K. Barish Kenneth N. Barish ( for Kinichi Nakano) for the PHENIX Collaboration CIPANP 2009 San Diego, CA May 2009 Measurement of  G at RHIC PHENIX Drawings by Àstrid Morreale

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

K. Barish Leading hadrons as jet tags Hard Scattering Process qg+gq qq gg Double longitudinal spin asymmetry A LL is sensitive to  G

K. Barish Philosophy (initial design): Philosophy (initial design): High rate capability & granularity High rate capability & granularity Good mass resolution & particle ID Good mass resolution & particle ID  limited acceptance The PHENIX Detector for Spin Physics    detection Electromagnetic Calorimeter      e Drift Chamber Ring Imaging Cherenkov Counter Electromagnetic Calorimeter , J  Muon Id/Muon Tracker Relative Luminosity Beam Beam Counter (BBC) Zero Degree Calorimeter (ZDC) Local Polarimetry - ZDC Filters for “rare” events

K. Barish Longitudinally Polarized Year  s [GeV] Recorded LPol [%]FOM (P 4 L) 2003 (Run 3) pb nb (Run 4) pb nb (Run 5) pb nb (Run 6) pb nb (Run 6) pb nb (Run 9)500~10 pb -1 ~35~150 nb (Run 9)200in progress

K. Barish prompt photon cc  eX bb  e  X J/  GS95 x  G(x) Robust measurement covering wide x g region through multiple channels: A LL Measurements Measurements π 0 200GeV – Run 3, 4, 5, 6 64GeV – Run 6 π  Run 5, 6 (prelim) Photon Run 5, 6 (prelim)  Run 5, 6 (prelim) Heavy Flavor  Run 5, 6 (prelim)

K. Barish (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 Measuring A LL at RHIC-PHENIX + - = ++ = + +

K. Barish  0 cross section at 200GeV NLO pQCD calculations are consistent with cross-section measurements G2G2 GqGq q2q2  Phys.Rev.D 76, (2007)

K. Barish  0 A LL PHENIX Run6 (  s=200 GeV) arXiv: GRSV model: “  G = 0”:  G(Q 2 =1GeV 2 )=0.1 “  G = std”:  G(Q 2 =1GeV 2 )=0.4 Statatistical uncertainties are on level to distinguish “std” and “0” scenarios

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

K. Barish arXiv: Sensitivity of  0 A LL to  G (with GRSV) Generate  g(x) curves for different Calculate A LL for each  G Compare A LL data to curves (produce  2 vs  G)

K. Barish Systematic uncertainty  Primary systematic uncertainties are from polarization ( Δ P) and relative luminosity ( Δ R).  Polarization uncertainty is insignificant when extracting Δ G.  Uncertainty in relative luminosity while small cannot be neglected when extracting Δ G. Systematic uncertainty gives an additional +/- 0.1  G: experimental uncertainties arXiv:

K. Barish  G: theoretical uncertainties  g(x) Parameterization  Vary  g’(x) =  g(x) for best fit and generate many A LL  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]. Theoretical Scale Dependence: Vary theoretical scale  :  =2p T, p T, p T /2  0.1 shift for positive constraint  Larger shift for negative constraint arXiv:

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

K. Barish Extend x Range Extend to lower x at  s = 500 GeV Extend to higher x at  s = 62.4 GeV To measure  G, need as wide an x g range as possible.  By measuring at different center of mass energies, we can reach different x g ranges.  We can extend our x g coverage towards higher x at  s = 62.4 GeV.  Run6  We can extend our x g 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 x g ~ present (  0 ) x -range  s = 200 GeV

K. Barish  0 A  s=62.4 GeV  Short run with longitudinal polarized protons  A LL  probes x range from.06 to 0.4 »Better statistical precision at higher x than previous measurements at 200GeV PRD79, (2009) NLL may be  s=62 GeV PRD79, (2009)

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

K. Barish Other Probes II Heavy Flavor Production dominated by gluon gluon fusion Measured via e + e -,  +  -, e , eX,  X Future luminosity and detector upgrades will significantly improve. Direct 200 GeV Direct Photon Quark gluon scattering dominates Direct sensitivity to size and sign of  G Need more P 4 L ~80%

K. Barish 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 PRL 101, (2008)   g(x) small is current RHIC measured range  Best fit has a node at x~0.1  Low-x unconstrained RHIC range

K. Barish 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  0 A LL data provide a significance constraint on  G in the x g 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<  G x=[0.02;0.3] <0.5 is nearly shape independent Other PHENIX A LL data are available » ,  ± - will be included in the  G constraint » , e,  - need more P 4 L Extending x coverage is crucial »Other channels from high luminosity and polarization »Different  s »Upgrades

K. Barish Extra slides…

K. Barish 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 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

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

K. Barish 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. BLUE YELLOW Raw asymmetry  Use neutron asymmetry to study transversely polarized component. BLUE YELLOW Raw asymmetry  Local Polarimety at PHENIX

K. Barish Measured Asymmetry During Longitudinal Running = 10±2(%) = 99.48±0.12±0.02(%) LR  2 /NDF = 88.1/97 p0 = ± LR UD  2 /NDF = 82.5/97 p0 = ± X F >0 X F <0  2 /NDF = 119.3/97 p0 = ± UD  2 /NDF = 81.7/97 p0 = ± Fill Number = 14±2(%) = 98.94±0.21±0.04(%) Also confirmed in Run6 analysis Measurement of remaining transverse component  spin pattern is correct (2005)

K. Barish Relative Luminosity Number of BBC triggered events (N BBC ) used to calculate Relative Luminosity. For estimate of Uncertainty, fit for all bunches in a fill with Year[GeV] RR  A LL 2005 *2001.0e-42.3e *2003.9e-45.4e * e-32.8e-3 * Longitudinal

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

K. Barish A LL of jet-like cluster at  s=200GeV Run 5 »“ Jet ” detection: tag one high energy photon and sum energy of nearby photons and charged particles »Definition of p T cone: sum of p T measured by EMCal and tracker with R =  (|  | 2 +|  | 2 ) »Real p T of jet is evaluated by tuned PYTHIA 

K. Barish Forward Neutron asymmetry reduced at 62 GeV, but still measurable. xpos Red : transverse data, Blue : longitudinal data Blue Forward Blue Backward Yellow Backward Yellow Forward BLUE0.065 ± YELLOW0.132 ± BLUE ± YELLOW ± P L BLUE 100% – 2.3% P L YELLOW 100% – 2.2% 62 GeV: Local Polarimetry

K. Barish Calculate A LL (  +BG) and A LL (BG) separately. Get background ratio (w BG ) from fit of all data. Subtract A LL (BG) from A LL (  +BG): A LL (  +BG) = w  · A LL (  ) + w BG · A LL (BG) This method is also used for other probes with two particle decay mode: , J/    +BG region : ±25 MeV around    peak BG region : two 50 MeV regions around peak Calculating  0 A LL