1. 1 STAR 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. 2 STAR Inclusive Charged Pion A LL Adam Kocoloski Why Charged Pions? Two complementary measurements with different contributions from polarized quark PDFs For qg processes, A LL (  + ) - A LL (  - ) tracks sign of  G STAR is capable of efficient reconstruction and identification of charged pions over a large range of transverse momenta ++ --

3. 3 STAR Inclusive Charged Pion A LL Adam Kocoloski Measuring A LL at STAR 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 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 J. Adams, et al. Phys. Lett. B637, 161-169 (2006).

4. 4 STAR Inclusive Charged Pion A LL Adam Kocoloski Jet patch p T Minimum bias  Jet patch  Analysis Method 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

5. 5 STAR Inclusive Charged Pion A LL Adam Kocoloski 2005 Inclusive  +/- A LL 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).

6. 6 STAR Inclusive Charged Pion A LL Adam Kocoloski Systematic Summary Trigger Bias {3.0 - 7.3}, p T dependent Non-longitudinal polarization3.0 Relative Luminosity2.2 Particle Identification1.7 Beam Background0.3 All uncertainties are 10 -3 on A LL :

7. 7 STAR Inclusive Charged Pion A LL Adam Kocoloski 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 A LL 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 p T and charge sign Other Cross-Checks Charge-summed asymmetry consistent with neutral pions “Near-side” and “away-side” asymmetries consistent with each other

8. 8 STAR Inclusive Charged Pion A LL Adam Kocoloski 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

9. 9 STAR Inclusive Charged Pion A LL Adam Kocoloski Looking Ahead 2006 saw improvements in: –polarization – –trigger acceptance and thresholds Begin to look at non-inclusive measurements…

10. 10 STAR Inclusive Charged Pion A LL Adam Kocoloski Looking Ahead: Away-side A LL 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

11. 11 STAR Inclusive Charged Pion A LL Adam Kocoloski Summary First spin result for inclusive charged pion production at STAR. EMC-based triggering setup limits statistics at high p T and introduces a bias in the measured A LL. 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 A LL reduces bias from jet trigger

12. 12 STAR Backup Slides

13. 13 STAR Inclusive Charged Pion A LL Adam Kocoloski Comparison With Neutral Pions