Adam Kocoloski, MIT For the STAR Collaboration Kyoto University October 3 2006

1. Double Longitudinal Spin Asymmetries of Inclusive Charged Pion Production in Polarized p+p Collisions at 200 GeV Adam Kocoloski, MIT For the STAR Collaboration Kyoto University October 3 2006 • Motivation • Analysis Method • Asymmetries • Systematic Uncertainties • Summary

2. Why Charged Pions? • Two complementary measurements with different contributions from polarized quark PDFs • For qg processes, ALL(+) - ALL(-) tracks sign of G • STAR is capable of efficient reconstruction and identification of charged pions over a large range of transverse momenta + - Adam Kocoloski

3. Measuring ALL at STAR • STAR TPC • || < 1.6 and 0.5 < r < 2.0 m inside 0.5T solenoid • Efficient reconstruction of charged tracks to 20 GeV; particle ID via dE/dx up to 10 GeV • 3 Separate Measurements • Beam Polarizations • Measured at RHIC polarimeters • Relative Luminosities • Beam-Beam Counter (BBC) scintillator tiles • Spin-sorted Yields • BBC and Barrel EMC trigger on events • Time Projection Chamber (TPC) reconstructs and identifies pions J. Adams, et al. Phys. Lett. B637, 161-169 (2006). Adam Kocoloski

4. Analysis Method Minimum bias  Jet patch pT Jet patch  • Triggering • All triggers require BBC coincidence • Statistics dominated by jet patch triggers: EM energy deposition in  x  = 1.0 x 1.0 patch • Cuts • Select high-quality sample of TPC tracks at || < 1. • Particle ID accomplished using TPC dE/dx • Use BBC timing window for vertex selection Adam Kocoloski

5. 2005 Inclusive +/- ALL GRSV polarized PDFs: M. Glück, E. Reya, M. Stratmann, W. Vogelsang, PRD63, 094005 (2001). B. Jäger, M. Stratmann and W. Vogelsang, PRD70, 034010 (2004). Fragmentation functions modified from KKP: B. A. Kniehl, G. Kramer and B. Pötter, Nucl. Phys. B582, 514 (2000). KKP modification: Charge-separated versions of KKP pion fragmentation functions obtained by multiplying favored partons by (1+z) and unfavored by (1-z). Adam Kocoloski

6. Systematic Summary All uncertainties are 10-3 on ALL: Adam Kocoloski

7. Trigger Bias • Majority of pions are sub-leading particles in trigger jet • Significant statistics from “away-side”, untriggered jet as well • PYTHIA afterburner used to construct “polarized” event generator • Calculate ALL in simulation with and without trigger requirement • Bias estimated using average of GRSV-min and GRSV-std scenarios • 3.0 - 7.3 x 10-3 as a function of pT and charge sign Other Cross-Checks • Charge-summed asymmetry consistent with neutral pions • “Near-side” and “away-side” asymmetries consistent with each other Adam Kocoloski

8. Particle ID Background • Plot track dE/dx in terms of standard deviations from mean of pion dE/dx band • Estimate >90% purity in acceptance window from multi-Gaussian fit • Shift dE/dx window to select a background sample and calculate its double-spin asymmetry • B.g. fraction x (asymmetry + 1 sigma)  1.7 x 10-3 Adam Kocoloski

9. Looking Ahead • 2006 saw improvements in: • polarization • trigger acceptance and thresholds • Begin to look at non-inclusive measurements… Adam Kocoloski

10. Looking Ahead: Away-side ALL • Calculate for each pion relative to trigger jet • Originally motivated by trigger bias studies • “away-side” sample free from fragmentation bias • Reasonable statistical precision • Needs theoretical guidance Adam Kocoloski

11. Summary • First spin result for inclusive charged pion production at STAR. • EMC-based triggering setup limits statistics at high pT and introduces a bias in the measured ALL. This bias is estimated in simulation to be less than the size of the statistical uncertainties. • Promising Outlook in 2006: • Significant increase in FOM • Away-side ALL reduces bias from jet trigger Adam Kocoloski

12. Backup Slides

13. Comparison With Neutral Pions Adam Kocoloski