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Spin Physics at RHIC

This overview discusses the current status and open questions in spin physics at the Relativistic Heavy Ion Collider (RHIC) at the RIKEN BNL Research Center. Topics include nucleon spin, proton-proton physics at RHIC, and the long-term perspective for RHIC spin.

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Spin Physics at RHIC

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  1. Spin Physics at RHIC Abhay Deshpande RIKEN BNL Research Center QCD 2002 Indian Institute of Technology, Kanpur

  2. Overview NUCLEON SPIN • Present status and open questions RHIC SPIN (Present: RECENT RESULTS) • Relativistic Heavy Ion Collider at BNL • Status of polarized proton Collider (Year 2001-2002) -- Expectation for Year 2002-2003 • Polarized p-p physics at RHIC results FY02 -- Expectations FY03 • Long term perspective for RHIC Spin (pp) Electron Ion Collider at RHIC(Future) • Electron ring at RHIC • Physics goals of EIC (… mostly e-p… but also e-A) • Status & Plans Spin Physcis at RHIC

  3. Parton Distributions (well known) Nucleon (moderately well known) (unknown) (moderately well known) (unknown) Spin Physcis at RHIC

  4. Our knowledge of spin structure function g1 F2 105 10 103 10 1 102 Q2 (GeV2) Q2 (GeV2) Spin Physcis at RHIC

  5. SMC, B. Adeva et al. Phys. Rev. D 112002 (1999) Nucleon Spin: Status & Open Questions Quark Spin Contribution: Gluon Spin Contribution: Proton Spin Puzzle remains unsolved! constrained, need to measure Spin Physcis at RHIC

  6. Relativistic Heavy Ion Collider RHIC accelerates heavy ion beams up to and polarized proton beams to 250 GeV this is test PHENIX STAR Two large detectors PHENIX and STAR have extensive Spin Physics Programs Spin Physcis at RHIC

  7. 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 Spin Physcis at RHIC

  8. 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 RHIC Polarimetry Spin Physcis at RHIC

  9. RHIC PHENIX STAR LINAC AGS Siberian Snakes Effect of depolarizing resonances averaged out by rotating spin by large angles on each turn 4 helical dipoles  S. snake 2 snakes in each ring -- axes orthogonal to each other Spin Physcis at RHIC

  10. 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 ! Spin Physcis at RHIC

  11. Cheers! Spin Physcis at RHIC

  12. RHIC Luminosity FY02 Machine Luminosity 300 nb-1 /week Peak 1.8x1030 cm-2s-1 PHENIX 150 nb-1 350 300 250 STAR 300 nb-1 200 150 100 50 0 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 Spin Physcis at RHIC Days into run (from 12/20/01)

  13. Polarization Year 1 Yellow Ring Blue Ring Spin Physcis at RHIC

  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 Spin Physcis at RHIC

  15. Machine Performance Expectations Spin Physcis at RHIC

  16. RHIC Spin Physics Program • Spin Structure of Nucleon • 1/2=(1/2)DS+DG+Lq+Lg • DG: gluon polarization • Dq: Anti-quark polarization • New Structure Functions • h1: transversity • Test of pQCD • Use asymmetries sensitive ONLY to the higher orders (AN at high PT etc.) • NEW tool to study hadronic processes • W,Z @500GeV • flavor sensitive studies on the structure functions • cc/bb • Production mechanism • Spin in fragmentation • Parity,CP violating interaction? ?QCD triumph? or ?beyond ? Spin Physcis at RHIC

  17. RHIC spin program Production W Production Heavy Flavors STAR +PHENIX STAR + PHENIX STAR +PHENIX Direct Photon BRAHMS, STAR, PHENIX, Local Polarimeter Jet Photon Spin Physcis at RHIC

  18. PHENIX Detector EMCal Resolution EM Calorimeter Beam-Beam Counter Muon Tracking Chambers Time Expansion Chamber Central Arms Muon ID Panels Pad Chambers North Muon Arm Multiplicity/Vertex Detector Background/Signal Drift Chambers Time of Flight Panels South Muon Arm Ring Imaging Cerenkov Spin Physcis at RHIC

  19. PHENIX Preliminary Normalization error of 30% not shown. On the way to DG… p0 spectrum PHENIX p0 cross section (Preliminary) PT spectrum over 8 order of magnitude Comparision with NLO pQCD calculation --CTEQ5M PDFs --Potter, Knielh, Kramer (PKK) fragmentation functions --Uncertainty shown: m= pT/2, 2pT Consistent with data within scale dependence Spin Physcis at RHIC

  20. 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 Spin Physcis at RHIC

  21. STAR Performance • Time Projection Chamber worked beautifully! Au-Au Collision at STAR Spin Physcis at RHIC

  22. 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. Spin Physcis at RHIC

  23. STAR Forward rapidity high xFp0 AN AN Theory predictions at pT = 1.5 GeV/c Collins effect Anselmino, et al. PRD 60 (1999) 054027. Sivers effect 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 Spin Physcis at RHIC xF ~E / 100 GeV

  24. Neutron Veto EM Cal Base Charge Veto PbWO4 Hadron Cal Base Scintillator Post-shower Pb W+Fiber Cal 12 o’clock  PHENIX test setup p0 Spin Physcis at RHIC

  25. EMCal ZDC Asymmetries Spin Physcis at RHIC

  26. Asymmetries seen at RHIC so far… 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% Spin Physcis at RHIC

  27. Upcoming Run FY03 3 pb-1 and 50% Expectation DG will be probed PHENIX Charged STAR JET Spin Physcis at RHIC

  28. Search for new physics: • Anomalous parity violation in jet production • Contact Interaction (Scale L) • CDF L>1.8 TeV • D0 L>2.4 TeV • RHIC Spin Reach L~3.3 TeV • New gauge boson Z’ P. Taxil & J-M. Virey, Phys. Rev. D (55) 2457 (1999) Spin Physcis at RHIC

  29. RHIC Spin Schedule (PHENIX & STAR) Year CM Energy Weeks Int. Lum. Remarks FY2002 200 GeV 5 5 pb-1(1/15) Gluon pol. with pions FY2003 200 GeV 8(3) 160 pb-1 Gluon pol. with jets 500 GeV 2(0)? 90 pb-1 PV W production, u-quark pol. 500 GeV (1) 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 200 GeV 10 210 pb-1 Spin Physcis at RHIC

  30. Summary & Outlook • RHIC spin program has begun: -- Polarized protons were injected and stored for extended times in RHIC -- CNI polarimeters have measured non zero asymmetries indicating polarization at 100 GeV proton beam energies -- Detectors are functional and will be 100% completed in 2004-5 -- A first round of single spin asymmetries have been measured • Next run 2002-3 promises to be the first one to get us a first look at DG -- First trials of 500 GeV run will be made and Ws produced • A 5 year run plan exists for the RHIC spin physics -- to explore DG, transversity, Dq & Dqbar is on the way Spin Physcis at RHIC

  31. 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 Spin Physcis at RHIC

  32. Deep Inelastic Scattering • Observe scattered electron/muon & hadrons in current jets • Observe spectator or remnant jet Spin Physcis at RHIC

  33. Why Collider in the Future? • Past polarized DIS experiments: MOSTLY FIXED TARGET • Collider has distinct advantages --- Confirmed at HERA • 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 Spin Physcis at RHIC

  34. EIC vs. DIS Facilities (I) • New kinematic region • Ee = 2-10 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= (0.3 – 1.0) X 1033 cm-2 sec-1 Spin Physcis at RHIC

  35. EIC vs. Other DIS Facilities (II) Variable beam energy Variable hadron species Hadron beam polarization Large luminosity TESLA-N Spin Physcis at RHIC

  36. 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 Spin Physcis at RHIC

  37. 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 photoproduction physics -- exclusive reaction measurements -- nuclear fragmentation region measurements Spin Physcis at RHIC

  38. 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…. Spin Physcis at RHIC

  39. A. Deshpande & V. W. Hughes Spin structure function g1 at low x ~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 Spin Physcis at RHIC

  40. A. Deshpande & V. W. Hughes Low x measurement of g1 of Neutron • With polarized He3 or deuteron • ~ 2 weeks of data at EIC • 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 inv.fb Spin Physcis at RHIC

  41. 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 • Measurements at EIC will be complimentary with RHIC with a very different set of systematic uncertainties - high Q2 assures no problems with interpretation of results • Deep Inelastic Scattering kinematics at EIC -- Scaling violations (pQCD analysis at NLO) of g1 -- (2+1) jet production in photon-gluon-fusion 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 Spin Physcis at RHIC

  42. A. Deshpande, V. W. Hughes & J. Lichtenstadt 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 -- coupled to better low x knowledge of spin structure -- less dependence on factorization & re-normalization scale uncertainty Spin Physcis at RHIC

  43. 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 results -- Consistent with scaling violation F2 results on G Signal: PGF Background QCD Compton Spin Physcis at RHIC

  44. G. Radel, A. De Roeck, A. Deshpande, V. W. Hughes & J. Lichtenstadt 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 • If combined with scaling violations of g1: factors of 5 improvements • in uncertainties observed in the same time. • Better than 3-5% uncertainty can be expected from EIC DG program Spin Physcis at RHIC

  45. G. Radel & A. De Roeck Di-Jet at EIC vs. World Data for DG/G EIC 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. Spin Physcis at RHIC

  46. 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! Spin Physcis at RHIC

  47. M. Stratmann & W. Vogelsang 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 Spin Physcis at RHIC

  48. Parity Violating Structure Function g5 • This is also a test • Experimental signature is a huge • asymmetry in detector (neutrino) • Unique measurement • Unpolarized xF3 measurements • at HERA in progress • Will access heavy quark • distribution in polarized DIS For EIC kinematics Spin Physcis at RHIC

  49. J. Contreras & A. De Roeck Measurement Accuracy PV g5 at EIC Assumes: • Input GS Pol. PDfs • xF3 measured by then • 4 fb-1 luminosity Positrons & Electrons in EIC  g5(+) >> Issues for linac vs. ring design of EIC Spin Physcis at RHIC

  50. S. Bass, A. De Roeck & A. Deshpande Drell Hern Gerasimov Spin Sum Rule • DHG Sum rule: • At EIC n range: GeV  few TeV • Although contribution from to the this sum rule is small, the high n behavior is completely unknown and hence theoretically biased in any present measurements at: Jefferson Lab., MAMI, BNL • Inclusive Photo-production • measurement • Using electron tagger in • RHIC ring • Q2 ~ 10-6 10-2 GeV2 • Sqrt(s) ~ 25  85 GeV Spin Physcis at RHIC

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