Recent Results from PHENIX Longitudinal Spin Program

1. Recent Results from PHENIX Longitudinal Spin Program Kieran Boyle (Stony Brook U.) for the PHENIX Collaboration • Outline: • Quick Physics overview • RHIC and PHENIX, and ALL requirements • Run5 and Run6 new Results

2. Motivation Dg2 DgDq Dq2 with DS ~20%, Dg, DL not well constrained How to measure Dg: p0 Hard Scattering Process ~ agg * Dg2 + bgq * Dg + cqq

3. ALL Requirements • Helicity Dependent Particle Yields • (Local) Polarimetry • Relative Luminosity (R=L++/L+-) • ALL ++ same helicity + opposite helicity

4. RHIC BRAHMS & PP2PP (p) PHENIX (p) STAR (p) RHIC CNI (pC) Polarimeters Absolute Polarimeter (H jet) Siberian Snakes Spin Rotators Partial Siberian Snake LINAC BOOSTER Pol. Proton Source AGS AGS Internal Polarimeter 200 MeV Polarimeter Rf Dipoles * Longitudinal ** Not yet finalized

5. PHENIX Detector BBC ZDC ZDC p0/g/h detection • Electromagnetic Calorimeter (PbSc/PbGl): • High pT photon trigger to collect p0's, h’s, g’s • Acceptance: h<|0.35|, f = 2 x p/2 • High granularity (~10*10mrad2) p+/ p- • Drift Chamber (DC)/Ring Imaging Cherenkov Counter (RICH) • High pT charged pions (pT>4.7 GeV). J/Y • Muon Id/Muon Tracker • Multiple muon triggers. Relative Luminosity • Beam Beam Counter (BBC) • Acceptance: 3.0< h<3.9 • Zero Degree Calorimeter (ZDC) • Acceptance: ±2 mrad Local Polarimetry • ZDC LvL2 data filter • Filters “rare” events for fast analysis • Dimuon for J/Y • pT>2.5 GeV photon for p0

6. Use Zero Degree Calorimeter (ZDC) to measure a L-R and U-D asymmetry in forward neutrons (Acceptance: ±2 mrad). When transversely polarized, we see clear asymmetry. When longitudinally polarized, there should be no asymmetry. Local Polarimetry at PHENIX Raw asymmetry Raw asymmetry YELLOW BLUE f f Raw asymmetry Raw asymmetry YELLOW BLUE f f Idea: Use neutron asymmetry to study transversely polarized component.

7. Measured Asymmetry During Longitudinal Running (2005) LR c2/NDF = 82.5/97 p0 = -0.00423±0.00057 c2/NDF = 88.1/97 p0 = -0.00323±0.00059 UD XF>0 XF>0 UD c2/NDF = 119.3/97 p0 = -0.00056±0.00063 c2/NDF = 81.7/97 p0 = -0.00026±0.00056 LR XF<0 XF<0 <PT/P>= 10.25±2.05(%) <PL/P> = 99.48±0.12±0.02(%) <PT/P>= 14.47±2.20(%) <PL/P> = 98.94±0.21±0.04(%) Fill Number Fill Number

8. ATT • Here • ATT • azimuthally independent double transverse spin asymmetry. • ALL background. • expected to be small, but previously unmeasured. • In Run5, PHENIX took a short transverse run specifically to measure ATT. • Consistent with zero.

9. Relative Luminosity • Number of BBC triggered events used to calculate Relative Luminosity. • For estimate of Uncertainty, fit where • Limited by ZDC statistics. * Longitudinal

10. ALL Dg2 DgDq Dq2 probe Hard Scattering Process • From Run5 and Run6, we are currently studying an array of probes: • p0, p+, p- • Direct photon • h • multiparticle “cone” • J/Y

11. Calculating p0 ALL • Calculate ALL(p°+BG) and ALL(BG) separately. • Get background ratio (wBG) from fit of all data. • Subtract ALL(BG) from ALL(p°+BG): ALL(p°+BG) = wp° · ALL(p°) + wBG · ALL(BG) • This method is also used for other probes with two particle decay mode: • h, J/Y

12. p0 in Run6 • In Run6, there were two separate longitudinal running periods: • April 27-June 5 @ s=200 GeV • June 12-June 20 @ s=62.4 GeV • s=62.4 GeV • Due to the small size of the s=62 GeV data set, we were able to finish production and measure p0 ALL. • s=200 GeV • As was mentioned earlier, PHENIX filters data for rare signals. • In Run6, we have also used this filtered data (here, for high pT photons) to produce a high pTp0 ALL @ s=200 GeV with much improved uncertainties compared to Run5.

13. 62 GeV • Initial, 62 GeV p+p was needed for heavy ion comparison. • Thanks to CAD, we were able to get longitudinally polarized beam at PHENIX.

14. But why? • By definition: • Measuring p0 ALL at s=62.4 GeV allows us to test a higher xT range with lower statistics than currently possible at s=200 GeV. • As stated earlier, uncertainty in ALL @ 62 GeV due to relative luminosity is 2.8x10-3, which is less than our statistical uncertanty.

15. 62 GeV: Local Polarimetry Red : transverse data Blue : longitudinal data • Forward Neutron asymmetry reduced at 62 GeV, but still measurable. Blue Forward Blue Backward xpos xpos Yellow Forward Yellow Backward xpos xpos

16. 62 GeV Results • ATT still to be measured with short transverse data set taken during rotator commisioning. • Assume remaining transverse component ~21% • 0.212ATT ~ 0.04ATT contribution to measured ALL • p0 unpolarized cross section at s=62 GeV is not yet finished. • Unclear how well NLO pQCD describes our data. • Validity of comparison with expected ALL theory curves calculated from NLO pQCD is NOT clear. • Result expected soon

17. p0 ALL @ s=62 GeV • As there is no cross section at s=62 GeV, we do not calculate confidence levels. • Grey band is systematic uncertainty from relative luminosity, which is independent of pT. GRSV: M. Gluck, E. Reya, M. Stratmann, and W. Vogelsang, Phys. Rev. D 53 (1996) 4775.

18. Comparison with 200 GeV • Converting to xT, we can get a better impression of the significance of the s=62 GeV data set, when compared with the Run5 preliminary data set. • Awaits the unpolarized cross section for estimating 62 GeV significance.

19. 200 GeV • As shown earlier, the Run6 longitudinal data set had a figure of merit 7.5 times that of Run5. • Use data filtered for high pT photon. • Due to low efficiency in our filter at medium pTp0’s data for pT<5 GeV is statistically limited. • We only show data with pT>5 GeV. • Uncertainty from relative luminosity for the sqrt(s)=200 GeV longitudinal running period gives an uncertainty in ALL of 1.5e-4. • For local polarimetry, we need full production. • Currents for Rotator and Main magnets for both STAR and PHENIX are monitored during the run • Enough historical evidence exists for understanding spin direction and magnet current correlation. • Conclude that spin orientation is fine.

20. Run5 p0 Cross Section • Consistent with previous results. • Extends previous results to pT of 20 GeV/c. • Theory is consistent with data over nine orders of magnitude.

21. Run6 p0 ALL (200 GeV) • Run6 Data set from 2.0-2.7 times improvement on statistical uncertainties from Run5. • Variation due to LvL2 “turn on.” • Due to unreleased absolute polarizations, which act a scale factor in ALL and which contain correlated and uncorrelated part, we have not combined the two data sets. • For confidence levels, assume complete correlation. GRSV: M. Gluck, E. Reya, M. Stratmann, and W. Vogelsang, Phys. Rev. D 53 (1996) 4775.

22. What about Dg? • Confidence levels from a simple c2 test between our data and the four curves plotted. • Theoretical uncertainties are not taken into account. • Run 6 rules out maximal gluon scenarios. • Expect clearer statement when lower pT data from Run6 is available.

23. What about Dg? • To remove possibility that soft physics is influencing the result through the pT<2 data, we calculated confidence levels excluding this point. • Theoretical uncertainties are not taken into account. • No significant difference seen. • Expect clearer statement when lower pT data from Run6 is available. • More detailed analysis of Dg constraint underway.

24. High pT Charged Pion Hard Scattering Process p+, p- Dg2 DgDq Dq2 • First “Proof of concept” measurement • Charged pions begin firing the RICH at pT~4.7 GeV, which is used for particle ID. • Higher pT more sensitive to gluon polarization. • See A. Moreale’s talk

25. p+p h + X Dg2 DgDq Dq2 Hard Scattering Process h • Similar analysis technique as with p0, using two photon decay channel. • Independent measure for gluon polarization. • See F. Ellinghaus’ talk later today.

26. Multiparticle ALL Dg2 DgDq Dq2 • Definition of pT cone: sum of pT measured by EMCal and tracker with R = (||2+||2) < 0.3 rad. • Relationship between pTcone and pTjet is evaluated with PYTHIA and GEANT. • See K. Nakano’s talk. Hard Scattering Process

27. J/Y (Run5 & Run6) • New Run6 result from LvL2 filtered data • LvL2 filters data on defined rare condition • Here, LvL2 uses dimuon event. • Shows clear improvement over Run5. • Second year in which J/Y has been measured using LvL2 filtered data. • See M. Liu’s talk

28. Direct photon Hard Scattering Process g DgDq DqDq RUN5 hep-ex/0609031 • First step, direct photon cross section using isolation cut. • Isolation cut: • ETot<0.1Ecandidate within 0.5 rad. Gluon-photon compton dominant Isolation cut R=0.5, f=0.1 minE=0.15GeV Pmin=0.2GeV Pmax=15GeV

29. Direct photon • Background from merged p0 removed by shower shape (calibrated with test beam). • Background from isolated p0 photon <15% above 10 GeV. • Asymmetry analysis underway. Results expected soon. • See T. Horaguchi’s talk. signal isolated pi0 photon

30. Conclusions • PHENIX is well positioned to constrain Dg with a new significantly better data set from Run6. Many other complimentary analyses are on the way. • 62 GeV data give information at higher xT, and may give powerful independent constraint on Dg.