1. Oct 6, 2008Amaresh Datta (UMass) 1 Double-Longitudinal Spin Asymmetry in Non-identified Charged Hadron Production at pp Collision at √s = 62.4 GeV at Amaresh Datta (UMass, Amherst)

2. Oct 6, 2008Amaresh Datta (UMass) 2 Proton Spin and Search for Gluon Polarization Orbital ang. momenta Gluon spin contrib. Quark spin  0.33  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

3. Oct 6, 2008Amaresh 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 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 Fractional Contribution

4. Oct 6, 2008Amaresh Datta (UMass) 4 Hard Scattering Processes in p+p: Factorization and Universality Hard Scattering Process The cross section of a hard scattering process is convolution of: –Parton distribution functions (need experimental input) –pQCD hard scattering rates (calculable in pQCD) –Fragmentation functions (need experimental input)

5. Oct 6, 2008Amaresh Datta (UMass) 5 Motivation for Charged Hadron Asymmetry Measurement at √s = 62.4 GeV Measurements of A LL 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 A LL at PHENIX Charged hadron asymmetries can be helpful in determining sign of ∆g  A significant positive ∆g can be reflected in the asymmetries as A LL (π + ) > A LL (π 0 ) > A LL (π - ); (for ∆g(x) without any node)  A negative ∆g will cause reverse order in asymmetries

6. Oct 6, 2008Amaresh 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 Neutral Pion cross-section in Run-6 at 62.4 GeV (submitted to PRD) Charged hadron cross-section from Run-2 (PRL 95, 202001)

7. Oct 6, 2008Amaresh 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

8. Oct 6, 2008Amaresh 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

9. Oct 6, 2008Amaresh 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

10. Oct 6, 2008Amaresh 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 A LL is corrected for background A LL Short-lived ( cτ ~ 1-10 cm ) decay contribution estimated to be ~ 7±7 % and no correction to A LL for this background is performed

11. Oct 6, 2008Amaresh Datta (UMass) 11 Reduction of Backgrounds  Spectra of charged tracks (from data) before and after specific cuts within p T range of interest  Higher p T region contains particles that do not originate from event vertex and get reconstructed with (false) high-p T  RICH veto and constraints on matching variables from PC hits reduce background from analyzed tracks

12. Oct 6, 2008Amaresh Datta (UMass) 12 Asymmetry and Statistical Uncertainty ++ same helicity +- opposite helicity R = Relative Luminosity = L ++ /L +-

13. Oct 6, 2008Amaresh Datta (UMass) 13 Fill-by-Fill Combination of A LL Count N and luminosity for same and opposite helicity configurations (summed over all crossings) and calculate A LL for each fill Average A LL over fills Perform checks:  Parity-violating A L consistency with zero  Comparison of statistical uncertainty to width of distribution of A LL with randomized spin configurations  Fill-by-fill consistency (stability of fit checked with χ 2 /NDF)

14. Oct 6, 2008Amaresh Datta (UMass) 14 Theoretical Predictions for A LL NLO pQCD calculations in the GRSV ( Phys. Rev. D 63, 094005 (2001) ) model assuming different input values of ∆g

15. Oct 6, 2008Amaresh Datta (UMass) 15 A LL of Charged Hadrons Double longitudinal spin asymmetries of charged hadrons

16. Oct 6, 2008Amaresh Datta (UMass) 16 Asymmetries of Charged Hadrons and Neutral Pions (Neutral Pion Asymmetry result from hep-ex: 08100694) x T scaling of Pi 0 A LL shows consistency of asymmetries with results at different center of mass energy

17. Oct 6, 2008Amaresh 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 A LL 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

18. Oct 6, 2008Amaresh Datta (UMass) 18 Thank You

19. Oct 6, 2008Amaresh Datta (UMass) 19 Backup: Single Spin Asymmetry (Blue Beam)

20. Oct 6, 2008Amaresh Datta (UMass) 20 Backup: Single Spin Asymmetry (Yellow Beam)