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Quest for Nucleon Spin: Past, Present & Future

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Quest for Nucleon Spin: Past, Present & Future

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  1. Quest for Nucleon Spin: Past, Present & Future Abhay Deshpande RIKEN BNL Research Center Stony Brook University April 2nd, 2003 RIKEN BNL Research Center

  2. Overview NUCLEON SPIN (Quick review of the Past) • Present status and open questions RHIC SPIN (Present) • Relativistic Heavy Ion Collider at BNL • Status of RHIC as polarized proton collider • Recent results with polarized protons at RHIC • Long term perspective for RHIC Spin (pp) Electron Ion Collider (EIC) at RHIC(Future) • Electron ring at RHIC • Physics at the EIC (mostly pol. e-p and some e-A) • Status & Plans April 2nd, 2003 Quest for Nucleon Spin: Past, Present & Future

  3. Parton Distributions (well known) Nucleon (moderately well known) (unknown) (moderately well known) (unknown) April 2nd, 2003 Quest for Nucleon Spin: Past, Present & Future

  4. Our knowledge of spin structure function g1 F2 105 10 103 10 1 102 Q2 (GeV2) Q2 (GeV2) April 2nd, 2003 Quest for Nucleon Spin: Past, Present & Future

  5. Global NLO pQCD fit: SMC, B. Adeva et al. Phys. Rev. D 112002 (1998)

  6. 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 April 2nd, 2003 Quest for Nucleon Spin: Past, Present & Future

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

  8. Semi-inclusive DIS… • In addition to the scattered electron, one measures in addition, the hadronic final state(s) • Access to flavor separated parton distributions • HERMES has the most significant data on these April 2nd, 2003 Quest for Nucleon Spin: Past, Present & Future

  9. 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 April 2nd, 2003 Quest for Nucleon Spin: Past, Present & Future

  10. 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 & Yale Collaboration April 2nd, 2003 Quest for Nucleon Spin: Past, Present & Future

  11. 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

  12. 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 ! April 2nd, 2003 Quest for Nucleon Spin: Past, Present & Future

  13. Polarization in Run 2 (2001-2002) First polarized collisions ever at Sqrt(s)=200 GeV Yellow Ring Blue Ring April 2nd, 2003 Quest for Nucleon Spin: Past, Present & Future

  14. PRHIC 10% 20% 30% PAGS Why low polarization? Source Improvement New AGS SNAKE 2004-5 Ramp up Spead Injection 1st Year AGS power generator failure ½ ramp up speed 2x resonance effect Hot News: 20th March 2003: ~42% and growing April 2nd, 2003 Quest for Nucleon Spin: Past, Present & Future

  15. Machine Performance Expectations April 2nd, 2003 Quest for Nucleon Spin: Past, Present & Future

  16. RHIC spin program Production W Production Heavy Flavors STAR +PHENIX STAR + PHENIX STAR +PHENIX Direct Photon BRAHMS, STAR, PHENIX, Local Polarimeter Jet Photon April 2nd, 2003 Quest for Nucleon Spin: Past, Present & Future

  17. PHENIX Detector Run 2 Electrons & photons ( |h| < 0.35) Charged tracks (Beam-Beam, Drift Chamber, Pad Chambers) + RICH rings + EM Calorimeter clusters Muons (1.2 < h < 2.2) Muon Identifier + Muon Tracker April 2nd, 2003 Quest for Nucleon Spin: Past, Present & Future

  18. PHENIX Preliminary Normalization error of 30% not shown. On the way to DG… p0 spectrum PHENIX p0 cross section (Preliminary) From RHIC Run 2 (2001-2002) PT spectrum over 8 orders of magnitude Comparison with NLO pQCD calculation --CTEQ5M PDFs --Potter, Knielh, Kramer (PKK) fragmentation functions --Uncertainty shown: m= pT/2, 2pT Consistent with data within scale dependence April 2nd, 2003 Quest for Nucleon Spin: Past, Present & Future

  19. PHENIX Preliminary Rapidity distribution compared with PHITHIA simulation Total Cross section vs. the Color-Evaporation Model prediction e+e- µ+µ- Br(J/l+l-) (total) = 226  36 (stat.)  79 (syst.) nb  (p+pJ/X) = 3.8  0.6 (stat.)  1.3 (syst.) µb • CEM Parameters are fixed by fitting low energy data • The result agrees with the CEM prediction at s=200GeV April 2nd, 2003 Quest for Nucleon Spin: Past, Present & Future

  20. STAR Performance • Time Projection Chamber worked beautifully! Au-Au Collision at STAR April 2nd, 2003 Quest for Nucleon Spin: Past, Present & Future

  21. Single spin asymmetries: L-R Essential for proton spin orientation information at IPs E704 at Fermilab at s=20 GeV, pT=0.5-2.0 GeV/c: PT XF 0.2 0.4 0.6 0.8 STAR TPC PHENIX MUON PHENIX CENTRAL STAR FPD BBC pp2pp 0o CAL 0 1 2 3 4 5 Rapidity Possible Origins: Transversity, Higher Twist, Fragmentation, kT, Orbital. Etc. April 2nd, 2003 Quest for Nucleon Spin: Past, Present & Future

  22. Neutron Veto EM Cal Base Charge Veto PbWO4 Hadron Cal Base Scintillator Post-shower Pb W+Fiber Cal RIKEN-BNL Research Center + Kyoto + PHENIX 12 o’clock  PHENIX test setup p0 April 2nd, 2003 Quest for Nucleon Spin: Past, Present & Future

  23. EMCal ZDC Asymmetries EMCal EMCal April 2nd, 2003 Quest for Nucleon Spin: Past, Present & Future

  24. STAR Forward rapidity high xFp0 AN AN Theory predictions at pT = 1.5 GeV/c Anselmino, et al. PRD 60 (1999) 054027. Anselmino, et al. Phys. Lett. B442 (1998) 470. Twist 3 effectQiu and Sterman, Phys. Rev. D59 (1998) 014004. Y.Koike PaNic02 0.4 STAR FPD Preliminary Data Assuming AN(CNI)= 0.013 pT=1.1 - 2.5 GeV/c 0.2 0.0 Systematic uncertainty +- 0.05 0 0.2 0.4 0.6 0.8 1.0 -0.2 xF ~E / 100 GeV April 2nd, 2003 Quest for Nucleon Spin: Past, Present & Future

  25. Asymmetries seen at RHIC so far… … will be used to tune the spin rotators in Run 3! PT XF 0.2 0.4 0.6 0.8 p0 +10 ~ +20% STAR TPC PHENIX MUON PHENIX CENTRAL STAR FPD BBC pp2pp Neutron -10% g ~0 % p0 ~0% 0o CAL 0 1 2 3 4 5 Rapidity Charged +1% April 2nd, 2003 Quest for Nucleon Spin: Past, Present & Future

  26. Upcoming Run FY03 3 pb-1 and 50% Expectation DG will be probed PHENIX Charged STAR JET April 2nd, 2003 Quest for Nucleon Spin: Past, Present & Future

  27. RHIC vs. DIS Kinematic Coverage prompt photon April 2nd, 2003 Quest for Nucleon Spin: Past, Present & Future

  28. W Production in Polarized pp Collisions Single Spin Asymmetry • Backgrounds from decays of other • hadrons produced in pp scattering • constitutes the main background. • Different energies of muons • Different event topologies Improvements in muon trigger under Study factor of 50 seems possible and sufficient W Z April 2nd, 2003 Quest for Nucleon Spin: Past, Present & Future

  29. Flavor Decomposition • Statistical errors for 800 pb-1 • Flavor decomposition will reduce the uncertainty in current pol-PDF models. • GS95LO(A): Gehrmann and Stering • (Z.Phys.C65(1995)461) • BS: pol-PDF set by Bourrely and Soffer • (PLB314(1993)132) April 2nd, 2003 Quest for Nucleon Spin: Past, Present & Future

  30. RHIC Spin Luminosity Collider Accelerator Department’s Projections (early ’02) Year CM Energy Weeks Int. Lum. Remarks FY2002 200 GeV 5 5 pb-1(1/15) Single spin asymmetries and Commissioning FY2003 200 GeV 8(3) 9 pb-1 Gluon pol. with p0s & jets(?) 500 GeV ?? Machine Studies, identify Ws. FY2004 200 GeV 8 160 pb-1 Gluon pol. with g + jet/ TT 500 GeV 2 120 pb-1 First ubar,dbar pol. meas.. FY2005 500 GeV 8 480 pb-1 Gluon pol. with g+jet, g,jet+jet, heavy flavor, ubar, dbar pol. 200 GeV 2 48 pb-1 Gluon pol. with g, g+jet, heavy flavor/TT FY2006 500 GeV 5 300 pb-1 More statistics 200 GeV 5(?) 120 pb-1 FY2007 (?) GeV 10 ?? More statistics April 2nd, 2003 Quest for Nucleon Spin: Past, Present & Future

  31. Global Analysis for nucleon Spin Structure Functions: In near future we will have data from: -- Fixed target polarized DIS experiments (l-p scattering)  NLO pQCD analysis exists (SMC, SLAC Exp.s & theoretical groups)  Constrain polarized quark distributions well, polarized gluons largely unconstrained. ( See detailed analysis: SMC, PRD 112002 (1998))  Adding eRHIC/EIC data is trivial and possible -- RHIC Spin data on various polarized pp interactions  Additional constraints on polarized gluon distributions -- Should use all available data to get the best possible constraints on all polarized parton distributions. -- Something like CTEQ/GRSV groups but for a global data set to understand polarized parton distributions -- A. D., W. Vogelsang & M. Stratmann towards a “Global Analysis” See tremendous opportunity for a completely new venture. Will develop this summer with many others joining us. April 2nd, 2003 Quest for Nucleon Spin: Past, Present & Future

  32. Summary & Outlook • RHIC spin program has begun very successfully! -- Polarized protons were injected, accelerated, stored -- CNI polarimeters have measured non zero asymmetries indicating polarization at 100 GeV proton beam energies -- Detectors operating - will be 100% completed in 2003-5 -- Single spin asymmetries (1% to 20%) have been measured • Next run (Apr.03) promises: a first glimpse of DG and -- First trials of 500 GeV CM collisions and W’s produced • A ~5 year run plan exists for the RHIC spin physics -- to explore DG, transversity, Dq & Dqbar -- and also perhaps physics beyond SM(?) April 2nd, 2003 Quest for Nucleon Spin: Past, Present & Future

  33. The Electron Ion Collider A high energy, high intensity polarized electron beam facility at BNL to collide with the existing RHIC heavy ion and polarized proton beam would significantly enhance RHIC’s ability to probe fundamental and universal aspects of QCD April 2nd, 2003 Quest for Nucleon Spin: Past, Present & Future

  34. Deep Inelastic Scattering • Observe scattered electron/muon & hadrons in current jets • Observe spectator or remnant jet April 2nd, 2003 Quest for Nucleon Spin: Past, Present & Future

  35. 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 April 2nd, 2003 Quest for Nucleon Spin: Past, Present & Future

  36. EIC vs. DIS Facilities (I) • New kinematic region • Ee = 5-10 GeV • Ep = 30 – 250 GeV • Sqrt(s) = 20 – 100 GeV • Kinematic reach of EIC x = 10-4 0.6 Q2 = 0  104 GeV • High Luminosity L ~1033 cm-2 sec-1 April 2nd, 2003 Quest for Nucleon Spin: Past, Present & Future

  37. EIC vs. Other DIS Facilities (II) Variable beam energy Variable hadron species Hadron beam polarization Large luminosity TESLA-N April 2nd, 2003 Quest for Nucleon Spin: Past, Present & Future

  38. Scientific Frontiers Open to EIC • 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 April 2nd, 2003 Quest for Nucleon Spin: Past, Present & Future

  39. http://www.bnl.gov/eic Unpolarized DIS e-p at EIC • Large(r) kinematic region already covered at HERA but additional studies at EIC are possible & desirable • Uniqueness of EIC: high luminosity, variable Sqrt(s), He3 beam, improved detector & interaction region • Will enable precision physics: -- He3 beams  neutron structure  d/u as x0, dbar(x)-ubar(x) -- precision measurement of aS(Q2) -- flavor separation (charm and strangeness) -- precision gluon distribution in x=0.001 to x=0.6 -- slopes in dF2/dlnQ2 -- precision photo-production physics -- exclusive reaction measurements -- nuclear fragmentation region measurements April 2nd, 2003 Quest for Nucleon Spin: Past, Present & Future

  40. http://www.bnl.gov/eic Polarized DIS at EIC • 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…. April 2nd, 2003 Quest for Nucleon Spin: Past, Present & Future

  41. 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 April 2nd, 2003 Quest for Nucleon Spin: Past, Present & Future

  42. 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 EIC w.r.t. ~ 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) EIC 1 fb-1 April 2nd, 2003 Quest for Nucleon Spin: Past, Present & Future

  43. Polarized Gluon Measurement at EIC • 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 EIC 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 EIC -- Single and di-jet production in PGF -- Open charm production in PGF April 2nd, 2003 Quest for Nucleon Spin: Past, Present & Future

  44. Photon Gluon Fusion at EIC • “Direct” determination of DG -- Di-Jet events -- High pT leading hadrons • High Sqrt(s) at EIC -- 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 April 2nd, 2003 Quest for Nucleon Spin: Past, Present & Future

  45. 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 April 2nd, 2003 Quest for Nucleon Spin: Past, Present & Future

  46. A. De Roeck, A. Deshpande, V. W. Hughes & J. Lichtenstadt,G. Radel EIC WS, Yale’00 Di-Jet events at EIC: 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 EIC April 2nd, 2003 Quest for Nucleon Spin: Past, Present & Future

  47. Polarized PDFs of the Photons Direct Photon Resolved Photon • Photo-production studies with single and di-jet • Photon Gluon Fusion or Gluon Gluon Fusion (Photon resolves in to its partonic contents) • Resolved photon asymmetries result in measurements of spin structure of the photon • Asymmetries sensitive to gluon polarization as well… but we will consider the gluon polarization “a known” quantity! April 2nd, 2003 Quest for Nucleon Spin: Past, Present & Future

  48. M. Stratmann & W. Vogelsang EIC WS at Yale’01 Will measure the photon PDFs… • Stat. Accuracy estimated for 1 fb-1 running (2 weeks at EIC) • Single and double jet asymmetries • ZEUS acceptance • Will resolve photon’s partonic spin contents Direct Photon Resolved Photon April 2nd, 2003 Quest for Nucleon Spin: Past, Present & Future

  49. A Case for EIC • The polarized e-N facility at the EIC will enable the polarized DIS studies of nucleons in a completely new x-Q2 that no other present or future facility will be able to access • The measurements with variable Sqrt(s) & light polarized nuclei will include: -- inclusive physics in DIS as well as photo-production regime -- semi-inclusive physics -- exclusive physics leading to DVCS, DES GPDs • In addition a lot of spin measurements which would study target and current fragmentation for the first time in polarized DIS will be possible… • And then there is an exciting un-polarized e-A physics program which proposes to measure partonic matter under extreme conditions…. April 2nd, 2003 Quest for Nucleon Spin: Past, Present & Future

  50. A Case for EIC … for e-A • Through its large luminosity, beam energy & beam species variability, the EIC will explore a new universal and fundamental aspects of QCD including looking for the new states of matter at high gluon densities…. • It is natural to assume that these measurements probe the initial conditions in the nuclei for parton distributions… as such this knowledge would be essential to fully understand the QGP which is being pursued at RHIC • The e-A physics at RHIC will allow for the first time a large number of measurements which have never been performed beyond the fixed target regime… They will be at high energies where pQCD could be used reliably to understand the nuclear structure April 2nd, 2003 Quest for Nucleon Spin: Past, Present & Future