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Inclusive Jet Longitudinal Spin Asymmetry Measurements with Polarized p+p Collisions at STAR

Inclusive Jet Longitudinal Spin Asymmetry Measurements with Polarized p+p Collisions at STAR. Lake Louise Winter Institute, February 23, 2008 David Staszak (UCLA) STAR Collaboration. The Proton Helicity Distribution. 1/2 = ∆S q + ∆G + L q,g. Gluon Helicity:.

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Inclusive Jet Longitudinal Spin Asymmetry Measurements with Polarized p+p Collisions at STAR

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  1. Inclusive Jet Longitudinal Spin Asymmetry Measurements with Polarized p+p Collisions at STAR Lake Louise Winter Institute, February 23, 2008 David Staszak (UCLA) STAR Collaboration

  2. The Proton Helicity Distribution 1/2 = ∆Sq + ∆G + Lq,g Gluon Helicity: ∆Sq: sum of spin contributions from all quarks, anti-quarks G= Measured experimentally by DIS in the kinematic range 0.003 < x < 0.8 We know 20-30% of proton’s total spin ∆G: contribution from gluons Poorly Constrained from DIS, this is a major goal of the RHIC Spin Group Lq,g: gluon and quark angular momentum contributions The future…

  3. Accessing ∆G via ALL + + +… Several contributing sub-processes: B. Jager et. al, Phys Rev D70 034010 Inclusive Jet Signal: High Cross Section + Avoid fragmentation functions

  4. Vogelsang and Stratmann G Models x·∆G(x) • Many different models of ∆G • GRSV has set up an inclusive jet/hadron framework to translate ∆G  ALL at RHIC energies and STAR kinematics • GRSV represents a good “first guess” Q2=100GeV2/c2 x·∆G — GRSV — GS — BB — LSS — AAC — DNSI x Full G integral not covered by STAR acceptance

  5. STAR Detector 100 GeV Polarized Proton Beams • Beam-Beam Counter: • MinBias Trigger • Relative Luminosities • 3.4<||<5 EMC Barrel • Time Projection Chamber: • Charged Tracks PT • -1.4<<1.4 TPC BBC BBC • EM Calorimeter (Pb/Scintillator): • Particle Neutral Energy • Barrel 0<<1 (2003-2005) -1<<1 (2006) • Endcap 1.09<<2.0 EndCap EMC All detectors have full azimuthal coverage

  6. Experimentally Measuring ALL Numbers of Jets Nij Reconstructed for Different Bunch Patterns Relative Luminosity R from BBC Coincidence Rates for different Bunch Patterns Polarization of Beams from CNI Polarimeters taken at set time intervals

  7. First Results: 2003+2004 Cross Section and ALL Published: Phys. Rev. Lett. 97 252001 (2006) • Limited Statistics • Theory curves based on ∆G parameterizations of DIS data • GRSV-STD is best fit to DIS data • Agreement within systematics with NLO QCD over 7 orders of magnitude • Theory: B. Jager et. al, Phys Rev D70 034010

  8. Final 2005 ALL 0.2 <  < 0.8 • Gehrmann-Sterling (GS-C) model calculation inserted into GRSV’s inclusive jet framework Phys.Rev.D53:6100-6109(1996) • Error bars are statistical only • Grey bands are systematic uncertainty

  9. ALL Systematics Trigger Bias:The natural interaction mix (gg/qg/qq) can be biased in our sample from our triggers which rely on neutral energy only. Reconstruction Bias: 25% jet resolution mixed with steeply falling pT spectrum means on average that we over-estimate the jet energy. Combining PYTHIA partonic information with polarization models of G, we can calculate: ALL(PARTONIC) ALL (GEANT) ALL(GEANT+TRIGGER) Reconstruction Bias is the difference between ALL(PARTONIC) and ALL (GEANT) Trigger Bias is the difference between ALL(PARTONIC) and ALL(GEANT+TRIGGER)

  10. Vogelsang and Stratmann GRSV DIS 2005 ALL - ∆G Constraints *Theoretical Uncertainties not included  Within GRSV framework, G can’t be much larger than STD GRSV DIS best fit=0.24 1 = -0.45 to 0.7 PRD 63, 094005 (2001)

  11. 2006 Preliminary ALL -0.7 <  < 0.9 2006 Improvements • 2  4 pb-1 (more on the way!) • BEMC fully instrumented, EEMC towers included • 50  55% Beam Polarization • Increased trigger thresholds  better statistics at high pT - Only Jet Patch Data Shown

  12. 2006 Preliminary ALL *GRSV-STD excluded with 99% CL * g < -0.7 excluded with 90% CL

  13. Summary and Outlook Inclusive jet channel is one way in which the RHIC Spin Group is able to access ∆G 2005 and 2006 inclusive jet results are a significant contribution to global understanding of ∆G 500pp GeV running is on the horizon  expanded x-range From STAR, Di-jet and Gamma-Jet measurements are on the way. Gamma-Jet can measure G(x) as a function of x, whereas Inclusive Jet can only measure an integrated x-range. A global analysis of worldwide measurements is necessary to come to a definitive answer for ∆G

  14. Backup Slides

  15. Comparison: 2006 - 2005 ALL

  16. Vogelsang and Stratmann Model Dependent ALL Curves

  17. STAR Jet Reconstruction and Triggering detector • Jet Reconstruction • Midpoint Cone Algorithm • 0.5 GeV seed energy • 0.4 Cone Radius (2005), 0.7 C.R. (2006) hep-ex/0005012 particle • 2005/2006 Trigger Mix • MinBias - BBC Coincidence • HighTower - ∆x = .05x.05EMC patch above threshold • JetPatch - ∆x = 1x1EMC patch above threshold parton

  18. Data/MC Comparison PRL 97, 252001 (2006)

  19. 2006 Systematic Uncertainties

  20. Step 1: Use PYTHIA+GEANT to estimate the pT shift from detector jets to particle jets Jet Reconstruction and Trigger Bias Step 2: Simulate the difference in ALL between detector and particle jets for various gluon polarization scenarios Particle jets Shifted detector jets Detector jets Step 3: Choose the largest difference for each jet pT bin

  21. Single Spin Asymmetries

  22. Relative Luminosity Systematic Calculated using the BBC: Cross-checked using theZero Degree Calorimeter (ZDC),another luminosity monitor Difference (below) interpreted as a systematic on the relative luminosity Systematic estimated as the difference between ALL(R3) and ALL(R3 ± 0.001) ALL(R3 + 0.001) - ALL (R3) R3(BBC) - R3(ZDC) ALL(R3 - 0.001) - ALL (R3) Difference between BBC and ZDC is 0.001

  23. Background Removed from analysis Difference between High Background and Low Background Samples Background Systematic Background manifests itself as jets with large neutral energy deposit Jet EEMC/ETot Background Asym Background Fraction JP2 AbgLL

  24. Non-longitudinal Beam Polarization Systematic • Non-longitudinal beam polarization changes ALL: • To bound this effect, • Calculate A from transverse data: |A |  0.1 • Estimate the beam transverse polarization component • Local polarimetry (BBC up-down and left-right asymmetries)

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