Amaresh Datta (UMass, Amherst)

1. Double-Longitudinal Spin Asymmetry in Non-identified Charged Hadron Production at pp Collision at √s = 62.4 GeV at Amaresh Datta (UMass, Amherst) Amaresh Datta (UMass)

2. Orbital ang. momenta Gluon spin contrib. Quark spin  0.33 Proton Spin and Search for Gluon Polarization • At PHENIX, polarized proton-proton scattering is studied to probe gluon polarization • At √s = 62.4 GeV, mid-rapidity hadron production is sensitive to polarized gluon distribution and probes interaction of partons with momentum fraction 0.06 < x < 0.4 Amaresh Datta (UMass)

3. Subprocess Contributions to Mid-rapidity Charged Hadron Production as a Function of COM Energy 17.3 GeV 62.4 GeV 130 GeV 200 GeV gg qg qq Fractional Contribution Calculations by W. Vogelsang In the low transverse momentum range of our interest (0.5 < pT < 4.5 GeV/c), ‘qg’ process is the dominant contributor Amaresh Datta (UMass)

4. Hard Scattering Process Hard Scattering Processes in p+p:Factorization and Universality • The cross section of a hard scattering process is convolution of: • Parton distribution functions (need experimentalinput) • pQCD hard scattering rates (calculable in pQCD) • Fragmentation functions (need experimental input) Amaresh Datta (UMass)

5. Motivation for Charged Hadron Asymmetry Measurement at √s = 62.4 GeV • Measurements of ALL will be additional contribution to global analysis for constraining ∆g • Will probe slightly higher x-range than higher (200 GeV) energy measurements • Will be corroboration of gluon polarization found in neutral pion ALL at PHENIX • Charged hadron asymmetries can be helpful in determining sign of ∆g • A significant positive ∆g can be reflected in the asymmetries as ALL(π+) > ALL(π0) > ALL(π-); (for ∆g(x) without any node) • A negative ∆g will cause reverse order in asymmetries Amaresh Datta (UMass)

6. Cross-sections • Cross-section of charged hadrons will be measured and compared with NLO and NLL calculations • Charged hadron cross-section from 2002 run at 200 GeV and neutral pion cross-section from 2006 run at 62.4 GeV have been measured and show good agreement with theoretical predictions • 62.4 GeV data suggests NLL corrections may be relevant at this energy Charged hadron cross-section from Run-2 (PRL 95, 202001) Neutral Pion cross-section in Run-6 at 62.4 GeV (submitted to PRD) Amaresh Datta (UMass)

7. Data Set • Run-6 data (2006) • 1 week of longitudinally polarized pp collision data at √s = 62.4 GeV recorded at Relativistic Heavy Ion Collider (RHIC) • Analyzed data ~ 40 nb-1 • Events analyzed were triggered (PHENIX minimum-bias trigger) by requiring coincidence of hits on Beam-Beam Counters (BBC) on both sides of the centre of nominal interaction region Amaresh Datta (UMass)

8. Measurement at PHENIX • Charged hadron tracking: • Drift Chamber (DC) • Pad Chamber (PC) • Luminosity Detectors: • Beam-Beam Counter (BBC) • Zero Degree Calorimeter (ZDC) • Background sources • Electrons from event vertex and decays and conversions • Hadrons from decay of long-lived particles • Hadrons from decay of short lived particles Tracking starts from DC Amaresh Datta (UMass)

9. Tracking of Charged Particles • Charged particles hit Drift Chamber • Almost no magnetic field after DC • Tracks projected onto outer Detectors (e.g. Pad Chamber) • Hits on outer detectors within acceptable deviation are associated with tracks Amaresh Datta (UMass)

10. Treatment of Backgrounds • Electron backgrounds vetoed by Ring Imaging Cherenkov Detector (RICH) • Electrons fire RICH at ~ 17 MeV/c • RICH theshold for pions ~ 4.7 GeV/c • Contribution from decays of long-lived (cτ ~ 1-10 m) particles are estimated using broadened distribution of hits on Pad Chamber and ALL is corrected for background ALL • Short-lived (cτ ~ 1-10 cm) decay contribution estimated to be ~ 7±7 % and no correction to ALL for this background is performed Amaresh Datta (UMass)

11. Reduction of Backgrounds • Spectra of charged tracks (from data) before and after specific cuts within pT range of interest • Higher pT region contains particles that do not originate from event vertex and get reconstructed with (false) high-pT • RICH veto and constraints on matching variables from PC hits reduce background from analyzed tracks Amaresh Datta (UMass)

12. Asymmetry and Statistical Uncertainty ++ same helicity +- opposite helicity R = Relative Luminosity = L++/L+- Amaresh Datta (UMass)

13. Fill-by-Fill Combination of ALL • Count N and luminosityfor same and opposite helicity configurations (summed over all crossings) and calculate ALL for each fill • Average ALL over fills • Perform checks: • Parity-violating AL consistency with zero • Comparison of statistical uncertainty to width of distribution of ALLwith randomized spin configurations • Fill-by-fill consistency (stability of fit checked with χ2/NDF) Amaresh Datta (UMass)

14. Theoretical Predictions for ALL NLO pQCD calculations in the GRSV (Phys. Rev. D 63, 094005 (2001) ) model assuming different input values of ∆g Amaresh Datta (UMass)

15. ALL of Charged Hadrons Double longitudinal spin asymmetries of charged hadrons Amaresh Datta (UMass)

16. Asymmetries of Charged Hadrons and Neutral Pions (Neutral Pion Asymmetry result from hep-ex: 08100694) xT scaling of Pi0 ALL shows consistency of asymmetries with results at different center of mass energy Amaresh Datta (UMass)

17. Conclusion • Longitudinal double spin asymmetry results found to be consistent with small gluon polarization in the x-range measured by other probes (e.g. neutral pions) at PHENIX • ALL results will contribute to global analysis to constrain ∆g • With more events in future runs, the asymmetry of charged hadrons can be helpful in determining the sign of ∆g Amaresh Datta (UMass)

18. Thank You Amaresh Datta (UMass)

19. Backup: Single Spin Asymmetry (Blue Beam) Amaresh Datta (UMass)

20. Backup: Single Spin Asymmetry (Yellow Beam) Amaresh Datta (UMass)