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In Quest of Nucleon Spin Vernon W. Hughes The Last Decade: 1993-2003

In Quest of Nucleon Spin Vernon W. Hughes The Last Decade: 1993-2003. Abhay Deshpande RIKEN-BNL Research Center SYMMETRIES & SPIN PRAGUE, JULY 2003. Parton Distributions. (well known). Nucleon. (moderately well known). (unknown). (moderately well known). (unknown).

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In Quest of Nucleon Spin Vernon W. Hughes The Last Decade: 1993-2003

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  1. In Quest of Nucleon SpinVernon W. HughesThe Last Decade: 1993-2003 Abhay Deshpande RIKEN-BNL Research Center SYMMETRIES & SPIN PRAGUE, JULY 2003

  2. Parton Distributions (well known) Nucleon (moderately well known) (unknown) (moderately well known) (unknown)

  3. 1993: Background and times…. • Late 50s and early 60s V.W.Hughes develops polarized electron • source at Yale : Why?… I once asked… • “… it seemed it would provide an interesting tool for atomic and high energy physics experiments…” • 1966 Bjorken Sum Rule (published) • “… of little consequence since no measurement techniques • are presently or foreseen in future…” – J.D. Bjorken • 1969 Proton substructure presented by Panofsky at Vienna • V.W.Hugheset al. try to develop polarized nuclear targets • - Collaboration with J. Kuti to calculate spin effects in nucleons • – effort abandoned after observation that they may be • small in nuclei • 1974 Ellis-Jaffe Spin Rule • 1980s V.W.Hughes leaves SLAC to join EMC @ CERN • -- SLAC decides to emphasize Linear Collider Development • SLAC Experiments: Talk by E. Hughes in this meeting • 1989 EMC Spin Puzzle/Crisis • E142/143 Proposed at SLAC, SMC Proposed at CERN

  4. First moments & Spin Sum Rules

  5. NA47 Experiment at CERNSpin Muon Collaboration (SMC) Polarized m-N inclusive & semi-inclusive scattering Polarized muon beam, polarized twin target setup, spectrometer • Polarized m beam from weak decays of p: • Shape of Michel Spectrum of positron from • m decays in flight • m e  m e scattering • Pbeam~ 0.79 +/- 0.03 • Polarized Target: • 2.5 T longitudinal field • 0.5 T transverse field •  Polarization reversal every • 5hrs • Dynamic Nuclear Polarization • Polarization measurement with ~10 • coils embedded in the target volume

  6. SMC Spectrometer

  7. A1 Q2 dependent?

  8. Global NLO pQCD fit*: SMC, B. Adeva et al. Phys. Rev. D 112002 (1998) *Based on: Ball et al. Phy. Lett. B378 255 (1996)

  9. SMC, B. Adeva et al. Phys. Rev. D 112002 (1998) Nucleon Spin: Status & Open Questions • 1/2=(1/2)DS+DG+Lq+Lg 1/2=(1/2)DS+DG+Lq+Lg Extensive uncertainty studies Quark Spin Contribution: Gluon Spin Contribution: Proton Spin Puzzle remains unsolved! constrained, need to measure

  10. Low x behavior of g1(p)! Clear need for low x measurements!

  11. SMC, PRD58, 112001 &112002, 1998

  12. E154 Neutron SMC Neutron

  13. Bjorken Sum Rule

  14. Kinematic Coverage from Fixed Target Experiments HERMES

  15. Some spin surprises… • 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 • E704, AGS pp scattering, HERMES (1990s) Transverse spin asymmetries (??) • RHIC Spin (2001) Transverse spin asymmetries (??)

  16. Some Low x Surprises • 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  Unpolarized 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(??)

  17. Our knowledge of structure functions g1 F2 105 10 103 10 1 102 Q2 (GeV2) Q2 (GeV2)

  18. Extended Kinematic Coverage Of HERA Accelerator Issues: Polarized Beams in HERA non-trivial Studies initiated with VWH’s efforts

  19. AT DESY: A strong physics motivation to go to low x and high Q2 with spin variables was developed HERA Existed….. Polarized electrons existed…. Accelerator Physicists working on e and p beams existed… H1 and ZEUS detector existed along with collaborators… HERMES polarized DIS community existed… “Polarized Proton Beam” was the ONLY missing item…! A linear collider seems to comes in again (!) for V.W.Hughes…

  20. BRAHMS & PP2PP (p) PHENIX (p) STAR (p) RHIC Accelerator Complex RHIC pC Polarimeters Absolute Polarimeter (H jet) Siberian Snakes Spin Rotators 2  1011 Pol. Protons / Bunch e = 20 p mm mrad Partial Siberian Snake LINAC BOOSTER Pol. Proton Source 500 mA, 300 ms AGS AGS Internal Polarimeter 200 MeV Polarimeter Rf Dipoles RHIC accelerates heavy ions to 100 GeV/A and polarized protons to 250 GeV

  21. RHIC PHENIX STAR LINAC AGS Siberian Snakes Depolarizing Resonance: Spin tune = no. of spin kicks Imperfection resonances: --magnet errors & misalignements Intrinsic resonances: --vertical focusing fields Effect of depolarizing resonances averaged out by rotating spin by large angles on each turn RIKEN/BNL 4 helical dipoles  S. snake 2 snakes in each ring -- axes orthogonal to each other April 2nd, 2003 Quest for Nucleon Spin: Past, Present & Future

  22. Carbon filament target (5mg/cm2)in the RHIC beam Measure recoil carbon ions at q~90º 100 keV < Ecarbon< 1 MeV up Si #6 Arrival time (ns) Si #1 Carbon left right Si #5 Si #2 Wave-Form Digitizer +FPGA high counting rates (~0.5 MHz) scaler measurement  dA ~ 310-4 in ~1 minute. Si #3 Si #4 down ADC values Beam’s View E950 Experiment at AGS (1999)  RHIC Polarimetry Now RHIC Polarimetry ANL, BNL, Kyoto, RIKEN/RBRC & YaleCollaboration

  23. Blue Ring, Run 1 (2000-2001) Successful Operation of the Snake • Injection with Spin Flipped:Asymmetry Flipped • Adiabatically Snake on:Horizontal polarization • Accelerate equivalent to 180o rotation:180o rotated Successful Single Snake Operation !

  24. Polarization in Run 2 (2001-2002) First polarized collisions ever at Sqrt(s)=200 GeV Yellow Ring Blue Ring

  25. Machine Performance Expectations

  26. RHIC spin program Production W Production Heavy Flavors STAR +PHENIX STAR + PHENIX STAR +PHENIX Direct Photon BRAHMS, STAR, PHENIX, Local Polarimeter Jet Photon

  27. Deep Inelastic Scattering • Observe scattered electron/muon & hadrons in current jets • Observe spectator or remnant jet

  28. Why Collider in the Future? • Past polarized DIS experiments: FIXED TARGET • Collider has distinct advantages • Better angular separation between scattered lepton & nuclear fragments  Better resolution of electromagnetic probe  Recognition of rapidity gap events (recent diffractive physics) • Better measurement of nuclear fragments • Higher center of mass (CoM) energies reachable • Tricky integration of beam pipe – interaction region -- detector

  29. eRHIC vs. other DIS Facilities (I) • New kinematic region • Ee = 5-10 GeV • Ep = 30 – 250 GeV • Sqrt(s) = 20 – 100 GeV • Kinematic reach of eRHIC x = 10-4 0.6 Q2 = 0  104 GeV • High Luminosity L ~1033 cm-2 sec-1 eRHIC

  30. eRHIC vs. Other DIS Facilities (II) Variable beam energy Variable hadron species Hadron beam polarization Large luminosity TESLA-N eRHIC

  31. Scientific Frontiers Open to eRHIC • Nucleon Structure: polarized & unpolarized e-p/n scattering -- Role of quarks and gluons in the nucleon -- Spin structure: polarized quark & gluon distributions -- Unpolarized quark & gluon distributions -- Correlation between partons  hard exclusive processes leading to Generalized Parton Distributions (GPD’s) • Nuclear structure: unpolarized e-A scattering -- Role of quarks and gluons in nuclei -- e-p vs. e-A physics in comparison • Hadronization in nucleons and nuclei & effect of nuclear media -- How do partons knocked out of nucleon in DIS evolve in to colorless hadrons? • Partonic matter under extreme conditions -- e-A vs. e-p scattering; study as a function of A

  32. http://www.bnl.gov/eic Polarized DIS at eRHIC • Spin structure functions g1 (p,n) at low x, high precision -- g1(p-n): Bjorken Spin sum rule better than 1% accuracy • Polarized gluon distribution function DG(x,Q2) -- at least three different experimental methods • Precision measurement of aS(Q2) from g1 scaling violations • Polarized structure function of the photon from photo-production • Electroweak structure function g5 via W+/- production • Flavor separation of PDFs through semi-inclusive DIS • Deeply Virtual Compton Scattering (DVCS)  Gerneralized Parton Distributions (GPDs) • Transversity • Drell-Hern-Gerasimov spin sum rule test at high n • Target/Current fragmentation studies • … etc….

  33. A. Deshpande & V. W. Hughes EIC WS at Yale ‘00 Spin structure function g1 at low x At HERA At EIC/eRHIC ~5-7 days of data 3 years of data 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

  34. A. Deshpande & V. W. Hughes EIC WS at Yale ‘00 Low x measurement of g1 of Neutron • With polarized He3 or deuteron • ~ 2 weeks of data at eRHIC vs. ~ 3 yrs of HERA data • Compared with SMC(past) & possible HERA data • If combined with g1 of proton results in Bjorken sum rule test of better than 1% within a couple of months of running (G.Igo & T. Sloan, AD & V. Hughes) eRHIC 1 fb-1

  35. Polarized Gluon Measurement at eRHIC • This is the hottest of the experimental measurements being pursued at various experimental facilities: -- HERMES/DESY, COMPASS/CERN, RHIC-Spin/BNL & E159/E160 at SLAC • Large kinematic range of eRHIC allows measurements using: -- Scaling violations (pQCD analysis at NLO) of g1 -- (2+1) jet production in photon-gluon-fusion (PGF) process -- 2-high pT hadro production in PGF • Photo-production (real photon) kinematics at eRHIC -- Single and di-jet production in PGF -- Open charm production in PGF

  36. Photon Gluon Fusion at eRHIC • “Direct” determination of DG -- Di-Jet events -- High pT leading hadrons • High Sqrt(s) at eRHIC -- no theoretical ambiguities • Both methods tried at HERA for un-polarized gluon determination & both are successful! -- NLO calculations exist -- H1 and ZEUS published results -- Consistent with G determined from scaling violation F2 Signal: PGF Background QCD Compton

  37. A. Deshpande, V. W. Hughes & J. Lichtenstadt EIC WS @ Yale’00 DG from Scaling Violations of g1 • World data (today) allows a NLO pQCD fit to the scaling violations in g1 resulting in the polarized gluon distribution and its first moment. • SM collaboration, B. Adeva et al. PRD (1998) 112002 DG = 1.0 +/- 1.0 (stat) +/- 0.4 (exp. Syst.) +/- 1.4 (theory) • Theory uncertainty dominated by the lack of knowledge of the shape of the PDFs in unmeasured low x region where EIC data will play a crucial role. • With approx. 1 week of EIC data, statistical and theoretical uncertainties on DG will be reduced by a factor of 3-5 -- coupled to better low x knowledge of spin structure -- less freedom for fits to depend on factorization & re-normalization scale uncertainty

  38. A. De Roeck, A. Deshpande, V. W. Hughes & J. Lichtenstadt,G. Radel EIC WS, Yale’00 Di-Jet events at eRHIC: Analysis at NLO • Stat. Accuracy for two luminosities • Detector smearing effects considered • NLO analysis • Easy to differentiate different DG scenarios: factor 3 improvements • in ~2 weeks of data • If combined with scaling violations of g1: factors of 5 improvements • in uncertainties observed in the same time. • Better than 3-5% uncertainty on DG can be expected from eRHIC

  39. G. Radel & A. De Roeck Di-Jet at eRHIC vs. World Data for DG/G eRHIC Di-Jet DATA 2fb-1 Good precision Clean measurement in x range 0.01< x < 0.3 Constrains shape of DG(x) Polarization in HERA much more difficult than RHIC.

  40. Moving Towards eRHIC…. • September 2001: eRHIC grew out of joining of two communities: 1) polarized eRHIC (ep and eA at RHIC) BNL, UCLA, YALE and people from DESY & CERN 2) Electron Poliarized Ion Collider (EPIC) 3-5 GeV e X 30-50 GeV polarized light ions Colorado, IUCF, MIT/Bates, HERMES collaborators • February 2002: White paper submitted to NSAC Long Range Planning Review  Received enthusiastic support as a next R&D project (see: US/DoE Nuclear Report on the Web) • Steering Committee: 7 members, one each from BNL, IUCF, LANL, LBL, MIT, UIUC, Yale + Contact person (Abhay Deshpande) • February 2003: NSAC Subcommittee Recommendation! • ~20 (~13 US + ~7 non-US) Institutes, ~100 physicists + ~40 accelerator physicists • See for more details: EIC Web-page at “http://www.bnl.gov/eic” (under construction) • Subgroups: Accelerator WG, Physics WG, Detector WG

  41. 2GeV (10 GeV) e 2-10 GeV IP12 p IP10 IP2 RHIC IP8 IP4 IP6 Present Collider Layout • Proposed by BINP & MIT/Bates presently being studied at BNL • E-ring is ¼ of RHIC ring • Collisions in ONE interaction region • Collision energies 5-10 GeV • Injection linac 2-5 GeV • Lattice based on “superbend” magnets • Self polarization using Sokolov Ternov Effect: (14-16 min pol. Time) • IP12, IP2 and IP4 are possible candidates for collision points OTHER DESIGNS:Ring with 6 IPS, Linac-Ring, Linac-Re-circulating ring

  42. A Detector for eRHIC A 4p Detector • Scattered electrons to measure kinematics of DIS • Scattered electrons at small (~zero degrees) to tag photo production • Central hadronic final state for kinematics, jet measurements, quark flavor tagging, fragmentation studies, particle ID • Central hard photon and particle/vector detection (DVCS) • ~Zero angle photon measurement to control radiative corrections and in e-A physics to tag nuclear de-excitations • Missing ET for neutrino final states (W decays) • Forward tagging for 1) nuclear fragments, 2) diffractive physics • The e-ring & the IR design  Detector Design

  43. A time line for eRHIC… “Predictions are very difficult to make, especially when they are about the future” --- A very wise man…. • Accelerator R&D started 2003 as part of “RHIC II and eRHIC” • ZDR Requested by January 2004 for machine design • Proposal/CDR0 by 2005 • Expected formal approval 2005-6 Long Range Review • Detector R&D money could start 2007 • Construction of IR and Detector begin 2009/10 • 3-5 years for staged detector and IR construction without interfering with the RHIC running • First collisions??? If any one knows how to do this earlier… -- I am listening.

  44. 1997-2003 Polarimetry for proton beams at RHIC 1990-1998 Spin Muon Collaboration at CERN Spokesperson Polarized target Analysis… + (g-2) of m at BNL + muonium exp. LANL + Lambshift of Hydrogen + …. 1995-2003 Polarized HERA Development on physics case/motivation Polarized proton beam development at HERA Development of high energy proton beam polarimetry 2000-2003 eRHIC at BNL Steering Committee Workshop on eRHIC physics motivation

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