recirculation passes Main ERL (1.9 GeV) STAR Beam dump • Subsequent stages/ alternative layouts could increase e-beam & ion-beam energies and L from nominal 10  250 GeV, ~3  1033 cm2s1 e+p Low energy recirculation pass Electron source Long-Term (>2020) Future of Spin Physics at RHIC: EIC  eRHIC

  15. EIC Science: Study of Force (Gluon)-Dominated Matter Gluons dominate the soft constituents of hadrons! But density must saturate… Search for supersymmetry @ LHC, ILC (?): seeking to unify matter and forces Electron-Ion Collider: reveal that Nature blurs the distinction Deep inelastic scattering @ HERA  EIC probes weak coupling regime of very high gluon density, where gauge boson occupancy >> 1. All ordinary matter has at its heart an intense, semi-classical force field -- can we demonstrate its universal behavior? See R. Milner talk, 10/6/08

  16. Polarized e + N at EIC • Polarized DIS,  -gluon fusion to determine gluon polarization down to x ~ few  104 • Bjorken sum rule test to ≲ 2% precision • SIDIS for low-x sea-quark polarization and transverse spin studies More luminosity-hungry: • Polarized DVCS, exclusive reactions + LQCD  GPD’s  map low-x transverse position-dep. PDF’s; Jq from Ji sum rule • Parity violation in e+p,d at high Q2 to study running of weak coupling below Z-pole See R. Milner talk, 10/6/08; Note INT workshops on EIC science, Fall ’09 and ’10.

  17. Stage I e-RHICwith ERL inside RHIC tunnel @ IP2: up to 2 (4) GeV e with RT (SC) magnets 2 x (0.5-0.7) GeV SRF linacs IP 2-4 passes, depending on top energy 100 MeV injector • Would enable few GeV e on 100 GeV/N heavy ions and 250 GeV p • First look at saturation surface for nuclei in e+A DIS, confirmation of nuclear “oomph” factor; e+A diffraction tests of high gluon occupancy • e-p program emphasizing transverse-spin SIDIS over broad Q2-range  TMD evolution; detection of boosted target fragments to probe spin-dependent correlations, intrinsic heavy flavor in nucleon; extend DIS. • Need todevelop science case, detector design, cost estimate. • Most equipment would be reused later in full EIC Intermediate-Term Possibilities: 1st (Medium Energy) Stage of EIC?

  18. ME-EIC parameters for e-p collisions (2 GeV option, 50 mA polarized e source, maintaining pp, pA, AA collisions at RHIC detectors) Also a test-bed for high-energy coherent e-cooling to prepare for full EIC.

  19.  g-2 ring @ AGS Physics Beyond the Standard Model: Supersymmetry SUSY working group report: Les Houches 2007 (Feb 08 archive) “The strongest hint for a TeV-scale modifica- tion of the Standard Model originates from the anomalous magnetic moment of the muon.” Possible Alternative Intermediate-Term Future: Precision Experiments in Storage Rings History: muon anomalous magnetic moment @ AGS See W. Marciano’s talk, 10/7/08

  20. Novel Storage Ring EDM Exp’ts @ AGS ? • Inject longitudinally pol’d p or d beam, via AGS, into dedicated storage ring • Choose magic momentum + static E, B combination (B=0 for protons) to ~cancel (g-2) horizontal spin precession • Search for EDM signature of vertical polarization build-up due to precession in strong E-field (static for p, v B for d) • Cancel many systematic errors by measuring for counter-rotating (vertically separated) beams simultaneously. • Sensitivity goal ~ few  1029 ecm for p, ~ 1029 ecm for d • If EDM  0 observed for n, p and/or d, the combination powerfully constrains the source. E.g., the three systems have quite different sensitivities to QCD vs. SUSY (latter strongly enhanced in d). See Y. Semertzidis talk, 10/07/08.

  21. Summary • Strong progress in recent years on luminosity and polarization for p+p collisions at RHIC, clear plans for reaching ‘enhanced’ design specs over next few years. • Despite budget-induced shortening of recent runs, RHIC spin data already important in constraining G(x) and origin of transverse spin asymmetries. • Next ~5 years should produce dramatic progress toward 3 milestones in nucleon spin structure, including 500 GeV W production for antiquark polarization. • Innovative electron lens and coherent e-cooling R&D plans can have great impact on future p+p and e+p luminosities. • eRHIC linac-ring concept, with possible 1st “medium-energy” stage  viable strategy toward spin physics at very low x. Much R&D and strengthening of science case needed before next U.S. Nuclear Physics Long Range Plan (~2012-13). • Charged-particle EDM searches in storage rings  intriguing possibility for complementary beyond-SM spin physics.

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