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 strid 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 0 200GeV Run 3, 4, 5, 6 64GeV Run 6 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 oclock) 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 G2G2 GqGq q2q2 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 ( P) and relative luminosity ( R). Polarization uncertainty is insignificant when extracting G. Uncertainty in relative luminosity while small cannot be neglected when extracting 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) G(x) C from Gehrmann Stirling present x-range Much of the first moment G = G(x)dx might emerge from low x! GSC-NLO: G = G(x)dx ~ 1.0 GSC-NLO GSC-NLO: G = 0.02 G(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