1. Mar. 17, 2006 Imran Younus Probing Gluon Polarization with Longitudinally Polarized p+p Collisions at  s = 200 GeV

2. 3/17/2006Imran Younus, Univ. of New Mexico. 22nd Winter Workshop on Nuclear Dynamics2 “Proton Spin Crisis” EMC Experiment at CERN J. Ashman et al., Nucl. Phus. B 328, 1 (1989) Proton-spin sum rule:  =  U +  D +  S  G = gluon polarization L Z = orbital angular momentum  Polarized DIS: contribution of quarks to proton spin is amazingly small  0.1- 0.3  Main candidate to carry proton spin – Gluons  Orbital angular momentum?  G measurement – main RHIC-spin goal

3. 3/17/2006Imran Younus, Univ. of New Mexico. 22nd Winter Workshop on Nuclear Dynamics3 QCD Factorization The cross-section is written as convolution of PDFs and partonic sub process cross- section, e.g.,  production: Unpolarized case: Polarized case: Unpolarized, polarized parton distribution functions, determined from experimental data. Fragmentation function, determined from experiment. Paronic level hard-scattering cross section. Calculated by perturbative QCD. Process dependant. f1p(x1)f1p(x1) f2p(x2)f2p(x2) p1p1 p2p2 X DfDf f2f2 f1f1 f 

4. 3/17/2006Imran Younus, Univ. of New Mexico. 22nd Winter Workshop on Nuclear Dynamics4 Parton Distribution Functions (PDF) Quark distributions (q= u,d,s…)  Unpolarized dist.  Helicity dist.  Transversity q(x,Q 2 ) ==  q(x,Q 2 ) =  q(x,Q 2 ) = Gluon distributions  Unpolarized dist.  Polarized dist. g(x,Q 2 ) =  g(x,Q 2 ) = PDFs - probability of scattering off of a parton carrying a particular fraction of the proton’s momentum. Polarized PDFs - the difference in probability between scattering off of a parton with one spin state vs. the other. Still as a function of the momentum fraction. Universality! PDFs extracted from the data in one process, can be used to make predictions for other processes.

5. 3/17/2006Imran Younus, Univ. of New Mexico. 22nd Winter Workshop on Nuclear Dynamics5 Precision Data From DIS Precision Data in Wide Kinematical Range - Q 2 evolution agrees with pQCD Only Fixed Target Spin Experiments so far. Need a collider to extend kinematical coverage.

6. 3/17/2006Imran Younus, Univ. of New Mexico. 22nd Winter Workshop on Nuclear Dynamics6 Polarized PDFs and Uncertainties  Valence Dist’s are determined well.  Sea Dist’ is poorly constrained.  Gluon Dist’ can be either >0, =0, <0. Gluon polarization (  G) remains poorly constrained Asymmetry Analysis Collaboration M. Hirai, S. Kumano and N. Saito, PRD (2004)

7. 3/17/2006Imran Younus, Univ. of New Mexico. 22nd Winter Workshop on Nuclear Dynamics7 Measuring Gluon Polarization at RHIC Spin asymmetries for cross-sections A LL : double longitudinal spin asymmetry – useful in extracting  g(x),  q(x). Various channels to extract  g(x).  Inclusive  o production  Prompt photon  Heavy quark production  Jets

8. 3/17/2006Imran Younus, Univ. of New Mexico. 22nd Winter Workshop on Nuclear Dynamics8 RHIC as Polarized Proton Collider L max = 2  10 32 s -1 cm -2 70% Polarization 50   s  500 GeV Run05: L = 4 pb -1 47% Polarization  s = 200 GeV

9. 3/17/2006Imran Younus, Univ. of New Mexico. 22nd Winter Workshop on Nuclear Dynamics9 PHENIX Detector Central Arms: |  |<0.35,  =2  90 0 Charged particle ID and tracking; photon ID. EM Calorimetry. Muon Arm: 1.2<|  |<2.4 Muon ID and tracking. Global Detectors Collision trigger Collision vertex characterization Relative luminosity Local Polarimetry Philosophy: – High resolution at the cost of acceptance – High rate capable DAQ – Excellent trigger capability for rare events

10. 3/17/2006Imran Younus, Univ. of New Mexico. 22nd Winter Workshop on Nuclear Dynamics10  ,  Cross sections Measured un-polarized cross section at  s=200 GeV are well described by the Next-to-Leading Order cross sections. Necessary Confirmation that pQCD can be used successfully at RHIC to extract PDFs.

11. 3/17/2006Imran Younus, Univ. of New Mexico. 22nd Winter Workshop on Nuclear Dynamics11 Measuring A LL P 1,P 2 – Polarization of the colliding beams. N ++ (N +- ) – experimental yields for same (opposite) helicity collisions. R – Relative luminosity, determined at PEHNIX using BBC LL1 trigger counts. Run5:  R=10 -4

12. 3/17/2006Imran Younus, Univ. of New Mexico. 22nd Winter Workshop on Nuclear Dynamics12 Local Polarimetry at PHENIX Longitudinal Pol. Transverse Pol.  Left-Right Asymmetry of Neutrons in transversely polarized p+p was discovered at IP12.  Use neutron asymmetry to estimate longitudinal and transverse components of polarization.  ZDC/SMD make local polarimetry measurement at PHENIX ~ 98 – 99 % ~ 10 – 14%

13. 3/17/2006Imran Younus, Univ. of New Mexico. 22nd Winter Workshop on Nuclear Dynamics13 A LL (   ) f1p(x1)f1p(x1) f2p(x2)f2p(x2) p1p1 p2p2 X DfDf f2f2 f1f1 f  pp  X is sensitive to gg  gg and gq  gq (at low/moderate p T ) ++ Fractional contribution to pp  X at  s=200 GeV at mid-rapidity

14. 3/17/2006Imran Younus, Univ. of New Mexico. 22nd Winter Workshop on Nuclear Dynamics14 Calculating A LL (   )  Calculate A LL (   +BG) and A LL (BG) separately.  Get background ratio (w BG ) from fit of all data.  Subtract A LL (BG) from A LL (   +BG): A LL (   +BG) = W  · A LL (   ) + W BG · A LL (BG) W BG =1- W , and W  =   /(   +BG).   +BG region : ±25 MeV around  peak BG region : Two 50 MeV regions p T (GeV)   stat. (W BG ) 1-217484k (32%) 2-310156k (14%) 3-41971k (7%) 4-5381k (5%) 5-693k (5%) 6-728k (5%) 7-811k (5%) 8-94.2k (5%)

15. 3/17/2006Imran Younus, Univ. of New Mexico. 22nd Winter Workshop on Nuclear Dynamics15 Run5 A LL (   ) Results RunInt.Lum.Pol.F.O.M.(P 4 L) Run 3 (2003)220 nb -1 27%1.17 nb -1 Run 4 (2004)75 nb -1 40%1.92 nb -1 Run 5 (2005)1.8(2.7) pb -1 47%87.8(132) nb -1 Consistent with GRSV-std and GRSV  G=0. Excludes GRSV-max. Run5 results consistent with previous results. GRSV: M. Gluck, E. Reya, M. Stratmann, and W. Vogelsang, Phys. Rev. D 53 (1996) 4775.

16. 3/17/2006Imran Younus, Univ. of New Mexico. 22nd Winter Workshop on Nuclear Dynamics16 Run6 Expectations We expect both polarization and luminosity increases This will decrease our uncertainty by a factor of ~4 (~3 when all Run5 data is considered). Run6 Expectation: Int. Lum.: 11.4 pb -1 Polarization: 60% F.O.M. (P 4 L): 1.48 pb -1

17. 3/17/2006Imran Younus, Univ. of New Mexico. 22nd Winter Workshop on Nuclear Dynamics17 Heavy Quark Production  Provide direct access to gluon polarization  Gluon Fusion dominates at LO PHYTHA estimate: GeVCharmBeauty 20095:585:15 50097:392:8 J/  x a LL (gg  J/  + X) model dependant.

18. 3/17/2006Imran Younus, Univ. of New Mexico. 22nd Winter Workshop on Nuclear Dynamics18 A LL (J/  ) PHENIX, PRL 92, 051802 (2004) Partonic asymmetry for gg  J/  X CEM: a LL ~ +1CSM: a LL ~ -1 COM: Theoretical predictions of J/  production at RHIC are in good agreement with the PHENIX data. COM process dominant –PRD 68 (2003) 034003 G. Nayak, M. Liu, F. Cooper –PRL 93 (2004) 171801 F. Cooper, M. Liu, G. Nayak

19. 3/17/2006Imran Younus, Univ. of New Mexico. 22nd Winter Workshop on Nuclear Dynamics19 A LL (J/  ) J/  Yield measurement: J/  +  -, 1.2  |  |  2.2 Fill by Fill yields: N(  +  - ) – {N(  +  + ) + N(  -  - )} Fixed mass range; Open charm and DY background. Purity of J/  sample: 92% Gaussian + Exponential Fit. Used for cross check and background determination. Run05 data used for the analysis 3.2 pb -1 dimuon trigger data. N (J/  ) ~ 7300 47% polarization. M(  )

20. 3/17/2006Imran Younus, Univ. of New Mexico. 22nd Winter Workshop on Nuclear Dynamics20 A LL (  ) Cleanest mode for extracting  g(x) Gluon Compton Dominates –At LO no fragmentation function –Small (  15%) contamination from annihilation p2p2 p1p1 x2x2 x1x1 NLO pQCD describes cross-section well  can be used to interpret A LL (  )

21. 3/17/2006Imran Younus, Univ. of New Mexico. 22nd Winter Workshop on Nuclear Dynamics21 A LL (  ) projection Prompt photon cross-section measured with Run3 data. Run5 analysis is going on. A LL (  ) needs large luminosity. Run6 may give us first results. 2008-09 projection. GRSV-std

22. 3/17/2006Imran Younus, Univ. of New Mexico. 22nd Winter Workshop on Nuclear Dynamics22 Summery  RHIC as a polarized p+p Ccollider is a powerful tool to probe gluon structure!  Measurements at PHENIX will allow us to constrain the gluon contribution to the proton’s spin.  First significant results of A LL of  o from RHIC Run05 conclusively exclude GRVS-max scenario.  Study of other channels, prompt photons, heavy quarks production, is going on.  Run6 will improve FOM by a factor of 10 over Run5, and will provide us first measurement of prompt photon asymmetry.