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M. Grosse Perdekamp University of Illinois, Urbana Champaign

STAR. Quark- and Gluon-Spin Structure of the Proton from High Energy Polarized Proton-Proton Collisions at RHIC. M. Grosse Perdekamp University of Illinois, Urbana Champaign. Seminar Saclay, March 16 th , 2012. Overview. Scientific Motivation Studying Nucleon spin structure

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M. Grosse Perdekamp University of Illinois, Urbana Champaign

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  1. STAR Quark- and Gluon-Spin Structure of the Proton from High Energy Polarized Proton-Proton Collisions at RHIC M. Grosse Perdekamp University of Illinois, Urbana Champaign SeminarSaclay, March 16th, 2012

  2. Overview • Scientific Motivation • Studying Nucleon spin structure • in polarized proton-proton collisions at RHIC • Gluon Spin • Experimental results from RHIC • Global analysis • Future Steps • W-production? • First results with W → e at mid-rapidity • Status of Measurements W → μ at forward rapidity With input and slides from Alexander Bazilevsky! Quark and Gluon Spin Structure of the Proton

  3. Motivation: The Nucleon as QCD Laboratory The proton is the fundamental bound state of QCD; Quarks and gluons are the Consituents: Can we understand the wave function of the nucleon from first principles QCD ? Present (modest) status: Description of proton in hard scattering processes with parton distribution functions. Quark and Gluon Spin Structure of the Proton

  4. Motivation: Proton Spin Structure Constituents: quarks = u, d, s and gluons Quark and Gluon Spin Structure of the Proton

  5. Motivation:Spin Sum Rule De-composition of the Proton Spin Orbital Angular momentum Quark Spin Gluon Spin Quark and Gluon Spin Structure of the Proton

  6. Proton Spin Structure from Inclusive Deep Inelastic Lepton-Nucleon Scattering spin Large Q2: measure photon-quark absorption cross section double spin asymmetry spin electron or muon probe proton target Extract spin dependent quark distribution functions from the spin structure function g1(x,Q2) Quark and Gluon Spin Structure of the Proton

  7. The Importance of Low x : Example Quark Spin ΔΣ Quark Spin Contribution to the Proton Spin. Measurements at SLAC: 0.10 < xSLAC <0.7 vs CERN: 0.01 < xCERN <0.5 A1(x) 0.1 < xSLAC < 0.7 Note: evaluation of ΔG=∫01G(x)dx may require large x coverage in particular towards low x QPM expectation ! E130, Phys.Rev.Lett.51:1135,1983: >400 citations. Spin Crisis ! EMC, Phys.Lett.B206:364,1988: >1400 citations in SPIRES EMC, Nucl.Phys.B328:1,1989, >1200 citations in SPIRES 0.01 < xCERN < 0.5 x-Bjorken Quark and Gluon Spin Structure of the Proton

  8. Quark Spin Contribution from Analysis of Spin Dependent Lepton-Nucleon Scattering Proton Neutron COMPASS Phys.Lett. B693 (2010) 227-235 • Fraction of proton spin • carried by quarks: • ΔƩ = 0.33 ± 0.025(exp) ± 0.030 (th) Deuteron Limitation: lepton probes couple to electric charge, sensitivity to gluons from scaling violations Quark and Gluon Spin Structure of the Proton

  9. Nucleon Spin Structure: 30 Years of Experiment Quark Spin – Gluon Spin – Transverse Spin – GPDs – Lz SLACE80-E155 CERN EMC,SMC COMPASS FNAL E704 DESY HERMES JLAB Halls A, B, C RHIC BRAHMS, PHENIX, STAR 2000 ongoing 1995 2007 ongoing ongoing experimental innovations high current polarized proton sources, high energy proton polarimeters, polarized collider polarized pp Quark and Gluon Spin Structure of the Proton

  10. A novel experimental method:Probing Proton Spin Structure in High Energy Polarized Proton Collisions Instrumentation High current polarized proton source High energy proton polarimetry Control of spin coherence during acceleration + storage Spin sorted luminosity measurements Physics Probes directly sensitive to color charge Utilize Parity violation in W-production Large Q2  clean pQCD interpretation RHIC pC Polarimeters Absolute Polarimeter (H jet) Siberian Snakes BRAHMS & PP2PP PHOBOS RHIC Spin Instrumentation Development 1995-2005 Siberian Snakes Spin Flipper PHENIX STAR Spin Rotators Helical Partial Snake Partial Snake Strong Snake Polarized Source LINAC AGS BOOSTER 200 MeV Polarimeter Rf Dipole AGS pC Polarimeter Quark and Gluon Spin Structure of the Proton

  11. RHIC SPIN: Proton Structure with Quark and Gluon Probes At ultra-relativistic energies the proton (roughly) represents a jet of quarks and gluons Example: Production of neutral pions ~ probe gluon content with with quark probes! experimental double spin asymmetry Jet,π0 gluon quark gluon quark Jet,π0 DIS QCD ? Quark and Gluon Spin Structure of the Proton

  12. G Measurements at RHIC • Polarized Gluon Distribution Measurements : • Use a variety of probes with variety of kinematics • Access to different gluon momentum fraction x • Different systematics • Use different beam energies • Access to different gluon momentum fraction x Quark and Gluon Spin Structure of the Proton

  13. Unpolarized Cross Sections and pQCD Calculations in pp at √s = 200 GeV PHENIX pp 0 X PRD76, 051106 STAR: ppjet X PRL 97, 252001 PHENIX pp X PRL 98, 012002 ||<0.35 ||<0.35 Good agreement between NLO pQCD calculations and data  pQCD can be used to extract spin dependent pdf’s from RHIC data. Quark and Gluon Spin Structure of the Proton

  14. Probing G in Polarized pp Collisions Double longitudinal spin asymmetry ALL is sensitive to G pp  hX Quark and Gluon Spin Structure of the Proton

  15. Double Spin Asymmetries ALL for Inclusive Jets Observed with STAR 20 10 Process Fraction STAR Preliminary Run6 , s=200 GeV pT [GeV] Good discriminative power between calculations with different assumption for G Quark and Gluon Spin Structure of the Proton

  16. ALL for Inclusive 0with PHENIX Process Fraction PHENIX Run5+6 √s = 200 GeV: PRL103, 012003 5 10 pT(GeV) 0pTwBG 2 GeV/c 20% 5 8% 10 5% Quark and Gluon Spin Structure of the Proton 16

  17. From ALL(pT) to G Compare ALL(pT) data with calculated ALL(pT) for a variety of PRL103, 012003 (2009) 2(G) • From pQCD: • pT = 212 GeV/c  • xgluon = 0.02  0.3 Quark and Gluon Spin Structure of the Proton

  18. G: Global QCD Based Fit DSSV: Daniel de Florian Rodolfo Sassot Marco Stratmann Werner Vogelsang • Phys. Rev. Lett. 101, 072001(2008) • First truly global analysis of all available polarized data including RHIC results • Uncertainty estimation: • 2=1 • 2/2=2% RHIC data A node? Quark and Gluon Spin Structure of the Proton

  19. Run9 0 ALL : PHENIX Preliminary Run5 Run6 Run9 Tendency to positive ALL? Quark and Gluon Spin Structure of the Proton

  20. Global Fit Including PHENIX Run9 0 ALL By S.Taneja et al (DIS2011) based on code from DSSV xG(x) xG(x) DSSV DSSV + PHENIX Run9 0 ALL No node Uncertainties decreased node at x~0.1 Quark and Gluon Spin Structure of the Proton

  21. Run9 0 ALL : STAR Preliminary • Run9: • 3-4 smaller stat. uncertainties than in Run6: • Trigger upgrade • DAQ upgrade (increased rate, lower ET threshold) Run9 data will have considerable impact on G global fit and its uncertainty Quark and Gluon Spin Structure of the Proton

  22. Other probes of ΔG Analysis similar to 0 Different flavor structure Independent probe of G PHENIX PRD83,032001(2011) ± Preferred fragmentation u+ and d - u>0 and d<0  different qg contri-butions for +, 0, -  sensitivity to sign of G   Quark and Gluon Spin Structure of the Proton

  23. Other probes of ΔG ~80% • Direct Photon • Quark gluon scattering dominates • Direct sensitivity to size and sign of G • Need more P4L • Heavy Flavor • Production dominated by gluon gluon fusion • Measured via e+e-, +-, e, eX, X • Need more P4L Quark and Gluon Spin Structure of the Proton

  24. Extend x-range  different s 0 at ||<0.35: xg distribution vs pT bin s=62 GeV 2-2.5 GeV/c 4-5 GeV/c 9-12 GeV/c s=200 GeV  2-2.5 GeV/c 4-5 GeV/c 9-12 GeV/c s=500 GeV Quark and Gluon Spin Structure of the Proton

  25. 0 at s=62 and 500 GeVUnpolarized Cross Sections s=62 GeV: PHENIX, PRD79, 012003 s=500 GeV: PHENIX Preliminary May need inclusion of NLL to NLO Data below NLO at =pTby (3015)% Quark and Gluon Spin Structure of the Proton

  26. PHENIX ALL for π0 s=62 GeV PHENIX, PRD79, 012003 • Very limited data sample (0.04 pb-1, compared 2.5 pb-1 from Run2005 s=200 GeV) • Clear statistical improvement at larger x; extends the range to higher x (0.06<x< 0.4) • Overlap with 200 GeV ALL provides measurements at the same x but different scale (pT) • s=500 ALL results will be available soon (from Run2009 with L~10 pb-1 and P~0.4) Quark and Gluon Spin Structure of the Proton

  27. G: Path Forward • Limitations in current data: • Limited x-range covered • Weak sensitivity to the shape of G(x) • Improve precision of current measurements • Get more data • Extend xg-range • Move to forward rapidities • Constrain kinematics: map G vsxg • More exclusive channels: pp  + jet and pp jet + jet Quark and Gluon Spin Structure of the Proton

  28. Impact of Additional Data for Jets and π0 STAR pp jetX : projections PHENIX pp 0 X : projections Quark and Gluon Spin Structure of the Proton

  29. Probing Low x Through Forward Di-Hadrons merged p0s PHENIX central spectrometer magnet mid-fwd xgluon ~ 10-2 mid-fwd xgluon ~ 10-2 fwd-fwd xgluon ~ 10-4-10-3 ϕ Muon Piston Calorimeter (MPC) trigger EM-cluster 3.1<η<3.9 p p asssociated p0 or EM-clusters 3.1 < η < 3.9 MPC PbWO4 asssociated p0 3.1 < η < 3.9 p0 trigger p0 or h+/- |η|<0.35 Backward direction (South)  Forward direction (North)  Side View

  30. PHENIX Muon Piston Calorimeter Technology  ALICE(PHOS) PbWO4 avalanche photo diode readout Acceptance: 3.1 < η < 3.9, 0 < φ < 2π -3.7 < η < -3.1, 0 < φ < 2π Both detectors were installed for 2008 d-Au run. Assembly at UIUC PbWO4 + APD + Preamp MPC integrated in the piston of the muon spectrometer magnet. 30

  31. Forward Calorimetry: PHENIX MPC • Muon Piston Calorimeter (MPC): PbWO4 • 3.1 < || < 3.9, 2 azimuth • Gives access to lower: x10-3 • Fully available from 2008 STAR: 0 forward rapidity PRL 97, 152302 pQCD seems working even at forward rapidities MPC 0 500 GeV 300 pb-1 P=0.55 Quark and Gluon Spin Structure of the Proton

  32. STAR: di-Jet ALL Run9 data Projections for s=500 GeV Constrains kinematics  shape of G(x) Quark and Gluon Spin Structure of the Proton

  33. PHENIX Silicon Vertex trackers VTX (2011) & FVTX (2012) VTX barrel |h|<1.2 Q = c or b Q g g q g jet Q g q EMC and MPC: pT and photon VTX: jet Rejects hadronic background c/b separated measurements FVTX endcaps 1.2<|h|<2.7 mini strips Luminosity and polarization hungry Quark and Gluon Spin Structure of the Proton

  34. Flavor Separation of Quark- Anti-Quark Polarizations Presently from SIDIS: Fragmentation functions to tag (anti)quark flavor DSSV: PRL 101, 072001 (2008) p+p W  e  / +  • Parity violating W production: • Fixes quark helicity and flavor • No fragmentation involved • High Q2 (set by W mass) l + Quark and Gluon Spin Structure of the Proton

  35. W-Production: Sensitivty of AL vs l • STAR • Central (barrel) region (We , ||<1) • First data from 2009: PRL106, 062002 (2011) • Forward (endcap) region (We , 1<||<2) : • Forward tracker upgrade, first data in 2012 • PHENIX • Central Arms (We , ||<0.35) • First data from 2009: PRL106, 062001 (2011) • Forward Arms (W , 1.2<||<2.4) : • Trigger upgraded, first data from 2011 Quark and Gluon Spin Structure of the Proton

  36. Central region: W  e from Run9 • Triggered by energy in EMCal • Momentum from energy in EMCal • Charge from tracking in B field PHENIX: |e|<0.35 STAR: |e|<1 e- e+ L=12 pb-1 L=8.6 pb-1 e+ e- Quark and Gluon Spin Structure of the Proton

  37. Central region: W  e from Run9 Cross section P=0.39L=8.6/12 pb-1 in PHENIX/STAR PHENIX: PRL106, 062001 (2011) STAR: PRL106, 062002 (2011) STAR AL PHENIX AL e- e+ e- e+ Quark and Gluon Spin Structure of the Proton

  38. Muon Trigger Upgrade for W-Physics muTr trigger electronics(JSPS) Muon Trigger fully installed for run 2012 RHIC 2012 Luminosity at 200 GeV FPGA based level-1 trigger processors RPCs in Urbana (NSF) RPCs in PHENIX (NSF) Run at √s = 510 GeV starts next week! Quark and Gluon Spin Structure of the Proton

  39. Last Component of the RPC based Muon Trigger: Upstream Stations RPC-1 north & south installed in October and November 2011 PHENIX RPC-1 north (~ 3m) PHENIX RPC-3 north (diameter ~ 10 m) Quark and Gluon Spin Structure of the Proton

  40. PHENIX Forward Arm: W   • First data collected in 2011: • L~15 pb-1P~0.52 Raw yields with different triggers and cuts  trigger eff.  trigger rejection Expected W yield More challenging than We at ~0 PHENIX 2kHz Bandwidth Quark and Gluon Spin Structure of the Proton

  41. W  l : Projections for Quark Polarizations STAR: We PHENIX: We PHENIX: W Quark and Gluon Spin Structure of the Proton

  42. Summary • RHIC is the world’s first and only facility which provides collisions of high energy polarized protons • Allows to directly use strongly interacting probes (parton collisions) • High s  NLO pQCD is applicable • PHENIX&STAR continues producing results for different spin observables • Significant constraint on G for xg~0.02-0.03 from inclusive 0 and jet ALL at s=200 GeV • Other ALL measurements to be included in G global fit with different systematics and x-coverage • First AL results from W  ein central rapidity at s=500 GeV from 2009 run • First AL results from W  in forward rapidity at s=500 GeV from 2011 runcoming soon Quark and Gluon Spin Structure of the Proton

  43. Backup Quark and Gluon Spin Structure of the Proton

  44. Transition form Soft to Hard PRD76, 051106 (2007) • Exponent (e-pT) describes our pion cross section data perfectly well at pT<1 GeV/c (dominated by soft physics): • =5.560.02 (GeV/c)-1 • 2/NDF=6.2/3 • Assume that exponent describes soft physics contribution also at higher pTs  soft physics contribution at pT>2 GeV/c is <10% exponential fit pT>2 GeV/c – hard scale? Quark and Gluon Spin Structure of the Proton

  45. From pT to xgluon 10-3 10-2 10-1 x • NLO pQCD: 0 pT=212 GeV/c  xgluon=0.020.3 • GRSV model: G(xgluon=0.020.3) ~ 0.6G(xgluon =01 ) • Each pT bin corresponds to a wide range in xgluon, heavily overlapping with other pT bins • These data is not much sensitive to variation of G(xgluon) within our x range • Any quantitative analysis should assume some G(xgluon) shape Quark and Gluon Spin Structure of the Proton

  46. From ALL to G (with GRSV) Generate g(x) curves for different (with DIS refit) Calculate ALL for each G Compare ALL data to curves (produce 2 vs G) Quark and Gluon Spin Structure of the Proton

  47. G: theoretical uncertainties • Parameterization (g(x) shape) choice • Vary g’(x) =g(x) for best fit, and generate many ALL • Get 2 profile • At 2=9 (~3), consistent constraint: • -0.7 < G[0.02,0.3] < 0.5 •  Our data are primarily sensitive to the size of G[0.02,0.3]. • Theoretical Scale Dependence: • Vary theoretical scale : • =2pT, pT, pT/2 •  0.1 shift for positive constraint •  Larger shift for negative constraint Quark and Gluon Spin Structure of the Proton

  48. MPC: 0 cross section Quark and Gluon Spin Structure of the Proton

  49. W cross section Quark and Gluon Spin Structure of the Proton

  50. sPHENIX Quark and Gluon Spin Structure of the Proton

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