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Spin at RHIC Present Status and Future Plans

Spin at RHIC Present Status and Future Plans. OUTLINE Spin at RHIC: how its done, why its done, and who does it Status of A LL measurements at RHIC: sensitivity to D G Status of transverse single-spin asymmetries at RHIC Future plans. L.C. Bland, BNL IWHSS08, Torino 2 April 2008.

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Spin at RHIC Present Status and Future Plans

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  1. Spin at RHICPresent Status and Future Plans • OUTLINE • Spin at RHIC: how its done, why its done, and who does it • Status of ALL measurements at RHIC: sensitivity to DG • Status of transverse single-spin asymmetries at RHIC • Future plans L.C. Bland, BNL IWHSS08, Torino 2 April 2008

  2. RHIC Spin CollaborationConfederation of Groups Involved in the Effort • Accelerator Physicists • Primarily BNL Collider-Accelerator Department • RHIC spin is a successful accelerator physics experiment • Essential contributions from RIKEN for spin at RHIC • RHIC Experiments (PHENIX,STAR,BRAHMS) • RIKEN / RBRC, University and National Laboratory groups • RHIC spin planning fully integrated in experiment collaborations • Polarimetry • Primarily BNL effort, with “detailees” from RHIC experiments • Essential measurements required for RHIC spin results • Theory • RIKEN / RBRC, University and National Laboratory groups • RHIC spin results require QCD global analyses to extract physics

  3. Recall: simple quark model In QCD: proton is not just 3 quarks ! Rich structure of quarks anti-quarks, gluons RHIC Spin Goals - I How is the proton built from its known quark and gluon constituents? As with atomic and nuclear structure, this is an evolving understanding

  4. Spin Sum Rules Longitudinal Spin Transverse Spin PRD 70 (2004) 114001 RHIC Spin Goals - IIUnderstanding the Origin of Proton Spin Understanding the origin of proton spin helps to understand its structure

  5. RHIC Spin Goals - IIIMilestones and Other Objectives • Direct measurement of polarized gluon distribution (DG) using multiple probes • Direct measurement of flavor identified anti-quark polarization using parity violating production of W • Transverse spin: connections to partonic orbital angular momentum (Ly) and transversity (dS)

  6. pion or jet quark quark gluon RHIC Spin Probes - IPolarized proton collisions / hard scattering probes of DG Describe p+p particle production at RHIC energies (s  62 GeV) using perturbative QCD at Next to Leading Order, relying on universal parton distribution functions and fragmentation functions

  7. p + p  p0 + X, s = 200 GeV p + p, s = 200 GeV arXiv:0704.3599 [hep-ex] PRL 97 (2006) 252001 PRL 92 (2004) 171801 jets direct g PRL 98 (2007) 012002 RHIC Spin Probes - IIUnpolarized cross sections as benchmarks and heavy-ion references Good agreement between experiment and theory  calibrated hard scattering probes of proton spin

  8. RHIC pC Polarimeters Absolute Polarimeter (H jet) BRAHMS & PP2PP PHOBOS Siberian Snakes Siberian Snakes PHENIX STAR Spin Rotators (longitudinal polarization) Spin Rotators (longitudinal polarization) Pol. H- Source LINAC BOOSTER Helical Partial Siberian Snake AGS 200 MeV Polarimeter AGS pC Polarimeter Strong AGS Snake RHIC As a Polarized Collider 2005:Pblue =49.3% +/- 1.5% +/- 1.4% Pyellow=44.3% +/- 1.3% +/- 1.3% DP/P = 4.2% (goal=5%) 2006: 1 MHz collision rate; Polarization=0.6 (online)

  9. 100 x 100 Gev pp RUN05-06, PHENIX Integrated Luminosity Final delivered 45 40 ) -1 35 30 Integrated Luminosity (pb RUN05 25 RUN06 20 15 10 5 0 0 7 14 21 28 35 42 49 56 63 70 77 84 91 PHENIX Days in Physics mode RHIC Run-6 Plot by Phil Pile An extraordinary Run-6! Average Polarization 60%! Outstanding luminosity and polarization performance from RHIC for polarized proton collisions at s = 200 GeV

  10. BBC ZDC ZDC PHENIX Detector EMCal p0/g/h detection • Electromagnetic Calorimeter (PbSc/PbGl): • High pT photon trigger to collect p0's, h’s, g’s • Acceptance: |h|<0.35, f = 2 x p/2 • High granularity (~10*10mrad2) p+/ p- • Drift Chamber (DC) for Charged Tracks • Ring Imaging Cherenkov Detector (RICH) • High pT charged pions (pT>4.7 GeV). Relative Luminosity • Beam Beam Counter (BBC) • Acceptance: 3.0< h<3.9 • Zero Degree Calorimeter (ZDC) • Acceptance: ±2 mrad Local Polarimetry • ZDC • Shower Maximum Detector (SMD)

  11. STAR Run-6 STAR detector layout • Detectors used for jets: • Time Projection Chamber, ||<1.4Tracking • Barrel EM Calorimeter, ||<1Triggering & Calorimetry • Endcap EM Calorimeter, 1.09<<2 Triggering & Calorimetry • Beam-Beam Counters, 3.4<||<5Triggering, Luminosity, local Polarimetry

  12. Longitudinal Two-Spin (ALL) Status of probing for gluon polarization via measurements of ALLfor midrapidity jet,p0production

  13. PHENIX Preliminary Run6 (s=200 GeV) ALL: 0 5 10 pT(GeV) GRSV model: “G = 0”: G(Q2=1GeV2)=0.1 “G = std”: G(Q2=1GeV2)=0.4 Statistical uncertainties now to the point of distinguishing “std” and “0” scenarios? Run3,4,5: PRL 93, 202002; PRD 73, 091102; hep-ex-0704.3599

  14. From pT to xgluonmidrapidity neutral pion ALL • Each pT bin corresponds to a wide range in xgluon, heavily overlapping with other pT bins • Data are not sensitive to variation of G(xgluon) within our x range • Quantitative analysis needs to assume some G(xgluon) shape log10(xgluon) NLO pQCD: for0, 2< pT < 9 GeV/c  0.02 < xgluon < 0.3 GRSV model: G(0.02 < xgluon< 0.3) ~ 0.6G(0 < xgluon < 1 )

  15. Constraining G from p0 ALLSimilar approach as used for jets Calculations by W.Vogelsang and M.Stratmann  • “GRSV-std” scenario, G(Q2=1GeV2)=0.4, is excluded by data on >3s level • Only exp. stat. uncertainties are included (the effect of syst. uncertainties is expected to be small in the final results) • Theoretical uncertainties are not included

  16. Jet reconstruction in STAR • Midpoint cone algorithm(Adapted from Tevatron II - hep-ex/0005012 ) • Seed energy = 0.5 GeV • Cone radius in - • R=0.4 (2005) • R=0.7 (2006) • Splitting/merging fraction f=0.5 Data jets MC jets Geant Detector Pythia Particle Use Pythia+GEANT to quantify detector response

  17. Final 2005 Inclusive ALLjets Results STAR hep-ex arXiv:0710.2048 0.2 <  < 0.8 • Data are compared to predictions within the GRSV framework with several input values of G. B. Jager et.al, Phys.Rev.D70, 034010 GRSV-std • The inclusive measurements give sensitivity to gluon polarization over a broad momentum range

  18. Vogelsang and Stratmann GRSV DIS GRSV DIS best fit=0.24 1 DG varies from -0.45 to 0.7 PRD 63, 094005 (2001) Constraining DG from jet production ALLBefore global analyses… • Compute ALL in NLO pQCD varying integral DG, but maintaining GRSV shape • Perform 2 analysis between calculations and measured jet ALL

  19. STAR Run 2006 Data • Improved FOM • Luminosity : 2  4.7 pb-1 • Polarization: 50%  60% (online polarization) • Barrel EMC  coverage: [0,1]  [-1,1] • In addition • Jet Cone Radius: 0.4  0.7 • -0.7 < jet axis < 0.9 • Neutral Energy Fraction < 0.85 • Increased trigger thresholds • Inclusion of Endcap EMC towers • Improved tracking at large || STAR Preliminary

  20. STAR 2006 Inclusive ALLjets -0.7 <  < 0.9 GRSV curves with cone radius 0.7 and -0.7 <  < 0.9 • Using jet patch trigger (x = 1x1 patch of towers) only • Statistical uncertainties are 3-4 times smaller than 2005 in high pT region (pT>13 GeV/c)

  21. GRSV DIS STAR 2006 Inclusive ALLjets *Theoretical uncertainties not included GRSV DIS best fit=0.24 1 = -0.45 to 0.7 PRD 63, 094005 (2001) • Within GRSV framework: • g_std excluded with 99% CL • g<-0.7 excluded with 90% CL

  22. Summary of ALL Measurements • Data accumulated through RHIC run 6 forinclusive 0 and jetALL has reached high statistical significance to constrain G in the limited x range (~0.020.3) • G is found to be consistent with zero, to date • Theoretical uncertainties (x dependence) are significant • Future Plans for Probing DG • Improve statistical precision of midrapidity p0,jet ALL measurements and extend measurements to higher pT • Determine x-dependence of DG via correlation measurements: jet1+jet2 and g+jet • Extend gluon-x range probed to lower x via measurements of ALL at larger rapidity and higher s • Global analysis in NLO pQCD of RHIC data and HERMES,COMPASS data

  23. Transverse Single-Spin Asymmetries (AN) Probing for orbital motion within transversely polarized protons

  24. Expectations from Theory What would we see from this gedanken experiment? F0 as mq0 in vector gauge theories, so AN ~ mq/pT or,AN ~ 0.001 for pT ~ 2 GeV/c Kane, Pumplin and Repko PRL 41 (1978) 1689

  25. A Brief History… s=20 GeV, pT=0.5-2.0 GeV/c • QCD theory expects very small (AN~10-3) transverse SSA for particles produced by hard scattering. • The FermiLab E-704 experiment found strikingly large transverse single-spin effects in p+p fixed-target collisions with 200 GeV polarized proton beam (s = 20 GeV). • 0 – E704, PLB261 (1991) 201. • +/- - E704, PLB264 (1991) 462.

  26. Sivers mechanism requires spin-correlated transverse momentum in the proton (orbital motion). SSA is present for jet or g Collins/Hepplemann mechanism requires transverse quark polarization and spin-dependent fragmentation Two of the Explanations for Large Transverse SSASpin-correlated kT initial state final state Require experimental separation of Collins and Sivers contributions

  27. Transverse Single-Spin AsymmetriesWorld-wide experimental and theoretical efforts • Transverse single-spin asymmetries are observed in semi-inclusive deep inelastic scattering with transversely polarized proton targets •  HERMES (e); COMPASS (m); and planned at JLab • Collins fragmentation function is observed in hadron-pair production in e+e- collisions (BELLE) • Intense theory activity underway SPIRES-HEP: search title including: “Transverse spin, Transversity, single spin” Total number: 625 (1968~2006) Experimental results ~14%

  28. D. Morozov, for STAR [hep-ex/0512013] Spin Effects in the Forward DirectionStatus prior to RHIC run 6 J. Adams et al. (STAR), PRL 92 (2004) 171801; and PRL 97 (2006) 152302 • Transverse SSA persist at large xF at RHIC energies where unpolarized cross sections are calculable

  29. STAR Results vs. Di-Jet Pseudorapidity Sum Run-6 Result VY 1, VY 2 are calculations by Vogelsang & Yuan, PRD 72 (2005) 054028 AN pbeam  (kT  ST) jet Emphasizes (50%+ ) quark Sivers Boer & Vogelsang, PRD 69 (2004) 094025 pbeam into page jet Idea: directly measure kT by observing momentum imbalance of a pair of jets produced in p+p collision and attempt to measure if kT is correlated with incoming proton spin STAR • AN consistent with zero • ~order of magnitude smaller in pp  di-jets than in semi-inclusive DIS quark Sivers asymmetry! arXiv:0705.4629

  30. STAR High Precision Analyzing Powers (2003  2006) B.I. Abelev, et al, hep-ex/0801.2990  Precision measurements at s = 200 GeV provide stringent contraints on the models…

  31. STAR High Precision Analyzing Powers (2003  2006) B.I. Abelev, et al, hep-ex/0801.2990  No model fully describes the precision data More experimental (and theoretical) work needed…

  32. PHENIX Goes ForwardFirst results with muon piston calorimeter from run 6p+pp0+X, s = 62 GeV Transverse SSA persists with similar characteristics over a broad range of collision energy (20 < s < 200 GeV)

  33. SummaryTransverse Single Spin Asymmetry (SSA) Measurements • Feynman-x dependence of large-rapidity pion production shows large transverse SSA at RHIC energies, where cross sections are described by NLO pQCD • Feynman-x dependence of large-rapidity transverse SSA are consistent with theoretical models (Sivers effect  orbital motion / twist-3 calculations) • The pT dependence of large-rapidity p0 transverse SSA does not follow theoretical expectations • Direct measurement of spin-correlated kT (Sivers effect) via midrapidity di-jet spin asymmetries completed in RHIC run 6 and found consistent with zero. • Cancellations found in theory calculations subsequent to measurements also expect small di-jet spin asymmetries at midrapidity.

  34. Future RHIC Spin Plans • Measure parity violation for W production to determine flavor dependence of quark and antiquark polarization. • Requires completion of PHENIX muon trigger upgrade and STAR forward tracking for charge sign discrimination.

  35. Plans for Transverse Polarization MeasurementsRHIC run 8 and beyond • Experimental separation of Collins and Sivers effects via transverse single-spin asymmetry measurements for large rapidity p-p production • Extend measurements of transverse single spin asymmetries from hadron production to prompt photon production, including away-side correlations • Develop RHIC experiments for a future measurement of transverse single spin asymmetries for Drell-Yan production of dilepton pairs Transverse-Spin Drell-Yan Physics at RHIC L. Bland, S.J. Brodsky, G. Bunce, M. Liu, M. Grosse-Perdekamp, A. Ogawa, W. Vogelsang, F. Yuan http://spin.riken.bnl.gov/rsc/write-up/dy_final.pdf

  36. STAR Recycled FNAL E831 lead-glass for FMS Forward Meson SpectrometerQuantifying possible color glass condensate viaforward p0 and correlations in d+Au versus p+p at sNN=200 GeV North FMS half before sealing p+p data at s = 200 GeV also acquired Recorded 8 pb-1 in run 8

  37. Sivers in SIDIS vs Drell Yan Important test at RHIC of the fundamental QCD prediction of thenon-universality of the Sivers effect! requires very high luminosity (~ 250pb-1) Transverse-Spin Drell-Yan Physics at RHIC L. Bland, S.J. Brodsky, G. Bunce, M. Liu, M. Grosse-Perdekamp, A. Ogawa, W. Vogelsang, F. Yuan http://spin.riken.bnl.gov/rsc/write-up/dy_final.pdf

  38. Non-universality of Sivers Asymmetries: Unique Prediction of Gauge Theory ! Simple QED example: Drell-Yan: repulsive DIS: attractive Same inQCD: As a result:

  39. Experiment SIDIS vs Drell Yan: Sivers|DIS= − Sivers|DY *** TestQCD Prediction of Non-Universality *** HERMES Sivers Results RHIC Drell Yan Projections 0 Sivers Amplitude Markus Diefenthaler DIS Workshop Műnchen, April 2007 0 0.1 0.2 0.3 x

  40. Rapidity and Collision Energy Large rapidity acceptance required to probe valence quark Sivers function

  41. Backup

  42. Benchmarking Simulations p+p  J/+X  l+l-+X, s=200 GeV PHENIX, hep-ex/0611020 m+m- 1.2<|h|<2.2 e+e- |h|<0.35 J/ is a critical benchmark that must be understood before Drell-Yan

  43. cc bb Dilepton Backgrounds Drell-Yan J/  ’ Isolation needed to discriminate open heavy flavor from DY

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