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Spin Effects in Large Rapidity Neutral Pion Production at STAR

Spin Effects in Large Rapidity Neutral Pion Production at STAR. Steve Heppelmann Penn State University For the STAR Collaboration PANIC 2005 Sante Fe Oct 27. Measurement of Cross Sections for  ° production at rapidity >3 with comparison to PQCD.

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Spin Effects in Large Rapidity Neutral Pion Production at STAR

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  1. Spin Effects in Large Rapidity Neutral Pion Production at STAR Steve Heppelmann Penn State University For the STAR Collaboration PANIC 2005 Sante Fe Oct 27 • Measurement of Cross Sections for ° production at rapidity >3 with comparison to PQCD. • Measurements of Transverse Spin Asymmetries “AN” in this forward region, XF positive and in the backward region XF negative. • Observation of pT dependence of AN. • Future runs with staged electromagnetic calorimeter upgrades.

  2. For the STAR Collaboration

  3. Brookhaven National Lab STARExperiment

  4. STAR Forward Calorimetry Recent History and Plans • Prototype FPD • Run 2 polarized proton data (published 2004 spin asymmetry and cross section) Prototype FMS Run 6 Fall 2005 (FPD++) • FPD • Run 3-5 data • pp, dAu • (Preliminary An Results) FMS Forward Meson Spectrometer Run 7 2006 (hep-ex/0502040).

  5. Cross Sections and Analyzing Power published from RHIC Run 2 J. Adams et al. (STAR collaboration), Phys. Rev. Lett. 92 (2004) 171801 [hep-ex/0310058]. Similar asymmetry to many lower energy measurements. → R.D. Klem et al., Phys. Rev. Lett. 36 (1976) 929; W.H. Dragoset et al., Phys. Rev. D18 (1978) 3939; S. Saroff et al., Phys. Rev. Lett. 64 (1990) 995; B.E. Bonner et al., Phys. Rev. D41 (1990) 13; K. Krueger et al, Phys. Lett. B459 (1999); C.E. Allgower et al., Phys. Rev. D65 (2002) 092008. But now, for the first time, in a region where NLO PQCD calculations fairly accurately predict the cross section.

  6. Current FPD Detector • Both East and West of Interaction region we have: • 2 5x5 arrays of Pb Glass (up/down) • 2 7x7 arrays of Pb Glass (North/South)

  7. ppp0X cross sections at 200 GeV Presented at Moriond 2005:hep-ex/0505024 • The error bars are point-to-point systematic and statistical errors added in quadrature • The inclusive differential cross section for º production is consistent with NLO pQCD calculations at 3.3 < η < 4.0 • As η increases, systematics regarding the comparison with NLO pQCD calculations begin to emerge. The data at low pT are more consistent with the Kretzer set of fragmentation functions. Similar to what was observed by PHENIX. NLO pQCD calculations by Vogelsang, et al.

  8. Separated xF and pT dependence Similar to ISR analysis J. Singh, et al Nucl. Phys. B140 (1978) 189.

  9. Caveats: -RHIC CNI Absolute polarization still preliminary. -Result Averaged over azimuthal acceptance of detectors. -Positive XF (small angle scattering of the polarized proton). Run 2 Published Result. Run 3 Preliminary Result. -More Forward angles. -FPD Detectors. Run 3 Preliminary Backward Angle Data. -No significant Asymmetry seen. ( Presented at Spin 2004: hep-ex/0502040) Run 3 + Run 5 Preliminary <>=3.7,4.0 (Presented SPIN 2005 Dubna Sept 27-Oct 1)

  10. Sivers Effect on two pion correlations. Correlation between k┴ and transverse Spin of proton. 1 The pt1 + pt2 ~ k┴correlated with spin. 2

  11. Collins Effect • Correlation between transverse spinand transverse polarization of large x quark • HardScattering preserves quark transverse spin. • Fragmentation azimuthal dependence gives • rise to AN asymmetry.

  12. AN(pT) in run3+run5 at √s=200 GeV Online calibration of CNI polarimeter • Combined statistics from run3 and run5 allowed to distinguish nonzero effect in AN(pT) plot • There is an evidence that analyzing power at xF>0.4 decreases with increasing pT • Theoretical prediction’s needed (for constraint on Sivers function).

  13. FMS Design Forward Calorimeters FPD Run 3-5 (2003-2005) FPD++ Run 6 (2005-2006) FMS Run 7- (2006- )

  14. FPD ++ … To be Installed for 2005 PHYSICS OBJECTIVES • Prototype for FMS • Similar to Left-Right FPD modules but surrounded with active area (larger cells). • Direct Photons in small cells with active veto for isolation cuts. • An (Direct Photons) ….No Fragmentation….No Collins • Extra particles from fragmentation of jet and recoil jet.

  15. PHYSICS OBJECTIVES FMS …. To be Installed for 2006 • Near full EM coverage -1<<4 • Pairs of Forward Pions same side correlations (Fragmentation – Collins) • Opposite side correlated pions (dijets) • Sivers effect • d-Au (Gluon saturation in Nuclei) • Other future objectives • Forward Lepton pairs • Charm • Drell Yan Planned FMS Wall FNAL 831 Pb. Glass Wall (5.8 cm x 5.8 cm cells)

  16. Conclusion • Large rapidity p0 cross sections for p+p collisions at √s = 200 GeV is in agreement with NLO pQCD, unlike at lower √s • Large transverse single spin asymmetries are observed in forward p0 production for polarized p+p collisions at √s = 200 GeV • AN grows with increasing xF for xF>0.35 • AN is zero for negative xF • First result for the AN(pT) was obtained using combined statistics from run3 and run5. There is evidence that the p0 analyzing power at xF>0.4 decreases with increasing pT • For RHIC run-6 (2005): FPD++ gamma/π0 separation will be possible. • For RHIC run-7 (2006): FMS • probe low-x gluon densities • establish dynamical origin of AN (Sivers/Collins) with correlated pion pair studies.

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