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Recent . Results for A LL and Current Constraints on D G

Recent . Results for A LL and Current Constraints on D G. Kieran Boyle (RIKEN BNL Research Center). Outline: Quick Physics overview RHIC, PHENIX, and A LL Results from Run5 and Run6 Constraints on D G Current and Future Issues. Accessing D G in pp scattering.

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Recent . Results for A LL and Current Constraints on D G

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  1. Recent . Results for ALL and Current Constraints on DG Kieran Boyle (RIKEN BNL Research Center) Outline: • Quick Physics overview • RHIC, PHENIX, and ALL • Results from Run5 and Run6 • Constraints on DG • Current and Future Issues

  2. Accessing DG in pp scattering Hard Scattering Process p0 DG2 DGDq Dq2 • From Run5 and Run6, we consider an array of probes: • p0 large statistics, specified trigger • p+, p- large statistics, low trigger efficiency, PID only for pT<2.8 and pT>4.7 GeV/c • Direct photon low statistics, no DG2 very clean signal • h low statistics • multiparticle “cone” • J/Y with DS ~25%, DG not well constrained, L? ALL~ agg * DG2 + bgq * DG Dq + cqq Dq2

  3. Why ALL? • If Df = Dq, then we have this from pDIS • So roughly, we have From ep (&pp) (HERA mostly) From e+e- pQCD NLO +- = + = ++ +

  4. Measuring ALL • Helicity Dependent Particle Yields • p0, p+, p-, g, h, etc • (Local) Polarimetry • Relative Luminosity (R=L++/L+-) • ALL + - = Opposite helicity = + = + ++ = Same helicity

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

  6. PHENIX Detector BBC ZDC ZDC p0, h, g detection • Electromagnetic Calorimeter (PbSc/PbGl): • High pT photon trigger to collect 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) EMCal

  7. Use ZDC and SMD 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 Polarimetry at PHENIX Raw asymmetry Raw asymmetry YELLOW BLUE f f Raw asymmetry Raw asymmetry YELLOW BLUE f f

  8. 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 XF<0 XF<0 Fill Number Fill Number Also confirmed in Run6 analysis

  9. Relative Luminosity • R = L++/L+- ; L = luminosity. • Luminosity is given by the number of BBC triggered events (NBBC). • For estimate of uncertainty, measure ALL in the ratio of our two luminosity detectors * Longitudinal ** Online

  10. Strategy: • Measure Cross Section to confirm that pQCD is applicable to data • Measure ALL to extract DG

  11. pQCD works p0 @ 200 GeV Direct g @ 200 GeV arXiv:0704.3599 [hep-ex]

  12. 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) Two Photon Mass Spectrum p0+BG region : ±25 MeV around p0peak BG region : two 50 MeV regions around peak

  13. Final Run5 p0 ALL • Data is compared to GRSV model with several input values of DG. • To interpret data, we use pQCD Question: At what pT does soft physics contribution become small enough to allow comparison to pQCD models Adare et al., PRD76 (2007) 051106 9.4% scale uncertainty not included GRSV: M. Gluck, E. Reya, M. Stratmann, and W. Vogelsang, PRD 63 (2001) 094005.

  14. Soft physics exponential fit • By comparing p0 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.

  15. Final Run5 p0 ALL Adare et al., PRD76 (2007) 051106 • Measure below 1 GeV (~100% soft physics). ALL = 0.002±0.002. • Above pT=2 GeV/c, soft physics contribution estimated to be <10% • Contamination from soft physics asymmetry is small • Note that DSSV used data with pT>1 GeV Extend this approach 9.4% scale uncertainty not included

  16. Run6 p0 ALL • Run6 scaling error based on online polarization values. Final scaling error expected to be ~10% • Grey band is systematic uncertainty due to Relative Luminosity, and is pT independent. • Run6 Data favor “GRSV DG=0” over GRSV-std *Theoretical uncertainties not included

  17. Sensitivity of p0 ALL to DG Scaling Errors not included • Stat errors only • What about: • exp. syst.? • theory uncertainties?

  18. Polarization uncertainty: scales both the data and the error. Very small effect on interpretation in terms of DG Final results for Run6 will be similarly small with final pol. values Issues: Already below required limit of 5% per beam Note that this is fully correlated between all data points measured at RHIC (STAR and PHENIX) for a given year and energy Exp. Systematics Adare et al., PRD76 (2007) 051106 P-dP P+dP

  19. Relative Luminosity uncertainty: Effectively a common shift of all data. As the results for ALL are about zero, has more significant effect than polarization uncertainty, but still small Relative Luminosity In Run6, most significant experimental uncertainty in extracting DG Larger in Run6 than Run5. Expected to become worse in the future: higher luminositymore multiple collisions squeezing longitudinal bunch profile may increase problem Note that this is entirely correlated between all measurements at PHENIX, and so must be handled correctly To reduce effect, will REQUIRE spin flipper Exp. Systematics ALL+dALL|R ALL-dALL|R

  20. Sensitivity of p0 ALL to DG Scaling Errors not included present x-range

  21. From pT to xgluon • NLO pQCD: 0 pT=29 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 Log10(xgluon)

  22. Sign Ambiguity Hard Scattering Process p0 DG2 DGDq Dq2 • Dominance of two gluon interaction at low pT  present p0 ALL data cannot determine sign of DG. • Solution: • Higher pT higher FOM (P4L) • Look to other probes: • Direct Photon, in which DG2 term is not allowed at lowest order. • Charged pions

  23. Sign Ambiguity II Fraction of pion production • With PHENIX RICH, charged pions above 4.7 GeV can be identified. • At higher pT, qg interactions become dominant and so DqDg term in ALL becomes significant allowing access to the sign of DG • Expect if DG>0, then: ALL(p+)>ALL(p0)>ALL(p-) • Additional data will help.

  24. Direct photon Hard Scattering Process g DgDq DqDq RUN5 • First step, direct photon cross section. • ALL results from Run5 with very small statistics • Will need significant data set for this measurement (more than Run6) • Background ALL estimates increase errors by ~30% at low pT • Currently studying other methods to estimate background Gluon-photon compton dominant Isolation cut R=0.5, f=0.1 minE=0.15GeV Pmin=0.2GeV Pmax=15GeV

  25. p+p h + X Hard Scattering Process h Dg2 DgDq Dq2 • Similar analysis technique as with p0, using two photon decay channel. • Independent measure for gluon polarization. • Due to different fragmentation functions, expectations are slightly different. • Statistically limited currently

  26. Extending the x range: p0 ALL at s = 62.4 GeV for high x measurement

  27. p0 ALL @ s=62.4 GeV GRSV: M. Gluck, E. Reya, M. Stratmann, and W. Vogelsang, Phys. Rev. D 53 (1996) 4775. • Short run with longitudinal polarized protonsALL • Grey band is systematic uncertainty due to Relative Luminosity pQCD works measure ALL

  28. Comparison with 200 GeV • At fixed xT, p0 cross section is 2 orders of magnitude higher at 62.4 GeV than at 200 GeV • Converting to xT, we can get a better impression of the significance of the s=62.4 GeV data set, when compared with the Run5 final data set. Run5 200GeV final 2.7pb-1 (49%) Run6 62.4GeV prelm. 0.04 pb-1 (48%)

  29. A new theoretical fit • De Florian, Sassot, Stratmann and Vogelsang (DSSV) have recently included p0 data at 200 and 62 GeV from PHENIX. • First use of any pp data. • Only Experimental stat and syst (summed in quadrature) uncertainties • NO THEORETICAL UNCERTAINTIES were considered. • Results for DG were driven by RHIC data in the range x=[0.05-0.2]

  30. Conclusions • Cross sections have been measured at s=200 GeV and s=62 GeV and NLO pQCD describes our data well. • Run5 and Run6 p0 ALL are a significant constraint on the gluon spin contribution to the proton in the x range [0.02,0.3]. • Experimental systematic uncertainties are small, but are beginning to be significant. • Spin Flipper at RHIC will be needed to reduce Rel. Lumi. uncertainty • More luminosity at s=200 GeV will enable us to address the DG sign ambiguity with charged pions as well as direct photons. • Extending the measured x range will be needed, and has begun with measurements at s=62 GeV.

  31. Backups

  32. Scale

  33. Charged pion pt spectrum • All high quality ERT trigger tracks with an associated RICH hit with matching, dc acceptance, EM prob, E/p and momentum dependent energy cuts applied.

  34. Polarimetry: Direction • Require longitudinally polarized beams at PHENIX to measure ALL, and so use spin rotators. • How can we know direction? Consider a single spin asymmetry (SSA). SSA found in forward neutron production at RHIC in 2002 [Bazilevsky et al. PLB 650:325-330,2007] from M. Togawa

  35. ATT • If large, could lead to false ALL. • Theory expects it to be small • Experimentally found to be consistent with zero.

  36. What about polarized? DG DS~0.25 • Recall the unpolarized data. • In the polarized case, much less data exists, covering much smaller x and Q2 range. • Even with this small range of data, polarized quark distribution is reasonably well constrained. • DS~25% of proton spin  most of proton spin in either gluon spin, or OAM. • But from fixed target DIS, gluon is very poorly constrained. How can we measure the gluon?

  37. HJet results for target asymmetry are consistent between Run5 and Run6. Results from beam asymmetry differ, indicating change in polarization. Polarimetry results Run5 Run6

  38. Extending x range is crucial! GSC: G(xgluon= 01) = 1 G(xgluon= 0.020.3) ~ 0 GRSV-0: G(xgluon= 01) = 0 G(xgluon= 0.020.3) ~ 0 GRSV-std: G(xgluon= 01) = 0.4 G(xgluon= 0.020.3) ~ 0.25 Gehrmann-Stirling models GSC: G(xgluon= 01) = 1 GRSV-0: G(xgluon= 01) = 0 GRSV-std: G(xgluon= 01) = 0.4 Current data is sensitive to G for xgluon= 0.020.3

  39. 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 x range as possible. • Planned Upgrades such as the VTX, FVTX and Nosecone will help • By measuring at different center of mass energies, we can reach different x ranges. • We can extend our x coverage towards lower x at s = 500 GeV. Expected to start in 2009. • We can extend our x coverage towards higher x at s = 62.4 GeV.  Run6 present x-range s = 200 GeV

  40. Direct g Production g DgDq DqDq Run-3 hep-ex/0609031 • Gluon Compton scattering dominates • At LO no fragmentation function • Small contribution from annihilation

  41. SMC Fit to DIS Polarized gluon distribution poorly constrained

  42. Backup: SIDIS for G HERMES preliminary

  43. Backup: GFrom M. Stratmann

  44. Proton Spin

  45. Recent ALL Measurements arXiv:0704.3599 [hep-ex] p0 h Many independent probes to understand gluon spin

  46. Results From DIS • Basic Idea (Cartoon): • How many quarks have spin in direction of proton spin  polarized PDF • Look at DIS • So measure Asymmetry of proton polarized along photon vs. against photon = q l X =

  47. Nucleon Spin Structure  Gluons are polarized (G)  Sea quarks are polarized: For complete description include parton orbital angular momentum LZ: 1989 EMC (CERN): =0.120.090.14  Spin Crisis Naïve parton model: Determination of G and q-bar is the main goal of longitudinal spin program at RHIC

  48. Polarized PDF from DISAsymmetry Analysis Collaboration M. Hirai, S. Kumano and N. Saito, PRD (2004) Valence distributions well determined Sea Distribution poorly constrained Gluon can be either positive, 0, negative!

  49. Learning about structure with DS ~25%, DG not well constrained, L? • Primary method is Deeply Inelastic Scattering (DIS). • Scatter off quark with momentum fraction x, and understand probability to find a given quark at a given x, known as the Parton Distribution Function (PDF). Q2 = -q2

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