1. What can we learn from η production in proton-proton collisions? Joe Seele MIT and University of Colorado

2. J. Seele - SPIN 20082 Outline Proton spin puzzle η production in (polarized) proton-proton collisions Measurements of η production at PHENIX Extraction of η fragmentation functions Constraining Δ G with η production in polarized proton-proton collisions at PHENIX

3. J. Seele - SPIN 20083 The Proton Spin Puzzle Fairly well measured only ~30% of spin A future challenge The proton is viewed as being a “bag” of bound quarks and gluons interacting via QCD Spins + orbital angular momentum need to give the observed spin 1/2 of proton Beginning to be measured at RHIC (and hopefully EIC)

4. J. Seele - SPIN 20084 Double Helicity Asymmetries and translating… Take the asymmetry of proton helicity configurations

5. J. Seele - SPIN 20085 Cross Section and Fragmentation Functions High p T particle production provides information about the parton distribution functions and fragmentation functions

6. J. Seele - SPIN 20086 Why the η ? Want a final state that: 1)Produced in large quantities 2)Theoretical Motivation PHENIX - PRC 75 024909

7. J. Seele - SPIN 20087 Why the η ? Want a final state that: 1)Produced in large quantities 2)Theoretical Motivation Different flavor and gluon dependence of structure and fragmentation should give different sensitivities to hard subprocesses

8. J. Seele - SPIN 20088 RHIC Year  s [GeV]Recorded LPol [%]FOM (P 4 L) 2003 (Run 3)200.35 pb -1 323.7 nb -1 2004 (Run 4)200.12 pb -1 454.9 nb -1 2005 (Run 5)2003.4 pb -1 49200 nb -1 2006 (Run 6)2007.5 pb -1 57690 nb -1

9. J. Seele - SPIN 20089 PHENIX Central Arms: γ / π 0 / η detection –Electromagnetic Calorimeter (-0.35 < η < 0.35) –PC3 - Charge Veto Global Detectors: Relative Luminosity –Beam-Beam Counter (BBC) (+- 3.1 < η < 4.0) –Zero-Degree Calorimeter (ZDC) (+- 6.9 < η < infinity) Local Polarimetry - ZDC

10. J. Seele - SPIN 200810 Measuring the η at PHENIX ChannelBR (%) η->2γ 39.39 η->π 0 π 0 π 0 32.52 η->π + π - π 0 22.68 η->π + π - γ 4.69 Choose a decay channel that couples well with the capabilities of PHENIX

11. J. Seele - SPIN 200811 Measuring the η at PHENIX The number of η ’s in each p T bin are determined by fitting the peak+background in the di-photon invariant mass spectrum 2-33-44-55-6 6-77-9 9-11

12. J. Seele - SPIN 200812 η Cross Section - Results Run3 and Run5 cross section results

13. J. Seele - SPIN 200813 Measuring Helicity Asymmetries What to measure : 1)N’s - Final state - the η 2)P’s - Polarization at IR 3)R - Relative Luminosity PHENIX Central Arms PHENIX ZDCs + RHIC Polarimeters PHENIX ZDCs+BBCs

14. J. Seele - SPIN 200814 η Asymmetry - Results Scaling uncertainty (Run5 = 9.4% and Run6 = 8.3%) from polarization not shown *p T bins identical up to p T =6. Above that they use different binning.

15. J. Seele - SPIN 200815 η Fragmentation Functions None previously existed, so Marco Stratmann, Christine Aidala and myself extracted the η FFs from data on e + +e - and p+p.

16. J. Seele - SPIN 200816 η FFs - Comparison Describes e+e- data very well over a large range in energies. Plan to incorporate BABAR, and possibly some UA1/UA2 data.

17. J. Seele - SPIN 200817 η Cross Section and Theory NLO+ η FF ( μ =p T ) calculation done by Marco Stratmann *In a way this is more of a self- consistency check than a prediction.

18. J. Seele - SPIN 200818 η and π 0 Subprocess Fractions

19. J. Seele - SPIN 200819 η Asymmetry and Theory Calculations by Marco Stratmann

20. J. Seele - SPIN 200820 Constraining Δ G with the η A series of constrained fits were done by Vogelsang and Stratmann in the GRSV model. They constrained the integral of Δ G at the input scale.

21. J. Seele - SPIN 200821 Constraining Δ G with the η Each set yields a different A LL Does not give much power for the negative Δ Gs

22. J. Seele - SPIN 200822 Constraining Δ G with the η Allows a small positive or strongly negative Δ G. It should be noted that this is only for the GRSV fits. The data needs to be incorporated into a flexible global fit.

23. J. Seele - SPIN 200823 Constraining Δ G with the η and π 0

24. J. Seele - SPIN 200824 The Polarization of the Proton’s Glue PHENIX has measured the double helicity asymmetry in η production at mid-rapidity With the new fragmentation functions it will provide a constraint on Δ G Thanks!

25. J. Seele - SPIN 200825 Backup

26. J. Seele - SPIN 200826 η FFs - Data ExperimentSystemEnergy (GeV)# Points ALEPH ’92e+e-91.28 ALEPH ’00e+e-91.218 ALEPH ‘02e+e-91.25 L3 ‘92e+e-91.23 L3 ’94e+e-91.28 OPALe+e-91.29 ARGUSe+e-106 CELLOe+e-354 HRSe+e-2913 JADE ’85e+e-34.41 JADE ‘’90e+e-34.93 MARK IIe+e-297 PHENIX 2  p+p20012 PHENIX 3  p+p2006 PHENIX ’05 prelim.p+p20019

27. J. Seele - SPIN 200827 Relative Luminosity at PHENIX Measured using the Beam-Beam Counter (BBC) Coincidences Systematic Studies Include : 1.Spin Independent BBC cross section 2.Effects from multiple collisions per bunch crossing Currently δ R ~ O(10 -4 ) Statistical uncertainty in δ R is negligible, but systematics could become a problem in the near future

28. J. Seele - SPIN 200828 Local Polarimetry at PHENIX The neutrons are measured in the PHENIX ZDCs Spin rotators are not perfect and leave a small transverse component Exploit a forward neutron single spin asymmetry in transversely polarized p+p collisions

29. J. Seele - SPIN 200829 Polarimetry at RHIC RHIC uses 2 types of transversely polarized elastic scattering Provides fast, high statistics measurement Gives polarization profile of beam Analyzing power empirically determined Provides self-calibrating, low statistics measurement Analyzing power unknown Provides calibration for the p+C polarimeter A tour de force measurement as this is the first time bunch-by-bunch measurements were performed at any high energy collider

30. J. Seele - SPIN 200830 η Asymmetry Because the eta peak sits on a background we need to subtract a possible background asymmetry 700-800 MeV 300-400 MeV The background asymmetry is estimated using the blue sideband regions and subtracted from the peak asymmetry