Future D G Measurements at STAR

1. Future DG Measurements at STAR Renee Fatemi University of Kentucky RHIC Spin Meeting, LBNL, November 21st 2009

2. Discussion Outline Where we started. Where we are now. Where should we go next? When have we gone far enough? RHIC Spin Meeting, LBNL, November 21st 2009

3. “Pre-RHIC” and “Mid-RHIC”  & DG in DSSV Framework Q2 =10 GeV DeFlorian, Sassot, Stratmann and Vogelsang, Phys.Rev.Lett. 101:072001, 2008 DeFlorian, Sassot, Stratmann and Vogelsang, Phys.Rev.D 80:034030, 2009 RHIC Spin Meeting, LBNL, November 21st 2009

4. STAR DG DATA RANGE Inclusive Jets Inclusive neutral pions Inclusive charged pions X mapping • DG data (to date) integrates over X range while DIS/SIDIS accesses X directly. • Need to reduce integration bins in X. • Correlation data – di-jets and photon-jets. RHIC Spin Meeting, LBNL, November 21st 2009 DG data covers only one decade in X compared to the 3 decades for DS. Need to lower/raise X reach. Quark-gluon scattering in forward regions provide access to low x gluons. Move to higher center of mass scattering energies while measuring same kinematic range

5. X Mapping Techniques RHIC Spin Meeting, LBNL, November 21st 2009

6. Increased sensitivity to XBJ in Run 9 via Di-jets @ 200 GeV LO and NLO track fairly closely West BEMC + EEMC provides access to lowest x values! EBEMC+EEMC harder to measure due to smaller partonicaLL. But can access same kinematics in E+W BEMC. EBEMC+EBEMC EBEMC+WBEMC EBEMC+EEMC WBEMC+WBEMC WBEMC+EEMC RHIC Spin Meeting, LBNL, November 21st 2009

7. Framework 2009 Dijet ALL prepared Dijet X-sec from 2005 New preliminary result shown at DNP in October Corresponds with West-West BEMC x range Good agreement with NLO RHIC Spin Meeting, LBNL, November 21st 2009

8. Photon-jets @ 200 GeV in Run9 • Very clean and sensitive to partonic XBJ. • Relatively rare and difficult to measure. • LOTS ofdevelopment on algorithms and simulations. • Plot shows STAR sensitivity for : • pT,γ > 10 GeV/c • 1.09 < ηγ < 2 (EEMC) • √s = 200 GeV • 50 pb-1 @ 60% pol. • DOES NOT INCLUDE: • Efficiency and • background effects RHIC Spin Meeting, LBNL, November 21st 2009

9. Charged and Neutral pion channels @ 200 GeV Continue to look at inclusive channels with increased precision. RHIC Spin Meeting, LBNL, November 21st 2009

10. While moving toward jet-hadron correlation measurements. • NLO calculations show a strong correlation between the real x and z values and LO estimates from jet – hadronmeasurements. • de Florian Phys. Rev. D79:114014, 2009

11. Leading systematics, such as trigger + reconstruction bias, are reduced as constraints on DG increase. Run 6 Inclusive Jets @ 200 GeV RHIC Spin Meeting, LBNL, November 21st 2009

12. The stats fromrequested Run 9 @ 200 GeV xT = 2 pT / √s The stats from received Run9 200 GeV

13. Extending X reach RHIC Spin Meeting, LBNL, November 21st 2009

14. Moving to higher CM Energies • Higher √s WILL provide access to lower x gluons BUT this does NOT automatically translate into increased sensitivity to DG at low x. • The sub-process fractions are stable WRT to XT and the low “x” region is still dominated by gluon-gluon scattering. • DG is not large so we must enhance our sensitivity by using the larger valence quark analyzing power. • Optimize for qG scattering! Gluon goes forward and quark stays at mid-rapidity. RHIC Spin Meeting, LBNL, November 21st 2009

15. Di-jet Projections for 300 pb-1 @ 500 GeV EB+EB EB+WB EB+EE WB+WB WB+EE • Lower x reach • Brings smaller ALL • Assumes 30 pb-1 at 70% polarization

16. Stat Uncerts only What does this xT range correspond to? Very small ALL and errors! DSSV error ~0.0025 in this region so error bars bigger than this loose their utility quickly…. Inclusive Jet Projections for 100 pb-1 @ 500 GeV RHIC Spin Meeting, LBNL, November 21st 2009

17. … as far as we can! … until integral saturates? … range covered by DS? How far should we go? Current situation very different compared to DS. Apparent 2 decades ago from the EMC data that g1p was saturating. Measuring a small DG gives little indication about rest of integral. What mechanisms limit sea quark polarization at low/high x? These mechanisms must also limit gluon polarization at low/high x. How do you construct a reasonable functional form from the mechanisms in 3)? EMC Collaboration Nucl. Phys. B328, 1 (1989) RHIC Spin Meeting, LBNL, November 21st 2009

18. How do we sensible draw conclusions about the unmeasured part of the integral? RHIC Spin Meeting, LBNL, November 21st 2009

19. STAR’s inclusive measurements have had a strong impact on the determination DG. • If our goal is to measure DG as precisely as we have measured DS then we have to change our tactics. • Get a better grasp on functional form via correlation measurements. Dijets, jet-hadron correlations and photon-jets will allow more direct map from pT to x. • Expand x range by • higher precision inclusive measurements at higher roots • play the eta game – using polarized q to access low x gluons. Summary RHIC Spin Meeting, LBNL, November 21st 2009

20. Dijet Kinematics RHIC Spin Meeting, LBNL, November 21st 2009

21. Inclusive jet projection for 500 GeV Run 11 • Assume 100 pb-1 sampled at an average polarization of 50% • JP2+AJP take-all threshold at 13 GeV (same as Run 9) • ~250 Hz at C-AD projected max possible lumi • ~120 Hz at C-AD projected final average lumi • Above figure assumes a JP1 trigger at 7.3 GeV with <ps> = 30 • ~100 Hz at C-AD projected final average lumi • If an additional ~100 Hz is tolerable, a better choice would be: • ~100 Hz with JP thr ~ 5.5 GeV (i.e., Run 9 pp200 JP1 thr) • ~100 Hz with JP thr ~ 9 GeV (split diff with take-all level)