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Kenneth N. Barish ( for Kinichi Nakano) for the PHENIX Collaboration

Measurement of D G at RHIC PHENIX. Kenneth N. Barish ( for Kinichi Nakano) for the PHENIX Collaboration CIPANP 2009 San Diego, CA 26-31 May 2009. Drawings by Àstrid Morreale. Gluon contribution to proton spin. Hard Scattering Process.

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Kenneth N. Barish ( for Kinichi Nakano) for the PHENIX Collaboration

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  1. Measurement of DG at RHIC PHENIX Kenneth N. Barish (for Kinichi Nakano) for the PHENIX Collaboration CIPANP 2009 San Diego, CA 26-31 May 2009 Drawings by Àstrid Morreale

  2. Gluon contribution to proton spin Hard Scattering Process What is the gluon contribution to the proton spin (DG)? RHIC is sensitive to DG via strongly interacting probes • Probes gluon at leading order • High enough s for clean pQCD interpretation

  3. Leading hadrons as jet tags Hard Scattering Process qg+gq qq gg Double longitudinal spin asymmetry ALL is sensitive to G

  4. The PHENIX Detector for Spin Physics • Philosophy (initial design): • High rate capability & granularity • Good mass resolution & particle ID • limited acceptance • p0/g/h detection • Electromagnetic Calorimeter • p+/p- ,e • Drift Chamber • Ring Imaging Cherenkov Counter • Electromagnetic Calorimeter • m, J/y • Muon Id/Muon Tracker • Relative Luminosity • Beam Beam Counter (BBC) • Zero Degree Calorimeter (ZDC) • Local Polarimetry - ZDC • Filters for “rare” events

  5. Longitudinally Polarized Runs @PHENIX RHIC CNI (pC) Polarimeters Absolute Polarimeter (H jet) BRAHMS & PP2PP (p) Siberian Snakes Spin Rotators PHENIX (p) Partial Siberian Snake STAR (p) LINAC BOOSTER Pol. Proton Source AGS AGS Internal Polarimeter 200 MeV Polarimeter Rf Dipoles

  6. ALL Measurements GS95 xDG(x) prompt photon cceX bbeX J/ Robust measurement covering wide xg region through multiple channels: • Measurements • π0 200GeV – Run 3, 4, 5, 6 • 64GeV – Run 6 • π± Run 5, 6 (prelim) • Photon Run 5, 6 (prelim) • h Run 5, 6 (prelim) • Heavy FlavorRun 5, 6 (prelim)

  7. Measuring ALL at RHIC-PHENIX + - = + + ++ = • (N) Helicity dependent yields • (R) Relative Luminosity • BBC vs ZDC • (P) Polarization • RHIC Polarimeter (at 12 o’clock) • Local Polarimeters (SMD&ZDC) • Bunch spin configuration alternates every 106 ns • Data for all bunch spin configurations are collected at the same time •  Possibility for false asymmetries are greatly reduced

  8. 0cross section at 200GeV p0 DG2 DGDq Dq2 Phys.Rev.D 76, 051106 (2007) NLO pQCD calculations are consistent with cross-section measurements

  9. p0 ALL PHENIX Run6 (s=200 GeV) arXiv:0810.0694 Statatistical uncertainties are on level to distinguish “std” and “0” scenarios GRSV model: “G = 0”: G(Q2=1GeV2)=0.1 “G = std”: G(Q2=1GeV2)=0.4

  10. Relationship between pT and xgluon arXiv:0810.0694 arXiv:0810.0694 • NLO pQCD: 0 pT=212 GeV/c • GRSV model: G(xgluon=0.020.3) ~ 0.6G(xgluon =01 ) • Note: the relationship between pT and xgluon is model dependent • Each pT bin corresponds to a wide range in xgluon, heavily overlapping with other pT bins • Data is not very sensitive to variation of G(xgluon) within measured range • Any quantitative analysis assumes some G(xgluon) shape Log10(xgluon)

  11. Sensitivity of p0 ALL to DG (with GRSV) arXiv:0810.0694 Generate g(x) curves for different Calculate ALL for each G Compare ALL data to curves (produce 2 vs G)

  12. G: experimental uncertainties Systematic uncertainty Primary systematic uncertainties are from polarization (ΔP) and relative luminosity (ΔR). Polarization uncertainty is insignificant when extracting ΔG. Uncertainty in relative luminosity while small cannot be neglected when extracting ΔG. arXiv:0810.0694 Systematic uncertainty gives an additional +/- 0.1

  13. G: theoretical uncertainties arXiv:0810.0694 • Theoretical Scale Dependence: • Vary theoretical scale : • =2pT, pT, pT/2 •  0.1 shift for positive constraint •  Larger shift for negative constraint arXiv:0810.0694 • g(x) Parameterization • 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 •  Data are primarily sensitive to the size of G[0.02,0.3]. arXiv:0810.0694

  14. ΔG(x) C from Gehrmann Stirling Extending x-range is crucial present x-range xDG(x) x 0.3 GSC-NLO: ΔG = ∫0.02ΔG(x)dx ~ small Much of the first moment ΔG = ∫ΔG(x)dx might emerge from low x! GSC-NLO: ΔG = ∫ΔG(x)dx ~ 1.0 GSC-NLO

  15. Extend x Range Extend to higher x at s = 62.4 GeV Extend to lower x at s = 500 GeV To measure DG, need as wide an xg range as possible. • By measuring at different center of mass energies, we can reach different xg ranges. • We can extend our xg coverage towards higher x at s = 62.4 GeV.  Run6 • We can extend our xg coverage towards lower x at s = 500 GeV.  test: Run9 • Upgrades in the forward/backward direction (FVTX, FOCAL) have the potential to enable sensitivity to xg~10-3. present (0) x-range s = 200 GeV

  16. p0 ALL @ s=62.4 GeV PRD79,012003 (2009) • Short run with longitudinal polarized protonsALL • probes x range from .06 to 0.4 • Better statistical precision at higher x than previous measurements at 200GeV PRD79,012003 (2009) NLL may be important @ s=62 GeV

  17. Other Probes I • ± • Preferred fragmentation u+ and d-; • u>0 and d<0 different qg contributions for +, 0, - •  access sign of G   •  • Analysis similar to 0 • Different flavor structure • Independent probe of G

  18. Other Probes II Direct g @ 200 GeV ~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 • Future luminosity and detector upgrades will significantly improve.

  19. Recent Global Fit: DSSV First truly global analysis of polarized DIS, SIDIS and pp results PHENIX s = 200 and 62 GeV data used RHIC data significantly constrain G in range 0.05<x<0.3 RHIC range PRL 101, 072001(2008) • Dg(x) small is current RHIC measured range • Best fit has a node at x~0.1 • Low-x unconstrained

  20. Summary • RHIC is a novel accelerator which provides collisions of high energy polarized protons • Allows to directly use strongly interacting probes (parton collisions) • High s  NLO pQCD is applicable • PHENIX inclusive 0ALL data provide a significance constraint on G in the xg range ~[0.02;0.3] • The effect of stat. as well as experimental and theoretical syst. uncertainties are evaluated • At 3 level a constraint -0.7<Gx=[0.02;0.3] <0.5 is nearly shape independent • Other PHENIX ALL data are available • , ± - will be included in the G constraint • , e,  - need more P4L • Extending x coverage is crucial • Other channels from high luminosity and polarization • Different s • Upgrades

  21. Extra slides…

  22. Brazil University of São Paulo, São Paulo China Academia Sinica, Taipei, Taiwan China Institute of Atomic Energy, Beijing Peking University, Beijing Czech Charles University, Prague, Republic Czech Technical University, Prague, Czech Republic Academy of Sciences of the Czech Republic, Prague Finland University of Jyvaskyla, Jyvaskyla France LPC, University de Clermont-Ferrand, Clermont-Ferrand Dapnia, CEA Saclay, Gif-sur-Yvette IPN-Orsay, Universite Paris Sud, CNRS-IN2P3, Orsay LLR, Ecòle Polytechnique, CNRS-IN2P3, Palaiseau SUBATECH, Ecòle des Mines at Nantes, Nantes Germany University of Münster, Münster Hungary Central Research Institute for Physics (KFKI), Budapest Debrecen University, Debrecen Eötvös Loránd University (ELTE), Budapest India Banaras Hindu University, Banaras Bhabha Atomic Research Centre, Bombay Israel Weizmann Institute, Rehovot Japan Center for Nuclear Study, University of Tokyo, Tokyo Hiroshima University, Higashi-Hiroshima KEK, Institute for High Energy Physics, Tsukuba Kyoto University, Kyoto Nagasaki Institute of Applied Science, Nagasaki RIKEN, Institute for Physical and Chemical Research, Wako RIKEN-BNL Research Center, Upton, NY Rikkyo University, Toshima, Tokyo Tokyo Institute of Technology, Tokyo University of Tsukuba, Tsukuba Waseda University, Tokyo S. Korea Cyclotron Application Laboratory, KAERI, Seoul Ewha Womans University, Seoul, Korea Kangnung National University, Kangnung Korea University, Seoul Myong Ji University, Yongin City System Electronics Laboratory, Seoul Nat. University, Seoul Yonsei University, Seoul Russia Institute of High Energy Physics, Protovino Joint Institute for Nuclear Research, Dubna Kurchatov Institute, Moscow PNPI, St. Petersburg Nuclear Physics Institute, St. Petersburg Lomonosoy Moscow State University, Moscow St. Petersburg State Technical University, St. Petersburg Sweden Lund University, Lund 14 Countries; 68 Institutions; 550 Participants USA Abilene Christian University, Abilene, TX Brookhaven National Laboratory, Upton, NY University of California - Riverside, Riverside, CA University of Colorado, Boulder, CO Columbia University, Nevis Laboratories, Irvington, NY Florida Institute of Technology, FL Florida State University, Tallahassee, FL Georgia State University, Atlanta, GA University of Illinois Urbana Champaign, IL Iowa State University and Ames Laboratory, Ames, IA Los Alamos National Laboratory, Los Alamos, NM Lawrence Livermore National Laboratory, Livermore, CA University of Maryland, College Park, MD University of Massachusetts, Amherst, MA Muhlenberg College, Allentown, PA University of New Mexico, Albuquerque, NM New Mexico State University, Las Cruces, NM Dept. of Chemistry, Stony Brook Univ., Stony Brook, NY Dept. Phys. and Astronomy, Stony Brook Univ., Stony Brook, NY Oak Ridge National Laboratory, Oak Ridge, TN University of Tennessee, Knoxville, TN Vanderbilt University, Nashville, TN

  23. pQCD partonic level asymmetries HERMES (hadron pairs) COMPASS (hadron pairs) RHIC (direct photon) E708 (direct photon) CDF (direct photon) • High s and pT make the NLO pQCD analysis reliable • dependence of the calculated cross section on  represents an uncertainty in the theoretical predictions LO • NLO corrections are now known for all relevant reactions M. Stratmann and W. Vogelsang

  24. Use Zero Degree Calorimeter (ZDC) to measure a L-R and U-D asymmetry in forward neutrons (Acceptance: ±2 mrad). When transversely polarized, we see clear asymmetry. When longitudinally polarized, there should be no asymmetry. Local Polarimety at PHENIX Raw asymmetry Raw asymmetry YELLOW BLUE f f Raw asymmetry Raw asymmetry YELLOW BLUE f f Use neutron asymmetry to study transversely polarized component.

  25. Measured Asymmetry During Longitudinal Running (2005) LR c2/NDF = 82.5/97 p0 = 0.00423±0.00057 c2/NDF = 88.1/97 p0 = -0.00323±0.00059 UD • <PT/P>=10±2(%) • <PL/P> =99.48±0.12±0.02(%) XF>0 XF>0 • <PT/P>=14±2(%) • <PL/P>=98.94±0.21±0.04(%) UD c2/NDF = 119.3/97 p0 = 0.00056±0.00063 LR c2/NDF = 81.7/97 p0 = -0.00026±0.00056 • Measurement of remaining transverse component  spin pattern is correct Also confirmed in Run6 analysis XF<0 XF<0 Fill Number Fill Number

  26. Relative Luminosity • Number of BBC triggered events (NBBC) used to calculate Relative Luminosity. • For estimate of Uncertainty, fit • for all bunches in a fill with * Longitudinal

  27. Possible contamination from soft physics exponential fit • By comparing 0 data with charged pion data, which has very good statistics at low pT, can estimate soft physics contribution • Fitting an exponential to the low pT charged pion data (pT<1 GeV/c) gives an estimate on the soft physics contribution. • Fit result: a= 5.56±0.02 (GeV/c)−1 c2/NDF = 6.2/3 • From this, we see that for pT>2 GeV, the soft physics component is down by more than a factor of 10. For G constrain use 0 ALL data at pT>2 GeV/c PHENIX: hep-ex-0704.3599

  28. ALL of jet-like cluster at Ös=200GeV Run 5 g • “Jet” detection: tag one high energy photon and sum energy of nearby photons and charged particles • Definition of pT cone: sum of pT measured by EMCal and tracker with R = (||2+||2) • Real pT of jet is evaluated by tuned PYTHIA

  29. 62 GeV: Local Polarimetry Red : transverse data, Blue : longitudinal data • Forward Neutron asymmetry reduced at 62 GeV, but still measurable. Blue Forward Blue Backward xpos xpos Yellow Forward Yellow Backward xpos xpos

  30. Calculating p0 ALL • Calculate ALL(p°+BG) and ALL(BG) separately. • Get background ratio (wBG) from fit of all data. • Subtract ALL(BG) from ALL(p°+BG): • ALL(p°+BG) = wp° · ALL(p°) + wBG · ALL(BG) p0+BG region : ±25 MeV around p0peak BG region : two 50 MeV regions around peak • This method is also used for other probes with two particle decay mode: • h, J/Y

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