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Recent Spin Results from

Detailed overview of recent spin results from Columbia University on proton structure and parton distributions, emphasizing experimental data, polarized quark contributions, and the use of RHIC for in-depth analysis.

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Recent Spin Results from

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  1. Recent Spin Results from Columbia University Christine Aidala INFN, Sezione di Torino January 9, 2004

  2. Spin Structure of the Proton: Status Parton Distributions: (well known) (moderately well known) helicity flip (unknown) (moderately well known) (basically unknown) C. Aidala, INFN Torino, Jan. 9, 2004

  3. Experimental data on proton structure polarized unpolarized g1 F2 Data points on polarized structure function much sparser! C. Aidala, INFN Torino, Jan. 9, 2004

  4. Polarized quark and gluon distributions EMC, SMC at CERN E142 to E155 at SLAC HERMES at DESY M. Hirai et al (AAC collab) up quarks sea quarks Quark spin contribution to the proton spin: “Spin Crisis” Gluon contribution remains unconstrained. down quarks gluon C. Aidala, INFN Torino, Jan. 9, 2004

  5. RHIC at Brookhaven National Laboratory C. Aidala, INFN Torino, Jan. 9, 2004

  6. The Relativistic Heavy Ion Collider • Heavy ions, polarized protons • Most versatile collider in the world! Nearly any species can be collided with any other. • asymmetric species possible due to independent rings with separate steering magnets C. Aidala, INFN Torino, Jan. 9, 2004

  7. RHIC Specifications • 3.83 km circumference • Two independent rings • Up to 120 bunches/ring • 106 ns crossing time • Energy: • Up to 500 GeV for p-p • Up to 200 GeV for Au-Au(per N-N collision) • Luminosity • Au-Au: 2 x 1026 cm-2 s-1 • p-p : 2 x 1032 cm-2 s-1(polarized) C. Aidala, INFN Torino, Jan. 9, 2004

  8. BRAHMS & PP2PP (p) PHENIX (p) STAR (p) Polarization 2  1011 Pol. Protons / Bunch e = 20 pmm mrad RHIC Accelerator Complex RHIC pC Polarimeters Absolute Polarimeter (H jet) Siberian Snakes Spin Rotators Partial Siberian Snake LINAC BOOSTER Pol. Proton Source 500 mA, 300 ms AGS AGS Internal Polarimeter 200 MeV Polarimeter Rf Dipoles C. Aidala, INFN Torino, Jan. 9, 2004

  9. RHIC PHENIX STAR LINAC AGS Siberian Snakes Effect of depolarizing resonances averaged out by rotating spin by 180 degrees on each turn • 4 helical dipoles  S. snake • 2 snakes in each ring • - axes orthogonal to each other C. Aidala, INFN Torino, Jan. 9, 2004

  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 Si #1 left right Si #5 Si #2 Si #3 Si #4 down Beam’s View RHIC Polarimetry E950 Experiment at AGS (1999)  RHIC polarimetry now C. Aidala, INFN Torino, Jan. 9, 2004

  11. STAR RHIC’s Experiments C. Aidala, INFN Torino, Jan. 9, 2004

  12. PHENIX • Pioneering High Energy Nuclear Interaction eXperiment • Goals: • Broadest possible study of A-A, p-A, p-p collisions to • Investigate nuclear matter under extreme conditions • Examine systematic variations with species and energy • Explore the spin of the proton C. Aidala, INFN Torino, Jan. 9, 2004

  13. 12 Countries; 57 Institutions; 460 Participants PHENIX the Collaboration C. Aidala, INFN Torino, Jan. 9, 2004

  14. PHENIX the Detector • Philosophy: • High rate capability & granularity • Good mass resolution and particle ID • Sacrifice acceptance • 2 central spectrometers • - Track charged particles and detect electromagnetic processes • 2 forward spectrometers • - Identify and track muons • 3 global detectors • - Determine when there’s a collision C. Aidala, INFN Torino, Jan. 9, 2004

  15. 2001/2002 Au-Au 2002/2003 d-Au Au-Au and d-Au Collisions in the PHENIX Central Arms C. Aidala, INFN Torino, Jan. 9, 2004

  16. Determine the complete spin structure of the nucleon In particular, contributions from Gluon polarization (DG) Sea-quark polarization (Du , Dd) Why RHIC? High energy  factorization Polarized hadrons  gq, gg collisions High energy  new probes (W’s) Goals of the RHIC Spin Program C. Aidala, INFN Torino, Jan. 9, 2004

  17. Production Heavy Flavors Prompt Photon Proton Spin Structure at PHENIX C. Aidala, INFN Torino, Jan. 9, 2004

  18. Hard Scattering Processes in p+p Hard Scattering Process • “Hard” probes have predictable rates given: • Parton distribution functions (need experimental input) • pQCD hard scattering rates (calculable in pQCD) • Fragmentation functions (need experimental input) Universality C. Aidala, INFN Torino, Jan. 9, 2004

  19. Hard Scattering in Polarized p+p Hard Scattering Process C. Aidala, INFN Torino, Jan. 9, 2004

  20. Prompt Photon Production • A relatively clean channel to access DG, but experimentally challenging • No fragmentation functions to worry about • Small cross section need large statistics • Good background reduction with fine grained/high resolution EMCal in PHENIX C. Aidala, INFN Torino, Jan. 9, 2004

  21. AAC Preliminary Impact of RHIC Spin DG Measurement • If the projected PHENIX prompt photon data are included in a global QCD analysis: AAC Preliminary M. Hirai, H.Kobayashi, M. Miyama et al. C. Aidala, INFN Torino, Jan. 9, 2004

  22. Spin Running at RHIC • 2001-2 • Transversely polarized p+p collisions • Average polarization of ~15% • Integrated luminosity 0.15 pb-1 • 2003 • Longitudinally polarized p+p collisions achieved • Average polarization of ~27% • Integrated luminosity 0.35 pb-1 • 2004 • 5 weeks polarized p+p commissioning • Specifically to work on spin tune and AGS polarization • Commission hydrogen jet polarimeter • 2005 • Long spin run planned! C. Aidala, INFN Torino, Jan. 9, 2004

  23. Recent Results:p0 ALL from 2003 Run • Connections with pQCD • Polarization • Relative luminosity • p0 reconstruction and counting C. Aidala, INFN Torino, Jan. 9, 2004

  24. p0 Cross Section from 2001-2 Run accepted by PRL, hep-ex/0304038 • NLO pQCD consistent with data within theoretical uncertainties. • PDF: CTEQ5M • Fragmentation functions: • Kniehl-Kramer-Potter (KKP) • Kretzer • Spectrum constrains D(gluon p) fragmentation function • Important confirmation of theoretical foundation for spin program • Data from 2003 run reproduce 2001-2 results and extend the pT range • Will be released soon 9.6% normalization error not shown C. Aidala, INFN Torino, Jan. 9, 2004

  25. pQCD Scale Dependence at RHIC p0 data vs pQCD with different factorization scales: Theoretical uncertainty of pQCD calculations in channels relevant for gluon polarization measurements: HERMES (hadron pairs) 2μ (factorization scale) COMPASS (hadron pairs) μ μ/2 RHIC (direct photon) PHENIX (direct photon) PHENIX (inclusive hadrons) Statistical errors only CDF (direct photon) CDF direct photon C. Aidala, INFN Torino, Jan. 9, 2004

  26. Production Leading hadrons as jet tags Hard Scattering Process qg+gq qq gg C. Aidala, INFN Torino, Jan. 9, 2004

  27. PHENIX Local Polarimeter • Forward neutron transverse asymmetry (AN) measurements • Shower Max Detector (position) + Zero-Degree Cal. (energy) f distribution SMD Vertical  f ~ ±p/2 Radial  f ~ 0 Longitudinal  no asymmetry ZDC C. Aidala, INFN Torino, Jan. 9, 2004

  28. Blue Yellow Spin Rotators ON Current Reversed! Radial polarization Blue Yellow Spin Rotators ON Correct Current Longitudinal polarization! Blue Yellow Local Polarimeter:Spin Direction Confirmation Spin Rotators OFF Vertical polarization C. Aidala, INFN Torino, Jan. 9, 2004

  29. Relative Luminosity Must combine yields from different bunch crossings to obtain asymmetries ALL vs store • Systematic error study through comparison of counts from two different luminosity detectors—different kinematical regions, different physics signals • Look at crossing-by-crossing ratio of the 2 detector scalers : • a(i) = NA(i)/NB(i) • Ratio should be the same for all crossings (constant) if: • NA(i) = L * εA and NB(i) = L * εB • Fit this by the expected pattern: • a(i) = C[1+ALLP1(i)P2(i)] • C, ALL are the fitting parameters. • c2 is a very important check of systematic errors 30 2/NDF vs (ALL) 20 10 Not so good, but … C. Aidala, INFN Torino, Jan. 9, 2004

  30. Relative Luminosity After vertex correction Vertex width affects relative luminosity measurements ALL vs fill Ratio ZDC/BBC vs z-vertex width  2/NDF vs (ALL) 3 2 1 Now 2/NDF1 C. Aidala, INFN Torino, Jan. 9, 2004

  31. Relative Luminosity: Results • Achieved relative luminosity precision R=2.5x10-4 • Upper-limit estimation limited by ZDC statistics (30 times less than BBC statistics used in relative luminosity measurements) • Relative lum. contribution for p0ALL less than 0.2% • For average beam polarizations of 27% • ALL of BBC relative to ZDC consistent with 0 (<0.2%) • Strong indication that asymmetries seen by both detectors are zero (very different kinematical regions, different physics signals) C. Aidala, INFN Torino, Jan. 9, 2004

  32. Data set • Data collected with high-energy photon trigger • Based on EMCal; Threshold ~1.4 GeV/c • Rejection factor ~110 • Analyzed data sample:42.7M events (~0.215 pb-1) • sqrt(<PbPy>)~27% • Minimum bias data • To obtain “unbiased” 0 cross section at low pT • For high-pT photon trigger efficiency study C. Aidala, INFN Torino, Jan. 9, 2004

  33. h (0) High-Energy EMCal trigger EMCal-RICH trigger • EMCal part has two sums to collect photon shower • 2×2 towers non-overlapping sum (threshold at 0.8 GeV) • 4×4 towers overlapping sum (thresholds at 2 and 3 GeV) 2×2 4×4 C. Aidala, INFN Torino, Jan. 9, 2004

  34. Photon trigger efficiency for 0 • p0 efficiency plateaus for pT>4 GeV/c • Limited efficiency at pT<4 GeV/c: 1-2 GeV/c: 6% 2-3 GeV/c: 60% 3-4 GeV/c: 90% 4-5 GeV/c: 95% • Monte Carlo reproduces data well Data MC 0 pT (GeV/c) C. Aidala, INFN Torino, Jan. 9, 2004

  35. p0 Reconstruction for ALL Results obtained for four pT bins from 1 to 5 GeV/c p0 peak width varies from 12 to 9.5 MeV/c2 from lowest to highest pT bins Background contribution under p0 peak for 25 MeV/c2 mass cut varies from 45% to 5% from lowest to highest pT bins 1-2 GeV/c Bckgr=45% 2-3 GeV/c Bckgr=17% 3-4 GeV/c Bckgr=7% 4-5 GeV/c Bckgr=5% C. Aidala, INFN Torino, Jan. 9, 2004

  36. p0 Counting for ALL • N0: • 25 MeV/c2 around 0 peak (and also 15 and 35 MeV/c2 for cross checks) • Nbck1: • Two 50 MeV/c2 wide areas adjacent to 0 peak • Nbck2: • 250 MeV/c2 wide area between 0 and peaks N0 and Nbck accumulated statistics C. Aidala, INFN Torino, Jan. 9, 2004

  37. ALL Measurements N: # pions ++ same helicity + opposite helicity L: luminosity • Procedure • Count N and L for ++ and + configurations (sum over all crossings) and calculate ALL for each store • Average ALL over stores; use 2/NDF to control fit quality • Perform checks C. Aidala, INFN Torino, Jan. 9, 2004

  38. ALL Calculations: Signal + Background ALL averaged over stores 1-2 GeV/c 2-3 GeV/c • 1-2 GeV/c • ALL= -2.8%±1.2% • 2/NDF = 64/48 • 2-3 GeV/c • ALL= -2.2%±1.5% • 2/NDF = 34/48 • 3-4 GeV/c • ALL= -0.2%±3.3% • 2/NDF = 49/48 • 4-5 GeV/c • ALL= -2.3%±7.4% • 2/NDF = 39/48 4-5 GeV/c 3-4 GeV/c C. Aidala, INFN Torino, Jan. 9, 2004

  39. Bunch shufflingto check for systematic errors Bunch shuffling: Randomly assign helicity for each bunch crossing 2/NDF ALL 1-2 GeV/c 1-2 GeV/c 2-3 GeV/c 2-3 GeV/c 4-5 GeV/c 3-4 GeV/c 3-4 GeV/c 4-5 GeV/c Widths are consistent with obtained errors (ALL) All <2/NDF> are ~1 C. Aidala, INFN Torino, Jan. 9, 2004

  40. Parity-violating AL check For “yellow” beam: All are zero within 1.5 Similar results obtained for “blue” beam C. Aidala, INFN Torino, Jan. 9, 2004

  41. Other ALL Checks PID check ++ vs  and + vs + PID = Shower profile cut (0>96%) Consistent with 0 within 1.5 The same results with and without extra PID C. Aidala, INFN Torino, Jan. 9, 2004

  42. 0 ALL from pp at 200 GeV Polarization scaling error P ~30%: is not included • Enters ALL quadratically • Analyzing power AN(100 GeV) ~ AN(22 GeV) is assumed • P~30%: combined stat. and syst. error for AN(22GeV) (AGS E950) pT smearing correction is not included C. Aidala, INFN Torino, Jan. 9, 2004

  43. p0 Production and DG p0 can be used to constrain DG with limited luminosity and polarization. B.Jaeger et al., PRD67, 054005 (2003) • Double longitudinal asymmetry for neutral pions has been measured • Preliminary access to gluon polarization • Already stimulated theoretical interest • See B. Jaeger et al., hep-ph/0310197 • PHENIX publication expected this spring C. Aidala, INFN Torino, Jan. 9, 2004

  44. Summary • Successful first three years at RHIC and PHENIX! • RHIC has been successful as the world’s first polarized proton collider, opening up new kinematic regions for investigating the spin of the proton • The first spin results, including p0 ALL, from PHENIX are out and stimulating discussion within the theoretical community Many more years of exciting data and results to look forward to! • Long spin run planned for 2005 • Measure gluon polarization more cleanly via direct photon double longitudinal asymmetry • Probe gluon polarization from heavy flavor production (gg fusion) via electrons • Probe polarization of sea quarks via W boson single longitudinal asymmetry C. Aidala, INFN Torino, Jan. 9, 2004

  45. Extra Slides C. Aidala, INFN Torino, Jan. 9, 2004

  46. Quark and Gluon Distributions J. Pumplin et.al JEHP 0207:012 (2002) Errors about 10% for 0.001<x<0.5 C. Aidala, INFN Torino, Jan. 9, 2004

  47. E866 at FNAL J.C. Peng (UIUC) HERMES at DESY N. Makins (UIUC) C. Aidala, INFN Torino, Jan. 9, 2004

  48. Semi-inclusive DIS… • In addition to the scattered electron, one measures the hadronic final state(s) • Access to flavor-separated parton distributions • HERMES has the most significant data on these C. Aidala, INFN Torino, Jan. 9, 2004

  49. RHIC vs. DIS Kinematic Coverage prompt photon C. Aidala, INFN Torino, Jan. 9, 2004

  50. 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 Models:: Transversity, Higher Twist, Fragmentation, kT, Orbital Ang. Mom., etc. C. Aidala, INFN Torino, Jan. 9, 2004

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